3501 User Manual RevB
Contents
1. The chopping frequency as well as a number of other operating parameters can be viewed on the front panel display and cursor keys provide easy adjust ment of operating parameters From the front panel the user can store and recall up to nine instrument set ups An IEEE 488 interface provides remote operation of all instrument functions The chopper head can be mounted on a 1 2 diameter post or bolted directly to a standard optical bench The Model 3501 Optical Chopper is supplied with four chopper wheels and a wheel cover The Model 3510 Rack Mount Kit an accessory that is sold separately enables the chopper controller to be mounted in a rack see Page 21 lll Safety and Preparation for Use v Mounting the Chopper Head The Model 3501 Optical Chopper head may be secured to standard optical benches using 1 4 20 or M6 bolts The bolts pass through the mounting plate perpendicular to the plane of the optical bench The chopper head can be rotated off axis by loosening the 1 4 20 set screws on the side of the motor mount Do not over tighten the set screws The Model 3501 Optical Chopper head may also be mounted on standard optical bench rods First loosen the two 1 4 20 set screws which secure the mounting plate to the head Remove the mounting base Insert the 1 4 20 knob supplied with the chopper into the base of the head This knob is inserted into the same hole occupied by the do2. 0 STO Selects instrument set up for storage The STO command selects the instrument set up number in which to store the current chopper set up The STO query will return the selected instru ment set up number The data may range from 1 to 9 STO is used with MEMO to store the instrument set up STO9 Select instrument set up 9 for storage STO gt 9 109 MEMO Perform storage operation Command Description Explanation Example 1 SUB Set and query S The SUB command sets and queries S the subharmonic divide ratio which is used in H S mode The data may range from 1 to 15 SUB7 Sets S to 7 SUB gt SUB 39 40 Command Description Explanation Example 0 WHL Set and query the type of chopping wheel being used The WHL command sets and queries the type of chopping wheel that is being used WHLO 60 slots HL1 42 30 slots W WHL2 7 5 slots W HL3 2slot WHL1 Selects the 42 30 slot wheel WHL gt WHL1 IX Troubleshooting 1 When the instrument is properly connected to the power mains and a chopper head and the unit is turned on the front panel LEDs will blink and the dis play will show PASS before recalling the last control set up The motor should begin turning and come to speed within about 1 minute If nothing happens Check that the power cord is connected at the power entry module Check that the chopping h
3. H S 1 2 NORMAL Enables condition required for SRQ service request Bit 0 Unlock Bit 1 Data Ready Sets the synthesizer frequency to three significant digits 4 00 Hz 99 9 kHz in EXT mode range automatically limited in INT mode Sets the phase delay 180 0 179 0 Selects instrument set up for recall 0 9 0 factory default set up Use with MEM1 command Selects the parameter modified by the arrow keys 0 Oscillator frequency 1 Phase 2 Harmonic multiplier 3 Subharmonic divide ratio 4 Recall set up 5 Store set up 6 GPIB device address Returns status register Bit 0 Unlock Bit 1 Data Available The same information is available during a Serial Poll Selects instrument set up for storage 1 9 Use with MEMO command Sets subharmonic divide ratio S 1 15 Selects the wheel 0 60 slots 1 42 30 slots 2 7 5 slots 3 2 slots 25 26 Command Description Explanation Example v FR Frequency query The FR command is used to query the following frequencies associated with the Measure key on the chopper front panel Fyne Fouten OUT1 and OUT2 Data is returned in Hz FR1 Fyne FR2 Fouter FR3 OUTI FR4 OUT2 The chopping frequency is 1 23 kHz and the chopper is in NORMAL mode FR1 PRITZ30 0 FR2 gt FR21230 0 FR37 gt FR36150 0 The frequency at OUTI is 6 15 kHz Command Description Explanati
4. and 6 6 32 flathead screws The figure below illustrates how to use the rack mount kit to mount a single chopper controller or two chopper con trollers side by side 3510 Rack Mount Kit consists of 2 short ears 1 long ear 1 rack plate 6 6 32 flathead screws Rack Plate connects two units together Fig 6 Model 3510 rack mount kit 1 21 22 Vil Computer Control v The Model 3501 Optical Chopper may be programmed remotely by IEEE 488 interface The Model 3501 supports the IEEE 488 1 1978 interface standard and any computer that supports this interface may be used A total of fifteen commands are available that enable any front panel operation to be per formed remotely Before communicating with the chopper controller set the IEEE 488 device address This parameter may be selected by pressing the Set key until the IEEE LED is lit Use the arrow keys to change the device address The default device address is 12 Use a standard IEEE 488 cable to connect the instrument to the host computer ACT LED The ACTive LED flashes whenever data is sent or received on the communica tions interface Line Terminators For IEEE 488 operation the correct line termination is line feed and EOI end or identify Generally line terminations are set during the installation of the IEEE 488 interface card Consult the manufacturer s installation instructions for details Command Syntax Use ASCII character
5. kHz 42 30 84 Hz 4 48 kHz 7 5 14 Hz 746 Hz 2 4 Hz 213 Hz Fouter is the chopping frequency as measured by an optical pick up on the chopper head If a wheel has two sets of slots Fou ter frequency of the slots on the outer edge of the wheel refers to the chopping To change the wheel type push the Wheel key until the LED lights under the desired wheel type Sync The user may synchronize the chopping frequency to the chopper s internal synthesizer INT or the rising edge EXT or falling edge EXT of an externally supplied Sync Input signal When V is selected the user may drive the motor directly with an analog voltage applied at Vo on the back panel When using Voy or INT a signal applied to the Sync Input has no effect on the chopper To change the Sync source press the Sync key until the LED under the desired Sync source lights Vv Mode The Mode setting changes the reference signals available at OUT1 and OUT2 on the back panel as follows Mode Fouter OUT1 OUT2 H S B S Fyync H S Fyne H 7 S Fyne i Fyne Pouter Finner Fouter Finner NORMAL Fyne gt Fouter Finner To change the Mode push the Mode key until the LED under the desired Mode lights Fouter is the chopping frequency of the outer set of slots as measured by an optical pick up on the chopper head F pner is the chopping frequency of the inner set of slots For wheels with only one set of slots F is the chopping outer frequency an
6. Model 3501 User s Manual Optical Chopper 1 Contents 351007 Rev B 2 v II HII IV VI Vil Vill Warranty Introduction Safety and Preparation for Use Quick Start Operation Rack Mount Kit Computer Control Command Summary Troubleshooting AC Operating Voltages Specifications 21 22 24 41 43 45 y Is a registered trademark of New Focus Inc I Warranty 1 New Focus Inc guarantees the chopper head to be free of defects for 90 days from the date of shipment All other parts of the Model 3501 Optical Chopper are guaranteed to be free of defects for one year from the date of shipment This is in lieu of all other guarantees expressed or implied and does not cover incidental or consequential loss Il Introduction 0 The Model 3501 Optical Chopper is designed to interrupt light paths in optical experiments at frequencies from 4 Hz to 6 4 kHz Both single and dual beam experiments can be performed across a broad range of chopping frequencies The chopper has a crystal controlled frequency synthesizer that serves as an internal reference frequency for locking the chopper to a particular chopping frequency Reference frequencies can also be provided through the Sync Input to allow the chopper to lock to an external source A block diagram of the optical chopper system is shown in Figure 1 Several measures ensure that jitter and drift of the chopping frequency is red
7. RJ11 type IDC telephone cable Connect the cable from the connec tor on the side of the chopper head to the MOTOR connector on the back panel of the control unit The instrument has been tested with cable lengths up to 25 feet but the chopper is supplied with a shorter cable Replacement cables and longer cables may be purchased from electronics parts suppliers such as Digi Key Part H2662 14 ND 2 00 50 8 p 2 88 73 2 gt pp 5 00 127 0 5 74 145 8 5 48 139 2 e 4 03 102 4 O Bo fi pa Le E 0 50 12 7 2 25 57 1 le Fig 4 Chopper head with wheel cover 17 18 v Mounting the Chopper Head The Model 3501 Optical Chopper head may be secured to standard optical benches using 1 4 20 or M6 bolts The bolts pass through the mounting plate perpendicular to the plane of the optical bench This mounting method pro vides the advantage of allowing the wheel to be rotated off axis by loosening the 1 4 20 set screws on the side of the motor mount Do not over tighten the set screws The Model 3501 Optical Chopper head may also be mounted on standard optical bench rods First loosen the two 1 4 20 set screws that secure the mounting plate to the head Remove the head Insert the 1 4 20 knob into the base of the head This knob is inserted into the same hole o
8. arrow key to store the instrument s settings at the selected instrument set up The display will blink to indicate that the storage process is complete Location 0 is reserved for the factory default settings 42 30 wheel internal sync normal mode 84 Hz IEEE address 12 RECALL The user may recall instrument set ups in one of two ways First the control unit will retain the control settings when the power is removed When power is restored the instrument will recall the last control settings used Second the user may utilize one of ten programmable instrument set ups To recall a previously stored instrument set up use the up arrow and down arrow keys to select instrument set ups 0 9 Press the left arrow or right arrow key to recall the selected instrument set up The display will blink when the recall process is complete Location 0 is reserved for the factory default set tings Default settings Recalling set up 0 will restore the instrument to the factory default settings 42 30 wheel internal sync normal mode 84 Hz IEEE address 12 IEEE The user may select the Model 3501 s device address on the IEEE 488 bus The factory default setting is 12 Use the up arrow or down arrow key to change the device address Measure The Measure key selects which frequency measurement OUT1 OUT2 Fouter 2 Fyn 5 displayed on the front panel The instrument will contin ue to measure and update the display until another function key is pr
9. ccupied by the dowel on the mounting plate Slide the head onto the optical bench rod and tighten the knob Do not over tighten the knob Chopper Motor The operating life of the chopper motor is limited Long term use of the motor at high speed will result in faster wear and shorter life Contact New Focus for details about replacing the motor if this becomes necessary Mounting the Wheel Remove power from the control unit before attempting to change the chopper wheels Secure the chopping head to a work surface Remove the four 4 40 screws that secure the retaining cap over the wheel while taking care not to bend the wheel Install the replacement wheel retaining cap and 4 40 screws Do not over tighten the screws Diameter 4 50 114 3 mm 42 30 Slot 60 Slot Fig 5 The four chopper wheels that are supplied with the chopper 1 20 v Wheel Cover The wheel cover attaches to the chopper head with 4 screws The wheel cover is made of 030 aluminum with an anti reflective black anodized coating Two concentric slots etched in both faces of the cover allow apertures up to 3 and 4 inches wide over most of the chopping wheel surface The wheel cover dimensions are 5 x 5 x 0 5 The wheel cover is provided for safety The chopper wheel can cause injury if it is touched while rotating This is especially critical if you find yourself reaching into your optical set up with the lights off The wheel c
10. d F pner is not defined Foync is the frequency of the Sync source In INT Sync mode Fyyy is the fre quency of the chopper s internal frequency synthesizer In EXT or EXT Sync ne Fyne is the frequency of the externally supplied signal at the Sync nput Set The Set key selects which instrument parameter is modified by the cursor keys Press SET until the LED lights under the desired parameter The up arrow and down arrow keys will then change the parameter value In some cases the left arrow and right arrow keys select the significant digit to be modified FREQ The user may set the synthesizer frequency depending on the Sync source selected When EXT EXT or Voy sync has been selected the fre quency may range from 4 00 Hz to 99 9 kHz 11 12 v When INT Sync is selected the synthesizer frequency will be restricted to the working range of the particular chopping wheel In H S mode this range will be modified by the setting of H and S In this case the range limits may be calculated as follows Fupper Fouter highest S H and Flower Fouter lowest S H where S H 1 15 Setting FREQ The synthesizer frequency may be set to three significant digits The significant digit to be modified may be selected by the left arrow and right arrow keys The magnitude of the digit may be changed with the up arrow and down arrow keys If the display overflows or underflows the display will change the Hz kHz LEDs and
11. dex 24 v Commands that may be queried are followed by a A indicates that the command contains an index e g FR1 FR2 A bracket indicates that the command accepts a data value Data ranges are given in parenthesis Do not use a decimal point or comma in data For example 5 00 is sent as 500 Some commands can be used both to set and query an operating parameter For instance the PHS command can be used to set the chopping phase PHS900 or to read the value of the phase PHS The next two pages contain an index and brief description of all fifteen com mands Then the pages that follow give detailed information about each command There examples are given showing the command text followed by the response from the chopper For instance the example for IDN appears as follows IDN gt NEW FOCUS 3501 CHOPPER FR Y Measures frequency 1 F 3 OUTI syne 2 Fouter 4 QUT2 HAR Setsthe harmonic multiplier H 1 15 IDN Identification query Returns NEW FOCUS 3501 CHOPPER KEY Duplicates the action of pressing a front panel key 0 Right arrow 1 Down arrow 2 Up arrow 3 Left arrow 4 Set 5 Measure 6 Mode 7 Sync 8 Wheel 1 MEM MOD MSK OSCI 1 PHS 17 RCL SET STA STO 17 SUBI WHL Accesses instrument set up memory 0 Store 1 Recall Use with STO and RCL commands Selects the instrument mode 0
12. ead is connected to the control unit Do not con nect the chopping head when the control unit is powered Fuse Check the fuses in the power entry module Disconnect the power cord at the power entry module Open the cover of the power entry module using a small blade screwdriver or similar tool Slide the fuse holders out and examine the fuses Replace a blown fuse with the appropriate type and current rating For additional details see page 44 Mains Voltage Make sure that the power entry module is set for the correct mains voltage To set the mains voltage refer to AC Operating Voltages page 43 Fails test at start up This indicates a failure of the battery backed memory Consult with the facto ry for a replacement battery Instrument settings will not be maintained when power is removed 41 42 0 Motor fails to turn With power removed from the control unit check that the wheel is free to turn without obstructions Also this condition may be caused by a broken cable between the control unit and the head Substitution of a known func tional cable is the best solution See Page 17 for details on replacement cables Note that the life of the motor is limited Long term high speed use of the motor will result in faster wear and shorter life Because of this limited life time the chopper head has a 90 day warranty while all other parts have a one year warranty Motor oscillates wildly Recall the factory d
13. efault settings This will place the instrument into known conditions If the oscillation stops then the Sync Input signal may have been unstable Verify the stability of Sync Input with an oscilloscope or frequency counter The Sync Input frequency may have been outside of operating limits which are determined by the mode H S and the wheel type Refer to the sec tion on FREQ for more details Observe Foy fer On an oscilloscope If the cable or optical sensor is damaged the signal will remain high or low If this is the case replace the cable between the head and the control unit Check for the correct setting of Wheel on the front panel X AC Operating Voltages The Model 3501 Optical Chopper can operate at 100 120 220 or 240 V AC at AC frequencies of 47 63 Hz The unit is configured at the factory for the stan dard AC voltage in the purchaser s country To select a different operating volt age please refer to Fig 7 page 44 and follow the directions below Hua Disconnect the power cord bo Open the cover of the power entry module on the rear panel with a small blade screwdriver or similar tool Oy Insert the tool into the voltage selection slot and remove the wheel from the unit ow Turn the wheel and re insert into the module so the desired voltage is shown Do not attempt to rotate the wheel while it is still in the power entry module the wheel must be removed turned and then re inserted Clo
14. essed 13 14 v To change the Measure parameter press the Measure key until the LED lights under the desired parameter Sync Input The user may connect a TTL level sync frequency at the Sync Input EXT or EXT sync must be selected and the frequency must remain within the limits defined above in the FREQ section The UNLCK LED will blink if the Sync Input frequency is outside the limits Synthesizer Output The instrument provides the user with a TTL level square wave output for use in experiments The Synthesizer Output frequency is adjusted by setting the FREQ parameter from the front panel or via IEEE 488 With INT sync active the frequency will be limited as given above in the FREQ section With EXT EXT or Vegt the Synthesizer Output ranges from 4 00 Hz to 99 9 kHz Fouter The instrument provides the user with a TTL level square wave generated from an optical pick up on the chopper head ACT The ACT LED indicates when the IEEE 488 interface is busy UNLCK The red UNLCK LED indicates when the chopper is not synchronized to an internal or external sync frequency The UNLCK LED will blink when an external sync frequency exceeds the limits for a particular wheel Back Panel Operation 1 OUT1 The function of the OUT1 output depends on the instrument s operating mode In H S mode the instrument provides a TTL level pulse at fre quency H S Fyne In mode the frequency at OUT1 is F F outer Fin
15. ing frequencies In the other modes of operation the data may range from 4 00 to 99 9 kHz Only three digits of resolution are available The data is entered in Hz and no decimal point should be included 0SC54300 Sets the internal synthesizer to 543 Hz OSC OSC543 00 33 34 Command Description Explanation Example v PHS Set and query the phase delay The PHS command sets and queries the phase shifter The data may range from 180 0 to 179 0 degrees Do not use a decimal point in the data PHS 1234 Sets the phase shift to 123 4 degrees PHS gt PHS 123 4 PHS222 Sets the phase shift to 22 2 degrees Command Description Explanation Example 1 RCL Selects instrument set up for recall The RCL command will select a formerly stored instrument set up The RCL query will return the recall set up number The data may range between 0 and 9 Recall of set up 0 will restore the Model 3501 to factory default set tings RCL is used with MEM1 to recall the instrument set up RCLO Select factory default set up for recall MEM1 Perform recall operation RCL4 Select instrument set up 4 for recall RCL gt RCL4 MEM1 Perform recall operation 35 36 Command Description Explanation v SET Selects the parameter to be modified by the arrow keys The set command selects which parameter is activated so that it can be changed by the arro
16. lse 5 Fouter in NORMAL mode Fouter Finner in mode H S Fouter in H S mode OUT2 TTL level pulse Finner in NORMAL mode Fouter Finner 1n mode H 7 S Fone in H S mode Phase Shifter Range 180 0 to 179 0 Resolution 0 1 increasing to 0 25 at 6 4 kHz Harmonic Locking Subharmonic S Harmonic H 1 15 1 15 S and H may be set in any combination Operation Mode S H S 1 15 1 NORMAL 1 v 46 H OUT1 OUT2 1 15 H S Fone LOS 1 Fyne 12 Fouter y Finner Fouter T Finner 5 gt Fouter Finner External Voltage Control 0 to 10 0 V DC for 0 to 100 of maximum chopping frequency Wheel Apertures Wheel Outer Aperture Inner Aperture inches inches 60 09 42 30 14 12 7 5 60 a 2 1 25 General Dimensions 8 5 x 4x 14 5 inches Weight 14 pounds Power 90 240 V AC 50 60 Hz 35 W V m 47 48 0
17. ner 40d in NORMAL mode the frequency is 5 F OUT2 outer The function of the OUT2 output depends on the instrument s operating mode In H S mode the instrument provides the user with a TTL level pulse at frequency H 7 S Feyn In mode the frequency at OUT2 is Fouter Finner and in NORMAL mode the frequency is Finner 0000000 UE el eemo ave Taa IEEE 488 MOTOR 220 240 0 2 AMP MADE IN THE U S A Fig 3 Back panel of the chopper controller 15 16 v Vext When Voy Sync is selected the user may drive the chopper motor directly with a DC input voltage 0 to 10 V DC corresponds to 0 to 100 of the highest motor speed MOTOR Use the supplied cable to connect the chopping head to the chopper controller at the back panel IEEE 488 The instrument may be programmed remotely via IEEE 488 Use a standard cable to connect the instrument to the host computer system Power entry module The AC power is connected at the power entry module on the back panel The line voltage and power cord have been chosen at the factory to match the country of consignment If it is necessary to change the mains voltage con sult the section on AC Operating Voltages Page 43 Chopper Head 1 Cable The cable that connects the control unit to the chopper head is a six conduc tor reverse
18. on Example 1 HAR Set and query H The HAR command sets and queries the harmonic multiplier H which is used in H S mode The data may range from 1 to 15 HAR2 Sets H to 2 HAR gt HAR2 27 28 Command Description Explanation Example v IDN Identification query Returns the following string identifying the chopper NEW FOCUS 3501 CHOPPER IDN gt NEW FOCUS 3501 CHOPPER Command KEY Description Duplicates the action of pushing a front panel button Explanation The KEY command duplicates the action of pushing one of the 9 black front panel buttons The nine options are as follows KEYO Right arrow KEY1 Down arrow KEY2 Uparrow KEY3 Left arrow KEY4 Set KEY5 Measure KEY6 Mode KEY7 Sync KEY8 Wheel 1 56 30 Command Description Explanation Example v MEM Store and recall instrument set ups The MEM command along with the STO and RCL commands is used to store and recall one of the 9 instrument set ups After selecting which instrument set up number to use 1 through 9 using the STO command MEMO will store the current instrument set up After selecting which instrument set up to recall using the RCL command MEM1 recalls the selected set up MEMO Store instrument set up MEM1 Recall instrument set up STO5 Selects location 5 for storing the current chopper set up MEMO Activates storage to location 5 RCL1 Select
19. over is also provided to reduce the generation of stray light that could interfere with your measurements The chopper head uses an infrared sensor to detect chopper wheel motion The source in this sensor emits energy in the 870 950 nm wavelength range The wheel cover will greatly reduce the amount of sensor radiated IR light picked up by your detector To install the wheel cover first install a wheel on the chopper hub Then slide the wheel cover over the top of the wheel while spreading the 2 mounting flanges apart enough to avoid contact with the painted motor surface The motor is 060 080 wider than the mounting base Once the mounting flanges are lowered past the motor align one of the 4 flange holes with a threaded hole in the motor base and loosely attach the cover to the base with one of the 4 40 x 3 8 mounting screws Loosely fasten the 3 remaining screws Tighten the 4 screws after they are installed The cover must be removed to change the chopping wheel Remove the 4 screws holding the cover to the base From the motor side of the chopping wheel move the cover away from the motor while spreading the mounting flanges apart Now slide the cover up over the motor Vi Rack Mount Kit The Model 3510 Rack Mount Kit is a chopper accessory not supplied with the Model 3501 Optical Chopper that allows one or two chopper controllers to be mounted in a standard rack The kit consists of 2 short ears 1 long ear 1 rack plate
20. s location 1 for recalling a chopper set up MEM1 Activates recall of the set up stored in location 1 Command Description Explanation Example 1 MOD Select and query the mode of operation The MOD command allows the user to query the chopper s operating mode and to set the chopper operating mode as follows MODO H S MOD1 MOD2 NORMAL MOD2 Puts the chopper into NORMAL operating mode MOD gt MOD2 31 32 Command Description Explanation Example 0 MSK Enables condition required for SRQ The MSK command sets or clears bits in the SRQ service request enable mask A Service Request will be generated whenever either of the following bits is set DO the rightmost bit is for Unlock and D1 the next bit to the left is for Data Available The MSK query returns the SRQ enable mask MSK1 Generates a SRQ on Unlock MSK gt M5K00000001 MSK10 Generates a SRQ when data is available MSK gt MSKO0000010 MSK11 Generates a SRQ on Unlock or when data is available MSK gt M5K00000011 Command Description Explanation Example 1 oscr Set and query the synthesizer frequency The OSC command sets and queries the internal synthesizer In INT Sync mode setting the synthesizer frequency will set the chopping frequency In INT Sync mode the data supplied by the OSC command is limited by the chopper wheel minimum and maximum chopp
21. s to communicate with the Model 3501 Commands may be issued either in upper or lower case Some commands can be used to set operating parameters some commands can be used to query operating parameters and some commands can do both A command e g WHL consists of a mnemonic WHL and a optional suffix The three letter mnemonic WHL specifies the parameter or action to be taken by the Model 3501 The suffix indicates the command is a query that requests data from the Model 3501 The WHL2 command is used to set the type of wheel being used and in this case 2 is taken as a parame ter value Do not include decimal points in numerical data So to set the chopper fre quency to 1 23 kHz send the command 0SC123000 To set the phase to 90 degrees send the command PHS 900 Multiple commands on a single line must be separated by a semicolon Data to Host Data returned by the chopper controller to the host computer consist of a mnemonic a data value and a line terminator The mnemonic specifies the parameter WHL wheel or the quantity measured FR1 Feyne frequen cy Data is returned by the chopper with decimal points included e g 1230 0 Data to the host will be followed with a line termination line feed and EOI The line termination may be set when installing IEEE 488 into the host com puter Consult the manufacturer s installation guide for details 23 Vill Command Summary Command In
22. se the cover un 6 Verify that the proper voltage is showing through the module s window V m 43 The power entry module requires two 5x20 mm slow blow fuses such as Littlefuse s Slo Blo 239 series one for the hot line and the other for the neutral line Replacement fuses should be as follows AC Voltage Fuse Rating Littlefuse 100 VAC 0 4A 239 400 120 VAC 0 4A 239 400 220 VAC 0 2A 239 200 240 V AC 0 24 239 200 Figure 7 Power entry module for the Model 3501 Optical Chopper Voltage selection slot selection wheel Fuse holder 0 Xl Specifications Chopping Frequency Wheel Min Freq outer 60 120 Hz 42 30 84 Hz 7 5 14 Hz 2 4 Hz Internal Synthesizer Stability Drift Accuracy Resolution Range limits INT Range limits EXT Reference Input Sync Input Vv Max Freq Jitter ps p p Fouter Min Freq Max Freq 6 40 kHz 60 2 4 48 kHz 50 2 746 Hz 500 3 213 Hz 500 5 100 ppm after one hour warm up Less than 10 ppm C lt 1 5 of least significant digit 4 00 Hz 99 9 kHz 3 significant digits Upper Highest wheel frequency S H Lower Lowest wheel frequency S H 4 00 Hz 99 9 kHz TTL level pulse with same frequency limits as internal oscillator 45 Reference Output Sync Out TTL level square wave may be used as free running oscillator when using EXT EXT or Voy Sync Fouter TIL level square wave at the chopping frequency OUT TTL level pu
23. the decimal point to maintain three signifi cant digits of resolution PHASE The phase delay may be set from 179 0 to 180 0 The phase shift is always referred to the chopping frequency Fouter In NORMAL and modes F In H S mode F H S Psoe outer Pyne outer When the phase adjustment is active the DEG LED will be lit The left arrow and right arrow keys select the significant digit to be modified and this digit will blink The up arrow and down arrow keys change the magnitude of the digit H In H S mode the user may lock the chopper to a harmonic of the sync frequency H is set to the harmonic of interest Use the up arrow and down arrow keys to set H from 1 to 15 S The user may lock the chopper to a subharmonic of the sync frequency S is set to the subharmonic of interest Use the up arrow and down arrow keys to set S from 1 to 15 S and H may be set in any combination Changing S only has an effect when the chopper is in H S mode STORE The user may store an instrument set up in one of two ways First the control unit will retain the control settings when the power is removed 1 When power is restored the instrument will recall the last control settings used Second the user may utilize one of nine programmable instrument set ups To store an instrument set up press the Set key until STORE is lit Then use the up arrow and down arrow keys to select instrument set ups 1 9 Press the left arrow or right
24. tial electrical shock use only mains that provide a protective ground Wheel Hazard WARNING The moving wheel may inflict injury The operator should assure the safety of personnel who may be exposed to this hazard Safety is important The chopper wheel can cause injury if it is touched while rotating This is especially critical if you find yourself reaching into your opti cal set up with the lights off You may want to use the chopper wheel cover to reduce the chance of injury Environment The Model 3501 Optical Chopper may be operated in an ambient of 0 to 40 degrees C It is recommended to avoid direct sunlight on the LED display WARNING Hazardous voltages capable of causing death are present inside this instrument Do not operate the instrument with the covers removed IV Quick Start 0 Before operating the Model 3501 Optical Chopper please review the previous section to make sure the chopper is ready for use de 2 Mount the chopper head securely on an optical bench Mount the 42 30 wheel on the head Avoid bending the wheel The wheel should be free to turn without contact to the optical sensor or nearby equipment Connect the cable between the chopper head and the connector marked MOTOR on the back panel of the control unit Check that the correct line voltage has been selected and the proper fuse inserted into the mains power entry module at the back panel of the con trol unit Connect the instrument
25. to the power mains After insuring the safety of nearby personnel switch on the instrument Recall instrument set up 0 factory default setting Press SET until RECALL is lit Press the up down arrow keys until 0 appears in the display window Press the left or right arrow key to recall set up 0 The instrument will lock at 84 Hz within 1 minute To choose a particular chopping frequency press the Set key until the FREQ LED is lit and then use the up down arrows keys to adjust the chopping frequency V Operation This section describes operation of the chopper starting with an overview of the front panel functions This is followed by a description of the chopper back panel and the chopper head Measure pem V 3501 Optical Chopper a fd Ss S E Sync Synthesizer Input Output EQuier O O az aa 2 la SEHERE NEW FOCUS Inc Fig 2 Front panel of the Model 3501 chopper controller v 9 10 Front Panel Operation v Wheel The user may select from single or double slot wheels to perform single or dual path experiments Different wheel apertures may be selected to accom modate the chopping frequency of interest The table below summarizes wheel choices and chopping frequency ranges Wheel Type Lowest Frequency Highest Frequency slots Fouter Fouter 60 120 Hz 6 40
26. uced to a minimum Precision photo etched wheels are mounted on a high quality DC motor The motor head has a photo sensor for monitoring the chopping frequency of the outer part of the wheel Foytey The chopper controller then actively stabilizes the motor speed to match the desired chop ping frequency This technique minimizes phase noise at the chopping fre quency and provides for long term stable chopping with a minimum of fre quency drift Figure 1 shows a block diagram of the Model 3501 Optical Chopper system Programmable divide multiply circuitry allows for harmonic or subharmonic locking of the chopper to the reference frequency In addition the phase of the chopping frequency may be varied over a 180 to 179 degree range with respect to the reference frequency A variety of TTL level outputs are available for use in triggering lock in amplifiers oscilloscopes photon counters or box car averagers Fig 1 Block diagram of the Model 3501 Optical Chopper Synch In gt e Subharmonic ios Divide by 1 to 15 Motor l Controller Harmonic Multiplier 1 to 15 Optical Trigger Motor Synch Internal Frequency Out Synthesizer Chopping Head f Synch D f Outer gt DH gt f Outer Micro Out 2 processor e r Divide by 7 Divideby6b e Qut1 id IEEE 488 HAS Norm Out 1 Out 2
27. w keys SETO Synthesizer frequency SET1 Phase SET2 H SET3 5 SET4 Recall SET5 Store SET6 IEEE 488 device address Command Description Explanation 1 STA Returns the status register The STA query returns the 8 bit status register The status register indicates when the instrument is unlocked first bit and when the data is available second bit Since some commands require a wait before the data is avail able e g FR1 the user may wish to poll the instruments to determine when to collect the data Note A serial poll of the instrument provides the same information without generation of additional data ready messages The bits in the status register are arranged from right to left as shown below i e DO is the rightmost bit A value of 1 indicates the bit has been set and a value of O indicates the bit is clear Format of the bits in the status register DO Unlock sampled D1 Data available D2 Synthesizer locked sampled D3 Multiplier locked sampled D4 Motor locked sampled D5 Latched master unlock D6 Reserved for calibration D7 Reserved for calibration The master unlock bit D5 will be cleared when the status register is read with the STA command The master unlock will be set if the motor multipli er or synthesizer has been unlocked between the last and the current reading of the status register 37 38 Command Description Explanation Example
28. wel on the mounting plate Slide the motor mount onto the optical bench rod and tighten the knob Do not over tighten the knob Mounting the Wheel Remove power from the control unit before attempting to change the chopper wheel Secure the chopper head to a work surface Remove the four 4 40 screws that secure the retaining cap over the wheel while taking care not to bend the wheel Install the replacement wheel retaining cap and 4 40 screws Do not over tighten the screws Control Cable Connect the 6 wire cable from the connector at the side of the chopper head to the MOTOR connector at the back of the control unit WARNING Do not connect or disconnect the chopper head while the control unit is powered or damage to components may occur Always shut off the instrument and allow the motor to stop before disconnecting the cable v Line Voltage Selection The instrument may be damaged if operated with the line voltage selector set at the wrong voltage or with the wrong fuses installed in the power entry module When the instrument ships from the factory it will be programmed for the standard AC voltage in the user s country To select a different operat ing voltage refer to the AC Operating Voltages section Page 43 Grounding The line cord is a three wire power cord for connection to the power mains and a protective ground The chassis is connected to the protective ground to reduce the risk of electric shock To avoid poten
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