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3300/2400 Series - Quantar Technology Incorp.

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1. page 17 Figure 1 6 System Interconnection and Biasing 2 MCP Sensors page 20 Figure 1 7 System Interconnection and Biasing 3 MCP Option 010 Sensors page 21 Figure 1 8 System Interconnection and Biasing 5 MCP Sensors page 22 Figure 1 9 Digital Output Connector Rear Panel page 27 Figure 1 10 Complete System Block Diagram With Typical Data System page 29 Figure 2 1 SUM Pulse Residual Noise trailing portion of SUM waveform 20 mV cm page 32 Figure 2 2 Analog SUM Signal Pulse Height Distribution Oscilloscope Photo page 34 Figure 2 3 Typical Digital Histogrammed Pulse Height Peak Amplitude Distribution of SUM pulse page 35 Figure 2 4 Electronic Dead Time Curves Analog Only and Digital Options page 38 Figure 2 5 Definition of Spatial Resolution Resolvable Element page 41 Figure 3 1 Analog X Y Image Full Active Area page 43 Figure 3 2 Analog X Y Image Emission Point Defect page 43 Figure 3 3 Analog X Y Image Input Leads Interchanged page 44 Figure 3 4 Analog X Y Image One Corner Not Connected Properly page 44 Figure
2. interchanged RAE signals adjacent channels Ion type pumps MCP Deadtime ce O O O O I Meter Count Rate function Meter dead time percent function Meter Input Level Function 3300 2400 System Manual rc e ce oooo oo o eee eee page 33 page 37 page 45 page 32 page 31 page 15 page 33 page 14 page 15 page 15 page 15 page 14 page 14 page 14 page 23 page 23 page 23 page 35 page 36 page 19 page 42 page 39 page 37 page 35 page 37 page 39 page 15 page 9 page 36 page 16 page 17 page 43 page 15 page 19 page 19 page 36 page 18 page 11 page 19 page 23 page 33 page 19 page 19 page 30 page 36 page 44 page 31 page 39 page 35 page 35 page 36 18 Nov 2013 Rev I missing RAE signals one channel ee missing RAE signals two opposing channels Mounting hole locations 25 mm Model
3. o oD Oo Z axis 240 blanking POSITION COMPUTER 18 Nov 2013 Rev I Figure 1 7 System Interconnection and Biasing 3 MCP Option 010 Sensors Models 3391 010 and 3395 010 series resistors to limit VACUUM current in event of INTERFACE discharges in sensor y r a 100k 1M INPUT EM J MERA MCP INCOMING 7 FLUX I gt 1450 1950 V mee ELECTRON CC pre CENTER mcr 3 MULTIPLIERS 5 a 500 900 V OUTPUT EM 200 300 V IM ed re cate ss KU 1000 pF j mounted on LSKV L _ iT sensor P baseplate dc blocking coax shields capacitors to protect preamp Shield all signal leads carefully avoid ground loops in ground shields Signal leads must use coax or other shielding method with minimum capacitance and lead length Rev D 3300 2400 System Manual vctr 7 2 McPctri1 i 1 l vout I d 3 MCPout and Lo Bypass capacitors 0 001 pF 24012 PRE AMP page 21 x Select HV divider resistors to main tain 600 1000 nA min divider current H Y PRE AMP_POWER Typical HV Bias Voltages exact voltages depend on gain of specific MCP s used MCP 1 2 1450 1950 volts MCP 3 500 900 volts MCP Out to RAE 200 300 volts Typical floating HV supply 2150 3150 Adjust HV for best PHD gain and background Either or side can be grounded depending on application requirements Orre VOITages i DISPLAY SCOP
4. The count rate function indicates on a log scale the RATE of incoming pulses This rate signal is derived from the look ahead circuitry which is fed by the E preamp All pulses from this pre amp greater than 150 mv referred to SUM signal will be included in the rate count even though the position computing circuitry rejects signals less than 300 mv and greater than 5 volts This is done to afford the user a better estimate of real input activity Because this indication is on a log scale the meter will indicate offscale to the left for count rates below 1 count per second 2 3 2 DEAD TIME PERCENT Indicates the percent of incoming events as measured by RATE signal that are fully processed to position outputs as measured by STROBE signal or X Y outputs The inverse of this is percent of incoming events lost 3300 2400 System Manual page 35 18 Nov 2013 Rev I 2 3 3 INPUT LEVEL When operating with a Gaussian distribution of event pulse heights this function indicates the average input level size of charge pulse deposited on RAE by MCP s A black band spanning the 40 to 60 of full scale range on the meter indicates the optimum range for this average It is important to understand how this function is derived If the incoming signal is greater than approximately 1 75 volts 1 25 volts in earlier models the meter is set to full scale until another pulse come in If a pulse is less than that value the meter is set to zero until the next p
5. 5 4 3 2 y 10 18 Nov 2013 Rev I These dead times as indicated by the dead time curves discussed above and shown in Figure 2 4 combined with the pulse pair rejection capability of the Model 2401B has the overall effect of on the processing of successive events as follows Time Separation T Between Events Effects On Processing T lt 400 nanoseconds Events merged into single event with spatial position calculated as geometric mean Multiple events within 400 nsec spacing often are vetoed because they exceed upper level Overload discriminator 400 nsec lt T lt 1 usec Both events are vetoed and eliminated from processing 1 usec lt T lt EDT usec First event is processed normally second event is vetoed from processing and eliminated EDT effective dead time depends on option version 3 4 usec for analog only 4 usec for 8 bit 6 usec for 9 bit 10 usec for 10 bit T gt EDT usec Both first and second events are processed normally 2 5 1 4 Dead time Correction Live Time Dead Time The approximate dead time percent can be observed on the front panel meter when the METER FUNCTION switch is in the Dead time position In addition by counting the RATE output which tracks the occurrence of normal gain events up to approximately 800 KHz to I MHz although with some dead time itself about 500 600 nsec relative to the STROBE output which outputs a single pulse only for each event that is accepted for proce
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7. i e both inside and outside the vacuum Longer leads may be used but some increased position jitter or noise pickup may be experienced depending on noise sources present may If signal leads are shorter than 4 inches shielding is typically not required except in extremely noisy electrical environments 1 3 3 ORIENTATION OF SIGNAL LEADS A B C D In order to produce a proper image the signals from the RAE must be connected in the proper orientation The following procedure is recommended for connection of the signals from the sensor First designate any of the four corners of the sensor as A Connect this output to preamp input A Moving counterclockwise around the sensor as viewed from the rear designate the next corner as B and likewise connect to preamp input B Continue this sequence for C and D The rotational orientation is arbitrary except for mirror imaging the signals However in any case the A B C and D leads must follow each other in consecutive order If any two adjacent leads are interchanged a twisted image will result see Maintenance section and Figure 3 3 1 3 4 SIGNAL LEAD DECOUPLING The preamp inputs are direct coupled and cannot tolerate any DC bias Each signal output lead is capacitively decoupled by 1000 pF ceramic block capacitors mounted on the rear of the ceramic baseplate These capacitors are rated at a maximum of 5000 VDC The purpose of these capacitors is to enable biasing of the anode at a hig
8. 24 CONNECTING POSITION ANALYZER TO EXTERNAL DEVICES page 24 ANALOG X AND Y POSITION SIGNALS LLLLLLL L LI page 24 ZAXI a be eG Stas Sethi heals A Sa de dad de ames page 25 STROBE Ca 293 00 AA AREA ER re Se er ee page 25 SUM Jasper NS AGE page 25 BUSY Ser SE er Al ei at oe ae page 25 RADE oro ro Sete Seneste ren goto seis page 26 VETO GATEINPUL 2233s a Se ot ele EU ska TA ENE page 26 DIGITAL X AND Y POSITION SIGNALS LLLLL ee page 26 DIGITAL STROBE coa os bo bn DA EN See eA Av EVE oz ava eee page 26 REAR PANEL SWITCHES k kaka page 28 Y AXIS DIGITAL OUTPUT MODE SWITCH 0 000004 page 28 1 D 2 D DIGITAL MEMORY MAPPING CABLE SWITCH page 28 SECTION 2 SYSTEM OPERATION ee page 30 INITIAL TURN ON AND CHECKOUT ee page 30 SYSTEM SETUP ene negi Pees etd Ce gato dd AG page 30 VACUUM PRESSURE co opos Sesh a oe A RANA ae ii ak tot page 30 PRELIMINARY HV CHECK vesi ii cee eee bene nen eees page 30 CONNECT XY MONITOR 3 5 94 aan sate al 4 ed VRE VAJ ETEN page 31 BV TURNON sco cutee ted are aa EGR oia ia ida Sande page 31 INITIAL OPERATION vrr cba Sa bok SR VIRA GA Ae ne page 32 CHECKING NOISE LEVEL seg se ee ass pe Seas es page 32 CHECKING SPATIAL RESOLUTION erverv raneren page 33 OPTIMIZING HV BIAS SETTINGS po persere treta ee page 33 METHOD 1 INPUT LEVEL METER 0 ee page 33 METHOD 2 OSCILLOSCOPE e rr page 33 METHO
9. 3 5 Analog X Y Image Two Opposite Corners Not Connected Properly page 45 Figure 3 6 Digital Image Incorrect ADC Span and Zero Adjustments page 45 Figure 3 7 Troubleshooting Decision Tree Image on CRT Not Circular page 46 Figure 3 8 Troubleshooting Decision Tree No Output From Detector page 47 Figure 3 9 Troubleshooting Decision Tree Insufficient Number of Events Detected page 48 Figure 3 10 Troubleshooting Decision Tree Background Too High or Hot Spots page 49 3300 2400 System Manual page 5 18 Nov 2013 Rev I This page is intentionally blank 3300 2400 System Manual page 6 18 Nov 2013 Rev I LIMITED WARRANTY Quantar Technology products are warranted against defects in material and workmanship for a period of one year from the date of shipment During the warranty period Quantar Technology will at our option repair replace or refund the purchase price of products which prove to be defective For warranty service or repair this product must be returned to Quantar Technology For products returned to Quantar Technology for warranty service Buyer shall prepay shipping charges to Quantar Technology and Quantar Technology shall pay shipping charge to return the product to Buyer However Buyer shall pay all shipping charges duties and taxes for products returned to Quantar Technology from another count
10. In addition under some circumstances there can be a third component associated with the MCP electron multipliers as discussed below 3300 2400 System Manual page 36 18 Nov 2013 Rev I 2 5 1 1 Preamp dead time 3 usec The output pulses from the charge sensitive preamplifiers have a relatively long decay time in order to assure that complete charge collection occurs from the resistive anode encoder RAE This is necessary since the 4 charge signals from the RAE carry the information regarding spatial position of an event At high count rates with a random time spacing between events this long decay time tail can introduce pulse pileup where a second pulse is superimposed on the tail of a preceding pulse In this case the amplified pulse is no longer a good measure of charge Q and this can lead to errors in determination of spatial position of events An important objective therefore is to ensure that the amplifier output is restored to the zero baseline prior to processing of the next event To minimize this pile up effect fast pulse shaping is used to eliminate the long tails from the charge sensitive amplifier while the amplitude of the pulse is not significantly affected This processing reduces the time reguired to re establish the baseline level of the preamps while maintaining desirable pulse amplitude and thus spatial position accuracy and spatial resolution In the Model 2401B this dead time is approximately 3 microseconds Th
11. connected to the STROBE output of the readout electronics and the Input Level Meter on the readout electronics At a HV power supply setting such that the voltage across each MCP is approximately 600 700 volts you should see background counts sporadically occurring Slowly increase the potential to the target operating voltage of the HV divider network you are using At this voltage you should see more background counts occurring Observe the spatial distribution of the background This should be random a concentration of counts in one area indicates either a hot spot on the MCP RAE Sensor or electronic transients being detected by one or more preamplifiers a common manifestation of electrical transient problems is an apparent hot spot near the center of the X Y monitor image due to signals being detected equally common mode by all four preamplifiers A test for this condition that is usually effective is to decrease the high voltage somewhat so real signals are sub threshold and see if the spot disappears The typical rate of background will be lt 10 counts sec for the 25 mm and 40 mm size sensors and up to 100 cps for the 75 mm size sensors The front panel meter with the Meter Switch in the Input Level position should indicate approximately mid scale with the HV at the target operating level If during these tests flashes of counts or other discharges are noted immediately decrease the HV to avoid damage to the MCP Investigate the c
12. involving signal or HV leads noise pickup inadequate vacuum or possibly hardware failure Check these factors carefully Use the procedures outlined to determine if the problem is present only when HV is ON or OFF or if the problem can be isolated to the MCP RAE Sensor or to the electronics Problems which occur at some point during normal operation without any changes in wiring mounting vacuum etc are generally of a somewhat different type and are more likely to involve hardware failure of some type However with complex experimental situations in UHV systems do not overlook the possibility that some other factor has in actual fact changed and is causing an observable abnormality at the detector while the detector itself is operating normally Refer to the Model 2401B Operation and Service Manual for detailed Theory of Operation Component Locators and Schematic diagrams for the electronic circuits When communicating with Ouantar Technology Customer Technical Support regarding installation or operational problems it is helpful to have answers to as many of the applicable guestions in the decision trees as possible 3300 2400 System Manual page 42 18 Nov 2013 Rev I Figure 3 1 Analog X Y Image Full Active Area Figure 3 2 Analog X Y Image Emission Point Defect 3300 2400 System Manual page 43 18 Nov 2013 Rev I Figure 3 3 Analog X Y Image Input Leads Interchanged 500mY ODM Figure 3 4 Analog X Y Image One Cor
13. 3390 3391 Mounting Hole Locations 40 mm Models 3394 3395 OSCILLOSCOPE XY Monitor 0 nana PIN FUNCTION sa ak je be ee ih ea ea anj ka SOs Preamp deadtime O ANI VNA Pressure vacuum effect on background Problem Diagnosis Troubleshooting pe as E VARI ik Problems circular image cut off by display border diagonal half circle image diagonal line image piwa emission points hot spots image high backgound count rate hot spots hourglass twisted image e ee insufficient number of event low sensitivity no output from detector ee Mounting methods sensor suggested L nea Mounting Sensor Assembly nea Mounting sensor from front surface Mounting sensor from rear baseplate Noise level checking on SUM pulse ccc cece nn OPERATING CONSIDERATIONS nanasa eens non circular image on CRT LLLL nana nena Pulse Height Distribution oo oooooooooooocrrrrrrrrrrrrrrororos pusle height analysis ore sd ges 8 Sa acai tah aren t
14. 401B only The RATE will always equal or exceed STROBE The ratio of STROBE to RATE enables calculation of fractional dead time loss 1 ratio The RATE output can be connected to a digital frequency counter for monitoring adjust counter s threshold carefully to avoid double counting This signal is equivalently monitored by the front panel meter when the Meter Switch is in the Count Rate position 1 5 7 VETO GATE INPUT Model 2401B version only beginning October 1990 This input provides for external time based digital control of processing Grounding of this rear panel input interrupts both analog and digital output until it is released from ground This capability is useful in applications where it is desirable to exclude processing of events to an external data system or memory during specified periods which are synchronized to external experimental conditions e g low rep rate pulsed laser excitation of a sample The precision time jitter for the cut on and cut off of processing is approximately 300 nsec This input is pulled up to the normal status by internal resistors when the input has no connection and signal input should never excess of 5 volts If an event is NOT to be vetoed the VETO GATE signal must be in high state no later than 20 30 nsec after the event occurs when the FAST RATE signal appears on Ul 15b and must continue to be in the high state up to approximately 800 nsec peak time PK TH If it is allowed to go low at an
15. D 3 EXTERNAL PULSE HEIGHT ANALYZER page 34 METHOD 4 BUILT IN DIGITAL PULSE HEIGHT ANALYZER page 34 3300 2400 System Manual page 3 18 Nov 2013 Rev I METER FUNCTIONS p a8 a Sa 35 RA ESSA SA Ev Sk DB RD EE FELE ESS page 35 COUNT RATE G erste Se ae bedere pg page 35 DEAD TIME PERCENT ae RR BES Gr EE page 35 INPUT LE VEL si 55 pt be ARNA page 36 EDGE GATING CONTROLS eruav vern r k ka k beeen an page 36 OPERATING CONSIDERATIONS e varar ve vare vr varer rare renere rare page 36 COUNT RATE AND DEAD TIME L ee page 36 SPATIAL RESOLUTION 2363 4 cyt edt ue ds page 40 SECTION 3 DIAGNOSTICS AND TROUBLESHOOTING 0 00 00 e eee eee ene page 42 PROBLEM DIAGNOSIS AND TROUBLESHOOTING ee page 42 APPENDIX TECHNICAL REFERENCES netere mane EE E E e page 50 3300 2400 System Manual page 4 18 Nov 2013 Rev I LIST OF FIGURES Figure 1 0 Model 2401 Position Analyzer and 3300 Series MCP RAE Sensor page 8 Figure 1 1 Suggested Sensor Mounting Methods page 10 Figure 1 2 Mounting Hole Locations 25 mm Models 3390 3391 page 12 Figure 1 3 Mounting Hole Locations 40 mm Models 3394 3395 page 13 Figure 1 4 Electrical Connections for 2 MCP versions and 3 MCP Option 010 versions page 16 Figure 1 5 Electrical Connections 5 MCP versions
16. E Do O 3 Z axis 240 POSITION blanking COMPUTER 18 Nov 2013 Rev I Figure 1 8 System Interconnection and Biasing 5 MCP Sensors Models 3391 and 3395 VACUUM INTERFACE Ez STAGE 1 gt 8 y stage ED G MICROCHANNEL JA PLATES P ED gt G STAGE 2 A 2 stage Y 4 4 BS E 1000 pr woo de blocking capacitors to protect preamp mounted on sensor baseplate coax shields EEE ee E A Shield all signal leads carefully avoid groun loops in ground shields Signal leads must use coax or other shielding method with minimum capacitance and lead length ssil Rev D 3300 2400 System Manual series resistors to limit current in event of discharge in sensor Fr TA 100k 1M vin 1 i MCPin Typical HV Bias voltages exact voltage depends on gain of specific MCP s used Stage l 1450 1900 volts Stage 2 1400 1800 volts V Z gap 50 150 retarding volts Zout to RAE 200 300 volts Maintain 600 1000 pamps current in voltage divider string minimum Zin MCPctr2 I pical floating HV supply 3050 4000 volts output vout MCPctrl Adjust HV for best PHD gain and background Zout MCPout Select HV divider resistors for minimum acceptable current and correct voltagas Either or side of HV supply can be grounded ULJ depending on application Bypass a a capacitors C dom
17. G OPT SE SE PRE AMP INPUT p PRE AMP INPUT Cc SHIELD PRE AMP INPUT B PRE AMP INPUT A GRY ANODE BIAS gt exact location of this contact pin and bias resistor may vary from drawing RED ELECTRON MULTIPLIER ene STAGE 2 OUTPUT out WHT ELECTRON MULTIPLIER ET STAGE OUTPUT 3300 2400 System Manual page 17 18 Nov 2013 Rev I 1 3 7 GROUNDING AND BYPASSING The signal leads are extremely susceptible to pickup of electrical noise radio frequency interference RFI and transients from the electrical environment Hence they should be adequately shielded Give particular attention to minimizing signal ground loops which will interfere with proper operation of the sensor by properly terminating grounded shields of coax cables and avoiding the use of multiple grounding points which may be at slightly different actual electrical potentials For example it is typically desirable to ground only one end of the signal coax cable shields not both ends If grounded at the sensor detector head end bring a single ground lead out from the common shield connection out through an isolated vacuum feedthrough and ground at a common point with the preamplifier See block diagram either Figure 1 6 1 7 or 1 8 The shields should be grounded at one point as physically near the MCP RAE sensor as possible Small ceramic bypass capacitors are recommended as shown in Figures 1 6 1 7 and 1 8 to provide extra current to th
18. ONTRACT TORT OR ANY OTHER LEGAL THEORY EVEN IF OUANTAR TECHNOLOGY HAS BEEN ADVISEDIN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES SUCH EXCLUDED LOSSES SHALL INCLUDE BUT ARE NOT LIMITED TO COSTS OF REMOVAL AND INSTALLATION LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON OR DAMAGE TO PROPERTY 3300 2400 System Manual page 7 18 Nov 2013 Rev I Figure 1 0 Model 2401 Position Analyzer and 3300 Series MCP RAE Sensor 3300 2400 System Manual page 8 18 Nov June 2013 Rev I GENERAL INFORMATION 1 0 SCOPE OF THIS MANUAL This Quantar Technology 3300 2400 SYSTEM INSTALLATION AND OPERATION MANUAL provides information regarding the system level set up installation and operation of the Series 3300 Open Face MCP RAE Sensors when operated together with the Model 2401 Position Analyzer It is intended to be used with the separate manuals for the 3300 Series Sensors and the Model 2401 Position Analyzer which provide more detail on these individual models especially regarding corrective repair and maintenance All circuit schematics and component locators for the Model 2401 are contained in its specific manual Manual Update Inserts may be provided with this manual that update information regarding manual errors or design changes 1 0 1 GENERAL DESCRIPTION A 3300 Series MCP RAE Sensor detector head operated with the Model 2401 Position Analyzer and auxiliary HV bias supplies and data collection systems forms a single event counting high
19. QUANTAR TECHNOLOGY 3300 2400 SERIES SYSTEM INSTALLATION AND OPERATION MANUAL Copyright 1990 2013 Quantar Technology Incorporated 2620A Mission Street Santa Cruz CA 95060 Tel 831 429 5227 FAX 831 429 5131 www guantar com 18 Nov 2013 Rev I This page is intentionally blank 3300 2400 System Manual page 2 18 Nov 2013 Rev I TABLE OF CONTENTS EIST OF FIGURES 242275 ENO as BI O BONO NED HESTE Hurt eas page 5 GENERAL INFORMATION svi erre ene page 9 SCOPE OF THIS MANUAL os ss eet Rita Siete BE eek serer Seed pev de a a vah get page 9 GENERAL DESCRIPTION cocos o dra a RR ee Sie eb ae BE ee page 9 SECTION 1 SYSTEM INSTALLATION EVE SAS a a a E ee eee page 11 SENSOR ASSEMBLY MOUNTING LLL 000 000 page 11 MOUNTING OF ELECTRONICS MODULES ee page 11 CONNECTING SENSOR TO PREAMP odeur eea ee page 14 SYSTEM INTERCONNECTION DIAGRAMS LL L page 14 SIGNAL LEADS p g tg Sri bes hoe ah beh eda ode Seen io e page 14 ORIENTATION OF SIGNAL LEADS A B C D page 15 SIGNAL LEAD DECOUPLING re eee E er eee page 15 DNV EBADS mn st EEN SA EE enn ok sten page 15 VACUUM FEBDTHROUGHS LLLL eee ee page 15 GROUNDING AND BYPASSING SERENE ERE page 18 HIGH VOLTAGE BIAS zna se spre Bi MG page 19 HIGH VOLTAGE DIVIDER NETWORK 0 0 0 0 eee eee eee page 19 HV BIAS CONFIGURATIONS LLLLL cece eee page 23 CONNECTING PREAMP TO POSITION ANALYZER ea page
20. are within certain ranges In turn these levels are directly related to the gain of the MCP s and thus operating HV bias voltage While these charge levels are too low typically 107 coulombs to conveniently measure at the RAE a monitor output called SUM is provided on most Quantar Technology readout electronics see Manual for Position Analyzer The SUM signal is representative of the total charge deposited on the RAE from the MCP s regardless of spatial position There are several ways to measure the SUM signal and thereby determine if MCP gain is proper This measurement is referred to as the Pulse Height Distribution this is the event to event statistical distribution to the gain particular events experience as they pass through the MCP stacks 2 2 1 METHOD 1 INPUT LEVEL METER The Model 2401B Position Analyzer is eguipped with a front panel meter that monitors the approximate SUM signal amplitude Put the Meter Switch in the INPUT LEVEL position The meter should indicate approximately in the black band zone on the bottom scale of the meter Note at very low count rates this method is not effective the meter needle will swing from zero to full scale erratically This is the least accurate method yet is useful for routine monitoring during normal operation 2 2 2 METHOD 2 OSCILLOSCOPE Connect an oscilloscope to the SUM output connector of the Quantar readout electronics Set the vertical sensitivity to I V cm and horizontal sw
21. ause and correct before proceeding to other tests CAUTION IF AT ANY TIME YOU OBSERVE A FLASH OF BACKGROUND COUNTS OR INTENSE AREAS OF BACKGROUND EMISSION IMMEDIATELY TURN OFF THE HV AND INVESTIGATE THE CAUSE EXCESSIVE BACKGROUND INDICATES A DISCHARGE OR EMISSION WHICH CAN PERMANENTLY DAMAGE THE MCP SURFACES When making this test be sure all sources of countable events capable of reaching the sensor surface have been turned off especially devices such as ionization type vacuum gauges or unshielded ion type pumps which will produce a large number of detected events in most vacuum systems and will be picked up by the detector Other sources of background may be corona from a bias lead electrical discharge or field emission Naturally occurring cosmic rays will also contribute some background depending on altitude above sea level but many of these will be vetoed by the system due to excessive pulse amplitude 3300 2400 System Manual page 31 18 Nov 2013 Rev I 2 1 6 INITIAL OPERATION If the background count rate observed is satisfactory turn on a test signal preferably at a count rate of 4000 5000 counts per second You should clearly see the additional events on the X Y monitor Depending on the count rate and the short persistence time of the X Y display device used you may or may not be able to visually view a recognizable image at lower count rates below 1000 counts per second but generally can do so at higher count rates when t
22. axis digitized output signal from the Model 2401 Move the rear panel Y Axis Digital Mode Switch to the PHA position the Y axis sample and hold and digitizer are now connected to the SUM signal rather than the Y axis position signal The collected data represents the Digital Sum Pulse Height Distribution A typical digital PHD is shown in Figure 2 3 USE OF UV EXCITATION IN PHD MEASUREMENTS Depending on photon energy angle of incidence and other experimental factors it may not be possible to obtain a fully saturated peaked Pulse Height Distribution when imaging far UV photons This is due to lower gain sometimes experienced by UV excited events resulting from multiple UV reflections down the MCP microchannels prior to secondary electron generation Generally it is preferable to use charged particle excitation e g electrons of greater than 100 eV kinetic energy in making PHD measurements Use of specific coatings on the input MCP may help in this situation 3300 2400 System Manual page 34 18 Nov 2013 Rev I Figure 2 3 Typical Digital Histogrammed Pulse Height Peak Amplitude Distribution of SUM pulse Number of events versus gain of each event Pulse Height Distribution 1X 1908 v Mean 1 5 to 2 0 V Counts Lower threshold 0 3 to 0 5 V J Sur Signal Volts 5 2 3 METER FUNCTIONS A selector switch on the Model 2401B front panel allows display of three different operating parameters on the panel meter 2 3 1 COUNT RATE
23. cessary to use slightly longer screws depending on the thickness of the mounting bracket The bracket should then be mounted securely to the vacuum chamber Even a few ohms resistance in this grounding path can result in ground loop noise voltages It may be necessary to experiment with the optimum grounding procedure for a particular setup to minimize noise pickup see SUM pulse diagnostic measurements section CHECKING NOISE LEVEL 1 3 BIASING AND ELECTRICAL CONNECTIONS CONNECTING SENSOR TO PREAMP 1 3 1 SYSTEM INTERCONNECTION DIAGRAMS See Figures 1 4 and 1 5 Electrical Connections for identification of contacts on rear of 3300 Series MCP RAE Sensors Figures 1 6 1 7 and 1 8 System Interconnection and Biasing provide schematic information for hookup of signal leads HV leads and the HV Bias Voltage Divider The following sections should be read with reference to these figures SAFETY WARNING The electrical potentials applied to this MCP sensor for proper operation are potentially harmful Personnel should use extreme care in handling HV leads making connections and performing tests 1 3 2 SIGNAL LEADS Signal connections from the 4 contacts corners of the RAE should be shielded if over about 4 inches 10 cm long due to the extreme sensitivity of the charge sensitive amplifiers to extraneous electrical signals which can be generated either inside or outside the vacuum system Use the lowest capacitance coax cable availabl
24. count rate and the direction of output count rate with increasing input count rate will identify at which point on the curve operation is taking place Care must be exercised to avoid inadvertent operation at extremely high count rates Figure 2 4 Electronic Dead Time Curves Analog Only and Digital Options Assuming no dead time correction for RATE channel and random time of arrival of events RENEE ITT EEE ei i EEE STROBE signal Output KHz FHIR si EU zre 3300 2400 System Manual i RT if nn o Htp ie E BEE Heter na prestige Get EE D es en Bet a EES HH re ho 3 Hi Hatt BA oa letini arty H IE iii ME ee ane Hk ene tami n iiih Ee 6 O MHE nein staj o ni a E E Ll o a me 2 3 LETER DEERE IA LEEN ME FE mi VEDEN dn HE ira pal HE Ha ti ertet dl FER ii 3 4 5 67891 mea 1 ring EUR Ls a Reece ce k pe CAT i moua eee os Ss 7 Maa nae 5 EA H Ha AA i 2 fe ERPE 4 Peer E H ideal a PE po H itt i 4 GENRE EE NISTE ESOS TEN en tal ELEN HEH ata E po iti i DO RATE signal Assumed Input KHz page 38 A i Sant IH EE MOSEL FUNKER IUII E EH BEE HB ROE ME t a 8 7 b 5 4 3 li inst R E 2 i i i En pokrij bari En oe e o ETE me ag SIGS oe ele E AAA O ee Ki SERIE Bie E is 4 2 ja Ha 8 7 6
25. ctronic readout unit You should detect zero counts in this HV OFF condition If the front panel Count Rate meter switch in the Count Rate position reads upscale above zero noise is being picked up by the electronics either from RFI type signals or ground loops These extraneous signals must be eliminated before proceeding further Make certain the preamplifier case is very well grounded to the vacuum system preferably with heavy ground strap or braid or is mounted directly on the vacuum flange with a metal bracket A single ground wire is NOT generally adequate for this purpose Resolve any noise problems before proceeding 3300 2400 System Manual page 30 18 Nov 2013 Rev I 2 1 4 CONNECT XY MONITOR Make the following connections to an oscilloscope set to operate in the X Y mode Model 2401B Oscilloscope Input X Position Analog Output Horizontal amplifier input high Z only not 50 ohms Y Position Analog Output Vertical amplifier input high Z only not 50 ohms Z Axis Output Z Axis Intensity Blanking input Set both horizontal and vertical amplifier sensitivity to 0 5 volts division Adjust the intensity control for what would be normal brightness when a valid event is displayed i e the Z Axis blanking signal is equal to OV In operation processed events will be displayed as intensified dots on the X Y CRT display 2 1 5 HV TURN ON SLOWLY increase the HV bias level from zero volts Carefully watch the X Y display a frequency counter
26. decreases such that the mean gain has moved from the target 1 5 to 2 0 volt range adjustment of the MCP HV bias should be made to re establish the proper gain level 2 6 SPATIAL RESOLUTION When the detector is operating at specified spatial resolution two input peaks of Gaussian shaped intensity profiles spatially separated by the specified FWHM of the resolvable element should be just resolvable approximately 10 valley between merged peaks A statistically significant 1000 number of counts should be accumulated in the peaks to make this measurement This is shown diagrammatically in Figure 2 5 Spatial Resolution From another perspective this spread function is simply the position jitter in the electronically calculated spatial positions of a large number of events which were incident on the theoretically exact same spatial position on the active sensor surface In Figure 2 5 also note the filled dots on the curve which represent the sampled digital data These digital samples of the analog position signals are taken at fixed positions across the active diameter of the sensor Note because the digital output is a sampled version of the analog position signals it is important to spatially oversample the analog signal by using an ADC which provides at least 2 digital channels per resolution elements width As an example a 3300 Series MCP RAE Sensor with 2 MCP s is capable of electron optically resolving at FWHM of the spatial reso
27. dering 3300 2400 System Manual page 27 18 Nov 2013 Rev I 1 6 REAR PANEL SWITCHES 1 6 1 Y AXIS DIGITAL OUTPUT MODE SWITCH PULSE HEIGHT MEASUREMENT This switch located on the rear panel selects the input signal to be digitized by the optional Y Axis A to D converter In the normal position the converter digitizes the Y Position signal In the PHA position the converter digitizes the peak values of the SUM pulses creating a digitized pulse height distribution number of events on vertical axis and relative SUM pulse amplitude on the horizontal axis which is useful for more precise evaluation of MCP gain Observation of this digitized Pulse Height Distribution requires a digital data collection system See Figure 2 1 and 2 2 Typical Pulse Height Distribution 1 6 2 1 D 2 D DIGITAL MEMORY MAPPING CABLE SWITCH This switch controls the mode of the optional Switchable Digital Memory Mapping Cable linking the ADC output with the address input port of the Model 2412A or 2415A Histogramming Buffer Memory It enables switching between 1 dimensional Y axis only and 2 dimensional Y and X axes operation without physically exchanging the Digital Memory Mapping Cable flat multiconductor ribbon cable which is normally required when changing between 1 D and 2 D data accumulation In 2401B units with SN 95467 and above approx Dec 1995 this 1 D 2 D switching function is implemented on the main board It is designed primarily to be controlled by Qua
28. ds Using an external HV divider for 2 MCP versions and 3 MCP Option 010 version the following are reguired RAE bias Vrae MCPout Vout MCPcenter Vctr MCP in Vin See Figure 1 6 amp 1 7 Using an external HV divider for 5 MCP versions the following are reguired RAE bias Stage 2 Out Zout Stage 2 In Zin Stage I out Vout Stage I in Vin See Figure 1 8 An additional HV feedthrough is reguired if the option SE Extra Front Ring is to be biased In addition it is often desirable to use a separate pin feedthrough for the common signal coax shield ground lead as shown in the diagrams 3300 2400 System Manual page 15 18 Nov 2013 Rev I Figure 1 4 Electrical Connections for 2 MCP versions and 3 MCP Option 010 versions Models 3390 and 3394 3391 010 and 3395 010 YEL ELECTRON MULTIPLIER Vetr CENTER ELECTRODE MCPetr1 i G R ELECTRON MULTIPLIER In Wale INPUT ELECTRODE ee EXTRA FRONT RING OPT SE SE PRE AMP INPUT D PRE AMP INPUT Cc SHIELD PRE AMP INPUT B PRE AMP INPUT A GRY ANODE BIAS Yed exact location of this contact pin and bias resistor may differ from drawing RED ELECTRON MULTIPLIER LR OUTPUT ELECTRODE 3300 2400 System Manual page 16 18 Nov 2013 Rev I Figure 1 5 Electrical Connections 5 MCP versions Models 3391 and 3395 YEL ELECTRON MULTIPLIER Zin FN STAGE 2 INPUT GRN ELECTRON MULTIPLIER Vin VE STAGE I INPUT ORANGE EXTRA FRONT RIN
29. e last MCP s during event multiplication and to bypass high frequency noise to ground Select capacitors with appropriate voltage ratings based the HV bias levels used A convenient way to observe and guantify the quality of the grounding is to connect an oscilloscope to the SUM output with the scope external trigger input connected to the RATE output of the Model 2401 Adjust the scope TRIGGER LEVEL manually This will display the incoming pulses in sync and allow them to be differentiated from noise By setting the scope sensitivity to about 5 mV per division the background noise can be also observed as the SUM pulse completes its positive leading bipolar cycle and returns to the baseline Background noise above 15 mv peak to peak can cause degradation in the system spatial resolution This is discussed further in Section 2 System Operation and Figure 2 1 SUM PULSE NOISE To isolate sources of local noises and interference monitor the noise on the SUM signal as described above and turn ON and OFF possible sources of noise ion gauges pumps stepper motors computer switching type power supplies etc until the source of noise is identified It can then often be corrected by improved grounding or shielding NOISE PICKUP AND GROUNDING The outer shield of a coaxial cable serves to interconnect the chassis of each instrument module with that of the next When all components are mounted in an instrument rack this electrical connection is often red
30. e that is compatible with your UHV environment requirements to minimize additive noise at the input of the charge sensitive amplifiers due to cable capacitance which will degrade the spatial resolution increase position jitter of the system A maximum of about 60 pF picofarads capacitance to ground is permissible in each signal lead to the preamplifier without adversely affecting spatial resolution Low capacitance coax cable with Teflon insulation e g RG187 188 type 30 pF per foot can be used if compatible with the specific vacuum environment and temperature requirements of the application probable maximum vacuum of 10 and maximum temperature of 150 degrees C Shielded bakeable ceramic bead insulated coax is available from Ceramaseal Corporation see below For UHV compatible bakeable shielded cable assemblies for use in bringing RAE signal leads from sensor to vacuum feedthrough it is suggested to contact Ceramaseal Corporation New Lebanon New York 121256 Tel 518 794 7800 or 800 752 7325 FAX 517 794 8080 www ceramseal com Or Insulator Seal Div of MDC Sarasota FL 34243 Tel 941 751 2880 FAX 941 751 3841 www isi seal com Request information on In Vacuum Cable Assemblies Desired cable lengths and connector types must be specified before ordering 3300 2400 System Manual page 14 18 Nov 2013 Rev I Generally attempt to keep the total length of signal leads less than 24 inches 0 6 meter from sensor to preamplifier
31. ed on the oscilloscope screen However in order to eliminate the fuzzy bright spot and traces which would appear on the display due to this dwell time the Z axis signal provides a properly timed 15 volt signal which blanks the CRT screen except at times when the outputs represent a valid event computation in which case a bright dot appears at the appropriate point on the screen CAUTION Do NOT connect or disconnect the Z axis cable while either the oscilloscope or the 2401 is powered on Due to the presence of appreciable voltages on the Z axis of some oscilloscopes the Z axis output circuit U120 of the Model 2401 can be damaged if this is done Always turn oscilloscope power and Model 2401 power OFF before connecting or disconnecting the Z axis lead The timing of the Z axis signal is the same as the Strobe signal The Z axis signal changes from 15 V to 0 volts for approximately the following periods 4 usec analog only and 8 bit digitized output options 6 usec 9 bit digitized output and 10 usec 10 bit digitized output This Z axis output is compatible with the Z axis Intensity Blanking function on the most popular laboratory oscilloscopes Tektronix HP etc 1 5 3 STROBE The analog strobe signal is a TTL level signal which normally goes to 5 volts for the time period during which the analog X Y position signal outputs are stable and readable It can be used to trigger external A to D conversion or other logic Connect to dig
32. eep to 1 usec cm Model 2401 Operate the detector with a count rate of approximately 1000 counts per second By adjusting the trigger control you will be able to observe the bipolar shaped pulses from the shaper amplifier The average zero to positive peak amplitude should be 1 5 to 2 0 volts There will be some larger peak amplitude pulses and some smaller Adjust the HV bias observing the maximum of 1000 volts per MCP to achieve an average of the proper height A display of what the waveform should look like is shown in Figure 2 2 3300 2400 System Manual page 33 18 Nov 2013 Rev I Figure 2 2 Analog SUM Signal Pulse Height Distribution Oscilloscope Photo 500n s 2 2 3 METHOD 3 EXTERNAL PULSE HEIGHT ANALYZER This is the same method as 2 above but instead of using an oscilloscope use a Pulse Height Analyzer Multichannel Analyzer which will sample each SUM pulse peak digitize and bin it so the exact distribution can be seen Again the centroid of the distribution should be in the 1 5 to 2 0 volt range and the FWHM of the distribution should be 80 140 of the mean value the narrower the better 2 2 4 METHOD 4 BUILT IN DIGITAL PULSE HEIGHT ANALYZER IN QUANTAR MODEL 2401 POSITION ANALYZER This is the same as Method 3 above but uses the built in PHA capabilities of the Model 2401 together with a histogramming data acguisition display system if one is available To do this connect the data acguisition system to read the Y
33. es sz LAY 0 001 pF E SCOPE OQ H gt me pe Z axis 2401 blanking POSITION COMPUTER X 66600000 240 FEE P LILI 0000 7 CI PREAMP col FP A PRE AMP POWER B page 22 18 Nov 2013 Rev I Each MCP requires approximately 700 1000 VDC The exact voltage to produce the desired level of electron gain and therefore spatial resolution without introducing excessive background varies from unit to unit The MCP voltage used in production tests will be indicated on the test data supplied with each sensor Some experimentation with this voltage by the user can often result in an optimum voltage for a specific application environment In no case should the bias voltage need to exceed 1000 VDC per MCP The voltage bias between the output of the last MCP and the RAE is not critical in most environments providing there are no strong transverse magnetic fields but should be at least 200 volts and no more than 500 volts The RAE is normally biased through the I megohm s vacuum compatible resistor supplied with the sensor and mounted on the rear surface of the ceramic baseplate This resistor presents a much higher impedance than the approximately 50 ohm input impedance of the preamplifiers and thus results in essentially no signal loss yet provides a fixed bias path to the RAE to maintain a uniform electric field between the last MCP surface and the RAE which is necessary for proper spatial imaging It is recommended that series current limiti
34. follows which will open the edge windows completely Y Fully clockwise to right Y Fully counter clockwise to left X Fully clockwise to right X Fully counter clockwise to left 2 5 OPERATING CONSIDERATIONS 2 5 1 COUNT RATE AND DEAD TIME In single event pulse counting detector systems each event is processed serially in time as a separate event This implies a processing time or detector system dead time for each event and thus an upper limit on the maximum number of separate events that can be processed in a given interval of time counts per second Furthermore in most applications the arrival of events at the detector are not on a fixed periodic time spacing but rather arrive with a randomly distributed time spacing between events At low count rates the processing of a second event is rarely discontinued due to its arrival too soon after a prior event As incoming count rates increase however increasingly more events are ignored due to this factor Finally at some input count rate the indicated detector output count rate goes through a maximum and actually decreases for further increases in incoming rate At this peak output count rate the percentage of input counts that are continuing to be processed will have generally dropped to approximately 40 of the incoming rate This relationship is shown graphically in Figure 2 4 Electronic Dead Time Curves In the Model 2401B this dead time is composed of two primary components
35. guration considerations discussed in Section 1 3 10 HV Bias Configurations of this manual 3300 2400 System Manual page 19 18 Nov 2013 Rev I Figure 1 6 System Interconnection and Biasing 2 MCP Sensors Models 3390 3392 and 3394 series resistors to limit VACUUM current in event of Typical HV Bias Voltages exact voltages INTERFACE discharges in sensor depend on gain of specific MCP s used G aay ee 7 100k 1M MCP 1 800 950 volts vin MCP 2 800 950 volts INPUT EM JA 1 Mcpin MCP Out to RAE 200 300 volts INCOMING FLUX 1 800 950 V MCP 1 vetr Typical floating ELECTRON K ax CENTER 2 McPctr1 HV supply uki MULTIPLIERS Z gt i I Vout I 3 MCPout 800 950 V Lj OUTPUT EM l YZ A A I ee A Y L 4 1000 pr mounted on Y Bypass LSAV LP J sensor Y iaee baseplate Y ki 0 001 uF dc blocking Y d coax shields capacitors to protect preamp 24012 Shield all signal leads carefully avoid ground loops in ground shields Signal leads must use coax or other shielding method with minimum capacitance and lead length Rev D 3300 2400 System Manual page 20 V PRE AMP 7 1800 2200V Adjust HV for best PHD gain and x Select HV divider background resistors to main tain 600 1000 pA min divider current Either or side can be grounded depending on application requirements gi i DISPLAY SCOPE seers SCILIZTIERTUT
36. h DC potential relative to ground and yet to avoid applying this high voltage to the preamplifier signal inputs which will be damaged by any substantial DC voltage and also to reduce the reguired voltage rating of the coaxial signal leads 1 3 5 HV LEADS The number of HV leads reguired depends on whether the HV Bias Voltage Divider is located inside the vacuum system or outside For all leads inside the vacuum system it is recommended that some type insulated wire be used to avoid corona discharge and shorting which would adversely affect detector operation Teflon insulated wire is suitable for use in some vacuum systems while other insulation methods should be used for other vacuum system environments depending on the application and level of operating pressure All HV leads outside the vacuum chamber should be appropriately insulated and shielded to avoid noise pickup 1 3 6 VACUUM FEEDTHROUGHS Separate BNC type and SHV type feedthrough connectors have been found to be most practical Multi pin feedthrough connectors can be used provided the voltage rating is sufficient and the interelectrode capacitance is minimized 1 2 pF Signals are not of the frequency range to require use of feedthroughs with a defined 50 Q impedance 4 BNC type feedthrough connectors are reguired for signal output leads and depending on the location ofthe HV Bias Voltage Divider network a suitable number of SHV type SKV rating HV feedthroughs for HV bias voltage lea
37. hannels in the MCP 3 The input count rate in the localized area 3300 2400 System Manual page 39 18 Nov 2013 Rev I Because of the possible variation in these parameters it is not possible to give exact predictions of these effects However in general conventional bias current MCP s have been observed to support a count rate of 50 200 counts per second per microchannel This typically leads to effects on observed count rates only when flux pattern geometries are considerably smaller than 300 x 300 microns If the upper localized MCP count rate limit is exceeded effects will first be seen on the localized gain measured by the pulse height distribution and therefore decreased spatial resolution and then at somewhat higher count rates as a decrease in the STROBE rate Finally effects will be seen as a decrease in the RATE signal itself 2 5 3 MCP GAIN AND BACKGROUNG COUNT RATE It is valuable to periodically check the electron multiplier MCP gain and background count rate This can be done most simply by repeating steps outlined in Section 2 2 Optimizing HV Bias Settings A slight degradation in gain as a function of time is to be expected especially in the spatial region on the MCP that is most frequently used In most clean low flux rate environments this amounts to only a few percent a year Measurement of the digital PHD is the most accurate method of comparison noting the HV bias and comparing to prior measurements If MCP gain
38. he image is more filled in With radiation flooding the detector a circular image should be seen 2 1 7 CHECKING NOISE LEVEL 1 Turn the Model 2401 power OFF Connect a second oscilloscope if available to the SUM BNC type connector on the rear panel of the Model 2401B If a second oscilloscope is not available the scope monitoring the X Y signals above may be used making sure to turn the units off before disconnecting the Z axis cable It is preferable to continue monitoring the X Y outputs as well if possible Connect the RATE output to the EXT TRIGGER of the oscilloscope for easiest triggering and set the horizontal SWEEP TIME to 1 usec per division 2 Turn the HV off Turn the Model 2401B ON Approximately 10 15 mV peak to peak white broadband noise will typically be seen with perhaps a few line related transients see Figure 2 1 About 5 10 mV of this noise is generated by the RAE and electronics and is not reducible All such transients should be smaller than 300 mV peak to peak or they will be interpreted by the electronics as real events Transients can be reduced by improving the detector system grounding by improving shielding or by isolating the system power supplies more completely 3 Leave the Model 2401B ON Adjust the HV supply to 0 volts and turn ON Slowly adjust to a low voltage 100 300 volts Observe any additional transients or noise present on the SUM output If the HV power supply is properly filtered and
39. ie ii built in internal analyzer ee ce ooo ooo oo se or ooo oo ooo oo see o e ooo oo e ooo o coo e o ooo eee PE 0 e oo ooo o ose se oo ooo o ooo 00 0 a e ooo o o ev ce oooooo o o external analyzer O EVE ALT A ARA REAR PANEL DIGITAL OUTPUT CONNECTOR ee References Technical jo asda ile ii ide Resistor HV current limiting ds Resolution Spatial EE RE AE VO ME ONI Lee vb wots Resolution spatial checking ee Series limiting resistors cenicienta seksere Ge 8 aw seie breene zaleti Signal connections 00d dit ika esse see Wr deeb Jers OI vere OO O rc o oo o SIGNAL LEADS AND HV LEADS o oooooocococococororococococo co EEEa Spatial resolution checking ooooooooooocroorrrorrrrrrrcrrrrrrrocro spatial resolution FWHM O keel mn cala O A RAVEN k System Interconnection and Biasing 2 MCP Sensors Models 3390 EN System Interconnection and Biasing 5 MCP Sensors Models 3391 UV excitation of MCP effect on PHD measurements Vacuum feedthroughs types ene Vacuum flanges AA O AAA e Vacuum pressure effect on background XY Monitor
40. is 3 usec dead time component is paralyzable this means it is retriggered restarted each time a threshold exceeding event is detected by the E channel fast preamp to have reached the charge sensitive preamplifiers The E channel preamp can distinguish separate events providing they are separated in arrival time by at least 400 nanoseconds and their amplitudes exceed a special RATE lower level threshold 2 5 1 2 ADC Dead time A second dead time component is due to the finite time reguired by the analog to digital converters ADC when this option is installed to produce a digitized version of the analog position pulse During this time period another event cannot be processed accurately The ADC digitization process itself starts 1 2 microseconds after detection of the event and continues for the following times depending on the digital resolution option installed Option 008 EC 8 bit 256 channel 2 usec Option 009 EE 9 bit 512 channel 4 usec Option 010 EJ 10 bit 1024 channel 9 usec In addition there is some additional overhead time approximately 0 5 1 0 sec associated with preparation for the conversion process and to enable stabilization of circuits in preparation for the next event The total dead time for units with digital output options installed is a combination of the preamp dead time above and these ADC dead times This results in a total effective dead time of 4 usec 8 bit 6 usec 9 bit and 10 usec 10 bit per event
41. isolated no change should be seen Figure 2 1 SUM Pulse Residual Noise trailing portion of SUM waveform 20 mV cm peak to peak noise should be less than 10 15 mV 20 mV maximum 3300 2400 System Manual page 32 18 Nov 2013 Rev I 4 Again increase the HV power supply voltage to the correct operating voltage for the MCP RAE sensor and voltage divider in use Turn on a source of countable events i e stray electrons from an operating ion vacuum gauge or a flashlight bulb filament operating in vacuum at about 50 70 of its rated voltage makes a convenient source if none is otherwise available Pulses similar to those shown in Figure 2 2 Analog Sum Pulse Height Distribution should be seen at the SUM output Make minor adjustments in the HV supply voltage until the mean 0 to peak height is between 1 5 to 2 0 volts without introducing excessive background see HV Optimization section in this manual It is suggested to clearly mark this HV setting on the HV Power Supply as a reminder of the correct operating voltage 2 1 8 CHECKING SPATIAL RESOLUTION Spatial resolution and spatial linearity tests can be made on the system by placing a transmission mask with appropriate details on it directly in front of the MCP surface and collecting the data on an appropriate digital data collection system 2 2 OPTIMIZING HV BIAS SETTINGS Spatial resolution is optimized in this type of detector system when the levels of the charge signals from the RAE
42. ital frequency counter to monitor STROBE count rate to measure total number of fully processed events per second There is a single STROBE pulse generated for every valid fully processed event Polarity is selected by a board level STROBE jumper see Control Logic Component Locator Jumper is located next to IC U122 use 2 pins nearest edge of board for OV to 5V leading edge use 2 pins farthest from edge of board for 5V to OV leading edge Duration of the STROBE pulse is dependent on the digitized output options similar in operation to the Z axis Note RATE is monitored by the front panel meter STROBE rate is not monitored 1 5 4 SUM The SUM signal is the arithmetic sum of the output signals from the four shaping preamps channels A through D It is used as a diagnostic signal for observing the total pulse amplitude levels indicating the size of the charge pulse deposited on the RAE from the MCP s and a direct indication of MCP electron gain and enabling the adjustment of the HV bias to the appropriate level to generate the proper MCP gain The SUM signal can also be used for observation of random noise and transient pickups by the system which can be detrimental to performance 1 5 5 BUSY The busy signal is a TTL level signal which goes from 0 volts to a logical high when triggered by the RATE lower level threshold comparator about 150 mV and indicates the BUSY one shot circuit is in a timing sequence The busy monostable produces a
43. lectronics Check supply also shorted filters Check preamps supply Y input Ckts Yes Check preamps sum Ckt 3300 2400 System Manual page 47 18 Nov 2013 Rev I Figure 3 9 Troubleshooting Decision Tree Insufficient Number of Events Detected Raise detector HV Correct No divider prob Raise HV on detector or bake Yes out detector 3300 2400 System Manual INSUFFICIENT NUMBER OF PARTICLES DETECTED Average SUM pulse gt 1 5 V Yes No Detector bias OK Usage history of MCP s Worn or contam inated No Troubleshoot electronies unit page 48 Many pulses Yes 75 v No Detector appears OK Check potential of deteetor input incident flux 18 Nov 2013 Rev I Figure 3 10 Troubleshooting Decision Tree Background Too High or Hot Spots Light leak Na 3300 2400 System Manual BACKGROUND IS TOO HIGH Gets better when HV is turned OFF background spatially localized Transient pickup on signal leads Possible sources PC Switching Pwr Supply Stepper motors Radio stations Turbo pumps Bright spot in center means common mode Yes pickup fuzzy spot is Z axis scope problem Does reduced detector voltage cure If around edges could be corona discharges Examine cooler for moisture and tube for signs of damage page 49 Transients being introduced by powe
44. llow aberrations in optics or electron optics to smear spatial separation of the input flux prior to reaching the detector Observed spatial resolution is a convolution of the detector spatial resolution spread function and the intrinsic spatial resolution spread of the input flux pattern itself In addition the measured spread function is subject to the usual statistical uncertainties of counting which decrease as the number of accumulated counts in the measurement increase These independent sources typically add in an RMS manner FWHM observes FWHM input FWHM ser FWHM xatistics Figure 2 5 Definition of Spatial Resolution Resolvable Element High Spatial Resolution Version Performance Shown 400 x 400 Resolvable Elements Infinitely Narrow Input LINE IMAGE l FWHM lt 62 5 MICRONS 400 x 400 RE SYSTEM RESPONSE 3300 2400 System Manual page 41 18 Nov 2013 Rev I SECTION 3 DIAGNOSTICS AND TROUBLESHOOTING 3 1 PROBLEM DIAGNOSIS AND TROUBLESHOOTING Operational problems that occur in this type of system must be carefully analyzed to efficiently determine the source of the problem and enable correction In this section a number of possible problem symptoms are described with possible tests for specific causes outlined in the form of decision trees Problems which arise at first turn on after installation or after re installation following a period of non use are often caused by basic problems
45. ltage being used 2 1 2 VACUUM PRESSURE When the sensor Is first installed substantial outgassing of the adsorbed gases on the large surface area of the MCP s and other components will normally occur It is recommended that the sensor be resident in the vacuum system at a pressure lower than 10 torr for at least 24 hours particularly after initial installation before applying high voltage Preferably the pressure at the sensor should be in the 107 range or better for operation Background count rate is very dependent on operating pressure The lower the pressure the better the performance of the sensor will be The importance of a clean oil and contaminant free vacuum cannot be overemphasized The MCP s can be permanently damaged by contamination such as pump oil backstreaming 2 1 3 PRELIMINARY HV CHECK With the sensor bias leads connected only to the HV supply and voltage divider network MCP sensor temporarily disconnected verify the bias voltages are correct by carefully measuring the voltages with a suitable very high input impedance high voltage probe and voltmeter Make sure the voltmeter probe is not loading the bias voltages down and giving falsely low readings Turn off HV and re connect the MCP RAE sensor to the HV bias leads if this check is satisfactory With the Model 2401B power ON but before turning the HV supply on check the front panel count rate meter or a frequency counter connected to the RATE output of the ele
46. lution spread function 100 elements across either the X or Y active area diameter Minimum acceptable digital oversampling reguires therefore 100 x 2 lt 200 digital data points The 8 bit 256 channel ADC would therefore be selected the 9 bit or 10 bit ADC would give even better digital spatial resolution fidelity at the expense of reduced maximum counting rates Likewise the 3300 Series MCP RAE Sensors using 5 MCP s can resolve 400 elements across either diameter so the minimum number of digital channels is 800 and the 10 bit ADC would be selected 3300 2400 System Manual page 40 18 Nov 2013 Rev I The appropriate number of digital channels to adequately oversample the analog position signal depends to some extent on the application as well In applications requiring careful re construction of line shapes or accurate determination of peak center locations such as in some types of spectroscopy the need is more critical In other applications the need may be less demanding Achievement of specified spatial resolution depends primarily on 1 Reduction of extraneous noise from being introduced into the system This can be diagnosed from the SUM pulse output observed on an oscilloscope 2 Adeguate gain in the MCP s which assures that the signal levels are sufficiently high relative to thermally generated noise such that the jitter in event to event position calculations is minimized In addition the user must be careful not to a
47. n Rev Sci Instrum 50 9 pp 1093 1097 September 1979 1 002 High Resolution Imaging with a Two Dimensional Resistive Anode Photon Counter C Firmani E Ruiz C W Carlson M Popon and F Paresce Rev Sci Instrum pp 570 574 May 1982 1 003 The Microchannel Image Intensifier Michael Lampton Scientific American VoL 245 No 5 pp 62 71 November 1981 1 004 MCP Based Sensors Detect Individual Par ticles Electronic Imaging Morgan Grampian Publishing Co March 1983 18 Nov 2013 Rev I ADC Deadtime ADC Span and Zero incorrect adjustment Background count rate Background from ion pumps Biasing HV RAE anode Black band input level meter function Cable coax Lovin Capacitors Capacitors ceramic HV chip Capacitors HV decoupling Ceramic bead insulated coax Coax cable Coax ceramic bead insulated Configuration Front MCP Surface at Ground Voltage Configuration Front MCP Surface at Non Ground Voltage Configurations HV Bias Count Rate vass ke see as eee eA ane er Count Rate and Deadtime relationship between Current minimum voltage divider Customer Technical Support Dead Time Correction Live Time Dead Time Dead Time Curves Dead Time Percent Deadtime ADC Dead
48. n set up e g energy analyzer potentials this is often the easiest way to operate the sensor 1 3 10 2 FRONT MCP SURFACE AT NON GROUND POTENTIAL In this case the front MCP will most often be operated at a high negative potential Each succeeding stage will be operated at a lower negative potential The RAE will then typically be at ground potential or close to ground Operation in this mode may result in stray charge particles in the vacuum chamber originating from various processes being attracted to the MCP and being detected as increased background In addition the sensor may be operated with both front MCP and RAE at non ground potentials providing the potential differences are correct between MCP stages always accelerating electrons toward the RAE and the voltage rating of the decoupling capacitors is not exceeded 3300 2400 System Manual page 23 18 Nov 2013 Rev I 1 4 CONNECTING PREAMP TO POSITION ANALYZER The preamp has 6 connections which go to the position analyzer including 5 signal outputs and a power connector Outputs A through D correspond to inputs A through D and carry amplified and shaped signals from the four corners of the detector Output E is a fast version higher bandwidth sum of the input signals to the preamp which is used by the position analyzer for look ahead and pulse pile up rejection timing Connect A to A B to B and so on Signals A through D come from identical preamps and may be interchanged to cor
49. nce holes 0 140 inch 3 6 mm diameter provided in the baseplate for mounting the sensor on machined support posts or tabs from the rear e g from a vacuum flange See Figure 1 1 1 2 25mm and 1 3 40mm Since the ceramic baseplate is electrically isolated from all electrodes supporting hardware can be maintained at any desired potential with respect to the detector If using machined mounting posts use either threaded ends with low profile nuts to avoid interference with the close proximity RAE substrate or machined C ring grooves and matching C rings and spring washers to hold the detector in place on the ends of the posts There is limited clearance space between the location of the mounting holes for such posts and the edge of the relatively fragile RAE substrate so care must be exercised to avoid damage due to tool slippage etc To mount from the front surface 0 80 size screws can be used to mount to the front ring which has several 0 80 threaded holes Be certain that the screws are not excessively long such that they could electrically short the front and rear rings which will result in arcing and improper operation If the sensor is to be mounted from the front ring be certain the surface to which it is to be mounted can be operated at the same electrical potential as the front ring which is at the same potential as the front MCP surface Whether the front surface of the sensor is operated at ground potential or a high negative po
50. ner Not Connected Properly 3300 2400 System Manual page 44 18 Nov 2013 Rev I Figure 3 5 Analog X Y Image Two Opposite Corners Not Connected Properly 50 500mv Figure 3 6 Digital Image Incorrect ADC Span and Zero Adjustments 1X Incorrect ADC Span and Zero 1828 Channel 3300 2400 System Manual page 45 18 Nov 2013 Rev I Figure 3 7 Troubleshooting Decision Tree Image on CRT Not Circular IMAGE ON OSCILLOSCOPE IS NOT CIRCULAR Signal cables interehanged hourglass shape Diagonal line 2 preamps or 2 signal leads defective Triangular shape Connection to anode corner defective Pattern stationary when input leads permuted Check preamp inputs with wire held in finger watch XY monitor One preamplifier defective 3300 2400 System Manual page 46 18 Nov 2013 Rev I Figure 3 8 Troubleshooting Decision Tree No Output From Detector NO DETECTOR OUTPUT Electronic Yes failure Check discrim preamp inputs touch SUM signal output peak gt 03 V No Small pulses present Yes Multiplier gain too low No output from MCP RAE sensor No Bias on detector OK Check divider feedthroughs microchannel plates Cheek for open R on divider contacts o MCP s Bias on detector OK No Isolation capacitors shorted Yes Change Yes capacitors 15V OK to e
51. ng resistors be installed in each HV lead from the voltage divider to the MCP s These will limit the current that can flow in the event of arcing or field emission upon application of high voltage bias This in turn will limit damage to the MCP s Any voltage drop across the series resistance must be accounted for in arriving at the correct bias voltage to the MCP itself Test data sheets supplied with the unit indicate the bias strip current of each MCP and are typically in the range of 25 to 60 microamps depending on type and size with special MCP types exhibiting even higher bias currents The HV bias levels shown on the test data supplied do NOT include any adjustment for a voltage drop across a series limiting resistor 1 3 10 HV BIAS CONFIGURATIONS The sensor may be operated in either of two configurations In either configuration electrical potentials must always become increasingly positive from the front surface of the detector to the RAE at the rear so secondary electrons are accelerated toward the RAE 1 3 10 1 FRONT MCP AT GROUND POTENTIAL In this case the front surface of the sensor is operated at ground potential Each succeeding stage must be operated at a progressively more positive potential so that electrons generated in the MCP s will be accelerated The RAE will be at the highest and positive potential in this configuration Assuming this configuration is satisfactory from the standpoint of the remainder of the applicatio
52. ntained between the last MCP surface and the RAE for proper imaging The HV bias provides both of these voltages through use of a user supplied resistive voltage divider network and HV power supply with low ripple and noise 1 3 9 HIGH VOLTAGE DIVIDER NETWORK The bias voltages for the sensor are typically provided by external resistive voltage dividers and HV power supplies It is also possible to construct resistive voltage dividers inside the vacuum system using vacuum compatible e g glass resistors that have been suitably cleaned of oils and silicone greases While less flexible and accessible due to location this method minimizes the number of HV vacuum feedthroughs that are required This method is particularly simple for 2 MCP sensors since only three resistors are essential ignoring the series current limiting resistors that are recommended but not required Proper operating HV levels differ slightly for each MCP RAE sensor based on differences in MCP gain versus voltage characteristics Consult the Final Performance Test Report supplied with each Quantar Technology 3300 Series MCP RAE sensor for values found to be suitable in final test Also see Section 2 2 HV Optimization in this manual Construct a HV resistive divider network in a shielded grounded protective metal enclosure that provides sufficient safety for operating personnel The total resistance of the voltage divider string should be such that a minimum of 400 500 mic
53. ntar Model 2251A MCA MCA2D Software It can be controlled by an optional rear panel switch as well which is normally not installed If the switch is installed it must be left in the 2 D position in order for the software to be able to control the switching function Consult the factory for details of installing this manual switch if desired 3300 2400 System Manual page 28 18 Nov 2013 Rev I Figure 1 10 Complete System Block Diagram With Typical Data System POSITION ANALYZER RATIO DISCRIM PILE UP REJECT FAST ADC MCP RAE SENSOR XY DISPLAY E lt x HISTOGRAMMING BUFFER MEMORY PARALLEL 1 0 HOST PROCESSOR 3300 2400 System Manual page 29 18 Nov 2013 Rev I ID 2D SOFTWARE SECTION 2 SYSTEM OPERATION 2 1 INITIAL TURN ON AND CHECKOUT 2 1 1 SYSTEM SET UP Connect the various system components as described in the SYSTEM INSTALLATION section of this manual WARNING The Model 2401B is equipped with a switchable AC power input module To avoid serious damage this module must be set to the appropriate LINE VOLTAGE before inserting the power cord The operating voltage is set by the orientation of the small removable printed circuit insert card in the power module To access this card slide the plastic cover to the left and remove the PC card with thin pliers Reinsert with the appropriate marking for 100 120 220 240 VAC in the position that matches the line vo
54. oper grounding procedures should be followed to avoid generation of noise and ground loop currents 3300 2400 System Manual page 11 18 Nov 2013 Rev I Figure 1 2 Mounting Hole Locations 25 mm Models 3390 3391 NOTCH Note For SE option equipped models all holes in front SE ring are rotated 90 CCW 0 80 TAPPED HOLE a 3 PLACES ON 1 625 DIA BOLT CIRCLE CERAMIC BASEPLATE 2 000 DIA Hole not available on 5 MCP version 0 144 DIA HOLE i 4 PLACES ON 1 750 DIA BOLT CIRCLE 6 32 TAPPED Hole in removable post 3300 2400 System Manual page 12 18 Nov 2013 Rev I Figure 1 3 Mounting Hole Locations 40 mm Models 3394 3395 NOTCH 315 0 80 TAPPED HOLE 4 PLACES ON 2 500 DIA BOLT CIRCLE CERAMIC BASEPLATE Hole not available 2 900 DIA on 5 MCP version 0 144 DIA HOLE 4 PLACES ON 2 500 DIA BOLT CIRCLE 6 32 TAPPED Hole in removable post 3300 2400 System Manual page 13 18 Nov 2013 Rev I The 24012 Preamplifier Module should be mounted as close to the MCP RAE Sensor as possible to minimize lead capacitance at the input of the charge sensitive circuits It is recommended that the preamp be mounted to a common electrical ground point on or close to the vacuum flange for the signal and HV vacuum feedthroughs It may be mounted on a user supplied metal bracket using two or more of the 4 40 size machine screws that can be seen on the bottom surface of the preamp module case It may be ne
55. properly settled These analog position signals are present for the following times which are slightly less than the total dead time of the Model 2401 version being used 3 usec analog only and 8 bit digitized output option 5 usec 9 bit option and 8 usec 10 bit option Note regarding use with external MCA s multi channel analyzers The standard quiescent level between events of these X and Y position signals is 2 5 volts As a result the leading edge of the X Y or both position pulses of an event located to the left and lower of the image center will have a negative going leading edge This confuses some MCA type pulse height analyzers especially those without an externally triggered Sampled Voltage Analysis Mode which reguire a positive going leading edge on all input pulses to enable the proper sampling of the peak voltage A special interface option is available for the Model 2401B called the MCA Interface Option for these situations and returns the inter event voltage to 0 volts so the leading edge of the position pulse is always positive going Up to Model 2401A serial number 7440 this option was supplied on a plug in board Starting with that serial number the components for this option are installed on a special section of the main board 3300 2400 System Manual page 24 18 Nov 2013 Rev I 1 5 2 Z AXIS The Analog X and Y position outputs return to their quiescent level between event computations and would normally be display
56. r supply 18 Nov 2013 Rev I APPENDIX TECHNICAL REFERENCES MCP TECHNOLOGY K 001 Detection of Extreme UV and Soft X Rays with Microchannel Plates A Review Oswald H W Siegmund and Roger F Malina Space Science Labs American Chemical Society pp 253 275 1983 K 002 Review of the Influence of Radiations of Channeltrons and Channel Plates J P Macau J Jamar S Gardier IEEE Transactions on Nuclear Science Vol NS 23 No 6 December 1976 K 003 Efficiency of Channel Electron Multipliers for Electrons of 1 50 keV R J Archuleta and S E DeForest University of California San Diego Review of Scientific Instruments Vol 42 No 1 pp 89 91 January 1971 K 004 High Quantum Efficiency Opaque CsI Photocathodes for the Extreme and Far Ultra violet O H W Siegmund E Everman J V Val lerga S Labov J Bixler and M Lampton SPIE Vol 687 Ultraviolet Technology p 117 1986 K 005 Ultraviolet Quantum Detection Efficiency of Potassium Bromide as an Opaque Photocathode Applied to Microchannel Plates Oswald H W Siegmund E Everman J V Valler ga J Sokolowski and M Lampton Vol 26 No 17 Applied Optics September 1987 K 006 Quantum Efficiencies of Imaging Detec tors with Alkali Halide Photocathodes 1 3300 2400 System Manual page 50 RAE TECHNOLOGY 1 001 Low Distortion Resistive Anodes for Two Dimensional Position Sensitive MCP Systems M Lampton and C W Carlso
57. rect for improper arrangement of the preamp inputs from the MCP RAE sensor or for purposes of troubleshooting An 8 foot 2 4 m cable is supplied for interconnecting these signals to the position analyzer A longer cable up to 17 feet 5 1 m in length may be substituted without significant signal degradation 1 5 CONNECTING POSITION ANALYZER TO EXTERNAL DEVICES The following sections discuss the function and characteristics of the rear panel outputs and switches on the Model 2401B Position Analyzer For additional detail on the waveforms of these signals consult the Model 2401B Operating and Service Manual 1 5 1 ANALOG X AND Y POSITION SIGNALS These signals are the primary analog event position outputs from the system They are intended to be connected to the X and Y axes of an oscilloscope producing a real time monitor image of the incoming flux They can also be connected to a user supplied analog to digital converter or digitizing multi channel analyzer MCA The amplitude voltage of the valid flat top portion of these pulsed position signals ranges from approximately 0 5 to 4 5 volts and is linearly proportional to the coordinate position of the most recently processed event starting from one edge of the active area diameter of sensor and ending at the other edge along diameter on each axis These signals should be read by external devices only during periods when the STROBE signal see below is valid This assures these signals are
58. roamps current flows in the divider resistor string at least about 10X the quiescent no signal bias current while the desired voltages are developed for each MCP and RAE electrode This ensures that the HV bias voltage will not fluctuate significantly due to varying signal currents in the MCP s which can result in fluctuating and decreased gain Often it is preferable to wire the HV resistors only to each other and connectors not using a PC board for mounting but relying on air dielectric for protection against breakdown If a PC board is used be certain the board and the lead spacing is of a suitable material to withstand the voltages involved Calculate and select each resistor of the divider chain to produce the desired voltage for a specific electrode contact in the MCP RAE Sensor It is recommended to use HV type resistors to avoid breakdown or use multiple resistors in series to keep the voltage across any single resistor within its rated limits During setup variable resistors with HV insulated shafts and mountings may be temporarily used to optimize voltages but should be replaced by fixed resistors in the final voltage divider To meet the desired voltage and total current requirement with commercially available resistor values may require several iterative calculations Calculate the power dissipation P F x R or P I x E of each resistor and select resistors of appropriate power rating The polarity of the HV is determined by the confi
59. ry LIMITATION OF WARRANTY The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by Buyer Buyer supplied software or interfacing unauthorized modification or misuse operation outside of the environmental specifications for the product or improper site preparation or maintenance Special Notes regarding MCP s and products containing MCP s microchannel plate electron multipliers Warranty does not cover damage to MCP s caused by warpage or cracking due to improper storage shock vibration contamination or improper handling Users are cautioned that MCP s are sensitive to water vapor absorption and may warp and crack if stored outside of clean vacuum systems for extended periods For sealed tube detectors warranty does not cover damage resulting from exposure to excessive input radiation levels thermal shock exposure to temperatures below 30 C or above 45 C excessively rapid rates of change of temperature mechanical shock or excessive high voltage applied to tube NO OTHER WARRANTY IS EXPRESSED OR IMPLIED WE SPECIFICALLY DISCLAIM IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE EXCLUSIVE REMEDIES THE REMEDIES PROVIDED HEREIN ARE BUYER S SOLE AND EXCLUSIVE REMEDIES NEITHER OUANTAR TECHNOLOGY NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT INDIRECT SPECIAL INCIDENTAL OR CONSEOUENTIAL DAMAGES ARISING OUT OF USE OF ITS PRODUCTS WHETHER BASED ON C
60. sensitivity position sensitive imaging detector system for scientific applications The detector system is sensitive to charged particles neutral particles and energetic photons EUV soft X ray and operates in vacuum environments This single event counting sensitivity combined with extremely low detector generated background results in exceptionally good signal to detector background performance Applications range from 1 D use in multichannel spectroscopy such as XPS to 2 D imaging spatially resolved spectroscopy to full 2 D X Y imaging The system is available in two versions The standard spatial resolution version FWHM resolution of 1 100 of active diameter uses 2 MCP s in the sensor with a mean electron gain of approximately 5 x 10 and the Option EM preamp The high spatial resolution version FWHM resolution of 1 400 of active diameter uses 3 or 5 MCP s in the sensor with a mean electron gain of approximately 5 x 10 and uses the Option EP Preamp Preamp gain is different in the two options to compensate for the output levels of the two sensor types 3300 2400 System Manual page 9 18 Nov 2013 Rev I Figure 1 1 Suggested Sensor Mounting Methods 3300 2400 System Manual page 10 18 Nov 2013 Rev I SECTION 1 SYSTEM INSTALLATION 1 1 SENSOR ASSEMBLY MOUNTING The detector assembly can be physically mounted either from the rear ceramic baseplate or from the front mounting ring To mount from the rear baseplate use the cleara
61. shown in the Specifications for these options This ADC related dead time component is non paralyzable it is not re triggered upon only detection of another event at the charge sensitive preamplifier inputs 2 5 1 3 Dead time Curves The combined result of the two dead time components discussed above regarding the counting rate of the Model 2401B is shown in Figure 2 4 Electronic Dead Time Curves for the analog only version and 8 bit 9 bit and 10 bit ADC option versions On these plots the X Y imaged event rate measured by the STROBE signal one pulse for each event that is fully processed and position determined is plotted on the vertical axis and the assumed true input rate as measured by the RATE signal and measured by the front panel meter is plotted on the horizontal axis The slight discontinuity in the digital option dead time curves at higher count rates is due to the effect of the separate non paralyzable ADC dead time component which enables somewhat higher throughput rates than would be possible if the ADC component were also paralyzable 3300 2400 System Manual page 37 18 Nov 2013 Rev I CAUTION It should be noted that monitoring only the STROBE rate signal can be misleading since the dead time curve is double valued as shown in the dead time curves referred to above That is a particular STROBE output rate vertical axis on plot can occur for both a lower true RATE and a higher RATE as well Observation of the input
62. signal slightly longer than the pulse duration of the four shaper amplifiers for a single detected event it has a 2 8 msec duration and is retriggerable Any additional pulse arriving within the busy period of a previous pulse will retrigger the busy timeout and will result in a longer pulse duration It is useful in observing the preamp associated dead time 3300 2400 System Manual page 25 18 Nov 2013 Rev I 1 5 6 RATE The RATE signal represents the total incoming rate of pulses which exceed the RATE threshold 150 mV on SUM signal A separate RATE pulse is generated for each event that is time separated by a least 400 nsec from a prior event Pulse duration is 0 6 usec and the leading edge moves from the TTL low level to the TTL high level Pulses are further tested for level and timing before actual processing and some events included in RATE may be vetoed later from further processing The RATE output is useful for determining actual true input rate as compared to output rate available at the strobe imaged output to determine the fraction of input pulses being processed See notes elsewhere in this manual regarding RATE channel deadtime The RATE includes events that may later be vetoed from further processing and not included in the Strobe due to edge gating settings failure to exceed the Strobe lower threshold 300 mV on SUM pulse pulse pile up rejection see dead time discussion below or pull down of the external Veto Gate Input 2
63. ssing the percentage dead time can be determined Many electronic digital frequency counters will calculate the ratio of these two signals automatically using A and B channels This percentage can then be used to normalize the imaged processed count rate data to the true count rate thereby compensating for input events that were vetoed by the system from position processing due to potential pulse pileup and consequent inaccuracies This compensation of position determined events assumes the dead time is uniform over the active area of the detector 2 5 2 MCP DEAD TIME In addition to the above electronic global dead time considerations there are spatially localized dead time effects associated with the MCP s microchannel plate electron multipliers These effects are seen only when input event count rates in a small spatial area exceed the aggregate re charge time of the group of microchannels involved in the multiplication process This effect is dependent on the following factors 1 Ouiescent no signal bias current also termed strip current of specific MCP s used This determines in part the re charge time for an individual channel which has fired The higher the bias current of the MCP the lower its resistance the faster the recharge time 2 The spatial dimensions of the input flux to the MCP s essentially how many individual microchannels are involved in the multiplication process and the diameter and spacing of the microc
64. tential depends on the biasing arrangement chosen by the user based on the application details Generally it is desirable to avoid potentials on the first MCP surface which will attract stray charged particles in the vacuum chamber If the sensor is eguipped with option 001 SE Additional Electrically Isolated Front Ring the sensor can be supported from this ring in the manner described above and the Option 001 SE ring can then be maintained at any desired potential within 2 kV the approximate breakdown voltage of the input MCP electrode voltage The sensor can be mounted on a standard Conflat type copper or O ring gasket vacuum flange rotatable type is sometimes preferred to enable alignment of detector axes if necessary Generally the smallest size flange that can be used for mounting is a 4 5 8 inch size Conflat type the smallest for the 25mm and 40 mm size sensors a 4 1 2 inch Conflat flange can be used but the ID of the copper sealing gasket generally must be modified An 8 inch diameter Conflat type flange is required for the Model 3392A 75 mm MCP RAE Sensor and larger sensors 1 2 MOUNTING OF ELECTRONICS MODULES The main chassis of the Model 2401 Position Analyzer may be used either as a stand alone unit or mounted in a standard 19 inch wide electronics rack using the rack mounting brackets supplied Handles for convenience in lifting are mounted on the rack adapter brackets When mounting in an electronics rack with other equipment pr
65. time MCP Decoupling capacitors HV Description General ce o oooon o o Edge Gating Controls Electrical Connections 2 MCP versions Feedthroughs vacuum flange Final Performance Test Report Gain MCP re spatial resolution Gating controls edge front panel Ground loops minimizing Holes clearance mounting HV Bias and Spatial Resolution HV Bias Configurations Choice of HV Bias Optimizing HV Divider current selection HV Polarity INITIAL TURN ON AND CHECKOUT M o odels 3390 and 3394 Electrical Connections 5 MCP versions Models 3391 and 3395 Emission Point Defect e Input Level Meter
66. ulse For high rates of inputs greater than 10 Hz the meter movement averages out these swings into a fairly stable reading At lower freguencies some interpretation will be necessary At freguencies in the 0 to 5 Hz range the needle will tend to swing from one extreme to the other and not necessarily be interpretable Note that a proper indication is only obtained for inputs with a distribution of input levels Note that for constant amplitude inputs such as those obtained from a pulse generator the meter will indicate zero or full value depending on whether the test pulse amplitude is above or below the MID threshold 2 4 EDGE GATING CONTROLS There are four edge gating controls located on the front panel of the Model 2401 Position Analyzer These enable the user to clip electronically window the image independently along the plus and minus X and Y axis directions This allows the operator to exclude veto portions of the image which are not desired Note however that although these events are not imaged to the output because the position of these events is calculated they do occupy processor time and therefore contribute to system dead time It is important to note that since these controls overlap in range it is possible to set them such that the entire image is blanked This situation is suspect when the meter indicates normal signal rate and level yet no outputs are observed When this occurs set the front panel Edge Gating controls as
67. undant When components are physically separate however the shield will tend to establish a common ground potential for all components If all chassis are not grounded internally to the same point some de current may need to flow in the shield to maintain the common ground potential In many routine applications this ground current is small enough to be of no practical conseguence However in low signal level systems like the Series 3300 2400 this current can be large compared to signal currents from the RAE If components are physically separated and internally grounded under widely different conditions the shield current can be large and its fluctuations may induce significant noise in the cable and preamp Under these conditions such ground loops must be eliminated by ensuring that all components are internally grounded to a single common point for the entire system 3300 2400 System Manual page 18 18 Nov 2013 Rev I 1 3 8 HIGH VOLTAGE BIAS CAUTION Carefully avoid placing any HV bias voltage on the preamplifier inputs To do so may permanently damage the input FET protection diodes and other circuitry Adequate MCP gain is necessary to enable the sensor to detect incoming events with desired spatial resolution In turn MCP gain is critically dependent on the magnitude of the HV bias applied to each MCP between its input surface electrode and output electrode In addition a sufficient and uniform electric field must be mai
68. without a Histogramming Buffer Memory board installed only are as follows PIN FUNCTION 25 1 1 Y axis LSB 2 2 Y axis o e 56 de 26 Y axis used only for 9 and 10 bit options Mic fo rear panel 10 Y axis used only for 10 bit options 11 X axis LSB 2 12 X axis 19 X axis used only for 9 and 10 bit options 20 X axis used only for 10 bit options 21 STROBE Digital 22 RATE Digital 23 No connection do not ground After 2401B S N 95467 with 1 D 2 D digitial switch circuit on main board this pin is used for control of this function by rear panel manual switch or software control 24 No connection do not ground 25 No connection do not ground 26 50 Grounded for each individual digital bit For Model 2401 units equipped with one of Quantar Technology s optional Histogramming Buffer Memory modules 2412 2415 etc the rear panel 50 pin connector is used for the interface to a computer IO board from the memory board The digitized output from the main board is connected to the input of the memory board Consult the manual for the appropriate model memory board for pin assignments for the rear panel 50 pin connector which differ from the above The current 3M Part Number for the 50 pin cable connector that mates to this rear panel connector is 3564 1001 other equivalent connectors from AMP or Amphenol should interface properly Verify desired configuration and part number before or
69. y time in this interval then the event will be vetoed from further processing If an event IS to be vetoed the VETO GATE must be pulled LOW at least sometime before 500 nsec after the event occurs and held low through about 800 nsec 1 5 8 DIGITAL X AND Y POSITION SIGNALS The digitized position output signals are TTL level positive true signals and are provided on data lines 8 9 or 10 lines each with a separate ground connection plus a Digital Strobe read me signal Refer to Figure 1 9 for details regarding the connector designations 1 5 8 1 DIGITAL STROBE 1 5 msec duration negative true logic TTL level pulse that accompanies digitized position signals to latch data or trigger to be read by external data device memory computer etc Digital Strobe starts immediately at end of ADC conversion later than the analog strobe which depends on digital option Not available on analog only versions Goes from TTL high level to TTL low level on leading edge 3300 2400 System Manual page 26 18 Nov 2013 Rev I Figure 1 9 Digital Output Connector Rear Panel ADC Output REAR PANEL DIGITAL OUTPUT CONNECTOR WITHOUT HISTOGRAMMING MEMORY INSTALLED For units eguipped with digital output options digital TTL level signals for both X and Y axes are available together with the Digital Strobe and Rate signals The connector pin assignments for the Digital Output Connector the 50 pin 3M brand D ribbon connector on the rear panel for units

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