MODEL SR400 GATED PHOTON COUNTER 1290-D Reamwood Avenue Sunnyvale, California 94089 Phone: (408) 744-9040 • Fax: (408) 744-9049 email: info@thinkSRS.com • www.thinkSRS.com Copyright © 1987, 1988, 1995, 1998, 2001 by SRS, Inc. All Rights Reserved. Revision 2.
Table of Contents TABLE OF CONTENTS CONDENSED INFORMATION Safety and Preparation for Use Specifications Menu Display List Abridged Command List 3 5 7 9 INSTRUMENT OVERVIEW Signal Inputs / Discriminators Counting Gating Count Modes Outputs Measurement Examples 11 12 13 14 14 17 OPERATION Front Panel Summary Power Liquid Crystal Display Menu Keys Spin Knob Start, Stop, and Reset Instrument Status Counter LED's Inputs Outputs Rear Panel Summary Power Entry Module IEEE-488 Port RS-232 Connector Input Outpu
Table of Contents USING PHOTOMULTIPLIER TUBES PMT Selection for Photon Counting Geometry Spectral Response Gain and Risetime Dark Counts PMT Base Design Dynode Biasing Snubbing PMT Base Conclusions Cathode Shielding Preamplifiers Gain Requirement Plateauing a PMT The 'Correct' Way The 'Fast and Pretty Good' Way Discriminators A and B Counters T Counter Start / Stop and Dwell Gate Generators Digital Delay Analog Delay Delay Reset Gates Power Supply 63 63 63 63 64 64 64 66 67 67 67 67 67 68 68 TYPICAL EXPE
Safety and Preparation for Use SAFETY AND PREPARATION FOR USE **** CAUTION **** LINE CORD This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the wrong ac line voltage or if the wrong fuse is installed. The SR400 has a detachable, three-wire power cord for connection to the power source and to a protective ground. The exposed metal parts of the instrument are connected to the outlet ground to protect against electrical shock.
SRS Symbols Symbols that may be found on SRS products Symbol Description Alternating current Caution - risk of electric shock Frame or chassis terminal Caution - refer to accompanying documents Earth (ground) terminal Battery Fuse On (supply) Off (supply) 4
SR400 Specifications SR400 SPECIFICATIONS Protection: OVERVIEW There are three complete counters identified as A, B, and T. All counters count up to 200 MHz. GATE GENERATORS There are two independent gates, AGATE and BGATE, which enable the A and B counters. Both gates are triggered by the TRIGGER input. The gates may be fixed in time or scanned. The GATE outputs show the positions of the gates with respect to the discriminator outputs. Counter A can count INPUT 1 or the 10 MHz internal clock.
SR400 Specifications The STOP key terminates the current count period and pauses the scan. If scanning, gates and disc levels are held at their last value. The STOP key pressed while in a paused condition will reset the scan and all scanned parameters will return to their start values. The START key pressed while paused resumes the scan by starting the next count period. D/A OUTPUT The front panel D/A Output is proportional to A, B, A-B, or A+B depending upon the counting mode selected.
Menu Display List MENU DISPLAY LIST MODE A GATE B GATE COUNT=A,B FOR T PRESET A=INPUT 1 B=INPUT 2 B SET=1E3 T=10MHZ T SET=1E0 s N PERIODS=2000 [at 1234] AT N=STOP DWELL=1E0s D/A=A D/A RANGE=LOG DISPLAY=CONTINUOUS AGATE=SCAN ∆=1.000 µs A DELAY=1.000 µs A WIDTH=1.000 µs BGATE=SCAN ∆=1.000 µs B DELAY=1.000 µs B WIDTH=1.000 µs LEVEL SETUP COM TRIG SLOPE=RISE TRIG LVL=+2.000 V A DISC SLOPE=FALL A DISC=SCAN ∆=-1.0 mV A DISC LVL=-10.0 mV B DISC SLOPE=FALL B DISC=SCAN ∆=-1.0 mV B DISC LVL=-10.
Menu Display List 8
Abridged Command List ABRIDGED COMMAND LIST The parameter i is 0,1,or 2 to select counter A,B, or T MODE CM j CI i,j CP i, n NP m NN NE j DT x AS j AM j SD j Set COUNT to mode j; A,B(0), A-B(1), A+B(2) for preset T,or A FOR B preset(3). Set counter i to input j; 10 MHz(0), INP 1(1), INP 2(2), TRIG(3). Set counter i preSET to 1 <= n <= 9E11. Set Number of PERIODS in a scan to 1 <= m <= 2000. Read current count period number or scan position. Set end of scan mode to mode j; START(1) or STOP (0).
Abridged Command List STORE/RECALL ST m Store instrument settings to location m (1 to 9). RC m Recall instrument settings from location m (1 to 9). RC 0 Recall default settings. INTERFACE CL SV m SS SS j SI SI j SW m SE j,k,l,m SE Clear instrument. Set GPIB SRQ mask to 0 <= m <= 255. Read status byte. Read bit j(0-7) of status byte. Read secondary status byte. Read bit j (0-2) of secondary status byte. Set RS-232 character wait interval to m*3.33 ms 0 <= m <= 25. RS-232 only.
Instrument Overview INSTRUMENT OVERVIEW 300 MHz AMPLIFIERS DISCRIMINATORS FAST LOGIC IN 1 A DISC A DISC SELECT 50Ω A - COUNTER CLR SELECT A GATE B DISC B DISC B - COUNTER 10.
Instrument Overview may be programmed to scan in either direction with selectable step size. output gated by B GATE. This is for gated ratio or reciprocal counting. COUNTING The SR400 may be programmed to cycle through 1 to 2000 COUNT PERIODS in a single scan. At the end of the programmed scan, the counters may be stopped or the scan may be restarted. If the end of scan mode is STOP, then after the last COUNT PERIOD in the scan, the counters are halted indefinitely.
Instrument Overview is START, the next EXTERNAL START begins the first COUNT PERIOD of the next scan. from the GATE outputs. The gates are open when the outputs are low. The gate outputs have a timing accuracy with respect to the discriminator outputs of 2 ns. This allows accurate timing of fast gates relative to the signal. SCANNING In all scan modes, a number of parameters may be scanned.
Instrument Overview source compensated. If the DWELL mode is EXTERNAL, an EXTERNAL START pulse starts counting and an EXTERNAL STOP pulse stops counting. The counters are enabled only during those gates which occurred between the two EXTERNAL pulses. intensity, then the COUNT PERIOD will adjust for fluctuations in the source. Counter A measures the ratio of its mean input rate and the mean rate of INPUT 2. COUNT MODES If Rt is INPUT 2, then the COUNT PERIOD is Nt/Rt.
Instrument Overview The front panel D/A output provides an analog output proportional to A, B, A-B, or A+B depending on the counting mode. The scale may be logarithmic (1V/decade) or linear to any 3 digits. If a chart recorder is used, the D/A output should drive the Y axis. The X axis can be recorder driven (strip chart mode) or the PORT1 or PORT2 outputs can be used to drive the X axis (scans). This latter method allows accurate determination of the X value of each point.
Instrument Overview 16
Measurement Examples MEASUREMENT EXAMPLES Example 1: Internally Triggered Gate Mode This example, described under the heading “QUICK TEST” on page 59 of this manual, is easy to perform and will quickly acquaint the user with the basic operation of the SR400. Example 2: Externally Triggered Gate Mode In this example, the SR400 is programmed to make 10 counting measurements of a 10 kHz pulse train.
Measurement Examples 1. Turn the SR400 off. Hold down the STOP (RESET) button while turning the SR400 on. Wait three seconds and release the button. 2. Press the MODE key. Using the four arrow keys and the front panel knob, select the following parameters. Unless otherwise indicated, leave all other settings at their default values: T = TRIG TSET = 1E0 N PERIODS = 10 [AT 0] AT N = STOP DWELL = 6E0 S 3.
Measurement Examples Example 3: Externally Triggered Gate Mode This example is a variation of Example 2, but requires no additional trigger pulses to begin the DWELL PERIOD. In this example, the SR400 is programmed to make 10 counting measurements of a 10 kHz pulse train. The counting gates, each 500 ms wide, are delayed 300 ms from external triggers arriving at a 1 Hz rate.
Measurement Examples 1. Turn the SR400 off. Hold down the STOP (RESET) button while turning the SR400 on. Wait three seconds and release the button. 2. Press the MODE key. Using the four arrow keys and the front panel knob, select the following parameters. Unless otherwise indicated, leave all other settings at their default values: T = 10 MHz TSET = 9E-1 s N PERIODS = 10 [AT 0] AT N = STOP DWELL = EXTERNAL (Turn the knob counterclockwise until “DWELL = EXTERNAL” is displayed.) 3.
Guide to Operation GUIDE TO OPERATION FRONT PANEL SUMMARY keys select the group of functions to be programmed. The four arrow keys select individual parameters within each menu. The selected parameter is displayed on the menu line of the display. POWER BUTTON The SR400 is turned on by depressing the POWER button. All instrument settings are stored in nonvolatile memory and are retained when the power is turned off.
Guide to Operation In general, pressing the STOP key twice in succession puts the counters into the reset condition. A FOR B PRESET, the T SET LED is on otherwise. INPUTS START begins the first COUNT PERIOD of the programmed scan. If the DWELL time is programmed, then the scan will continue automatically. A STOP will pause the scan; the current COUNT PERIOD is terminated and ignored. A START while paused will resume the scan. A STOP while paused resets the scan.
Guide to Operation DISC output should just be terminated at the front panel. The GATE outputs are 50 Ω, NIM level, outputs showing the actual gates to counters A and B. The GATE outputs are low (-.7 V) during the gate. The timing accuracy between the GATE outputs and DISC outputs is 2 ns. The D/A analog output provides a -10V to +10V output proportional to the count data with linear or logarithmic scaling. Output impedance is < 1 Ω and the maximum current output is 10 mA.
Guide to Operation REAR PANEL SUMMARY POWER ENTRY MODULE INPUT The power entry module is used to fuse the line, select the line voltage, and block high frequency noise from entering or exiting the instrument. Refer to the first page of this manual for instructions on selecting the correct line voltage and fuse. INHIBIT is a TTL input which disables the A,B, and Tdiscriminators when it is high. The minimum pulse width is 10 ns.
Guide to Operation - Menus FRONT PANEL MENUS The lower line of the LCD display is the menu line. Menu lines are grouped into six menus. To select a new group or menu, press a new menu key. The menu line that will be displayed is the most recently active menu line of the new menu. whether the count data measures rate, ratio, or reciprocal. Changing this line causes the counters to reset. A= Each menu contains several lines. Each line may consist of 1 or 2 displayed parameters.
Guide to Operation - Menus The input to counter T can be the internal 10 MHz timebase (rate measurement), the signal at INPUT 2 discriminated by T discriminator (ratio or reciprocal measurement), or the TRIGGER input discriminated by the trigger discriminator (constant gate aperture). The selected counter input can be viewed at the T DISC output. The appropriate T counter source LED is lit. parameters updated. The DWELL OUTPUT is TTL high during the DWELL time.
Guide to Operation - Menus COUNT is A,B FOR T PRESET, then the D/A output can follow either A or B. discriminated trigger pulses may be viewed through the T DISC output when counter T is preset and its input is TRIG. This can be helpful in selecting a trigger level. The minimum pulse amplitude required to trigger is 100 mV. D/A RANGE= LOG ##765#### A DISC SLOPE= The D/A output scale can be either logarithmic or linear.
Guide to Operation - Menus the fixed threshold when A DISC is FIXED and the starting level when A DISC is SCANned. B DISC LVL = -10.0 mV : -11.0 mV When the A DISC mode is SCAN and a scan is in progress, this line displays the current position of the A DISC level. The cursor is inactive and replaced by a ':'. The spin knob cannot adjust the threshold while it is scanning. When the mode is SCAN, the starting level may only be adjusted when the counters are in reset.
Guide to Operation - Menus The step size may also be changed during a scan. The new step size will be in effect at the end of the next count period. The scan is not reset or paused. When the PORT1 mode is SCAN and a scan is in progress, this line displays the current position of the PORT1 level. The cursor is inactive and replaced by a ':'. The spin knob cannot adjust the level while it is scanning. When the mode is SCAN, the starting level may only be adjusted when the counters are in reset.
Guide to Operation - Menus If the gate delay is scanned, then the right hand parameter is the step size. At the end of each count period in a scan, the delay is incremented by one step size. The step size can be varied from 0 to 99.92 ms. The range of a scan is N PERIODS times the step size. The starting value of the delay is set in the next menu line. GATE MENUS The A GATE and B GATE are identical in operation. The discussion below describes the A GATE menu.
Guide to Operation - Menus command. SETUP and COM parameters are stored on power down as part of the current setup only. number of scan steps needed to exceed the resolution. In all cases, the delay only steps from one allowed value to another and is as close to the desired value as will be allowed by the resolution. A WIDTH= Use the spin knob to select a storage location, 1 through 9. The right arrow key will store the setup. **** 1.000 µs RECALL=3 This line is inactive if A GATE is CW.
Guide to Operation - Menus RS-232 PARITY= NONE EVEN ODD The RS-232 parity can be even, odd, or none. RS-232 WAIT=6 The SR400 can be programmed to wait between each character it sends over the RS-232 interface. This is to accommodate computers with slow computer interfaces. The wait interval is programmed in units of 3.3 ms and can be set from 0 to 25. The default value is 6 and should be set to a smaller value whenever possible.
Instrument Setups INSTRUMENT SETUPS The SR400 Photon Counter is a very flexible instrument capable of many modes of operation. This section illustrates some of the measurements that can be made. B WIDTH= 0.
Instrument Setups PERIODS=10. Start a scan by pressing the START key. The counter should cycle through 10 count periods separated by the dwell time (1 s). The display shows the current scan position in brackets. Reset the scan using the STOP key. photons which occur outside the time interval of interest. Assume that the pulse rate is a function of time as shown below. The time scale may be nanoseconds up to hundreds of milliseconds. The A counter will be used to count the signal via INPUT 1.
Instrument Setups background during the chopper open state and the other counts the background during the chopper closed state. The difference between the two counters is the signal. If A counter is the signal counter and B counter the background counter, the two gates should be timed as shown below. Chopper State Open Open Close Close A GATE Signal + Noise B GATE Noise Only The two gate widths need to be the same width. The gates are triggered by the chopper reference signal.
Instrument Setups 36
Remote Programming REMOTE PROGRAMMING The SR400 Photon Counter is remotely programmable via both RS-232 and GPIB (IEEE488) interfaces. It may be used with laboratory computers or simply with a terminal. All front panel features (except power) may be controlled and read via the computer interfaces. The SR400 also has two programmable analog output ports available to provide general purpose control voltages. CI 0,1 set the input to counter A to INPUT 1 NP 5E2 set N PERIODS to 500 GD 0,1.
Remote Programming Note that the terminating characters are sent with each value returned by the SR400. Thus, the response to the command string CM;CI0;GD0 while using the RS-232 non-echo mode would be 111.2E-6. with an RS-232 port to the RS-232 connector on the rear panel of the SR400. A 'straight' RS-232 cable is required since the SR400 is a DCE and the terminal is a DTE. After connecting the terminal, hold down the STOP key while turning the unit on.
Remote Programming – Command List DETAILED COMMAND LIST The two letters in each command sequence specify the command. The rest of the sequence consists of parameters. Multiple parameters are separated by a comma. Those parameters shown in { } are optional while those without { } are required.
Remote Programming – Command List data points completed so far during the current scan and is shown in the brackets on the N PERIODS menu line. The NN command is a read only command. SD { j } If j = 1, the SD command sets the count display mode to HOLD. If j = 0, the display mode will be CONTINUOUS. If j is absent, the display mode is returned. NE { j } If j = 0, the NE command sets the scan end mode (AT N) to STOP. If j = 1, the mode is set to START. The scan end mode may be changed at any time.
Remote Programming – Command List discriminator is in the FIXED mode. Changing the scan step during a scan will affect the level for the next count period and all those that follow. affect the level for the next count period and all those that follow. PL i { ,v } The PL command sets and reads thePORT1 and PORT2 output levels. i=1 or 2 to select PORT1 or PORT 2 and is required. If v is included, the output level is set to v Volts where -10.000 <= v <= 10.000. The resolution is 0.005 V (5 mV).
Remote Programming – Command List 99.92E-3. The resolution is variable depending upon the 4 most significant digits of t. 4 most significant digits 1000 to 2048 2048 to 4096 4096 to 8192 8192 to 9992 GZ i The GZ command returns the gate delay position during a scan. i = 0 or 1 designates A gate or B gate and is required. If gate i is in the SCAN mode, its current delay position during a scan is read.
Remote Programming – Command List TIME is EXTERNAL, the CS command will start a count period. A CH command may be sent to terminate the count period. j 0 1 CH Sending the CH command has the same effect as pressing the STOP key. The CH command may be sent at any time. If recieved while scanning, the scan will pause. If received while paused, the counters will reset. If the DWELL TIME is EXTERNAL, the CH command may be used to terminate count periods.
Remote Programming – Command List j,k 3,2 3,3 terminating sequence is reset to the proper defaults.
Remote Programming – Command List the decimal ASCII codes (0-127) j,k,l, and m. If no argument is included, the end-of-record sequence returns to the default (a carriage return), otherwise, up to four characters may be specified. The end-of-record required by the SR400 when receiving commands is not affected. The SE command may only be sent via the RS-232 interface. QB m When m is included in a QA or QB command, buffered data from scan point m is read.
Remote Programming – Command List while counting returns the current counter contents. If the counters are in the dwell cycle, paused, or reset, the counter value will be zero. The display may still be showing the most recently completed count but the counters are already internally reset. The X command is generally only useful for long count periods and/or slow count rates. If the count rate is faster than the interface speed, then the returned count values may be in error.
Remote Programming – Command List addition, any commands remaining on the current command line (up to the next ) are lost. To aid in determining the cause of the error, the last 254 characters received by the SR400 may be viewed on the LCD display using the DATA line of the COM menu. The knob may be used to scroll through the command buffer. The display always returns to the most recent data whenever the menu line is brought up or a new character is received.
Remote Programming – Command List computer is not asserting the DTR line on the RS-232. COMMON SOFTWARE PROBLEMS INCLUDE: 1) You have sent the wrong command to ask for data from the SR400. Your program will wait forever for a response which is not going to come. This may not be your fault; we have seen Microsoft's Interpreted Basic on the IBM PC occasionally send a curly bracket (ASCII 253) when it was supposed to have sent a carriage return (ASCII 13).
SR400 with the RS-232 Interface SR400 WITH THE RS-232 INTERFACE The RS-232 is a popular serial interface standard for bit serial communication. Despite the existence of the standard there are many permutations of control lines, baud rates, and data formats. special terminating sequences to fit the requirements of some computers. This can be done with the SE command.
SR400 with the RS-232 Interface PROGRAM EXAMPLE 1: IBM PC, BASIC, VIA RS-232 In this example, the IBM PC's serial port (known as COM1:) is used to communicate with the SR400. Only two wires between the IBM PC's COM1: port and the SR400 are needed (pins #2 & #3 of the 25 pin RS-232 connector), but pins 5,6,8, and 20 should be connected together on the connector at the IBM end. 10 'EXAMPLE PROGRAM TO READ THE SR400 COUNTER DATA AND RAMP THE PORT 1 20 'ANALOG OUTPUT USING IBM BASIC AND THE COM1: RS-232 PORT.
SR400 with the RS-232 Interface PROGRAM EXAMPLE 2: IBM PC, MICROSOFT FORTRAN V4.0, VIA RS-232 Machine language routines to interface to the COM1: RS-232 port are provided in the file RS-232.OBJ found on the SR400 demo disk. These routines allow for simple interfacing to the SR400 at 19.2 kbaud from FORTRAN programs. To use these routines, the file 'for232.inc' (also on the demo disk) must be 'included' in the FORTRAN source.
SR400 with the RS-232 Interface c reset PORT1 value to zero x=0.0 c 10 reset and start new count period call txstr('CR;CS$') c 20 read counter A data into string str1 call txstr('QA1$') call rxstr(str1) c convert into integer variable n1 read(str1,1000) n1 format (bn,i15) 1000 c if data not ready yet, loop and try again if (n1.lt.0) goto 20 c ramp PORT1 by 5 mV x = x + .005 if (x.gt.10) x = 0.0 make PORT1 command string write(str2,2000) x format('PL1,',f7.
SR400 with the GPIB Interface SR400 WITH THE GPIB INTERFACE Before using the GPIB interface you must set the GPIB address in the COM menu. SERIAL POLLS AND SERVICE REQUESTS GPIB CAPABILITIES The SR400 can be programmed to generate a service request (SRQ) to the GPIB controller every time a given status condition occurs. This is done using the SV{j} command. The mask value, j (0-255), is the SRQ mask byte. The mask byte is always logically ANDED with the status byte.
SR400 with the GPIB Interface PROGRAM EXAMPLE 3: IBM PC, MICROSOFT BASIC, VIA GPIB This program requires the Capital Equipment Corporation GPIB card for the IBM PC. It has firmware in ROM to interface high level languages to the GPIB. Subroutine calls in Microsoft BASIC are done to memory locations specified by the name of the subroutine. The address is relative to the segment address specified by the DEF SEG statement preceding the CALL.
SR400 with the GPIB Interface 390 X = X+.
SR400 with the GPIB Interface PROGRAM EXAMPLE 4: IBM PC, MICROSOFT C V4.0, VIA GPIB This program requires the Capital Equipment Corporation GPIB card for the IBM PC. It has firmware in ROM to interface high level languages to the GPIB. The header file MS-C488.H contains definitions of all of the CEC firmware routines which can be called from C. Note that the order of arguments in the calls are reversed from those used by BASIC. To use these routines, the large model must be used.
SR400 with the GPIB Interface x = 0; /* init PORT1 value */ while (1) { TxGpib(sr400,"CR;CS"); /* reset and start new count period */ do { TxGpib(sr400,"QA1"); /* read counter a data */ GetGpib(sr400); /* into result string */ /* scan result for long integer */ if (!(sscanf(result, "%D", &n1))) Statcheck(255); } while (n1<0); /* until count period done */ x += 0.005; /* increment PORT1 level */ if (x>10) x=0; /* reset if at 10 Volts */ sprintf(portstr, "PL1,%6.
SR400 with the GPIB Interface Statcheck(status); strcpy(temp, " "); /* clear result string */ receive(&status, &length, temp); /* get answer */ Statcheck(status); strcpy(result, temp); /* move answer into global result string */ } /* ****************************************************** */ Statcheck(status) /* check GPIB status */ int status; { if (status) { printf("GPIB error: status = %d",status); exit(); } } 58
Troubleshooting TROUBLESHOOTING To start, make sure that the power entry module on the rear panel is set for the ac line voltage in your area and that the correct fuse is installed. The selected ac voltage may be seen through the window on the power entry module. Verify that the line cord is plugged all the way into the power entry module and that the power button on the front panel is pressed in. causes the unit to reinitialize the memory and assume the default setup.
Troubleshooting 5) Bad gate triggering. The trigger input may not be discriminated correctly. Check the trigger slope and level. The discriminated trigger pulses may be viewed through the T DISC output when the input to counter T is TRIG. Double triggering or the wrong slope can cause erroneous gates. COUNTING There are several reasons why a counter may not seem to be counting correctly. 1) Counting is not enabled. The COUNT led does not turn on when the START key is pressed.
Calibration and Repair CALIBRATION AND REPAIR Most of the calibration parameters are determined by a computer aided calibration procedure after burn-in at the factory. These calibration parameters are stored in the permanent memory of each unit. SIGNAL INPUT OFFSET To calibrate the input offset, connect a voltmeter to a signal input. P101 adjusts INPUT 1 and P121 adjusts INPUT 2. These potentiometers are located behind the signal inputs. Adjust the correct potentiometer for a reading of 0 ± .
Calibration and Repair 62
Using Photomultiplier Tubes USING PHOTOMULTIPLIER TUBES will not be detected. The quantum efficiency is a function of wavelength, so select the PMT for the best quantum efficiency over the wavelength region of interest. PHOTOMULTIPLIER SELECTION FOR PHOTON COUNTING Photomultiplier Tubes (PMT's) are high-gain, low noise light detectors. They can detect single photons over a spectral range of 180 to 900 nm.
Typical Experiment Conclusions: Select a PMT with a risetime < 3 ns and a current gain > 5 million. CAUTION: Lethal High Voltages are used in PMT applications. Use extreme caution when working with these devices. Only those experienced with high voltage circuits should attempt any of these procedures. Never work alone. DARK COUNTS PMT's are the quietest detectors available.
Using Photomultiplier Tubes Current for the electron multiplier is provided by the bias network. Current drawn from the bias network will cause the dynode potentials to change, and so change the tube gain. This problem is of special concern in lifetime measurements. The shape of exponential decay curves will be changed if the tube gain varies with count rate. To be certain that this is not a problem, repeat the measurement at half the original intensity.
Typical Experiment are usually connected in series. ( See Figure B ) risetime less than this.) The other end of this cable is connected to the anode of the PMT, together with the output signal cable. Bypassing the dynodes of a PMT may cause high frequency ringing of the anode output signal. This can cause multiple counts for a single photon. The problem is significantly reduced by using small resistors between the dynodes and the bypass capacitors, as shown in Figure B.
Using Photomultiplier Tubes RINGING WITHOUT SNUBBER For convenience, 50 Ohm systems are usually used. The current pulse from the PMT travels down a 50 Ohm cable which is terminated by the 50 Ohm input impedance of a preamplifier. The attenuation of RG-58 coax cable at 300 MHz is about 1 dB/ 10 ft. and so it does not significantly degrade performance in this application.
Typical Experiment There are two reasons for carefully selecting the input discriminator level. The first is to improve the signal-to-noise ratio by setting the discriminator level above most of the noise pulses, but below most of the signal pulses. The second reason is to reduce drift: if the discriminator threshold is set to the middle of the signal pulse height distribution, then small changes in the tube gain can cause a large change in the count rate.
Typical Experiment TYPICAL EXPERIMENT used to quickly populate the excited state, and decays from the excited state are seen through a bandpass interference filter centered on Ruby's 694.3 nm emission line. This experiment is typical of many photon counting experiments. A pulsed light source is used to pump atoms to an excited state. Decays from the excited state are observed, allowing the lifetime of the state to be measured. APPARATUS ENERGY LEVELS OF RUBY The apparatus is shown below.
Typical Experiment increase the pulse height to 100 mV, one amplifier in the SR445A preamp provides a gain of 5 with a 350 MHz bandwidth. The discriminator threshold is set to 20 mV. When viewed with a 300 MHz oscilloscope, it is apparent that this threshold setting will count the majority of output pulses, but will not count anode rings or amplifier noise. sent to the computer six times per second at the 60 Hz trigger rate.
Typical Experiment the photon counter mode, reads, displays and stores scan data, and can fit curves to experimental results. averaged to reduce statistical noise. When the data acquisition is complete, data reduction routines fit an exponential to the decay curve to determine the lifetime of the excited state. Finally, the data curves are printed (see figure below ), and stored to disk.
Typical Experiment 72
SR400 Circuit Description SR400 CIRCUIT DESCRIPTION The SR400 has five printed circuit boards. Almost all of the components are located on the main circuit board, including the microprocessor and interfaces, fast counters and discriminators, gate generators, and digital to analog conversion circuits. There is one circuit board in the power supply enclosure. The other three circuit boards are much smaller and are mounted to the front panel.
Typical Experiment are 2 address lines, chip select, power and ground, and display contrast control. temperature compensated bias voltage for the overload protection circuits which is adjusted by P101 to null the dc offset at the input. The electroluminescent backlight requires a 100 Vac, 100 Hz signal. This power is derived from the dc power supplies and is isolated from the ac main. DISCRIMINATORS (sheet 2) Comparators U202, U203, U204, U209 discriminate the AMP 1 and AMP 2 outputs into ECL levels.
SR400 Circuit Description from INPUT 1 and the signal A10MHZ_INH disables input from the 10 MHz timebase. The selected input is buffered by 4/4 of U301 to drive the A_DISC output drivers, Q301 and Q302. When both inputs to 1/4 of U301, !A_GATE and !TIMER are both low, the counter is enabled. (!SIGNAL means NOT_SIGNAL or SIGNAL_BAR) !TIMER is low the duration of the count period as determined by the preset condition. !A_GATE is low when the A gate is active. !A_GATE is always low if A gate is CW.
Typical Experiment clears the dwell latch, 2/2 U603, raising !COUNT high again. This also resets and enables the dwell counters in U1308 to count down the programmed dwell time. During the first 1 ms of the dwell time, the processor is reading and resetting the counters, reloading the T counter, and updating any scanned parameters. When the processor is finished, it strobes !T_REARM low which resets the timeout latch.
SR400 Circuit Description by the processor. When the digital portion of the delay is complete, !DLYA_TIMEOUT goes low which causes the differential pair, Q702 and Q703, to switch the current away from the operational transconductance amplifier (OTA) 1/2 U704 and to C706. The voltage on C706 then ramps up until it reaches -5 V at which point the differential comparator, Q704 and Q705, switches state and generates the EOD_A (end of delay) signals.
Typical Experiment 78
SR400 Parts List Main Board Parts List REF # BT1 C 101 C 102 C 103 C 104 C 105 C 106 C 107 C 108 C 109 C 121 C 122 C 123 C 124 C 125 C 126 C 127 C 128 C 129 C 130 C 131 C 132 C 133 C 201 C 202 C 203 C 204 C 205 C 206 C 207 C 208 C 209 C 210 C 211 C 212 C 213 C 214 C 215 C 216 C 217 C 218 C 219 C 220 C 221 C 222 C 223 C 224 C 601 SRS Part # 6-00001-612 5-00023-529 5-00033-520 5-00023-529 5-00023-529 5-00023-529 5-00033-520 5-00159-501 5-00100-517 5-00038-509 5-00023-529 5-00033-520 5-00023-529 5-00023-529
SR400 Parts List REF # C 701 C 702 C 703 C 704 C 705 C 706 C 708 C 709 C 711 C 712 C 713 C 714 C 715 C 716 C 718 C 719 C 720 C 721 C 801 C 802 C 803 C 804 C 805 C 806 C 807 C 808 C 809 C 811 C 812 C 901 C 902 C 903 C 904 C 905 C 906 C 908 C 909 C 911 C 912 C 913 C 914 C 915 C 916 C 918 C 919 C 920 C 921 C 930 C 931 C 1001 C 1002 SRS Part # 5-00023-529 5-00121-566 5-00023-529 5-00002-501 5-00023-529 5-00061-513 5-00023-529 5-00158-501 5-00023-529 5-00121-566 5-00023-529 5-00002-501 5-00023-529 5-00061-513 5
SR400 Parts List REF # C 1003 C 1004 C 1005 C 1006 C 1007 C 1008 C 1009 C 1021 C 1022 C 1023 C 1024 C 1025 C 1026 C 1027 C 1028 C 1029 C 1101 C 1102 C 1105 C 1106 C 1201 C 1202 C 1203 C 1204 C 1205 C 1206 C 1207 C 1302 C 1501 C 1502 C 1503 C 1504 C 1505 C 1506 C 1508 C 1509 C 1510 C 1511 C 1512 C 1513 C 1640 C 1641 C 1642 C 1643 C 1644 C 1645 C 1646 C 1647 C 1648 C 1649 C 1650 SRS Part # 5-00023-529 5-00002-501 5-00100-517 5-00150-525 5-00100-517 5-00023-529 5-00023-529 5-00002-501 5-00100-517 5-00023-529
SR400 Parts List REF # C 1651 C 1652 C 1653 C 1654 C 1655 C 1656 C 1657 C 1658 C 1659 C 1660 C 1670 C 1671 C 1672 C 1673 C 1674 D 101 D 102 D 103 D 104 D 121 D 122 D 123 D 124 D 130 D 201 D 202 D 701 D 711 D 801 D 811 D 901 D 911 D 1001 D 1021 D 1101 D 1201 D 1202 D 1203 D 1301 D 1401 D 1402 DS1401 DS1402 DS1403 DS1404 DS1405 DS1406 DS1407 DS1408 DS1409 DS1410 SRS Part # 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00023-529 5-00100-517 5-001
SR400 Parts List REF # DS1411 DS1501 DS1502 DS1503 DS1504 DS1505 DS1506 J1 J2 L 301 L 302 L 303 L 304 L 305 N 201 N 202 N 203 N 204 N 205 N 301 N 302 N 303 N 304 N 305 N 306 N 307 N 308 N 309 N 310 N 401 N 402 N 403 N 601 N 602 N 701 N 702 N 704 N 705 N 706 N 711 N 712 N 713 N 801 N 802 N 811 N 901 N 902 N 904 N 905 N 906 N 907 SRS Part # 3-00012-306 3-00012-306 3-00012-306 3-00012-306 3-00013-306 3-00013-306 3-00013-306 1-00016-160 1-00238-161 6-00017-630 6-00017-630 6-00017-630 6-00017-630 6-00017-630 4-
SR400 Parts List REF # N 908 N 911 N 912 N 1001 N 1002 N 1021 N 1022 N 1101 N 1201 N 1202 N 1301 N 1401 N 1402 N 1403 N 1404 N 1405 N 1406 N 1407 N 1408 N 1501 N 1502 N 1503 N 1504 P 101 P 121 P 1501 PC1 PC2 Q 101 Q 102 Q 121 Q 122 Q 130 Q 301 Q 302 Q 303 Q 304 Q 305 Q 306 Q 307 Q 308 Q 309 Q 310 Q 601 Q 602 Q 701 Q 702 Q 703 Q 704 Q 705 Q 711 SRS Part # 4-00369-421 4-00246-421 4-00262-425 4-00284-421 4-00331-421 4-00284-421 4-00331-421 4-00284-421 4-00335-425 4-00334-425 4-00223-425 4-00287-425 4-00243-42
SR400 Parts List REF # Q 712 Q 713 Q 714 Q 715 Q 801 Q 802 Q 803 Q 804 Q 811 Q 901 Q 902 Q 903 Q 904 Q 905 Q 911 Q 912 Q 913 Q 914 Q 915 Q 1001 Q 1002 Q 1003 Q 1004 Q 1021 Q 1022 Q 1023 Q 1024 Q 1101 Q 1201 Q 1202 Q 1203 R 101 R 102 R 103 R 104 R 105 R 106 R 107 R 108 R 109 R 110 R 111 R 112 R 113 R 114 R 115 R 116 R 121 R 122 R 123 R 124 SRS Part # 3-00022-325 3-00022-325 3-00027-325 3-00027-325 3-00021-325 3-00022-325 3-00022-325 3-00022-325 3-00022-325 3-00022-325 3-00022-325 3-00022-325 3-00027-325 3-0
SR400 Parts List REF # R 125 R 126 R 127 R 128 R 129 R 130 R 131 R 132 R 133 R 134 R 135 R 136 R 140 R 141 R 142 R 143 R 144 R 145 R 201 R 202 R 203 R 204 R 205 R 206 R 207 R 208 R 209 R 210 R 211 R 212 R 213 R 214 R 215 R 216 R 217 R 218 R 219 R 220 R 221 R 222 R 223 R 224 R 225 R 226 R 227 R 228 R 229 R 230 R 231 R 232 R 233 SRS Part # 4-00088-401 4-00079-401 4-00322-407 4-00327-407 4-00021-401 4-00322-407 4-00358-402 4-00234-407 4-00021-401 4-00021-401 4-00188-407 4-00134-407 4-00350-407 4-00351-407 4-0
SR400 Parts List REF # R 234 R 235 R 401 R 402 R 403 R 404 R 405 R 406 R 407 R 408 R 501 R 502 R 601 R 602 R 701 R 702 R 703 R 704 R 705 R 706 R 707 R 708 R 709 R 710 R 711 R 712 R 713 R 714 R 715 R 716 R 717 R 718 R 719 R 720 R 721 R 722 R 724 R 725 R 727 R 728 R 729 R 730 R 731 R 733 R 734 R 801 R 802 R 803 R 804 R 805 R 806 SRS Part # 4-00030-401 4-00030-401 4-00045-401 4-00045-401 4-00103-401 4-00081-401 4-00076-401 4-00103-401 4-00081-401 4-00076-401 4-00034-401 4-00021-401 4-00359-402 4-00359-402 4-0
SR400 Parts List REF # R 807 R 808 R 809 R 810 R 811 R 812 R 901 R 902 R 903 R 904 R 905 R 906 R 907 R 908 R 909 R 910 R 911 R 912 R 913 R 914 R 915 R 916 R 917 R 918 R 919 R 920 R 921 R 922 R 924 R 925 R 927 R 928 R 930 R 931 R 940 R 941 R 942 R 943 R 1001 R 1002 R 1003 R 1004 R 1005 R 1006 R 1007 R 1008 R 1009 R 1010 R 1011 R 1012 R 1021 SRS Part # 4-00305-401 4-00021-401 4-00305-401 4-00215-407 4-00030-401 4-00031-401 4-00164-407 4-00188-407 4-00067-401 4-00045-401 4-00031-401 4-00080-401 4-00375-407 4-
SR400 Parts List REF # R 1022 R 1023 R 1024 R 1025 R 1026 R 1027 R 1028 R 1029 R 1030 R 1031 R 1032 R 1105 R 1106 R 1201 R 1202 R 1203 R 1204 R 1205 R 1206 R 1207 R 1208 R 1302 R 1401 R 1501 R 1502 R 1503 R 1504 R 1505 R 1506 R 1507 R 1508 R 1509 SO1208 U 101 U 102 U 103 U 201 U 202 U 203 U 204 U 206 U 207 U 208 U 209 U 210 U 301 U 302 U 303 U 304 U 305 U 306 SRS Part # 4-00038-401 4-00347-407 4-00080-401 4-00031-401 4-00021-401 4-00305-401 4-00021-401 4-00305-401 4-00215-407 4-00030-401 4-00031-401 4-0002
SR400 Parts List REF # U 307 U 308 U 401 U 402 U 403 U 404 U 405 U 406 U 407 U 408 U 501 U 502 U 503 U 504 U 601 U 602 U 603 U 604 U 605 U 701 U 702 U 703 U 704 U 705 U 801 U 802 U 803 U 804 U 805 U 806 U 807 U 901 U 902 U 903 U 904 U 905 U 906 U 907 U 908 U 1001 U 1002 U 1003 U 1004 U 1005 U 1006 U 1101 U 1102 U 1103 U 1104 U 1105 U 1106 SRS Part # 3-00151-340 3-00207-340 3-00206-340 3-00194-340 3-00142-340 3-00207-340 3-00194-340 3-00208-340 3-00200-340 3-00151-340 3-00049-340 3-00045-340 3-00209-340 3-0
SR400 Parts List REF # U 1201 U 1202 U 1203 U 1204 U 1205 U 1206 U 1207 U 1209 U 1211 U 1301 U 1302 U 1303 U 1304 U 1305 U 1306 U 1307 U 1308 U 1309 U 1310 U 1311 U 1402 U 1403 U 1404 U 1405 U 1406 U 1407 U 1501 U 1502 U 1503 U 1504 U 1505 U 1506 U 1507 U 1508 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 SRS Part # 3-00158-340 3-00039-340 3-00045-340 3-00155-340 3-00217-340 3-00216-340 3-00046-340 3-00299-341 3-00037-340 3-00046-340 3-00046-340 3-00044-340 3-00491-340 3-00491-340 3-00491-340 3-00491-
SR400 Parts List REF # Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 SRS Part # 0-00233-000 0-00234-044 0-00236-004 0-00241-021 0-00259-021 0-00407-032 0-00418-000 0-00500-000 0-00893-026 1-00003-120 1-00032-130 1-00065-114 1-00073-120 1-00074-171 1-00075-171 1-00076-171 1-00077-171 1-00078-130 1-00079-130 1-00080-130 2-00026-220 5-00262-548 6-00212-630 7-00126-710 7-00130-720 7-00131-720 7-00138-720 7-00142-740 7-00826-709 8-00047-820 9-00192-917 9-00552-9
SR400 Parts List Power Supply Parts List REF # C 1601 C 1602 C 1603 C 1604 C 1605 C 1606 C 1607 C 1608 C 1609 C 1610 C 1611 C 1612 C 1613 C 1614 C 1615 C 1616 C 1617 C 1618 C 1619 C 1620 C 1621 C 1622 C 1623 C 1624 C 1625 C 1626 C 1627 C 1628 C 1629 C 1630 C 1631 C 1636 C 1675 C 1676 D 1601 D 1602 D 1603 D 1604 D 1605 D 1606 D 1607 D 1608 D 1609 D 1610 L 1606 LR1601 LR1602 LR1603 SRS Part # 5-00140-500 5-00140-500 5-00034-526 5-00141-503 5-00049-566 5-00006-501 5-00012-501 5-00023-529 5-00023-529 5-00023-
SR400 Parts List REF # LR1604 LR1605 P 1601 Q 1601 Q 1602 Q 1603 R 1601 R 1602 R 1603 R 1604 R 1605 R 1606 R 1607 R 1608 R 1609 R 1610 R 1611 R 1612 R 1613 R 1614 R 1615 R 1616 R 1617 R 1618 R 1619 R 1620 R 1621 R 1622 R 1623 R 1624 R 1627 R 1628 R 1629 R 1630 R 1631 R 1632 R 1639 SW1601 T 1601 U 1601 U 1602 U 1603 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 SRS Part # 6-00028-604 6-00028-604 4-00014-441 3-00222-325 3-00222-325 3-00224-329 4-01606-409 4-01606-409 4-00340-409 4-00341-402 4-00364-402 4-00341-402 4-00361-402
SR400 Parts List REF # Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 SRS Part # 0-00190-030 0-00200-043 0-00208-020 0-00209-021 0-00231-043 0-00243-003 0-00244-021 0-00438-021 0-00447-007 0-00478-055 0-00523-048 1-00066-112 6-00004-611 7-00137-720 7-00139-720 7-00148-701 9-00185-917 VALUE #8X1" #8 SHOULDER 4-40X3/8PF 4-40X3/8PP #4 SHOULDER TO-220 6-32X1-1/8PP 4-40X5/16PP TO-220 1.
SR400 Parts List 96
