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Polytec OFV3001

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1. 7 a 2 2 U L O l c O Figure 3 7 Front view of the sensor head OFV 512 1 LASER beam shutter key Pressing this key the beam shutter is opened and pressing this key a second time the beam shutter is closed again refer to section 5 2 The beam shutter is closed automatically when the controller is switched on key switch on the controller in position LASER STANDBY LED The LED goes on when the controller is switched on This then shows that the laser is operational However no laser beam is emitted yet as the beam shutter is still closed LED ON is out The LED goes out when the beam shutter key is pressed and thus the laser beam is emitted LED ON is then on LASER ON LED The LED goes on when the beam shutter key LASER is pressed and thus the laser beam is emitted At the same time the LED STANDBY goes out Pressing the beam shutter key LASER a second time the beam shutter is closed and the LED ON goes out and the LED STANDBY goes on again Signal level display The length of the bar is a measure of the amount of light scattered back from the surface of the object Fiber optic cable The fiber optic cable branches off via a Y piece The reference fiber is marked with a red dot 3 11 3 First Steps 3 12 6 Mini sensors Diameter 10mm Each mini sensor contains a lens to focus the laser beam The mini sensor of the reference fiber is marked
2. u2222222422220nnnnennennnnnnnnnnnnnnnnnnnnen nennen 4 1 4 1 2 Vibrometer with Sensor Head OFV 511 512 222222222222sneenennnnnnnnnnnnnnnnnnnnnn nennen 4 2 4 1 3 Displaying the Output Signals u 20ssssnsnnnannnnnnnnnnnnnnnnnen nn nnnnnnnnnnnnnnnnnnnnnnenn 4 3 4 2 Selecting Suitable Settings uusssnnsnsnnnnnnnnnennenennnnnnnnnnnnnnnnnnnnnnennen nn nnnnnnnnnnnnannnnnnnn 4 4 4 2 1 Velocity or Displacement Measurement usssesssssssnnnnnnnennenennnnnnnnnnnnnnnnnnnnnenn 4 4 4 2 2 Settings for Velocity Measurement umnssnnnnnnnnnnnsnnnnnnnnnennennnnnnnnnnnnannnnnnnnnenn 4 5 4 2 3 Settings for Displacement Measurement optional ummmnennnnnnnnsnnnnnnnn 4 10 4 2 4 Optimal Stand Off Distances for the Sensor Heads cccccsseeeeeceeaeeeeeeeeaaaeeeeees 4 14 Contents 5 Operating the Vibrometer 5 1 5 1 Switching On and Off naian ni einer 5 1 5 2 Beam Shutter and Emission Indicator 4ss44ssnnnnnnnnnnnnnnnnnnnnnenn nn nnnnnnnnnnnnnnnnnennenn 5 1 5 3 Signal Level Display u 2 222220 RE A eee ey Ri 5 2 5 4 Focusing the Laser Beam meets 5 2 5 5 Exchanging the Front Lens ccccceeeecceeeeeeeeeeeee eee EAE E 5 4 5 6 Making Single Point Measurements with the Sensor Head OFV 512 aeee 5 5 5 7 Fixing the Focus only OFV 353 u uussssnssssssnnnnnnnnennnnnnnnnnnnnnnnannnnnnnnnnen nenn nnnnnnnnnnnnnnnnn 5 5 5
3. Polytec User Manual Laser Doppler Vibrometer AER QR OSSD N Controller OFV 3001 Sensor Heads OFV 303 353 OFV 511 512 Warranty and Service The warranty for this equipment complies with the regulations in our general terms and conditions in their respective valid version This is conditional on the equipment being used as it is intended and as described in this manual The warranty does not apply to damage caused by incorrect usage external mechanical influences or by not keeping to the operating conditions The warranty also is invalidated in the case of the equipment being tampered with or modified without authorization To return the equipment always use the original packaging Otherwise we reserve the right to check the equipment for transport damage Please mark the package as fragile and sensitive to frost Include an explanation of the reason for returning it as well as an exact description of the fault You can find advice on fault diagnosis in chapter 6 Trademarks Brand and product names mentioned in this manual could be trademarks or registered trademarks of their respective companies or organizations Identification Labels Controller Sensor Head Contents Contents 1 Safety Information 1 1 Te Laser Safety manaira ere a a e aa a r aaa a aiaa eat 1 1 C2 Laser Warning Labolina ia E E regnen 1 2 te T EC GOUTE S aii ict Ai a ER hauen 1 2 T3 Laser Warning Labels u HH een
4. 1 or down J on the display This is used to select parameters or to change between menus refer to section 5 9 1 SETTING keys Using these keys the settings are changed to higher or lower values refer to section 5 9 1 3 3 3 First Steps 3 4 10 11 12 13 OVER indicator for the velocity The LED lights up when the output voltage exceeds either of the positive or negative full scale of the velocity measurement range If it lights up permanently the next highest velocity measurement range must be selected refer also to section 4 2 2 Analog voltage OUTPUT for the VELOCITY signal BNC jack The voltage at this output is proportional to the instantaneous vibration velocity of the object under investigation The voltage is positive when the object is moving towards the sensor head CLEAR input for the displacement decoder BNC jack This input is only active if a displacement decoder is installed It allows synchronized resetting of the displacement decoder This can be used to remove a DC component which is superimposed on a periodic vibration refer to section 4 2 3 Analog voltage OUTPUT for the DISPLACEMENT signal BNC jack This output is only active if a displacement decoder is installed The voltage at this jack is proportional to the instantaneous displacement of the object to be measured The voltage increases when the object is moving towards the sensor head CLEAR key for the d
5. 1 3 Laser Warning Labels 1 3 1 Non EC Countries Warning labels The laser warning labels for the sensor heads in non EC countries are shown in figure 1 4 Their position on the sensor head OF V 303 353 is shown in figure 1 5 and on the sensor head OFV 511 resp OFV 512 in figure 1 6 1 4 Laser class Il for OFV 303 353 and OFV 511 Laser class Illa for OFV 512 CAUTION LASER RADIATION DO NOT STARE INTO BEAM 1 mW max cw Wavelength 620 690 nm CLASS II LASER PRODUCT LASER RADIATION AVOID DIRECT EYE EXPOSURE 5 mW max cw Wavelength A 620 690 nm CLASS Illa LASER PRODUCT This equipment conforms to provisions of US 21 CFR 1040 10 and 1040 11 This equipment conforms to provisions of US 21 CFR 1040 10 and 1040 11 AVOID EXPOSURE Laser radiation is emitted from this aperture AVOID EXPOSURE Laser radiation is emitted from this aperture CAUTION Laser radiation when open DO NOT STARE INTO BEAM DANGER Laser radiation when open AVOID DIRECT EYE EXPOSURE Figure 1 4 Laser warning labels for the vibrometer in non EC countries Position Beam 1 Safety Information The position of the laser warning labels in non EC countries on the sensor head OFV 303 353 is shown in figure 1 5 Figure 1 5 Position of the laser warning labels on the sensor head OF V 303 353
6. 15 0 V 6 3 6 Fault Diagnosis A2 A1 7 1 O O 000 0 0 0 O 150 O O O O O O Og Figure 6 1 Pin configuration of the Sub D jack INTERFEROMETER 6 4 6 4 Checklist for Fault Diagnosis 6 4 1 Controller OF V 3001 with the Sensor Head OFV 303 353 Serial Number Controller Serial Number Sensor Head OFV 303 OFV 353 6 Fault Diagnosis The serial numbers can be found on the back of the instruments and also on the inside cover of this manual Target Actual 1 Is the LED POWER on the front of the controller lit up Yes 2 Is the LED LASER on the back of the sensor head lit up Yes 3 After approximately 20 minutes operation does the housing of the sensor Y es head feel warm to the touch as normal 4 Is the laser beam emitted Yes 5 Does the signal level display on the back of the sensor head react Yes 6 Does the signal level display on the display of the controller react Yes 7 Does the output signal VELOCITY OUTPUT on the front of the controller Y na es react to the movement of the reflective film 8 If the output signal does not react How high is the DC offset lt 20 mV 9 Is the output signal noisy when the laser beam is blocked Yes 10 Only for controller with displacement decoder Does the output signal DISPLACEMENT OUTPUT on the front of the Yes controller react to the movement of the reflective film 11 How high are the voltages at the Sub D ja
7. Focus the laser beam on the reflective film Does the signal level display react If the signal level display does not react the input section of the controller is faulty Now check the output signals of the controller as follows 2 Connect an oscilloscope to the BNC jack VELOCITY OUTPUT on the front of the controller Does the output signal react to the movement of the reflective film If the output signal does not react check whether a significant DC offset is present Normally a DC voltage of less than 20mV can be measured Set the oscilloscope to 1V DIV and block the laser beam Is the output signal noisy or is a straight line shown Noise must occur when the laser beam is blocked Connect the oscilloscope to the BNC jack DISPLACEMENT OUTPUT on the front of the controller Does the output signal react to the movement of the reflective film Now check the internal operating voltages of the vibrometer as follows 6 7 8 Switch off the controller by turning the key switch to position O Disconnect the cable to the sensor head from the back of the controller Using a multimeter measure the internal operating voltages at the Sub D jack INTERFEROMETER Figure 6 1 shows the pin configuration of the jack The following voltages must be measurable with a tolerance of 0 2V at the individual pins referred to GND Pin No Voltage 1 4 7 8 and 15 GND 3 6 and 9 16 0 V 2 5 0V 13 5 2 V 5and 10
8. interface Interface for an external PC based displacement decoder refer to section D 5 2 REMOTE FOCUS interface Interface for the optional hand terminal OFV 310 to focus the laser beam refer to section A 1 SIGNAL output BNC jack The DC voltage at this output is proportional to the logarithm of the optical signal level GPIB IEEE 488 interface Jack for the IEEE 488 GPIB cable refer to appendix E 3 5 3 First Steps 7 Cooling Fan Caution This opening must always be kept free to ensure sufficient cooling The distance from the wall should be at least 50mm 8 RS 232 interface Sub D jack Jack of the serial interface refer to appendix E 3 6 3 First Steps 3 3 2 Sensor Head OFV 303 The back panel and the front panel of the sensor head OF V 303 are shown in figure 3 3 OFF ON N EMISSION CONTROLLER O on AUTO MAN LASER rH gt rZza On f Figure 3 3 Rear view and front view of the sensor head OFV 303 1 Beam shutter In position OFF the laser beam is blocked Warning Only switch the beam shutter to position ON when you are making measurements CONTROLLER connector Sub D jack Jack for the connecting cable to the controller Signal level display The length of the bar is a measure of the amount of light scattered back from the surface of the object LASER LED The LED
9. 1 000mm 42 79 170 each additional meter plus 50 84 167 Maxima of visibility 232mm n 203mm n 0 1 2 1A label on the side of the sensor head shows the front lens model which is fitted The maximum stand off distance depends on the back scattering properties of the object It can range up to 250m for the sensor head OF V 303 and a surface with reflective coating 3 Measured from the front panel of the sensor head 7 6 60 0 LL R l Sot A a gt aE A lo LEN 9 QW an le oO A nnnn x m lO lo g p S N UUUYU N y AQ ARTA O ES N NE Saad Na Sa M NANN se VYUUY ar A CONTROLLER OFF S ON EMISSION O repzo u 80 120 7 Technical Specifications Figure 7 1 Rear view and bottom view of the sensor head OFV 303 353 dimensions not specified are given in mm 7 7 7 Technical Specifications 7 3 Sensor Head OFV 511 512 7 3 1 General Data Laser type Wavelength Cavity length Power consumption Output center frequency Operating temperature Storage temperature Relative humidity Minimum bending radius Dimensions without cable Weight OFV 511 Laser safety class Laser output power Length of fiber cable OFV 512 Laser safety class Laser output power Length of fiber cable from h
10. 5141 E mail polytecberlin polytec de Internet http www polytec de Polytec International Germany D POLYTEC GmbH Polytec Platz 1 7 D 76337 Waldbronn Tel 49 7243 604 0 Fax 49 7243 69944 E mail info vi polytec de Internet http www polytec com France F Polytec PI RMP S A 32 rue Delizy F 93694 Pantin Cedex Tel 33 1 48103930 Fax 33 1 48100803 E mail info polytec pi fr Internet http www polytec pi fr Great Britain GB Lambda Photometrics Ltd Lambda House Batford Mill GB Harpenden Hertfordshire AL5 5BZ Tel 44 1582 764334 Fax 44 1582 71 2084 E mail info lambdaphoto co uk Internet http www lambdaphoto co uk Japan J PI Polytec KK Akebono cho 2 38 5 Tachikawa shi J Tokyo 190 Tel 81 425 26 7300 Fax 81 425 267301 E mail info pi polytec co jp USA East Polytec PI Inc 16 Albert Street Auburn MA 01501 Tel 1 508 832 3456 Fax 1 508 832 0506 E mail info polytecpi com Internet http www polytecpi com USA West Polytec PI Inc 1342 Bell Avenue Suite 3A Tustin CA 92780 Tel 1 714 850 1835 Fax 1 714 850 1831 E mail info polytecpi com Internet http www polytecpi com Man Vib OFV3001 1202 05e
11. 8 Transport Safety Mechanism only OFV 511 512 uussnnssssnnennennenenennnnnnnnnnnnnnnnnnnnnnn 5 6 5 9 Operating the Vibrometer via the Display of the Controller usssnnnnnsnnnnnnnnnennnnn 5 7 5 9 1 Operating Philosophyi r s 0 0 ein aa aaa ia a E aAa 5 7 5 9 2 Organization of the Menus ssesssssssssssssssssssssossrssnrsrtrsnrrsreoserssnnsnnenntntrersesssenssnneneent 5 8 5 9 3 The Individual Men s neoko SA A E a S EAEE AA AN 5 9 5 10 Setting Measurement Ranges and Filters ccccecceceeeeeeeeeeeeeeeeeeeee cee aeaaeaaeeeseseeeseeeeeeeees 5 11 5 11 Displaying the Configuration of the Controller c ccceceeeeeeeeeeeeeeeeeeeeaaeaaeaaeeeeeeeeeeeeeees 5 11 5 12 Configuring the Interfaces unuusnsnnnnnnnnnnnnnnnnnnennnnnnnnnnnnnnnnnnnnnnnnnnennnnnnnnnnnnn nen 5 11 6 Fault Diagnosis 6 1 631 Generall Testswu nn tieren and tweets 6 1 6 2 NO Laser e Ha re tia ed beck atest isvavete teen hehe ees 6 2 6 3 No Measurement Signal 4444enssnnannnnnnnnnnnnnnnen nenn nnnnnnnnnnnnnnnnnnnnennnnnnnnnnnnnnnnannnnnnnnn 6 3 6 4 Checklist for Fault Diagnosis u susssnssssennnnnennennnnnnnnnnnnnnnnnnnnnnnnennnnnnnnnnnnnnnnnnnnnnnnnnenn 6 5 6 4 1 Controller OF V 3001 with the Sensor Head OFV 303 353 uuussssssannnnnnsnnnnnnnnnnnnnnn 6 5 6 4 2 Controller OFV 3001 with the Sensor Head OFV 511 512 uuunssssenssssssnsnnnnnnennnnn 6 6 7 Technical
12. ASCII character LF Line Feed i e decimal 10 hexadecimal OxOa In the examples given here this character is described with the escape sequence n according to its presentation in the programming language C Invalid settings are ignored Velocity Decoder Ta Answer with Command Description Answer ECHOON VELO Queries the measurement range Range number VELO1 set ASCII character VELO9 1 9 refer to table below VELO1 Sets the corresponding VELO1 VELO9 measurement range refer to VELO9 table below VELO Loads the initialization setting for VELO the measurement range refer to command RENDCL OVR Queries whether the full scale 0 no overrange OVRO range has been exceeded 1 overrange OVR1 Overrange If an OVD 01 is installed the measurement range is set to Measurement range Range number T V OVD 01 OVD 02 5 gt 6 25 2 7 125 3 8 1 000 4 9 Examples VELO2 n 255V VELO7 n VELO n If an OVD 02 is installed this velocity decoder is selected and the measurement range is set to 25 S V As an answer a string with the number of the velocity measurement range set is returned If the measurement range 25 3 V of the OVD 02 is selected the controller returns the string 7 n E 3 E Interface Operation RS 232 and IEEE 488 GPIB E 4 Displacement Decoder oh Answer with Command Description Answer ECHOON
13. ERRA PE oa teenie tarps 1 4 131 NOMEG CGo unliesr nn iR ER seas aaa ner 1 4 1 4 JEleetrieal Safety 229 Barrel ci el a ined 1 6 2 Introduction 2 1 Zeal SYSTEM OVE VEW a a HEILEN ECEENSPESBERTSTERRTLLTEETSUSETERTEEEETESFERSERSTRTHERSERELTSFREFT 2 1 2 2 Component Summary 2 0 ec cece cece cee a i aa a a o aeaa ai nennen 2 2 3 First Steps 3 1 3 1 Operating and Maintenance Requirement cccccceeeeeeeeeeeeeeeeeeeeeeeeeaeaaaaaeeteeeeeeeeeeeeeeees 3 1 3 2 Unpacking and Inspection ussnssennnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nn E EEA AENA 3 2 3 3 Control Elements of the Vibrometer 4z244444444440nen een nnnnnnnnnnnnnnnnnnnnnn nenn nnnnnnnnnnnnnnnnnnnn 3 3 3 93 21 GOMUMON EE E EN A AE EE A ASE AE S AE E cunpav ETE 3 3 3 3 2 Sensor Head OFV 303 2 a a SN AAE A E A 3 7 3 3 3 Sensor Head OF V 353 ccc nie uaan ine on adaa apanata ea eeeeeeeeeeaeesaaeaaaaaaaaaeeeeeeeeeeeseaaaaaea 3 8 3 3 4 Sensor Head OF V 511 le orcii E ES TRE T 3 9 3 3 5 Sensor Head OFV 51 2 2 2 2 2 Ae ek EATER NAE AN AAAA RENT 3 11 3 4 Installation and Functional Test aisis aeaaea eee S R 3 13 3 4 1 Vibrometer with Sensor Head OFV 303 353 sssessssssssssssrsrrrrrrrrrrsrrssssrrsrnrrrrrsrrens 3 13 3 4 2 Vibrometer with Sensor Head OFV 511 512 oo ceceecececeeeceeeeeeeeeaaeaaeeeeeeeeeeeeeeeeeeeeees 3 14 4 Making Measurements 4 1 Ae SOLAR Urs BASS FEEBEEESSERRUEHTRESTFER FEN a a a a NE 4 1 4 1 1 Vibrometer with Sensor Head OFV 303 353
14. Object Beam va men Q ini Sensor 7 N gt lt gt C p Reference Beam ij 1 Bragg Cell lt Detector Figure C 2 Optical configuration of the interferometer in the sensor head OFV 511 The light source is a helium neon laser which provides a linear polarized beam The polarizing beam splitter BS1 splits the beam into the object beam and the reference beam The object beam passes through the polarizing beam splitter BS2 and is focused into the fiber with an input coupler The beam is then emitted from the end of the fiber passes through a A 4 plate and is focused using the fiber head or the mini sensor on the object and scattered back from there The polarizing beam splitter BS2 then functions as an optical directional coupler together with the 4 plate and deflects the object beam to the beam splitter BS3 As both arms of the internal interferometer are symmetrical the optical path difference vanishes within the interferometer The resulting path difference is equal to twice the distance between the beam splitter BS2 and the object The Bragg cell in the reference arm generates the additional frequency offset to determine the sign of the velocity The resulting interference signal of the object beam and reference beam is converted into an electrical signal in the photo detector and subsequently decoded in the controller C 3 C Basics of the Measurement Procedure OFV 512 The optical configuration of th
15. The reference head is marked with a red dot Always mount the reference head to the reference fiber also marked with a red dot As described in section 4 2 4 the intensity of the optical signal varies periodically with the stand off distance The adjustable reference head OFV 152 is suitable for measurements which have to be carried out near a maximum of visibility but in which the stand off distance of the fiber head can not be changed e g using the fiber head OF V 130 3 or OF V 130 5 Using the OFV 152 the distance between mirror and fiber can be varied over a wide range This is achieved by moving the retroprism in the reference head In addition the intensity of the signal can be optimized by collimating the laser beam onto the retroprism with a lens It is easy to access the lens through a drilled hole in the reference head The reference head OFV 152 is shown in figure B 1 020 310 5 1 4 20G M6 OR 8 s 4 60 K DIN74 Kf3 Figure B 1 Side view and bottom view of the reference head OFV 152 dimensions not specified are given in mm B Optional Accessories for the Sensor Head OFV 511 512 Assembly 1 2 3 4 5 Do You will need an adapter and a swivel nut to mount the reference head OFV 152 You will find them both in the tool kit for the vibrometer The assembly of the reference head OFV 152 is shown in figure B 2 To mount the reference head proceed as foll
16. are technical limits which can not be exceeded even when in compliance with condition 4 4 Furthermore attention must be paid to the fact that the specified accuracy is only complied with up to a characteristic maximum frequency refer to section 7 1 5 The resulting range diagram for all measurement ranges is shown in figure 4 6 AN X um 4 Making Measurements 100 000 50 000 40 000 5 120 um V 25 000 10 000 1 280 um V 5 000 2 500 320 um V 1 000 640 500 80 um V 250 320 20 um V 100 64 50 8 um V 25 16 2 um V 10 Po L 0 5 um V o 0 5 0 25 practical lower amplitude limit 25 kHz 75 kHz 250 kHz 0 1 10 25 50 100 250 500 k 2 5k 5k 10k 25k 50k 100k 250k f Hz Figure 4 6 Combined range diagram for the displacement decoders OVD 10 OVD 20 and OVD 40 When the measurement range limits shown in figure 4 6 are exceeded overrange effects and loss of lock can occur which make a useful evaluation of the signal impossible refer also to figure 4 8 4 11 4 Making Measurements Optimizingthe The input of the vibrometer is equipped with an RF band pass filter refer to RF bandwidth Using the CLEAR function 4 12 section D 2 To achieve optimal adaptation to the FM signal bandwidth the RF bandwidth is automatically adjusted according to th
17. back of the instruments and also on the inside cover of this manual 4 Carefully retain the original packaging in case you have to return the instrument 5 Install the vibrometer and carry out a first functional test as described in section 3 4 1 sensor head OF V 303 353 or section 3 4 2 sensor head OFV 511 512 3 2 3 First Steps 3 3 Control Elements of the Vibrometer 3 3 1 Controller The front panel of the controller is shown in figure 3 1 Polytee oFv 3001 VIBROMETER CONTROLLER OVER OUTPUT DISPLACEMENT CLEAR LLO REMOTE O3 RESET Figure 3 1 Front view of 1 B the controller POWER LED The LED lights up when the key switch on the controller is turned to position and indicates that the controller is ready to operate Mains Switch This key switch disconnects the vibrometer from the mains position O and is used to switch it off in the case of danger Caution Always connect the connecting cable to the sensor head before switching the controller on 3 Liquid Crystal Display LCD with background lighting This display shows the configuration and the settings of the vibrometer The organization of the display and how to use it to operate the vibrometer are described in detail in section 5 9 FUNCTION keys Using these keys the cursor is moved vertically up
18. beam is subjected to a small frequency shift which is called Doppler shift fp and is a function of the velocity component in the direction of the object beam according to vi fp 2 5 Equation C 3 Superimposing object beam and internal reference beam i e two electromagnetic waves with slightly different frequencies generates a beat frequency at the detector which is equal to the Doppler shift The ratio C 3 to determine the velocity is however independent of its sign The direction of the velocity can be determined by introducing an additional fixed frequency shift f in the interferometer to which the Doppler shift is added with the correct sign Thus the resulting frequency at the detector fmoa is given by y N Equation C 4 Taga fg 2 Interferometers of this type which are directionally sensitive are described as heterodyne C Basics of the Measurement Procedure C 2 Optical Configuration in the Sensor Head OFV 303 353 C 2 In Polytec s vibrometers the velocity and displacement measurement is carried out using a modified Mach Zehnder interferometer The optical configuration in the sensor head OF V 303 353 is shown schematically in figure C 1 Laser BS 1 BS 2 r 4 Lens Object LG 700 fp Reference Beam y Bragg Cell Prism G BS3 2D Detector Figure C 1 Optical configuration of the interferometer in the sensor head OFV 303 353 The light source is a helium neon laser which
19. checklist in section 6 4 when you consult Polytec or your nearest representative 6 1 General Tests If the vibrometer does not function properly please first check the following 1 Is the controller connected to the mains 2 Is the mains switch in position 3 Is the LED POWER on the front of the controller lit up Warning Always disconnect from the mains before checking the fuses If the LED is not lit up it can be assumed that there is a a fault with the mains power supply Disconnect the mains plug and check the fuses on the back of the controller Note that there are two active fuses which can both lead to failure 6 1 6 Fault Diagnosis 6 2 No Laser Beam OFV 303 353 OFV 511 512 6 2 If no laser beam is emitted please check the following 1 Is the connecting cable between the controller and the sensor head installed correctly Are the jacks on the connecting cable screwed in securely Is the LED LASER on the back of the sensor head lit up after switching the controller on Warning Always disconnect from the mains before checking the fuses If the LED is not lit up it can be assumed that there is a a fault with the mains power supply of the controller Disconnect the mains plug and check the fuses on the back of the controller Note that there are two active fuses which can both lead to failure Is the beam shutter on the back of the sensor head in position ON After
20. lights up when the laser is switched on key switch on the controller in position I i e even if the beam shutter is closed refer to section 5 2 Switch AUTO MAN This knob is used to switch between remote controlled and manual focusing refer to section 5 4 Front lens Exchange of the front lens is described in section 5 5 Focusing ring Focusing ring for manual focusing of the laser beam refer to section 5 4 3 7 3 First Steps 3 3 3 Sensor Head OFV 353 The back panel and the front panel of the sensor head OF V 353 are shown in figure 3 4 S CONTROLLER LASER 0 au N o o OFF ON 5 EMISSION N 4 Figure 3 4 Rear view and front view of the sensor head OFV 353 1 Beam shutter In position OFF the laser beam is blocked Warning Only switch the beam shutter to position ON when you are making measurements 2 CONTROLLER connector Sub D jack Jack for the connecting cable to the controller 3 Signal level display The length of the bar is a measure of the amount of light scattered back from the surface of the object 4 LASER LED The LED lights up when the laser is switched on key switch on the controller in position i e even if the beam shutter is closed refer to section 5 2 5 Switch BRAKE ON OFF This knob is used to fix the focus refer to section 5 7 6 Front lens Exchange of
21. not be seen initially Press the CLEAR key several times After pressing the key several times the expected signal form should be visible on the oscilloscope refer to section 4 2 3 CLEAR function If not then the displacement measurement range is unsuitable and should be selected according to the information provided in section 4 2 3 The following sign convention for direction applies to the output signals A movement towards the sensor head is considered as being positive In this case the velocity output voltage is positive and the displacement output voltage is increasing 4 3 4 Making Measurements 4 2 Selecting Suitable Settings 4 2 1 Velocity or Displacement Measurement Dynamic range Resolution Signal to noise ratio 4 4 The vibrometer can provide both velocity and displacement signals independently of each other If the vibrometer is equipped with both velocity and displacement decoders for many measurements a decision then has to be made on which is the optimal quantity to be measured This applies in particular to harmonic vibrations as in this case the velocity and the displacement signal provide the same information according to V 2n f x Equation 4 1 velocity amplitude displacement amplitude frequency m XxX lt gt In contrast transient movements in most cases are shown much more clearly by the displacement signal Apart from these application specific aspects there are s
22. or the focusing ring of the fiber head mounted 5 3 5 Operating the Vibrometer 5 5 Exchanging the Front Lens OFV 303 353 By using different front lenses for the sensor head the vibrometer can be optimally adapted to the different ranges of stand off distance The standard front lens OFV MR mid range is suitable for stand off distances from 175mm to over 10m The ideal front lens for short range OFV SR short range has been optimized for distances from 65mm up to 5m For long range from 450mm to over 100m the front lens OFV QR long range should be used A label on the side of the sensor head shows the front lens model which is fitted The components of the front lens mount are shown in figure 5 1 Figure 5 1 The components of the front lens mount To exchange the front lens proceed as follows Caution Make sure that everything is kept clean and take great care when exchanging the front lens so that no dirt gets into the housing and the optical components are not damaged 1 Turn the threaded cover 5 anti clockwise until it can be removed Remove the mount 4 for the A 4 plate and put it to one side Pull the front lens 3 out of the lens mount 1 gt uw Carefully put the new front lens into the lens mount Turn it in the lens mount until the pin 2 slots into place 5 Put the 4 4 mount 4 in the lens mount in such a way that the pin slots into place in the slit in t
23. provides a linear polarized beam The polarizing beam splitter BS1 splits the beam into the object beam and the reference beam The object beam passes through the polarizing beam splitter BS2 as well as a i 4 plate is then focused by the lens on the object and scattered back from there The polarizing beam splitter BS2 then functions as an optical directional coupler together with the 2 4 plate and deflects the object beam to the beam splitter BS3 As both arms of the internal interferometer are symmetrical the optical path difference between the object beam and the reference beam vanishes within the interferometer The resulting path difference is equal to twice the distance between the beam splitter BS2 and the object The Bragg cell in the reference arm of the interferometer generates the additional frequency offset to determine the sign of the velocity The resulting interference signal of the object beam and reference beam is converted into an electrical signal in the photo detector and subsequently decoded in the controller C Basics of the Measurement Procedure C 3 Optical Configuration in the Sensor Head OFV 511 512 In Polytec s vibrometers the velocity and displacement measurement is carried out using a modified Mach Zehnder interferometer OFV 511 The optical configuration in the sensor head OF V 511 is shown schematically in figure C 2 Fiber Head Laser BS 1 BS2 Coupler Fiber a4 or Object Mini S GG
24. purpose in the tool kit for the vibrometer 2 Only set the transport safety mechanism to position MEASUREMENT when you are making measurements or when the system is kept in one and the same position 5 Operating the Vibrometer 5 9 Operating the Vibrometer via the Display of the Controller 5 9 1 Operating Philosophy The vibrometer is operated via a menu on the display of the controller using the keys FUNCTION and SETTING The operating structure is mainly self explanatory The individual menus are described in section 5 9 3 FUNCTION Using the keys T and J a menu is selected and within the menu a parameter is selected SETTING Using the keys and the setting of the parameter is changed The menu SETTINGS is shown in figure 5 2 as an example of the display Focus T gt Tracking Filter Fast Velocity Decoder HF Velocity Range 125 mm s V Velocity Filter off 1 5 MHz Displacement Range 5120 um V Signal Config J Figure 5 2 Example of the display The parameters are run through vertically on the display using the keys T and J Once the end of the display is reached it changes to the next menu The possibility of branching off to other menus is shown at the top and the bottom on the right The cursor gt on the left marks a selected parameter The setting of the parameter is changed to higher and lower values with the keys and Adjusted settings are activated straight away As the control process
25. resistance gt 10kQ 7 1 7 Technical Specifications 7 1 3 Low Pass Filter For typical amplitude and phase frequency response refer to section 4 2 2 Filter type Cutoff frequencies Frequency roll off Stop band rejection Bessel 3rd order 5kHz 20kHz 100kHz adjustable 60dB dec 18dB oct gt 70dB 7 1 4 Signal Voltage Output VELOCITY OUTPUT 7 2 General Data Output swing Output impedance Minimum load resistance Overrange indicator threshold 20V 50Q 10kQ 0 5 additional error typ 95 of full scale Maximum DC offset 20mV Measurement Ranges Velocity Measurement Full scale Sasse Maximum Maximum decoder range output frequency acceleration scaling factor peak peak S V F kHz g OVD 01 1 20 0 3 20 150 PLL 5 100 0 6 50 1 600 25 500 0 8 50 8 000 125 2 500 1 0 50 25 000 1 000 20 000 2 0 50 200 000 OVD 02 5 100 0 5 250 8 000 HF 25 500 1 5 1 500 240 000 125 2 500 2 0 1 500 1 200 000 1 000 20 000 5 0 1 500 9 600 000 1 Resolution is defined as the signal amplitude rms at which the signal to noise ratio is OdB in a 10Hz spectral bandwidth RBW measured at 3M Scotchlite Tape 2 1dB maximum error Calibration Accuracy 7 Technical Specifications Amplitude error Velocity Measurement decoder range T 25 5 C in the temperature range T 77 9 F 5C 40 C 41 F 104 F TV of
26. so called FM demodulators In the displacement decoder optionally the phase of the RF signal is demodulated In doing so an AC voltage is generated which is proportional to the instantaneous position of the object The individual demodulators require different reference frequencies which are in a fixed relationship to the driver frequency of the Bragg cell in the interferometer They are generated in the central oscillator block synchronized with the driver signal for the Bragg cell D Functional Description of the Controller The velocity decoder is followed by a low pass filter which suppresses spurious RF components and limits the bandwidth of the output signal to reduce background noise Via the system control various cutoff frequencies can be set for the low pass filter The last block in each signal path is an amplifier which scales the output signals and can optimally drive subsequent signal processing units The system control manages the communication of the controller with the environment via the front panel and PC interfaces and also the internal setting of all parameters for the individual functional blocks Not included in the block diagram is the power supply unit which generates all supply voltages for the sensor head and the controller D 2 Signal Conditioning Measurement of the input signal level Stabilization of the signal amplitude Limitation of the bandwidth D 2 The RF signal from the sensor head fi
27. soft dry cloth an optics brush and bellow It is very important to ensure that there is sufficient air circulation to keep the controller and the sensor head cool The air vents of the sensor head must never be covered up and the back panel of the controller must be at least 50mm away from the wall Opening up of the equipment without authorization is not necessary for its operation and will invalidate the warranty 3 1 3 First Steps 3 2 Unpacking and Inspection The vibrometer consists of the following components e controller OFV 3001 e sensor head OFV 303 353 or OFV 511 512 e connecting cable from the controller to the sensor head length 5m e earthed mains cable Caution Protect the unpacked sensor head from hard jolts as these can lead to misalignment of the interferometer Caution Handle the front lens of the sensor head with great care Dirt may only be removed very carefully with a soft dry cloth an optics brush and bellow Please pay attention to the following steps when unpacking 1 After unpacking check all components for external damage scratches loose screws damaged lens etc 2 Check the packaging for signs of unsuitable handling during transport 3 Inthe case of a wrong delivery damage or missing parts inform your local Polytec representative immediately and give them the serial number of the sensor head and the controller The identification labels can be found on the
28. to figure A 4 The optional telescope is fitted with an interference filter for the laser wavelength 632 8nm to enhance the spot in daylit conditions The ready assembled tip tilt stage is shown in figure A 3 Figure A 3 Tip tilt stage OFV P5 with fitted targeting telescope and sensor head The underside of the assembly has standard M6 and 1 4 threads as well as the mountings for the hexagonal quick release Manfrotto tripod system refer also to figure A 4 Tilt in horizontal direction 1 5 Tilt in vertical direction 1 Weight tip tilt stage 2 4kg Weight incl targeting telescope 3 0kg Dimensions refer to figure A 4 A 3 A Optional Accessories for the Sensor Head OFV 303 353 426 1 4 2xM6 A O fo d Mounting Plate ee T for Manfrotto Tripod 120 185 160 280 OFV 303 Telescope with Fixing 7 Figure A 4 Bottom view and side view of the OFV P5 with fitted targeting telescope and sensor head All dimensions are given in mm A 4 B Optional Accessories for the Sensor Head OFV 511 512 Appendix B Optional Accessories for the Sensor Head OFV 511 512 B 1 Reference Head OFV 152 If single point measurements are carried out with the sensor head OFV 512 one of the two fibers must be terminated with a reference head
29. via a key switch on the controller The key can only be removed when the controller is switched off It is not necessary to open the housing of the sensor head when using the vibrometer as intended Opening the housing will invalidate the warranty Please pay attention to the following safety precautions when using the vibrometer Never look directly into the laser beam with the naked eye or with the aid of mirrors or optical instruments Only switch the beam shutter to the ON position when you are making measurements To position the sensor head switch the beam shutter to the OFF position Only when the sensor head is roughly in place and has been fixed in a stable position switch the beam shutter to ON Do not use any reflective tools watches etc when you are working in the path of the laser beam 1 Safety Information 1 2 Laser Warning Labels 1 2 1 EC Countries Warning The laser warning labels for the sensor heads in EC countries are shown in labels figure 1 1 Label 2 3 and 4 are affixed or enclosed in the language of the customer s country Their position on the sensor head OF V 303 353 is shown in figure 1 2 and on the sensor head OFV 511 resp OFV 512 in figure 1 3 Laser class 2 for Laser class 3R for OFV 303 353 and OFV 511 OFV 512 1 2 Laser Radiation Laser radiation Do not stare into beam Avoid direct eye exposure Class 2 laser product Class 3R laser product According to EN 60825 1 According to EN 608
30. 25 1 P lt 1 mW cew X 620 690 nm P lt 5 mWiew A 620 690 nm 3 Caution Laser radiation when open Laser aperture Do not stare into beam 4 Caution Laser radiation when open Avoid direct eye exposure Figure 1 1 Laser warning labels for the vibrometer in EC countries 1 2 1 Safety Information Position The position of the laser warning labels in EC countries on the sensor head OFV 303 353 is shown in figure 1 2 Figure 1 2 Position of the laser warning labels on the sensor head OF V 303 353 in EC countries The position of the laser warning labels in EC countries on the sensor head OFV 511 resp OFV 512 is shown in figure 1 3 For the sensor head OFV 511 label 3 is affixed inside For the sensor head OFV 512 label 4 is affixed inside and label 3 is enclosed with the sensor head as it is not possible to affix it on the mini sensor due to its size Please affix this label clearly visible near the mounted mini sensor or fiber head ACHTUNG Bitte vor dem Transport O die Transportsicherung bet tigen O 8 CAUTION e H SIGNAL Please secure transport mechanism O s e PROCESSOR before shipment gt MEASUREMENT TRANSPORT Beam e TU Figure 1 3 Position of the laser warning labels on the sensor head OFV 511 512 in EC countries 1 Safety Information
31. 920 20 10 0 250 100 The resolution is defined as 1 increment of the fringe counter output which is equivalent to a 4mV output voltage step Calibration Accuracy Amplitude error Conditions Amplitude Linearity Maximum linearity error 1 of rms reading 1 increment Sinusoidal vibration f 100Hz amplitude 50 of full scale range load resistance gt 1 MQ Ranges 20um V 5 120um V Ranges 0 5um V 8um V 1 increment 2 increments 7 5 7 Technical Specifications Trigger CLEAR Input Threshold Hysteresis Maximum input voltage Pulse rate Input impedance 7 2 Sensor Head OFV 303 353 7 2 1 General Data Laser type Wavelength Cavity length Laser safety class Laser output power Power consumption Output center frequency Operating temperature Storage temperature Relative humidity 10mV typ rising edge 5mV typ 14V 40 Hz 16kHz gt 0 5kQ depending on the pulse frequency helium neon 633nm 203mm 2 in non EC countries Il lt 1mW ca 15W 40MHz 0 C 40 C 32 F 104 F 15 C 65 C 5 F 149 F max 80 non condensing Dimensions refer to figure 7 1 Weight 3 5kg 7 2 2 Optics Front lens Long range Mid range Short range QR MR SR Focal length mm 100 60 30 Minimum stand off distance mm 450 175 65 Aperture diameter 1 e mm 12 7 3 5 Spot size typ um 175mm 10 30 450mm 15 33 75
32. AMPL Queries the set measurement Range number AMPL1 range ASCII character AMPL7 1 7 refer to table below AMPL1 Sets the corresponding AMPL1 AMPL7 measurement range refer to AMPL7 table below AMPL Loads the initialization settings AMPL for the measurement range refer to command RENDCL RES Triggers the reset function of the RES displacement decoder Measurement range Range number um V OVD 10 OVD 20 0 5 0 1 2 20 3 3 80 4 4 320 5 5 1 280 6 6 5 120 7 7 Examples AMPL2 n If an OVD 20 is installed the measurement range is set to 8um V AMPL7 n The measurement range is set to 5 120 um V AMPL n As an answer a string with the number of the displacement measurement range set is returned If the measurement range 320 um V is selected the controller returns the string 5 n E Interface Operation RS 232 and IEEE 488 GPIB E 2 5 Filter Setting and Query Tracking Filter maar Answer with Command Description Answer ECHOON TRACK Queries the setting of the tracking 1 OFF TRACK1 filter 3 SLOW TRACK3 4 FAST TRACK4 TRACK1 _ Sets the tracking filter to this TRACK1 TRACK3 value TRACK3 TRACK4 TRACK4 TRACK Loads the initialization setting for TRACK the tracking filter refer to command RENDCL Low Pass Filter a Answer with Command Description Answer ECHOON FILT Queries the setting of the low 1 O
33. FF FILT1 FILT4 pass filter 2 100kHz 3 20kHz 4 5kHz FILT1 Sets the low pass filter to this FILT1 FILT4 FILT4 value FILT Loads the initialization setting for FILT the low pass filter refer to command RENDCL E 5 E Interface Operation RS 232 and IEEE 488 GPIB E 2 6 Signal Level Query and Motor Control Commands E 6 Signal Level aor Answer with Command Description Answer ECHOON LEV Queries the optical signal level 0 no level LEVO LEV40 1 level 1 2 level 1 and 2 3 level 1t0 3 40 level 1 to 40 Motor Control Commands we Answer with Command Description Answer ECHOON l Slowly drive the motor to the left until l the command N is received L Quickly drive the motor to the left until L the command N is received r Slowly drive the motor to the right until r the command N is received R Quickly drive the motor to the right until R the command N is received N Stops the motor N LIM Queries the status of the motor while it R reached right limit is in motion L reached left limit N not yet reached limit Polytec Deutschland POLYTEC GmbH Polytec Platz 1 7 D 76337 Waldbronn Tel 07243 604 0 Fax 07243 699 44 E mail info polytec de Internet http www polytec de POLYTEC Physik Instrumente Vertriebs und Beratungsb ro Berlin Schwarzschildstra e 1 D 12489 Berlin Tel 030 6392 5140 Fax 030 6392
34. OFV 3001 o D gt Ge a 4 Velocity decoders Displacement decoders OVD 01 o OVD 10 j OVD 02 is OVD 20 000 000 OVD 30 OVD 40 Figure 2 2 Compatibility of the controller OFV 3001 with sensor heads and decoders The modularity is achieved initially through strict separation of optics and electronics Every decoder can be combined with every sensor head The controller is equipped with one of the two available velocity decoders as standard A maximum of two velocity decoders can be installed The velocity decoders are described in section D 4 1 As an option the controller can be fitted with one of the four available displacement decoders as well as be supplemented by a PC based displacement decoder refer to section D 5 2 The various standard and fiber optical sensor heads comply with the different requirements of the vibrometer s optics For every sensor head a selection of lenses covers a wide range of stand off distances 3 First Steps 3 First Steps 3 1 Operating and Maintenance Requirements Operating environment Mains connection Warming up Assembly Transport Connecting cables Cleaning Optical components Cooling Opening up the equipment The vibrometer can be operated in dry rooms under normal climate conditions refer to chapter 7 In particular the optical components in the sensor head are sensitive to moisture high temperatures jolting and dirt
35. Specifications 7 1 7 1 Controller OFV 3001 2 22 ar alse Ge na ees Taiti ami ee 7 1 FAS General Datania N nee hate ede A ee ede A eee 7 1 Hadise Intertacess 2 ES ne A ie I Aird See eher ah Ae Ta 7 1 1 1533 LOWPASS Filter a et re erde are 7 2 7 1 4 Signal Voltage Output VELOCITY OUTPUT zuunssussssssssnnennennnnennnnnnnnnnnnnnnnnnnnnnnnnnnn 7 2 7 1 5 Signal Voltage Output DISPLACEMENT OUTPUT optional a se 7 5 7 2 Sensor Head OFV 303 353 seca Rinne 7 6 1 2 1 General Data m ves an neluleshertkanee 7 6 ERBE 0 O1 SEE HELEN EEE sae ceae de EEE EEE TIER EEE TE EEE EEE 7 6 7 3 sensor Head OEV 511 5 12 i122 tasers eke Rae Renee 7 8 1 331 GeneralDatas tesa nn ae ate tee itd AE heer eet ae 7 8 13 2 Oplie sun 1 Bea EL ln Heed a Per 7 8 Appendix A Optional Accessories for the Sensor Head OFV 303 353 Appendix B Optional Accessories for the Sensor Head OFV 511 512 Appendix C Basics of the Measurement Procedure Appendix D Functional Description of the Controller Appendix E Interface Operation RS 232 and IEEE 488 GPIB 1 Safety Information 1 Safety Information 1 1 Laser Safety The light source of the vibrometer is a helium neon laser It is important to understand that laser light has different properties than ordinary light sources Laser radiation is generally extremely intense due to the beam s low divergence and great care should be taken when handling laser instruments that the direct or reflected beam doe
36. When the vibrometer is taken into operation after being stored somewhere cool a sufficient acclimatization period should be allowed for before switching it on Avoid condensation on the optical components caused by a rapid change in temperature Before taking the vibrometer into operation please ensure that the supply voltage set with the voltage selector corresponds with the local mains voltage Only replace defective fuses by fuses of the same kind and equal rating The helium neon laser in the sensor head requires a certain period of time to reach optimum stability The vibrometer should thus be switched on 20 minutes before the first measurements are made to ensure that it is in thermal equilibrium with the surroundings The sensor head OF V 303 should not be positioned provisionally but mounted properly on a stable tripod using the threads provided The sensor head OFV 511 512 is equipped with a transport safety mechanism which always has to be activated before moving the sensor head refer to section 5 8 As a general rule the vibrometer must not be switched on until all cables are connected Make sure that all jacks are connected properly and firmly Protect the cables from mechanical damage and from high temperatures The housing surfaces of the instrument can be cleaned with mild detergent solutions Organic solvents must not be used Handle all optical components with great care Dirt may only be removed very carefully with a
37. a lens To mount this head onto the fiber it has to be partially opened and then you proceed as follows 1 Undo two of the four Allen screws on the back panel of the OF V 200 and remove one half of the back panel 2 Undo the four Allen screws on the front panel of the head and take off the front panel 3 Thread the fibers through the opened back panel and through the fiber head itself and screw the end of the fiber into the front panel until it sits tightly 4 Re assemble the head by starting with the front panel Make sure while doing so that you orient the bayonet mounting plate so that you can read the inscription on the front lens from above The fiber head can now be used B Optional Accessories for the Sensor Head OFV 511 512 B 4 Flexible Arm OFV 039 Technical Specification The flexible arm OFV 039 is a mount device for the mini sensor of the sensor head OFV 511 512 The mini sensor can thus be easily positioned in places which are difficult to access The heavy steel base ensures that it stands securely and if required the steel base can be screwed onto the surface beneath via the drilled mounting holes refer to figure B 5 Alternatively the flexible arm can be attached to any magnetic surface which is large enough using the magnetic base The flexible arm is shown in figure B 4 Figure B 4 Flexible arm OFV 039 for the mini sensor 1 Base plate with drilled mounting holes refer also to figure B 5 2 Magnet foo
38. aintained Loads the initialization settings and sets the status LOCAL The command corresponds to DCL GTL E 2 2 Control Commands IEEE 488 GPIB LOCAL REMOTE LLO The controller recognizes three different operating modes for remote control via the interface IEEE 488 GPIB The vibrometer is controlled via the display and the keys on the front of the controller The vibrometer can be controlled via the front panel and via the interface The status REMOTE is set when an IEEE 488 GPIB bus controller asserts the signal REN and addresses the controller LOCAL LOCK OUT The status LLO can only be set from the status REMOTE In this mode itis only possible to operate via the interface IEEE 488 GPIB Key input on the front panel is ignored only the key RESET retains its function The operating mode of the controller is shown on the front panel with the LEDs REMOTE and LLO as follows Operating mode ae REMOTE LLO LOCAL Off Off REMOTE On Off LLO On On E 2 3 Echo Commands ECHOON ECHOOFF E 2 As default the echo function is switched off when the system is being controlled remotely With this command an echo is returned for valid commands The echo function is switched off An answer is only returned on the corresponding commands E Interface Operation RS 232 and IEEE 488 GPIB E 2 4 Measurement Range Setting and Query All transmissions from and to the controller are terminated with the
39. and section B 1 and the other mini sensor with a fiber head Make sure that the key switch on the controller is in position O Fix the mini sensor as appropriate to the flexible arm OFV 039 refer to section B 4 or to the OFV 036 This ensures a secure position and makes it easier to focus on the object Position the mini sensor or fiber head according to the information on optimal stand off distances in section 4 2 4 Align the mini sensor or fiber head such that the laser beam points along the velocity vector to be measured i e in general perpendicular to the surface of the object Switch the controller on by turning the key switch to position Please allow 20 minutes for the laser to warm up before making measurements On the front of the controller the LED POWER lights up Providing the connecting cable has been installed correctly the LED STANDBY on the sensor head also lights up Laser light is not yet emitted as the beam shutter is still closed Before now opening the beam shutter remember the information on laser safety provided in section 1 1 Open the beam shutter on the sensor head by pressing the key LASER on the front of the sensor head The LED ON on the sensor head lights up At the same time the LED STANDBY goes out The laser beam is now emitted from the mini sensor or fiber head Focus the laser beam on the surface of the object The signal to noise ratio is maximal if the signal level display fully lig
40. approximately 20 minutes operation does the housing of the sensor head feel warm to the touch as normal indicating that the laser is operating Is the LED LASER STANDBY on the front of the sensor head lit up after switching the controller on Warning Always disconnect from the mains before checking the fuses If the LED is not lit up it can be assumed that there is a a fault with the mains power supply of the controller Disconnect the mains plug and check the fuses on the back of the controller Note that there are two active fuses which can both lead to failure Is the beam shutter key LASER on the front of the sensor head pressed once after switching the controller on The LED LASER ON lights up when the beam shutter key LASER is once pressed and thus the laser beam is emitted At the same time the LED LASER STANDBY goes out Pressing the beam shutter key LASER a second time the beam shutter is closed at the same time the LED LASER ON goes out and the LED LASER STANDBY lights up again Is a break of the optical fiber cable visible 6 Fault Diagnosis 6 3 No Measurement Signal Signal level display Velocity signal Displacement signal optional Internal operating voltages If the laser beam is emitted but there is no measurement signal check the following 1 Put a piece of reflective film at an optimal stand off distance according to the information given in section 4 2 4 in the beam path
41. as it directly determines the optical frequency offset in the interferometer and thus the center frequency of the carrier signal The phase reference signal for the displacement decoder is generated with a fixed relationship to the carrier frequency fp The variable mixing frequency f is automatically set by the system control dependent on the selected velocity measurement range D Functional Description of the Controller D 4 Velocity Decoder D 4 1 The Various Velocity Decoders OVD 01 OVD 02 Technically it is just about impossible to attain all desirable and realizable characteristics of the velocity decoder in a single universal subassembly The modular concept of the controller thus permits the use of two different velocity decoders which can be installed simultaneously The selection of the decoders depends on the application The models available are the OVD 01 and OVD 02 which feature the following characteristics The OVD 01 is a velocity decoder for applications in the acoustic frequency range up to approximately 20 kHz In this range it has excellent linearity and accuracy characteristics With five measurement ranges from 1 YV to 1 000 57V it covers the full dynamic range of the vibrometer with high resolution The upper four measurement ranges can be used up to frequencies of 50kHz and higher while retaining their good characteristics however amplitude accuracy and linearity decrease with higher frequencies The meas
42. at the edge of the opening 5 The distance from the edge of the opening 5 to the exit window 1 is about 130mm Fix the mini sensor by gently tightening the stud screw 6 Fix the holding device provided onto the grip 7 of the side exit head Position the side exit head at the measurement location a pP N You can position the exit window 1 subsequently by removing the knurled screw 3 turning the probe 2 and fixing the knurled screw again 6 Focus the laser beam by turning the focusing ring of the mini sensor 4 through the opening on the side exit head 7 Palytye 6 5 4 Figure B 3 Side exit head OFV C 110 with mini sensor mounted B 3 B Optional Accessories for the Sensor Head OFV 511 512 B 3 Fiber Heads Assembly OFV 101 OFV 102 OFV 130 3 OFV 130 5 Assembly OFV 200 B 4 The following fiber heads are available for the sensor head OFV 511 512 e OFV 101 e OFV 102 standard fiber head e OFV 130 3 for beam diameter 3um e OFV 130 5 for beam diameter 5um e OFV 200 high accuracy fiber head To mount the fiber head onto the fiber proceed as follows 1 Unscrew the mini sensor from the fiber and keep in a safe place because each mini sensor is exactly adjusted to its fiber 2 Screw the fiber head onto the end of the fiber until it is securely fixed The fiber head can now be used The fiber head OF V 200 is equipped with a Nikon bayonet mount which can take a Nikon camer
43. ating the vibrometer via the RS 232 interface on the back of the controller it is possible to switch between the transfer rates 4 800 Baud and 9 600 Baud refer to appendix E 5 9 5 Operating the Vibrometer Menu SETTINGS 5 10 In the menu SETTINGS the measurement ranges and filters are set The contents of the menu depends on the decoders installed The individual settings are described in the following Tracking Filter In this line you can set the tracking filter The input signal from the sensor head is pre processed with the tracking filter You will find information on the settings OFF SLOW FAST of the tracking filter in section 4 2 2 and in section 4 2 3 Velocity Decoder In this line you can set the active velocity decoder This line is only present if both decoders OVD 01 and OVD 02 are installed The velocity decoders are abbreviated as described above in table 5 1 Note If the PLL decoder is selected and the velocity measurement range 1 AN is set it is not possible to change to the HF decoder because this decoder does not have the velocity measurement range available Velocity Range In this line you can set the velocity measurement range The possible settings depend on the velocity decoder selected You will find information on setting the velocity measurement range in section 4 2 2 Velocity Filter In this line you can set the cutoff frequency of the low pass filter In position OFF the upper fr
44. bject by 1 2 The binary value of the signal DIRECTION provides the sign Both pulses are counted by the binary forward reverse counter the status of which thus corresponds with the instantaneous position of the object The counting range is of 12bit which corresponds to 4 096 increments As each increment is equivalent to 316 4nm total displacements of up to approximately 1 28mm 0 64mm amplitude can be measured in the so called direct counting mode with a resolution of 316 4nm To make use of the full counting range the counter is reset as appropriate with an external CLEAR pulse at each zero crossing of the object refer to section 4 2 3 CLEAR function To be able to present the displacement signal in real time with an oscilloscope e g the counter content is converted by a 12bit digital to analog converter into an analog voltage with a step resolution of approximately 4mV The steps are smoothed with a low pass filter at high frequencies A subsequent amplifier stage scales the signal according to the measurement range set In the high resolution displacement decoders OVD 20 and OVD 40 the additional functional block phase multiplier realizes an even higher resolution In this subassembly the interferometer signal mog is pre processed in the sense of an interpolation before the quadrature demodulator converts it into a pulse train with a higher resolution This generates integer multiples of the phase deviation Ag and thus increases the
45. by the internal low pass filter The maximum acceleration which the tracking filter can still follow depends on the filter bandwidth The low pass time constant is switched between SLOW and FAST via the system control and thus adapts the dynamic characteristics to the application The tracking filter can be turned off via a bypass if the accelerations are too high or in the case of good optical signals off Output eer EIER EAS Amplifier a er NGO on Input gt _ m 2 V ZN Control Bus Figure D 2 Block diagram of the tracking filter circuit D 3 D Functional Description of the Controller Down mixing of the frequency Down mixing of the frequency in the input section is required to convert the carrier frequency of the FM signal from 40 MHz originally to lower intermediate frequencies With these intermediate frequencies the velocity decoder can work optimally in the individual measurement ranges Down mixing is carried out by a mixing process which does not affect the modulation content of the FM signal The variable frequency f is produced by the so called local oscillator in a fixed relationship to the drive frequency of the Bragg cell D 3 Oscillator Section D 4 The oscillator section generates all drive frequencies for operating the other subassemblies in the vibrometer The drive frequency for the Bragg cell is of central importance
46. can now be used 5 7 Fixing the Focus only OFV 353 The OFV 353 sensor head is particularly suitable for applications in which the sensor head is subjected to some mechanical stress shaking etc If the front lens is fixed the focus remains stable for a long period of time The focus fixing mechanism is operated by the knob BRAKE ON OFF Proceed as follows 1 To fix the focus press the knob BRAKE ON OFF into the front panel until it stops BRAKE ON The mechanism is stopped internally with a series of cogs The fixing positions of the lens are therefore not continuous but are very close to each other 2 To release the fixing mechanism pull the knob BRAKE ON OFF out until it clicks into place BRAKE OFF Then turn the focusing ring until the adjustment mechanism clicks into place You can now focus the laser beam as described in section 5 4 5 5 5 Operating the Vibrometer 5 8 Transport Safety Mechanism only OFV 511 512 5 6 Caution Always activate the transport safety mechanism before moving the sensor head If the sensor head is being transported the shock absorbing feet of the housing do not provide sufficient protection For this reason the interferometer must additionally be secured with a transport safety mechanism To activate the transport safety mechanism you proceed as follows 1 Turn the screw on the back of the sensor head to position TRANSPORT A 5mm Allan key is supplied for this
47. ck INTERFEROMETER on the back of the controller Pin 1 4 7 8 and 15 GND Pin 3 6 and 9 16 0V Pin 2 5 0V Pin 13 5 2V Pin 5 and 10 15 0V Further observations 6 5 6 Fault Diagnosis 6 4 2 Controller OF V 3001 with the Sensor Head OFV 511 512 Serial Number Controller Serial Number Sensor Head OFV 511 OFV 512 The serial numbers can be found on the back of the instruments and also on the inside cover of this manual Target Actual 1 Is the LED POWER on the front of the controller lit up Yes 2 Is the LED LASER ON on the front of the sensor head lit up Yes 3 After approximately 20 minutes operation does the housing of the sensor Y es head feel warm to the touch as normal 4 Is the laser beam emitted Yes 5 Is a break of the optical fiber cable visible No 6 Does the signal level display on the front of the sensor head react Yes 7 Does the signal level display on the display of the controller react Yes 8 Does the output signal VELOCITY OUTPUT on the front of the controller Y EHE es react to the movement of the reflective film 9 If the output signal does not react How high is the DC offset lt 20 mV 10 Is the output signal noisy when the laser beam is blocked Yes 11 Only for controller with displacement decoder Does the output signal DISPLACEMENT OUTPUT on the front of the Yes controller react to the movement of the reflective film 12 How h
48. d the beam shutter on the sensor head is in position OFF Check the setting on the mains voltage selector on the back of the controller as well as the fuses Plug the connecting cable into the Sub D jack CONTROLLER on the back of the sensor head and into the Sub D jack INTERFEROMETER on the back of the controller Fix the connections with the screws provided All connections must be easy to plug in If not check the plug for bent contact pins to avoid serious damage being incurred Use the earthed mains cable to connect the controller to a wall outlet providing protective grounding Switch the controller on by turning the key switch to position I On the front of the controller the LED POWER lights up Providing the connecting cable has been installed correctly the LED LASER on the sensor head also lights up Laser light is not yet emitted as the beam shutter is still closed Before now opening the beam shutter remember the information on laser safety provided in section 1 1 Open the beam shutter on the sensor head by turning the knob to position ON The laser beam is now emitted from the sensor head Put a piece of reflective film enclosed in this manual at approximately 45cm from the front panel of the sensor head in the beam path OFV 303 Pull the knob AUTO MAN out until it clicks into place and turn the focusing ring until the adjustment mechanism clicks into place OFV 353 Pull the knob BRAKE ON OFF out until it cl
49. e of the controller is shown in figure D 1 PC based Displacement Decoder y y Amplifier Pmod Displacement Displacemen Decoder optional Output Signal Pret IEEE 488 Conditioning Oscillator Sensor RL flo SD oO Disp gt me e NL System Control ee Input FR NL O Velo Bragg Cell fi ragg B Front Panel Drive Out m Control Bus N Level Detector Afoa Af Vinod e m M ae Demodulator v Signal Vv Level a ae Velocity Signal Level Display IND u Output 4 Output Switch Low Pass Amplifier Aa Al Vinod p BEE EEE Demodulator II Figure D 1 Block diagram of the controller OF V 3001 The RF signal from the sensor head sensor input initially passes the functional block signal conditioning where it is pre processed to optimally drive the following blocks Subsequently the signal path is split up into the branches velocity signal decoding below and displacement signal decoding above If the controller is fully equipped there are two velocity decoders installed demodulator and demodulator II The velocity is modulated on the radio frequency of the input signal In the velocity decoder an AC voltage is generated which is proportional to the instantaneous velocity of the object with the aid of
50. e sensor head OF V 512 is shown schematically in figure C 3 Fiber Head Laser BS 1 BS 2 Coupler Fiber 2 4 or Object 1 Mini Sensor A Object Beam f i ff Reference Beam y Bragg Cell 1 I BS 4 Coupler C Detector Fiber 2 4 Fiber Head or Mini Sensor Object 2 hr A 0 NO Figure C 3 Optical configuration of the interferometer in the sensor head OFV 512 In contrast to the OFV 511 the beam is coupled out of the reference arm as well as the object arm here As the resulting signal only depends on the path difference this allows optical generation of a true difference signal With the OFV 512 the prism in the reference arm is replaced by another beam splitter BS4 which has the same characteristics as the beam splitter BS2 The signal measured here is thus the relative velocity or displacement between the two objects C 4 D Functional Description of the Controller Appendix D Functional Description of the Controller D 1 Overview The main function of the controller is to demodulate the radio frequency signal RF signal provided by the interferometer in the sensor head The frequency of the signal is the carrier of the velocity information and the phase is the carrier of the displacement information Secondary functions such as human interfacing display and filters improve the user friendliness of the vibrometer An overview of the functional structur
51. e velocity measurement range set As this process also affects the input signal of the displacement decoder the setting of the velocity measurement range is relevant even if only the displacement output is being used The signal to noise ratio of the displacement measurement can be improved with targeted limitation of the RF bandwidth which is particularly important in the case of weak optical signals This means that the velocity measurement range should be selected to be as low as the application allows The maximum velocity must not exceed the respective full scale range i e 10 times the scaling factor e g 50mm s for the measurement range 5 YV If the LED VELOCITY OVER lights up continuously or the displacement signal breaks down the next highest velocity measurement range has to be selected If however the optical signal is constantly good the range 1 000 s V should be selected as it does not limit the bandwidth and therefore its influence does not need to be taken into consideration As there is no lower frequency limit for the displacement decoder it can also measure stationary signals DC After setting a certain displacement measurement range a certain voltage is present at the output the so called DC offset which depends on the distance of the object to the sensor head and on the thermal drift of the interferometer Dynamic displacements of the object AC are correctly added to or subtracted from this DC offset as long as t
52. ed and the most suitable setting for the tracking filter should be determined with the aid of figure 4 1 4 13 4 Making Measurements 4 2 4 Optimal Stand Off Distances for the Sensor Heads OFV 303 353 OFV 511 OFV 512 Maxima of visibility 4 14 The stand off distance is measured from the front panel of the sensor head OFV 303 353 The optimal stand off distances are 232mm n 203mm n 0 1 23 i e at 232mm 435mm 638mm etc The stand off distance is measured from the shoulder of the connector for the mini sensor or the fiber head The optimal stand off distances are 135mm n 203mm n 0 1 2 i e at 135mm 338mm 541mm etc When making two point measurements the stand off distance is the difference between the stand off distances of both arms The optimal stand off distances are Omm n 203mm n 0 152 i e at 0mm 203mm 406mm etc When making single point measurements with the reference head OFV 151 the stand off distance is measured from the shoulder of the connector for the mini sensor or the fiber head The optimal stand off distances are 63mm n 203mm n 0 152 i e at 63mm 266 mm 469mm etc The light source of the vibrometer is a helium neon laser This is a multimode laser in which a maximum of two modes can exist The interference of the two modes leads to the intensity of the resulting optical signal varying periodically with the stand off distance The inte
53. elected In all velocity measurement ranges the LED OVER on the front of the controller lights up if either the positive or negative end of range is exceeded As a general rule the next highest measurement range should then be selected Please note however that the LED is activated by very short overrange already which could be caused by noise spikes In such cases the velocity measurement range can be retained as long as it is suitable for the amplitude of the required signal Observing the signal on the oscilloscope will provide clarification on this refer to section 4 1 3 The tracking filter is used to improve the signal to noise ratio of the input signal from the sensor head This is advantageous to bridge short dropouts in particular which always occur due to the speckled nature of the light scattered back from the object The bridging capability is generally better with a high time constant SLOW however it may not be possible to follow highly dynamic signals any more In this case FAST or OFF has to be selected The best setting therefore has to be determined from case to case or be estimated based on the range diagram in 4 1 The range diagram shows the dynamic limits for both settings of the tracking filter plotted versus the frequency Velocity m s 10 velocity limit 3 m s ZH 001 Huu Aouanbay 0 01 0 03 0 1 0 3 1 3 10 30 100 300 Frequency kHz Figure 4 1 Range d
54. ement range should be selected such that the output signal is as high as possible but with its peak values definitely remaining below the maximum signal amplitude of 8V refer also to section 4 2 3 CLEAR function Another aspect is the maximum expected velocity For technical reasons the absolute velocity limit of the vibrometer 10 m s can only be made use of in the upper displacement measurement ranges 80 um V 320um V 1 280 um V 5 120 um V In the lower displacement measurement ranges however several counts per fringe are generated by interpolation whereby bandwidth and count frequency multiply correspondingly refer to section D 5 3 As a result the maximum permissible velocity decreases to about the same extent as the displacement resolution increases Due to this correlation the peak values of the lower displacement measurement ranges 0 5um V 2um V 8um V 20um V can only be made use of for frequencies of up to approximately 2 5kHz Above this value the maximum measurable amplitude x decreases with increasing frequency according to equation V 2n f x const Equation 4 4 v velocity amplitude x displacement amplitude f frequency From the correlations described it can be concluded that the frequency also has to be taken into consideration when selecting the displacement measurement range The specified maximum frequency can only be measured in the upper displacement measurement ranges In the lower ranges there
55. equency limit of the active velocity decoder is shown You will find information on setting the low pass filter in section 4 2 2 Displacement Range This line is only present if a displacement decoder is installed In this line you can set the displacement measurement range The possible settings depend on the displacement decoder installed You will find information on setting the displacement measurement range in section 4 2 3 Signal This line shows the optical signal level as a bar display Menu FOCUS only with OFV 303 5 Operating the Vibrometer This menu is only available in vibrometers with the sensor head OFV 303 In this menu the motor which moves the front lens is controlled using the and keys The movement of the motor is shown on the display of the controller with following symbols lt and gt Motor is running slowly lt lt and gt gt Motor is running quickly lt lt and gt gt Motor has stopped at the end of the adjustment range The bar in the lower line of the display shows the optical signal level 5 10 Setting Measurement Ranges and Filters Controller Interface You set the measurement ranges and filters via the display of the controller in the menu SETTINGS refer to section 5 9 3 You can also set the measurement ranges and filters via the RS 232 interface or the IEEE 488 GPIB interface on the back of the controller Adjusting the settings via the PC interfaces is described in ap
56. ernally but can in the simplest case be taken from the VELOCITY OUTPUT itself Each zero crossing of a rising velocity signal then resets the displacement decoder This requires however a certain quality of the velocity signal If it is too noisy the displacement signal becomes unstable As the CLEAR input has a relatively low input impedance an amplitude error of 5 to 10 is induced at the velocity output in this type of operation refer to section 7 1 5 The correlations shown in section 4 2 2 for the tracking filter also apply in principle for the displacement measurement If the range limits shown in figure 4 1 are exceeded the tracking filter loses lock and induces phase jumps in the input signal which make the displacement signal discontinuous The oscilloscope trace in figure 4 8 shows the distorted displacement signal of a sinusoidal vibration at an acceleration where the tracking filter loses lock Tek Stop M Pos 0 0005 CURSOR sh PEPPPPPEE WEREEFEFEFPEPPELFEEFEFEFRFFFPPELEELFFFEFFFEPFPLEERSERFEFFFFRPEPEPERFFFEFFERGFPFELEELEEERFEFPFPPPEPERE ET CH1 Delta 16 2 Beer ctrhrcarerrrckrrrrrrrrrgrrrrrrrrrhrrrrrerrrderyr x Cursor 1 eas ARE E A oes eS STL BREITER be a ERROR ee ee ak Cursor 2 i 3 5 B20 CHT S 00vEy CH2 Soom M4 ims CHT 7 140V RefB 5 00 Ims fend Figure 4 8 Displacement signal when the tracking filter loses lock In this case the velocity signal should be evaluat
57. f the object 3 9 3 First Steps 5 Fiber optic cable 6 Mini sensor Diameter 10mm The mini sensor contains a lens to focus the laser beam Exchange of the mini sensor with a fiber head is described in section B 3 Note Each mini sensor is exactly adjusted to its fiber Never exchange the mini sensor with a mini sensor of another sensor head The back panel of the sensor head OF V 511 is shown in figure 3 6 lo oN ACHTUNG Bitte vor dem Transport die Transportsicherung betatigen CAUTION SIGNAL Please secure transport mechanism PROCESSOR before shipment MEASUREMENT TRANSPORT 0000000 o00000000 Figure 3 6 Rear view of the sensor head OFV 511 7 Transport handle Caution Always activate the transport safety mechanism before moving the sensor head 8 Sensor mount To transport the sensor head the mini sensor can be plugged into this sensor mount 9 SIGNAL PROCESSOR connector Sub D jack Jack for the connecting cable to the controller 10 Transport safety mechanism The transport safety mechanism is de activated by turning the screw with the Allen key provided refer to section 5 8 3 10 3 First Steps 3 3 5 Sensor Head OFV 512 The front panel of the sensor head OF V 512 is shown in figure 3 7 en O FIBER INTERFEROMETER Polytet oFv 51 SIGNAL
58. he A 4 mount 6 Turn the threaded cover 5 on the lens mount until it is securely seated 7 Exchange the label for the front lens model on the side of the sensor head OFV 511 512 Exchange of the mini sensors with fiber heads is described in section B 3 5 4 5 Operating the Vibrometer 5 6 Making Single Point Measurements with the Sensor Head OFV 512 Assembly If single point measurements are carried out with the sensor head OFV 512 one of the two fibers must be terminated with a reference head The reference head is marked with a red dot Always mount the reference head to the reference fiber also marked with a red dot As default each sensor head OFV 512 is delivered with the reference head OFV 151 The reference head is exactly adjusted to its sensor head Therefore each reference head has a own serial number which is noted in the examination protocol Note Never exchange the reference head of a sensor head with a reference head of another sensor head Optionally you can use the reference head OF V 152 with adjustable stand off distance You will find information on this in section B 1 To mount the reference head OFV 151 onto the reference fiber proceed as follows 1 Unscrew the mini sensor from the reference fiber and keep in a safe place because each mini sensor is exactly adjusted to its fiber 2 Screw the reference head onto the end of the fiber until it is securely fixed The reference head
59. he key switch on the controller is in position O 4 Check the setting on the mains voltage selector on the back of the controller as well as the fuses 5 Plug the connecting cable into the Sub D jack SIGNAL PROCESSOR on the back of the sensor head and into the Sub D jack INTERFEROMETER on the back of the controller Fix the connections with the screws provided All connections must be easy to plug in If not check the plug for bent contact pins to avoid serious damage being incurred 6 Use the earthed mains cable to connect the controller to a wall outlet providing protective grounding 7 Switch the controller on by turning the key switch to position I On the front of the controller the LED POWER lights up Providing the connecting cable has been installed correctly the LED STANDBY on the sensor head also lights up Laser light is not yet emitted as the beam shutter is still closed 8 Before now opening the beam shutter remember the information on laser safety provided in section 1 1 9 Open the beam shutter on the sensor head by pressing the key LASER on the front of the sensor head The LED ON on the sensor head lights up At the same time the LED STANDBY goes out The laser beam is now emitted from the mini sensor Test 3 First Steps 10 Put a piece of reflective film enclosed in this manual at approximately 12cm from the front lens of the mini sensor in the beam path 11 Focus the laser beam on the reflecti
60. he output voltage does not exceed 8V Otherwise the output voltage will jump from the positive end of range to the negative and vice versa as the internal counter overflows refer to section D 5 3 and as a result the AC signal is distorted This is shown as an example in the oscilloscope trace in figure 4 7 Tek aol ese Stop Mi Pos 0 0005 CURSOR Set Cee eet eee er eee eee EEREP TERETE PEPE PEPPER RPE ERT EEE EZ EEE ZZ Eu Cursor 1 ees Sa Aueh EEEE E ies Cursor 2 CH1 S 00VEy CH2 S 0m BA Ims CH1 1 404 Ref S00 250 us Figure 4 7 Displacement signal when the counter overflows due a DC offset Tracking filter 4 Making Measurements Before making a measurement the DC offset should therefore be reset to zero to make use of the full displacement measurement range This can be done by pressing the CLEAR key on the front of the controller or by feeding an electrical pulse to the corresponding BNC jack The latter is particularly advantageous in the case of periodic signals with a superimposed translation In such cases the counter quickly overflows due to the DC signal of the translation A higher displacement measurement range must be selected which then however provides worse resolution of the vibration The best AC resolution can be maintained however by periodically resetting the counter and thus suppressing unwanted DC drift of the signal The CLEAR signal does not necessarily have to be provided ext
61. hts up You can often still make measurements even if none of the bar LEDs is lit up The output signal in this case however contains more noise If the signal level is low or highly fluctuating change the stand off distance by 10cm as it may be that the mini sensor or fiber head has been positioned at an unsuitable distance refer to section 4 2 4 4 Making Measurements 4 1 3 Displaying the Output Signals Velocity signal Displacement signal optional Sign convention To display the output signals proceed as follows 1 Connect an oscilloscope to the BNC jack VELOCITY OUTPUT on the front of the controller With a suitable selected measurement range the expected signal form should be visible at the VELOCITY OUTPUT Select the next highest measurement range if the LED OVER is continuously lit up at the front of the controller refer to section 4 2 2 Then the maximum velocity exceeds the full scale range The display may light up briefly while a different velocity measurement range is being set or due to noise spikes Increase the intensity of the light scattered back by various surface materials The noise level of the velocity output decreases The minimum noise level shows the optimal alignment and focusing for the surface quality present Connect an oscilloscope to the BNC jack DISPLACEMENT OUTPUT on the front of the controller At the DISPLACEMENT OUTPUT as a general rule the expected signal form can
62. iagram of the tracking filter A constant velocity limit of approximately 3m s is characteristic for the lower frequency range If the velocity exceeds this value the tracking filter can generally not be used and has to be switched off For special applications a tracking filter can be installed for which this velocity limit does not apply This is however coupled at worse noise suppression In the medium frequency range the velocity limit changes over to become an acceleration limit i e the velocity limit decreases inversely proportional to the frequency refer to equation 4 2 4 Making Measurements In the upper frequency range a constant velocity limit becomes effective again To set the tracking filter the range diagram in figure 4 1 can be summarized with the following rules of thumb Below a particular velocity no dynamic limits have to be taken into consideration Thus in the lower measurement ranges 17V and 5 V the setting SLOW can generally be selected For medium velocities and frequencies the acceleration limits of the tracking filter have to be taken into consideration The optimal setting must be found with the range diagram If the velocity or acceleration limits are exceeded the tracking filter loses lock refer to section D 2 This will cause serious signal distortions an example of which can be seen on the oscilloscope trace in figure 4 2 The signal A shows a sinusoidal velocity signal with the tracking filter
63. icks into place and turn the focusing ring until the adjustment mechanism clicks into place Now the laser beam can be focused Focus the laser beam on the reflective film using the focusing ring on the sensor head Providing the sensor head and the input section of the controller are working correctly the signal level display will fully light up If you have not been able to observe the effect described under 10 check the signal level again after 20 minutes After this warm up phase the laser has reached its working temperature refer also to section 4 2 4 3 13 3 First Steps If the functional test has been successful you can now make measurements as described in chapter 4 If your vibrometer does not perform as described above read through the information on fault diagnosis provided in chapter 6 and if necessary contact your local Polytec representative 3 4 2 Vibrometer with Sensor Head OFV 511 512 Preparing Cabling Switching on 3 14 For the installation and an initial functional test of the vibrometer proceed as follows 1 Only OFV 512 Unscrew the mini sensor from the reference fiber The reference fiber is marked with a red dot Mount the reference head OFV 151 on the reference fiber as described in section 5 6 2 Deactivate the transport safety mechanism on the back of the sensor head by turning the screw with the Allen key provided to position MEASUREMENT refer to section 5 8 3 Make sure that t
64. igh are the voltages at the Sub D jack INTERFEROMETER on the back of the controller Pin 1 4 7 8 and 15 GND Pin 3 6 and 9 16 0V Pin 2 5 0V Pin 13 5 2V Pin 5 and 10 15 0V Further observations 6 6 7 Technical Specifications 7 Technical Specifications 7 1 Controller OF V 3001 7 1 1 General Data Mains voltage Power consumption Fuses Protection class Operating temperature Storage temperature Relative humidity Dimensions Weight Calibration recommended Standards Applied Electrical safety EMC Laser safety 7 1 2 Interfaces RS 232 IEEE 488 GPIB REMOTE FOCUS EXT DEC SIGNAL 100 115 230 VAC 10 50 60Hz adjustable at the back panel max 150VA 1 0A slow blow for 230 V 2 0A slow blow for 100 115V protective grounding 5 C 40 C 41 F 104 F 15 65 C 5 F 149 F max 80 non condensing 450mm x 355mm x 135mm 10 8kg every 2 years EN60950 IEC 950 EN61010 IEC 1010 Emission EN50081 1 FCC Class B Immunity EN50082 1 EN 50082 2 IEC 801 1 5 EN60825 1 CFR1040 10 CFR1040 11 8 data bits no parity baud rate 4 800 or 9 600 9 pin female Sub D cable to the workstation 1 1 wired according to IEEE 488 1 special interface for the hand terminal OFV 310 special interface for the PC based displacement decoder VibSoft FC 0V 3V DC proportional to the logarithm of the optical signal level load
65. in non EC countries The position of the laser warning labels in non EC countries on the sensor head OFV 511 resp OF V 512 is shown in figure 1 6 Label 4 is affixed inside Label 3 is enclosed with the sensor head as it is not possible to affix it on the mini sensor due to its size Please affix this label clearly visible near the mounted mini sensor or fiber head a f ACHTUNG Bitte vor dem Transport O die Transportsicherung bet tigen O ge CAUTION S SIGNAL Please secure transport mechanism O peg e PROCESSOR before shipment MEASUREMENT TRANSPORT O o m Figure 1 6 Position of the laser warning labels on the sensor ead OFV 511 512 in non EC countries 1 5 1 Safety Information 1 4 Electrical Safety 1 6 The vibrometer complies with the electrical safety class I Electrical shock protection is achieved by a fully metallic housing connected to protective ground Please pay attention to the following safety precautions when using the vibrometer The vibrometer should only be connected via a three pin mains cable to an AC mains supply 50 60Hz with a grounded protective conductor with a nominal voltage which corresponds to the voltage set on the voltage selector Defective mains fuses may only be replaced by fuses of the same kind with their rating given on the back of the controller None of the eq
66. in position OFF Signal B shows the signal with the tracking filter in position SLOW The tracking filter is on the limit of the range where it loses lock the signal is partly distorted Tek sl lhe Stop M Pos 0 0005 CURSOR CHT edia CH So MSdus CHT ron Ref 5 004 SOus RefB 5 00 50s gas N 21 4 36 6 E Ah ioak Figure 4 2 True velocity signal A and signal when the tracking filter loses lock B For frequencies above 100kHz as a general rule the tracking filter should be switched off In principle it can follow higher frequencies but in this range amplitude errors of up to approximately 10 can occur due to dynamic errors With good optical signals the tracking filter can not improve the signal to noise ratio due to physical reasons It should be switched off if unfavorable effects are observed 4 7 4 Making Measurements Low pass filter 4 8 The controller is equipped with an adjustable low pass filter which adapts the bandwidth of the measurement signal to the respective application When displaying a signal in the time domain the signal to noise ratio can be improved by limiting the bandwidth to the necessary extent When analyzing in the frequency domain with an external FFT analyzer filters only play a subordinate role Here they can prevent the FFT analyzer from overranging due to noise spikes In the OFV 3001 controller low pass filters with 3rd order Bessel characteristics are u
67. ing Measurements The amplitude error caused by the filter can be determined from figure 4 4 Amplitude error 0 20 25 30 M 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 10 f Figure 4 4 Amplitude error of a 3rd order Bessel low pass filter in the passband The phase frequency response of the filter is shown in figure 4 5 Phase degrees 0 20 40 60 80 100 _ 0 0 0 2 0 4 0 6 0 8 10 Figure 4 5 Phase frequency response of a 3rd order Bessel low pass filter in the passband 4 9 4 Making Measurements An additional time delay is caused by the velocity decoder It depends on both velocity decoder and velocity measurement range and is approximately a few microseconds The resulting overall phase shift Ab can be estimated using the following simple equation A 100 t Py f Equation 4 3 c f frequency in kHz fo cutoff frequency of the low pass filter in kHz Pu specific phase roll off refer to section 7 1 4 4 2 3 Settings for Displacement Measurement optional Measurement range 4 10 The most important consideration for selecting the displacement measurement range is of course the maximum expected displacement To prevent the displacement decoder overranging however a higher displacement measurement range often has to be selected if low frequency interference vibrations are present Basically the displacement measur
68. ional Accessories for the Sensor Head OF V 303 353 Appendix A Optional Accessories for the Sensor Head OFV 303 353 A 1 Hand Terminal OFV 310 With the hand terminal OF V 310 shown in figure A 1 the laser beam of the sensor head OFV 303 can be remotely focused SIGNAL FOCUS a ee Polytee OFV 310 FOCUS CONTROL N 5 Figure A 1 Hand terminal OFV 310 The hand terminal is connected to the jack REMOTE FOCUS on the back of the controller Using the two keys the laser beam is focused as follows e to focus on infinity key A e to focus close up key V If the keys are pressed for more than approximately one second the motor switches over to fast mode For fine positioning the keys can be repeatedly pressed briefly At the end of the adjustment range the motor stops automatically and the respective directional symbol A or V lights up There is also a signal level display on the hand terminal which helps to optimize the focus The signal shown is identical to that on the sensor head and on the display of the controller A Optional Accessories for the Sensor Head OFV 303 353 A 2 Side Exit Adapter OFV C 128 Assembly A 2 Using the side exit adapter OF V C 128 the laser beam can be deflected by 90 degrees and allows thus the use of the sensor head OF V 303 353 on otherwise inaccessible parts The telescopic front tube can be rotated by 360 degrees and it can be extended fr
69. isplacement decoder This key is only active if a displacement decoder is installed Using this key the displacement decoder can be reset manually refer to section 4 2 3 RESET key Using this key the controller processor can be reset The setting of the controller is subsequently the same as it was straight after switching on the mains REMOTE LED The LED is lit when the controller is being operated remotely via one of the PC interfaces refer to appendix E Manual operation with the keys T 4 s also still possible as oppose to the status Local Lock Out LLO LED This LED is lit when the status Local Lock Out has been activated via one of the PC interfaces refer to appendix E The keys T J are then deactivated and the controller can only be operated via the PC interfaces 3 First Steps The back panel of the controller is shown in figure 3 2 ce GPIB IEEE 488 Figure 3 2 Rear view of the controller 1 INTERFEROMETER connector Sub D jack Jack for the connecting cable to the sensor head Mains connection combination Socket for standard power cord with built in fuses and mains voltage selector refer to section 3 1 Warning Always disconnect from the mains before checking the fuses Always check the setting of the voltage selector as well as the fuses before installing the Caution controller 3 EXTernal DECoder
70. lder of the connector for the mini sensor or the fiber head 2 Difference between the stand off distances of both arms Focusing motion A circular motion of the laser beam is visible during focusing At 1m stand off distance the maximum diameter of the circle is for the mini sensor 5mm for the fiber head OF V 101 imm for the fiber head OFV 102 0 25mm Dimensions of the Fiber Heads OFV 101 Length ca 43mm Diameter 20mm Diameter of the focusing ring 22 5mm OFV 102 Length 57mm Diameter 20mm Diameter of the focusing ring 24mm OFV 130 3 OFV 130 5 Length ca 105mm Diameter 20mm Diameter of the focusing ring 24mm OFV 200 Dimensions incl objective 165mm x 79mm x 68mm 7 9 7 Technical Specifications 7 10 Dimensions of the Side Exit Heads OFV C 102 257 5 157 5 O15 D oa a Poytee EN 75 ca 130 Figure 7 2 View of the side exit head OFV C 102 dimensions not specified are given in mm OFV C 110 257 5 157 5 96 5 O15 10 mm 9 Polytec 85 ca 130 Figure 7 3 View of the side exit head OFV C 110 dimensions not specified are given in mm Dimensions of the Reference Heads OFV 151 Length ca 70mm Diameter 20mm Diameter of the focusing ring 22 5mm OFV 152 refer also to figure B 1 Length ca 310 5mm Diameter 20mm A Opt
71. look directly into the laser beam with the naked eye or with the aid of mirrors or optical instruments 4 When you are looking onto the front panel of the sensor head e to focus on infinity turn clockwise to the right e to focus close up turn anti clockwise to the left OFV 353 OFV 511 512 5 Operating the Vibrometer Remote focusing To switch to remote focusing you proceed as follows 1 Press the knob AUTO MAN into the front panel until it stops 2 You can now focus remotely e via the display of the controller as described in section 5 9 3 e via the PC interfaces as described in appendix E e with the optional hand terminal OFV 310 as described in section A 1 To focus the laser beam you proceed as follows 1 Pull the knob BRAKE ON OFF out until it clicks into place 2 Then turn the focusing ring until the adjustment mechanism clicks into place 3 You can now focus the laser beam by turning the focusing ring Warning Never look directly into the laser beam with the naked eye or with the aid of mirrors or optical instruments 4 When you are looking onto the front panel of the sensor head e to focus on infinity turn clockwise to the right e to focus close up turn anti clockwise to the left 5 To fix the focus press the knob BRAKE ON OFF into the front panel until it stops refer also to section 5 7 To focus the laser beam you proceed as follows e Turn the mini sensor
72. mall portion of its energy if the driving force is briefly interrupted but continues to run at almost the same number of revolutions per minute and can drive a subsequent mechanism without disruption It is easy to see that this effect gets better the higher the inertia of the wheel is At the same time the flywheel however loses the ability to follow rapid changes in the revolutions per minute i e the dynamic response of the drive system gets worse The same correlation also applies to the electronic tracking filter which thus always represents a compromise between the regeneration effect and the dynamic tracking behavior of the input signal Basically good drop out elimination or noise suppression is always involved with limited dynamic response If the maximum acceleration is exceeded the synchronization between the input signal and the oscillator is lost the tracking filter loses lock which leads to drastic signal distortions at the signal output Practical advice for setting the tracking filter can be found in section 4 2 2 and section 4 2 3 The internal structure of the tracking filter circuit is shown in figure D 2 The function of the voltage controlled oscillator VCO has already been mentioned The control signal which synchronizes the oscillator is generated in the phase detector which monitors the phase difference between the input signal and the oscillator signal The dynamic characteristics of the configuration are mainly determined
73. nally the displacement decoder Two voltage signals are generated which are respectively proportional to the instantaneous VELOCITY and to the instantaneous position DISPLACEMENT of the object Both signals are available at the front of the controller as an analog voltage and can be processed further externally Additional functions such as filters and signal level display raise the level of comfort for the vibrometer user The settings of the vibrometer are selected via the display of the controller or via PC interfaces To display and analyze measurement results on a workstation the Polytec Vibrometer Software VibSoft is available optionally The software is described in a separate manual 2 1 2 Introduction 2 2 Component Summary 2 2 Polytec assembles the vibrometer on the modular principle thus permitting a user specific configuration The combination of the controller OF V 3001 with the most useful decoders as well as a suitable sensor head provide the solution to a multitude of measurement tasks Thus a manageable number of components cover a wide range of applications A summary of the components is shown in figure 2 2 Fiber optical Standard sensorheads OFV 511 sensorheads OFV 303 OFV 512 OFV 353 z Sa
74. nds are supported e query and change the settings of the controller e query the overrange e query the optical signal level e focus the laser beam only for vibrometers with the sensor head OF V 303 The interfaces can be configured via the display of the controller in the menu CONFIG refer to section 5 9 3 The two following configurations are possible e 9 600Baud 8 data bits 1 stop bit no parity bit factory setting e 4 800Baud 8 data bits 1 stop bit no parity bit For the interface IEEE 488 GPIB every address in the range from 0 up to and including 30 can be set The factory setting is Address 5 The interface has the following functions which comply with the standard IEC 488 1 SH1 AH1 T4 L2 TEO LEO SRO RL1 PPO DC1 DTO CO E 2 Interface Commands E 2 1 Control Commands RS 232 REM GTL REN LLO Queries the operation mode Answer Answer with ECHOON 0 LOCAL REMO 1 REMOTE REM 1 2 LLO REM2 Sets the status LOCAL REM 0 Sets the status REMOTE REM 1 Sets the status LLO LOCAL LOCK OUT REM 2 E 1 E Interface Operation RS 232 and IEEE 488 GPIB RENDCL DCL IFC Sets the status REMOTE and loads the following initialization settings TRACK 1 OFF VELO 4 1 000mm FILT 1 OFF AMPL 7 5 120um V Loads the initialization settings see above without changing the current REM status i e the respective status LOCAL REMOTE or LLO is m
75. nsity increases to a maximum i e a maximum of visibility is present if the optical path difference is an even numbered multiple of the length of the laser cavity 203mm As the optical path difference is equal to twice the stand off distance the beam goes there and back a maximum of visibility is present once per laser cavity length In practice it is not usually necessary to search for the maximum of visibility as the vibrometer is sensitive enough to make a measurement even close to the minimum A minimum is indicated during the warm up phase by periodic fluctuation on the signal level display 5 Operating the Vibrometer 5 Operating the Vibrometer 5 1 Switching On and Off OFV 303 353 OFV 511 512 The vibrometer is switched on by turning the key switch on the front of the controller to position I The LED POWER above the key switch then lights up and shows that the controller is ready to operate Providing the connecting cable from the controller to the sensor head has been correctly installed the LED LASER on the back of the sensor head also lights up and shows that the sensor head is ready to operate and that the laser is active even if the beam shutter is closed refer to section 5 2 Providing the connecting cable from the controller to the sensor head has been correctly installed the LED LASER STANDBY on the front of the sensor head also lights up and shows that the sensor head is ready to operate and that the laser i
76. nu INTRO Menu CONFIG After switching on or RESET the controller shows that it is ready to operate with the menu INTRO It is not possible to change back to this menu as it does not have a control function This menu provides information on the decoders and interfaces installed The individual configurations are described in the following Velocity Decoder This line shows the velocity decoders installed and the number of available velocity measurement ranges The following abbreviations are used for the individual decoders Table 5 1 Abbreviations of the individual velocity decoders Abbreviation Decoder PLL OVD 01 HF OVD 02 Example 5PLL 4HF means that the velocity decoder OVD 01 is installed with 5 velocity measurement ranges and the velocity decoder OVD 02 is installed with 4 velocity measurement ranges Displacement Decoder This line is only present if a displacement decoder is installed This line shows the number of available displacement measurement ranges Remote Focus This line shows whether the option REMOTE FOCUS is installed With this option the laser beam can be remotely focused using the sensor head OFV 303 refer to section 5 4 IEEE Bus Interface When operating the vibrometer via the IEEE 488 GPIB interface on the back of the controller in this line the instrument address can be set in the range 1 30 The preset address is 5 refer to appendix E Serial Interface When oper
77. often have low frequencies but high displacement amplitudes To prevent overranging the displacement measurement range must be selected taking the amplitude of the background vibrations into consideration If the required signal is then resolved at all at least a bad signal to noise ratio is obtained at the output 4 Making Measurements The situation for the velocity measurement is however quite different For the same displacement amplitude but a higher frequency the velocity amplitude of the required signal is a factor of 2r f higher than the background vibration refer to equation 4 1 Thus at velocity measurement the signal to noise ratio is higher per definition A realistic ultrasound application should make this clearer Vibration to be measured e g F signal 100kHz X signal um gt Vigna 6 28 10 m s refer to equation 4 1 Background vibration typically fBackground lt 1 00Hz X Background lt 1 Oum V Background lt 6 28 10 m s Thus the signal to noise ratio here for velocity measurements is two orders of magnitude higher even with a 10 times higher amplitude of the background vibrations If the displacement signal is expressly required it can be calculated very precisely by external signal integration after cutting off the interference frequencies below 1kHz with a suitable high pass filter 4 2 2 Settings for Velocity Measurement Measurement range When selecting a suitable velocity measuremen
78. olved with the aid of electronic interpolation techniques This is realized in the measurement ranges below 80um V in which resolutions down to 2nm can be attained The specified resolution corresponds to one increment count pulse which is accumulated directionally sensitive by a 12bit counter in the displacement decoders OVD 10 and OVD 20 For certain applications in particular for low frequency vibrations the limitation of the measurement range to 1 3mm in the direct counting mode due to the 12bit counting range may not be sufficient The displacement decoder has therefore been equipped with three adjustable range extensions which cover a displacement measurement range up to 82mm 41mm amplitude The measurement range is extended by digitally dividing the number of counts by integers This procedure of course decreases the resolution however the accuracy is retained D 5 2 The Various Displacement Decoders OVD 10 OVD 20 OVD 30 VibSoft FC OVD 40 In the following sections the digital phase modulation of the standard displacement decoders OVD 10 and OVD 20 will be described The displacement decoder OVD 30 is suitable for ultrasonic measurements at frequencies down to 20 MHz and operates with analog phase demodulation It is described in a separate manual The PC based displacement decoder VibSoft FC extends the counting range of the internal displacement decoders OVD 10 and OVD 20 to 32bit and thus offers a significant exten
79. om 297mm to 377mm The maximum of visibility refer also to section 4 2 4 lies between 40mm and 120mm from the protective window depending on the telescopic extension The side exit adapter is shown in figure A 2 Protective Window 16 Telescopic Front Tube Clamping Ring Adapter Tube Figure A 2 Side exit adapter OF V C 128 The high sensitivity of the sensor head OF V 303 353 is maintained because a high reflectivity mirror is used and the protective window is tilted Caution Always take great care to keep the protective window clean To mount the side exit adapter proceed as follows 1 Turn the threaded cover on the sensor head anti clockwise until it can be removed 2 Screw the side exit adapter on in its place Store the threaded cover ina safe place to be used again when returning to normal operation 3 To extend or rotate the telescopic front tube release the chromium plated clamping ring one or two turns Position the tube as required and tighten the clamping ring again before taking the sensor head into operation A Optional Accessories for the Sensor Head OFV 303 353 A 3 Tip Tilt Stage OFV P5 with Optional Targeting Telescope Technical specification The OFV P5 is a tip tilt assembly which allows fine positioning of the laser beam when working at long distances With this unit the laser beam can be tilted 1 5 degrees in horizontal direction and 1 degree in vertical direction refer
80. ome aspects affecting the choice of the quantity to be measured which depend on the measurement procedure These are explained in the following Due to the 12bit digital resolution of the fringe counter system the relative resolution of each displacement measurement range is 2048 steps with a symmetric output voltage swing This corresponds to a dynamic range of approximately 66dB The background noise lies generally below the resolution and therefore does not affect the measurement In contrast the resolution in velocity measurement is only limited by the background noise With good optical signals e g on reflective film and a spectral resolution bandwidth of several Hertz the background noise is typically more than 100dB below full scale range This corresponds to a dynamic range which is about 100 times higher than that of the displacement measurement If the absolute noise limited resolution of the velocity decoder approximately 0 2 ZAE is rearranged according to equation 4 1 to obtain the corresponding amplitude of a sinusoidal vibration with a frequency of 100 kHz this results to approximately 3 10 mm or 0 3 pm This means that with high frequencies in particular significantly higher resolutions can be attained with the velocity measurement The vibration to be measured is usually superimposed by interference vibrations from the surroundings or from the object itself These background vibrations e g building vibrations
81. or has a battery supported memory the settings are stored when the controller is switched off The settings are reloaded when the controller is switched on again or after RESET This saves time making adjustments for repeated measurements Operating the vibrometer with a PC via the PC interfaces RS 232 or IEEE 488 GPIB is described in appendix E 5 7 5 Operating the Vibrometer 5 9 2 Organization of the Menus 5 8 The organization of the menus is shown in figure 5 3 SETTINGS ES g FOCUS CONFIG T Figure 5 3 Organization of the controller s menus menu FOCUS only with OFV 303 The two menus CONFIG and SETTINGS are available as standard Vibrometers with the sensor head OFV 303 have a third menu FOCUS The menus are organized as follows INTRO SETTINGS CONFIG FOCUS The start menu appears after switching on the controller or after RESET This is the most important menu in which all settings for a measurement are made i e the measurement ranges and the filters are selected It also displays the signal level This menu provides information on the configuration of the controller i e the decoders and interfaces installed The interfaces can be configured in this menu This menu is only available in vibrometers with the sensor head OFV 303 The laser beam can be remotely focused in this menu It also displays the signal level 5 Operating the Vibrometer 5 9 3 The Individual Menus Me
82. ousing to Y junction Y junction to fiber head helium neon 633nm 203mm ca 15W 40MHz 0 C 40 C 32 F 104 F 15 C 65 C 5 F 149 F max 80 non condensing 50mm 235 mm x 355mm x 140mm approx 8 0kg 2 in non EC countries Il lt 1mW 2 000mm 3 000mm for option OF V C 11 3R in non EC countries Illa lt 5mW lt 1mW per fiber 1 500mm 2 400 mm for option OFV C 21 500mm 600 mm for option OF V C 21 7 3 2 Optics Mini Fiber head sensor OFV 101 OF V 102 OFV 200 OFV 130 3 OFV 130 5 Focal length mm 16 20 20 50 60 80 Minimum stand off distance mm 60 80 80 600 55 2 76 2 Aperture diameter 1 e mm 3 2 4 4 10 16 16 Spot size typ um 55mm 15 3 76mm 20 5 100mm 27 27 27 300mm 90 75 75 1 000mm 320 250 250 100 each additional meter plus 320 250 250 100 With standard objective Nikon The maximum stand off distance depends on the back scattering properties of the object and is measured form the shoulder of the connector for the minisensor or the fiber head 7 8 7 Technical Specifications Maxima of Visibility Sensor head Maxima of visibility OFV 511 135mm n 203mm n 0 1 23 OFV 512 two point measurement Omm n 203mm n 0 1 25 OFV 512 single point measurement 63mm n 203mm n 0 1 2 with the reference head OFV 151 1 Measured from the shou
83. ows Swivel m Fiber End Unscrew the mini sensor from the reference fiber and keep in a safe place because each mini sensor is exactly adjusted to its fiber Slide the swivel nut over the end of this fiber Screw the adapter onto the end of the fiber and gently tighten the stud Screws Remove the protective cap from the OFV 152 and plug the adapter into the drilled hole on the OFV 152 Screw the swivel nut tight OFV 152 Stud Screw Figure B 2 Mounting the reference head OF V 152 B 2 Den You can now use with the reference head as described above B Optional Accessories for the Sensor Head OFV 511 512 B 2 Side Exit Head OF V C 102 and OFV C 110 Assembly The side exit heads have a mirror and a side exit window The laser beam can thus be deflected by 90 degrees from the output direction from the fiber The following side exit heads are available for the sensor head OF V 511 512 e OFV C 102 90 steering head diameter 5mm e OFV C 110 90 steering head diameter 10mm The side exit head OF V C 110 with mini sensor mounted is shown in figure B 3 The assembly of the side exit head OF V C 102 are made in the same way To mount the side exit head proceed as follows 1 Place the mini sensor 4 into the side exit head as far as the shoulder of the connector for the mini sensor is positioned
84. pendix E 5 11 Displaying the Configuration of the Controller The configuration of the controller is displayed in the menu CONFIG refer to section 5 9 3 You will find information about the velocity and displacement decoders installed Additionally the display shows whether the option REMOTE FOCUS is installed and the configuration of the PC interfaces 5 12 Configuring the Interfaces The interfaces RS 232 and IEEE 488 GPIB can be configured via the display of the controller in the menu CONFIG refer to section 5 9 3 and section E 1 5 11 5 Operating the Vibrometer 5 12 6 Fault Diagnosis 6 Fault Diagnosis Simple tests are described in the following which you can carry out yourself in the case of malfunction In the case of more difficult faults in individual functions please contact our service personnel The tests described here are not meant to lead you to carry out maintenance work yourself but to provide our service personnel with information which is as accurate as possible Testing the vibrometer is limited to such tests in which the housing does not have to be opened Opening the housing without authorization invalidates the warranty If required please contact our service department Based on your fault description further procedure will be determined If the vibrometer has to be sent back for repair always use the original packaging and enclose an exact description of the fault Please use the corresponding
85. quency The phase shift depends however on the measurement range set Velocity Measurement range Time delay t typ Specific sew roll off pg decoder en typ s V us kHz OVD 01 1 23 9 8 6 5 7 1 2 56 25 and 125 6 0 2 15 1 000 5 2 1 9 OVD 02 5 6 4 2 3 25 and 125 1 9 0 7 1 000 0 9 0 33 Harmonic Distortions Velocity Measurement range THD f 1kHz decoder mn y 10 90 of full scale range OVD 01 1 lt 0 25 lt 52dB 5 25 125 and 1 000 lt 0 10 lt 60dB OVD 02 5 and 25 lt 0 20 lt 54dB 125 and 1 000 lt 0 30 lt 50dB 7 4 7 Technical Specifications 7 1 5 Signal Voltage Output DISPLACEMENT OUTPUT optional General Data Voltage swing Output impedance Minimum load resistance Measurement Ranges 16V 500 10kQ 0 5 additional error Displacement Measurement Full scale Maximu l Max frequency decoder range output Resolution velocity Bandwidth for specified scaling factor peak peak accuracy um V um um m s kHz kHz OVD 10 20 320 0 08 2 5 0 250 100 80 1 280 0 32 10 0 250 100 320 5 120 1 3 10 0 250 100 1 280 20 480 5 0 10 0 250 100 5 120 81 920 20 10 0 250 100 OVD 20 0 5 8 0 002 0 06 0 25 10 and 32 0 008 0 25 0 75 15 OVD 40 8 128 0 032 1 0 75 25 20 320 0 08 2 5 0 250 100 80 1 280 0 32 10 0 250 100 320 5 120 1 3 10 0 250 100 1 280 20 480 5 0 10 0 250 100 5 120 81
86. resolution of the displacement decoder by the same factor This means that in the lowest measurement range 0 5um V an increment of approximately 2nm is attained As the counting range is always 12bit the total measurement range is decreased by the respective multiplier In the lowest range thus displacements up to approximately 8um 4um amplitude can be measured Bear in mind D Functional Description of the Controller however that due to the phase multiplication both the original bandwidth of the modulated signal and the pulse frequency at the counter are increased The technical limits in the direct counting mode are reached at a velocity of 10m s however in the high resolution ranges this value decreases approximately by the multiplier refer also to section 4 2 3 Measurement range D 5 4 Accuracy Due to its working principle the displacement decoder attains its highest accuracy in the direct counting mode As long as the optical signal is free of drop outs exactly one COUNT pulse is generated and accumulated for each phase cycle of the interferometer The accuracy of the equivalent increment of 316 4nm is solely determined by the wavelength stability of the helium neon laser which is in the order of magnitude of 10 Helium neon lasers are a generally recognized standard for length measurements Apart from the digital residual error the status of the digital fringe counter thus very accurately corresponds with the instantaneous po
87. rms reading of rms reading OVD 01 1 1 000 1 0 1 2 OVD 02 5 1 0 1 5 25 1 0 2 0 125 and 1 000 1 0 2 5 Conditions sinusoidal vibration f 1kHz amplitude 70 of full scale range load resistance gt 1MQ Amplitude Linearity Velocity decoder One particular range of rms reading Maximum linearity error Overall of rms reading OVD 01 0 5 1 0 OVD 02 1 0 2 5 1 Linearity error is defined as the amplitude dependent relative deviation of the scale factor referred to the scale factor under calibration conditions Amplitude Frequency Response Flatness Velocity decoder Measurement range Max additional error referred to f 1kHz eV OVD 01 1 0 5 Hz 10 Hz 0 5dB 10 Hz 15 kHz 0 1dB 15 kHz 20 kHz 0 1dB 0 25dB 5 and 25 0 5 Hz 10 Hz 0 5dB 10 Hz 20 kHz 0 1dB 20 kHz 50 kHz 0 2dB 125 and 1 000 0 Hz 20 kHz 0 1dB 20 kHz 50 kHz 0 2dB OVD 02 5 0 5 Hz 10 Hz 0 5dB 10 Hz 100 kHz 0 1dB 100 kHz 250 kHz 0 1dB 1dB 25 125 and 1 000 0 5 Hz 10 Hz 0 5dB 10 Hz 250 kHz 0 1dB 250 kHz 1 5 MHz 0 5dB 1dB These two measurement ranges can be used from the frequency OHz full DC capability 7 3 7 Technical Specifications Phase Frequency Response With the low pass filter switched off the vibrometer behaves as a system of constant time delay i e the phase shift is proportional to the fre
88. roller on by turning the key switch to position Please allow 20 minutes for the laser to warm up before making measurements On the front of the controller the LED POWER lights up Providing the connecting cable has been installed correctly the LED LASER on the sensor head also lights up Laser light is not yet emitted as the beam shutter is still closed Before now opening the beam shutter remember the information on laser safety provided in section 1 1 Open the beam shutter on the sensor head The laser beam is now emitted from the sensor head Focus the laser beam on the surface of the object The signal to noise ratio is maximal if the signal level display fully lights up You can often still make measurements even if none of the bar LEDs is lit up The output signal in this case however contains more noise If the signal level is low or highly fluctuating change the stand off distance by 10cm as it may be that the sensor head has been positioned at an unsuitable distance refer to section 4 2 4 4 1 4 Making Measurements 4 1 2 Vibrometer with Sensor Head OFV 511 512 Setup Switching on Measuring 4 2 10 OFV 511 If desired exchange the mini sensor with a fiber head refer to section B 3 OFV 512 If desired exchange both mini sensors with fiber heads refer to section B 3 or for single point measurements exchange the mini sensor of the reference fiber with a reference head refer to section 5 6
89. rst of all has to be pre processed to optimally drive the various demodulators The signal conditioning includes the following functions e Measurement of the input signal level e Stabilization of the signal amplitude e Limitation of the bandwidth e Drop out reduction via the tracking filter e Down mixing of the frequency The measurement of the input signal level is required to provide the user with information of the back scattering properties of the object and as a help to optimally focus the laser beam The level is converted to a logarithmically scaled DC voltage This signal is visualized on the sensor head and on the controller as a bar display and is available at the BNC jack SIGNAL for external usage Stabilization of the signal amplitude is necessary for the following signal processing steps as the input signal level can fluctuate by several orders of magnitude due to the extremely different back scattering properties of the objects Limitation of the bandwidth at the input of the signal processing electronics is required because for low velocities only a narrow section of the system bandwidth is occupied by the FM signal In the remaining bandwidth only noise is recorded For this reason at the input section of the controller a switchable filter is installed which limits the noise bandwidth depending on the velocity measurement range set As this is carried out right at the input however the bandwidth limitation also affects
90. s active even if the beam shutter is closed refer to section 5 2 5 2 Beam Shutter and Emission Indicator OFV 303 353 OFV 511 512 The sensor head is equipped with a beam shutter This can be used to block the laser beam without switching off the laser thus keeping the system ata thermal equilibrium Warning Only open the beam shutter when you are making measurements Warning To position the sensor head switch the beam shutter to the OFF position Only when the sensor head is roughly in place and has been fixed in a stable position switch the beam shutter to ON The rotary knob for the beam shutter is on the back of the sensor head and is labeled EMISSION ON OFF To block the laser beam turn the knob clockwise until the red mark points at OFF The emission indicator is the LED LASER on the right of the rotary knob The LED is lit when the laser is active key switch on the front of the controller in position I The LED is lit regardless of whether the beam shutter is open or closed The key for the beam shutter is on the front of the sensor head and is labeled LASER When the controller is switched on the beam shutter is automatically closed To open the beam shutter press the LASER key To close the beam shutter again press the LASER key a second time The emission indicators are two LEDS STANDBY and ON next to the shutter key The LED STANDBY lights up when the controller is switched on This
91. s not enter the eye To ensure this the following precautions have been taken In general Polytec equipment complies with the standards EN 60825 1 DIN VDE 0837 and CFR 1040 10 US The optical output of the laser is less than 1mW for the sensor heads OFV 303 353 and OFV 511providing the equipment is used in the manner for which it was intended This means that the vibrometer conforms with laser class 2 Il and is generally very safe Even when optimally focused the laser radiation is not intense enough to harm the skin The optical output of the laser is less than 5mW lt 1mW per fibre for the sensor head OFV 512 providing the equipment is used in the manner for which it was intended This means that the vibrometer conforms with laser class 3R Illa and is generally very safe Even when optimally focused the laser radiation is not intense enough to harm the skin The sensor head has been equipped with a beam shutter which can be used to block the laser beam during the warm up phase or when the vibrometer is not in use although switched on The emission indicator on the sensor head indicates the activity of the laser and thus potential harm caused by emitted laser beams The beam shuiter is always less then 2m away from the aperture of the laser beam Special editions of the fiber optical sensor heads with fiber lengths of 3m are fitted with an additional emission indicator which is integrated in the fibers The laser is switched on
92. sed Characteristic of this type of filter is the phase linearity from the frequency zero up to the cutoff frequency i e the phase shift increases proportionally to the frequency These filters however cause amplitude errors in the passband which can be roughly estimated e Up to 40 of the cutoff frequency the amplitude error is less than 5 This range can be considered to be exact for amplitude measurement e Up to 70 of the cutoff frequency the amplitude error increases to about 15 e The upper 30 of the passband should only be used for orientation measurements At the cutoff frequency of the filter the amplitude error is 3dB approximately 30 The phase shift increases proportionally to the frequency from close to zero degree at a few Hertz to approximately 100 degrees at the cutoff frequency refer to figure 4 5 Due to this linear phase frequency response the filter shows optimal transmission behavior for pulses as all frequencies of a complex wave are subjected to the same time delay Thus the shape of the pulse is not falsified but it is merely delayed The complete amplitude frequency response of a 3rd order Bessel low pass filter is shown in figure 4 3 The frequency is normalized to the cutoff frequency f Amplitude dB 10 20 30 40 50 60 f T 0 1 0 2 0 5 1 2 5 10 20 Figure 4 3 Amplitude frequency response of a 3rd order Bessel low pass filter 4 Mak
93. sion of the measurement range The counter content is handled directly as a numerical value thus increasing the measurement accuracy The PC based displacement decoder is also described in a separate manual The model OVD 40 has been designed exclusively for operation with the external PC based displacement decoder VibSoft FC It provides the same resolution as the OVD 20 but does not generate an analog displacement signal D 7 D Functional Description of the Controller D 5 3 Operating Principle Phase Multiplier The functional structure of the displacement decoder is shown schematically in figure D 3 Oscillator ORG N u a Pret D A Converter Low Pass DIRECTION i bit N X Pmod D e Counter he Sns a A Displacement COUNT Signal Control Bus CLEAR Figure D 3 Block diagram of the displacement decoder D 8 The subassembly phase multiplier is only included in the high resolution models OVD 20 and OVD 40 In the displacement decoder OVD 10 the modulated signal 4 is processed directly in the functional block quadrature demodulator Here the displacement information is digitally reconstructed from the phase difference between the reference signal and the modulated signal mog AS a result the pulses COUNT and DIRECTION are generated Each COUNT pulse corresponds to one period of the interferometer signal i e a displacement of the o
94. sition of the object independent of the influence from electronic components The same applies for the extended measurement ranges where only every nth COUNT pulse is accumulated Due to tolerances and drift of the analog components however the subsequent digital to analog conversion and amplification cause an additional static calibration error of maximum 1 of the measurement value At higher frequencies the amplitude frequency response of the smoothing filter causes an additional frequency dependent error of 0 5 In the high resolution ranges the interpolation phase multiplication is an additional potential source of error As with every interpolation additional linearity errors can occur between the known values which depend on the frequency and acceleration of the object Up to a characteristic frequency for every measurement range this dynamic amplitude error can practically be ignored as it remains below 1 Above this frequency which is to be taken from the decoder specifications the amplitude error can increase up to approximately 10 A precise error diagram can not be presented in a clear way due to the dependency on acceleration D 9 D Functional Description of the Controller D 10 E Interface Operation RS 232 and IEEE 488 GPIB Appendix E Interface Operation RS 232 and IEEE 488 GPIB E 1 Configuration of the Interfaces RS 232 IEEE 488 GPIB Using the interfaces RS 232 and IEEE 488 GPIB the following comma
95. ssing before the low pass also shows a linear phase response and thus this advantage is retained even when the filter is switched on Due to the characteristics of the Bessel filter however signal amplitudes are attenuated even at relative low frequencies This has to be taken into consideration for accurate measurements The filter characteristics as well as rules of thumb for using them are provided in section 4 2 2 D Functional Description of the Controller D 5 Displacement Decoder D 5 1 Mode of Operation The phase of the interferometer signal is the carrier of the displacement information To be directionally sensitive Polytec s vibrometers work on the heterodyne principle i e the phase is modulated onto a carrier signal The information required thus rides on the phase difference between the driver signal for the Bragg cell and the modulated signal at the photo detector A displacement of the object by A 2 produces a full demodulation period a fringe passage at the photo detector The number of fringes counted is thus a measure of the displacement of the object with an accuracy and resolution of A 2 which is 316 4nm for the helium neon laser The mode of operation in which merely the number of fringes is counted is called the direct counting mode It corresponds with the measurement range 80um V As the interferometric phase changes continuously with the displacement of the object displacements of less than A 2 can also be res
96. t range the maximum expected values for velocity acceleration and frequency have to be taken into consideration Orientation purely on the velocity is often not enough as the various velocity decoders and measurement ranges have different bandwidths and maximum accelerations The respective values are given in the specifications refer to section 7 1 4 It is easiest to select the velocity measurement range for the universal decoder OVD 02 As long as the frequency remains below 250 kHz any of the four measurement ranges can be selected To maximize the signal to noise ratio however the smallest possible range should be used in which the output signal is not clipped For frequencies above 250 kHz only the top three measurement ranges are suitable Acceleration limits usually do not have to be taken into consideration Even with maximum amplitude it can still process the highest specified frequency in every measurement range With the decoder OVD 01 the technical limits for acceleration have to be taken into consideration in some velocity measurement ranges According to the relation a 2n f v Equation 4 2 a acceleration amplitude v velocity amplitude f frequency 4 5 4 Making Measurements Tracking filter 4 6 in these ranges the permissible frequency decreases with increasing amplitude If the condition 4 2 is infringed upon the signal is seriously distorted In this case a higher velocity measurement range has to be s
97. t with switch 3 Locking wheel for the joints 4 Knurled screw for fine positioning 5 Mount for the mini sensor 6 Allen screw M3 to mount the mini sensor Weight incl base plate 3 2kg Height max 400mm Base plate dimensions refer to figure B 5 B 5 B Optional Accessories for the Sensor Head OFV 511 512 2x 45 Countersinking DIN74 Km6 3x Figure B 5 Base plate for the flexible arm OFV 039 dimensions not specified are given in mm B 6 C Basics of the Measurement Procedure Appendix C Basics of the Measurement Procedure C 1 Theory of Interferometric Velocity and Displacement Measurement Optical interference can be observed when two coherent light beams are made to coincide The resulting intensity e g on a photo detector varies with the phase difference Ag between the two beams according to the equation max 2 Ag 1 cosAg Equation C 1 The phase difference Ag is a function of the path difference AL between the two beams according to AG 20 77 Equation C 2 where A is the laser wavelength If one of the two beams is scattered back from a moving object the object beam the path difference becomes a function of time AL AL t The interference fringe pattern moves on the detector and the displacement of the object can be determined using directionally sensitive counting of the passing fringe pattern On scattering from the object the object
98. ter max frequency deviation 32 MHz max modulation frequency 1 5 MHz In the OFV 3001 controller different respectively optimally adapted modulators are switched on in the individual velocity measurement ranges A maximum of two velocity decoders can be installed which in measurement ranges which are in part the same satisfy differing requirements with regards to the maximum frequency or linearity The decoders and measurement ranges are selected via the system control and the internal bus At the same time the corresponding settings on the subassemblies oscillator and signal conditioning are carried out internally D 4 3 Low Pass Filter D 6 The signal generated by the FM demodulator always contains spurious RF components and its noise bandwidth corresponds with the maximum frequency of the respective measurement range A subsequent low pass filter suppresses the RF components and limits the noise bandwidth according to its cutoff frequency This makes a rough adaptation of the measurement bandwidth to the application possible and makes the signal evaluation in the time domain significantly easier due to the improved signal to noise ratio The filters are adjusted via the system control In the OFV 3001 controller low pass filters with 3rd order Bessel characteristics are used Bessel filters have the advantage of a linear phase response and thus optimal transmission behavior for pulses Bessel filters were selected as the signal proce
99. the displacement decoding and under certain circumstances has to be taken into consideration refer also to section 4 2 3 Optimizing the RF bandwidth Drop out reduction via the tracking filter D Functional Description of the Controller Drop out reduction via the tracking filter plays a very important role in optical signal processing The light scattered back from the object has a speckled nature i e at any instant the detector sees a light or a dark speckle The low signal amplitude of the dark speckle can lead to loss of signal so called drop outs When decoding the velocity this interruption of the input signal causes short but high noise signals so called spikes which make it very difficult to analyze the output signal These drop outs are effectively reduced by a so called tracking filter integrated in the input section of the controller This is done by an electronic circuit to regenerate high frequency signals based on the principle of the phase locked loop PLL The principle of signal regeneration by the tracking filter is based on replacing the input signal with a distorted amplitude by a stable signal from a voltage controlled oscillator which is synchronized with the frequency and the phase of the input signal Suitable circuit design can make it possible to maintain the synchronized condition approximately even if the input signal is temporarily lost The mechanical analog for this design is a flywheel which may lose a s
100. the front lens is described in section 5 5 7 Focusing ring Focusing ring for focusing of the laser beam refer to section 5 4 3 8 3 3 4 Sensor Head The FIBER INTERFEROMETER Figure 3 5 Front view of 1 2 Polytec orFv 51 SIGNAL o LASER oN CO STANDBY C 3 First Steps OFV 511 front panel of the sensor head OFV 511 is shown in figure 3 5 the sensor head OFV 511 LASER beam shutter key Pressing this key the beam shutter is opened and pressing this key a second time the beam shutter is closed again refer to section 5 2 The beam shutter is closed automatically when the controller is switched on key switch on the controller in position LASER STANDBY LED The LED goes on when the controller is switched on This then shows that the laser is operational However no laser beam is emitted yet as the beam shutter is still closed LED ON is out The LED goes out when the beam shutter key is pressed and thus the laser beam is emitted LED ON is then on LASER ON LED The LED goes on when the beam shutter key LASER is pressed and thus the laser beam is emitted At the same time the LED STANDBY goes out Pressing the beam shutter key LASER a second time the beam shutter is closed and the LED ON goes out and the LED STANDBY goes on again Signal level display The length of the bar is a measure of the amount of light scattered back from the surface o
101. then shows that the laser is active but the laser beam is not emitted yet as the beam shutter is still closed When the beam shutter key LASER is pressed the LED STANDBY goes out and the LED ON lights up This then shows that the laser beam is being emitted 5 1 5 Operating the Vibrometer 5 3 Signal Level Display OFV 303 353 OFV 511 512 The signal level display helps you to optimize the focus of the laser beam The signal level is shown as a 20 part bar on the display of the controller refer to section 5 9 The signal level is also shown on the back of the sensor head as a 10 part bar display The signal level is also shown on the front of the sensor head as a 10 part bar display 5 4 Focusing the Laser Beam OFV 303 5 2 There are different ways to focus the laser beam of the sensor head OFV 303 e manually with the focusing ring e remotely via the display of the controller e remotely with a PC via the interfaces RS 232 or IEEE 488 GPIB e remotely with the hand terminal OFV 310 optional You can switch between manual focusing and remote focusing with the knob AUTO MAN on the front of the sensor head Manual focusing To switch to manual focusing you proceed as follows 1 Pull the knob AUTO MAN out until it clicks into place 2 Then turn the focusing ring until the adjustment mechanism clicks into place 3 You can now focus the laser beam manually by turning the focusing ring Warning Never
102. uipment may be used with open housing As a general rule before removing parts of the housing the mains cable has to be unplugged Air inlets and outlets must always be kept uncovered to ensure effective cooling If the cooling fan stops working the vibrometer is to be switched off immediately 2 Introduction 2 Introduction 2 1 System Overview Polytec vibrometers are instruments for non contact measurement of surface vibrations based on laser interferometry The vibrometer consists of the controller OFV 3001 and the sensor head OF V 303 353 or OF V 511 512 The signal paths in the vibrometer are shown schematically in figure 2 1 Sensor head E e wee can Object finod Pmo fo i x t Velocity v t dx dt Po 1 decoder Frequency Af ee III vit V Displacement decoder optional Phase Ag at J_ x t Figure 2 1 Signals in the vibrometer The beam of a helium neon laser is focused on the object under investigation scattered back from there and coupled back into the interferometer in the sensor head The interferometer compares the phase 9 4 and frequency fmoa of the object beam with those of the internal reference beam 9 and f The frequency difference is proportional to the instantaneous velocity and the phase difference is proportional to the instantaneous position of the object In the controller the resulting signal is decoded using the velocity decoder and optio
103. urement ranges 125 3 V and 1 000 7 V can be used from the frequency OHZ full DC capability The OVD 02 as a broad band decoder is suitable universally for almost all applications in the frequency range up to 1 5 MHz Four measurement ranges from 5TYV to 1 000 7V cover most technical applications with sufficient amplitude resolution Characteristic is the excellent amplitude and phase frequency response with extremely good amplitude flatness up to the highest frequencies In the measurement ranges 125 YV and 1 000 7V the OVD 02 can detect DC velocity components This is useful e g when measuring on rotating discs When setting up the sensor head large DC components which might otherwise overload the measurement range can then be minimized D 5 D Functional Description of the Controller D 4 2 Operating Principle The velocity decoder determines the essential measurement properties of the vibrometer Velocity decoding is in principal an FM demodulation process which converts the velocity dependent Doppler frequency of the interferometer signal into an AC voltage The linearity and bandwidth of the demodulator determine the accuracy of the vibrometer In contrast to FM radio which works with the same modulation procedure considerably higher frequency deviations occur in the vibrometer which make significantly higher demands on the demodulators FM radio max frequency deviation 75 kHz max modulation frequency 53kHz stereo Vibrome
104. ve film by turning the mini sensor Providing the sensor head and the input section of the controller are working correctly the signal level display will fully light up 12 If you have not been able to observe the effect described under 11 check the signal level again after 20 minutes After this warm up phase the laser has reached its working temperature refer also to section 4 2 4 If the functional test has been successful you can now make measurements as described in chapter 4 If your vibrometer does not perform as described above read through the information on fault diagnosis provided in chapter 6 and if necessary contact your local Polytec representative 3 15 3 First Steps 3 16 4 Making Measurements 4 Making Measurements 4 1 Start up 4 1 1 Vibrometer with Sensor Head OFV 303 353 Setup Switching on Measuring Make sure that the key switch on the controller is in position O and the beam shutter on the sensor head are in position OFF Fix the sensor head as appropriate with the M6 or 1 4 threaded mounting holes onto a universal tripod with a fluid head This ensures secure support and makes it easier to focus on the object Position the sensor head according to the information on optimal stand off distances in section 4 2 4 Align the sensor head such that the laser beam points along the velocity vector to be measured i e in general perpendicular to the surface of the object Switch the cont
105. with a red dot Exchange of the mini sensors with fiber heads is described in section B 3 Note Each mini sensor is exactly adjusted to its fiber Never exchange the mini sensors of a sensor head with each other or with mini sensors of other sensor heads The back panel of the sensor head OF V 512 is shown in figure 3 8 OO A N A MA ACHTUNG Bitte vor dem Transport die Transportsicherung bet tigen o CAUTION S SIGNAL Please secure transport mechanism So PROCESSOR before shipment s MEASUREMENT TRANSPORT i Figure 3 8 Rear view of the sensor head OFV 512 7 Transport handle Caution Always activate the transport safety mechanism before moving the sensor head 8 Sensor mount To transport the sensor head the mini sensors can be plugged into this sensor mount 9 SIGNAL PROCESSOR connector Sub D jack Jack for the connecting cable to the controller 10 Transport safety mechanism The transport safety mechanism is de activated by turning the screw with the Allen key provided refer to section 5 8 3 First Steps 3 4 Installation and Functional Test 3 4 1 Vibrometer with Sensor Head OFV 303 353 Preparing Cabling Switching on Test For the installation and an initial functional test of the vibrometer proceed as follows 10 11 Make sure that the key switch on the controller is in position O an

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