MODEL SR540 OPTICAL CHOPPER
Contents
1. Connect the chopper head to the controller with the supplied coiled cord Mount the 30 slot wheel for 400 Hz to 3 7 kHz or the 6 slot wheel for 4 Hz to 400 Hz and set the MAX FREQ SLOT switch on the front panel for the desired frequency range Set the REFERENCE MODE switch up In this position the right BNC output is at f the chop frequency of the outer row of slots and the left BNC output is at finner the chop frequency of the inner row of slots Connect the lock in s reference input to the output that corresponds to the row of slots that will be used Turn the power switch on and adjust the 10 turn dial for the desired chop frequency STANFORD RESEARCH SYSTEMS INC C IEEE MODEL SR540 CHOPPER CONTROLLER CONTROL VOLTAGE CHOPPER FREQUENCY fl Hz 0 0 VDC WARNING NO USER SERVICEABLE PARTS INSIDE REFER TO USER MANUAL FOR SAFETY NOTICE e LIME FUSE 100720 lt CHOPPER HEAD LILOW BLO 220 240 WA CABLE Figure 3 Chopper Controller Front and Rear Panels OPERATING INSTRUCTIONS INTRODUCTION The Model SR540 Optical Chopper is used to square wave modulate the intensity of optical signals The unit can chop light sources at rates from 4 Hz to 3 7 kHz Versatile low jitter reference outputs provide the synchronizing signals required for several operating modes single or dual beam sum amp difference frequency and synthesized chopping to 20 kHz FREQUENCY OF OPERATION The choice of opera2. Crystal Dial Hardware Misc Lugs Nut Kep Tie Washer Flat Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 24 UL1007 Strip 1 4x1 4 Tin Wire 24 UL1007 Strip 1 4x1 4 Tin Wire 24 UL1007 Strip 1 4x1 4 Tin Screw Flathead Phillips Grommet Power Entry Hardware Screw Panhead Phillips Insulators Screw Panhead Phillips Z0 20 20 20 20 20 Z0 20 0 00222 021 0 00238 026 0 00447 007 0 00524 048 0 00594 050 1 00003 120 1 00053 172 3 00556 340 7 00064 720 7 00065 720 7 00066 709 SR540 PARTS LIST 6 32X 1 4PP 6 32X TO 220 8 1 4 18 4 1 2 18 BLUE BNC USA HDSP 5323 SR540 7 SR540 8 SR540 11 18 Screw Panhead Phillips Screw Black All Types Heat Sinks Wire 18 UL1015 Strip 3 8 x 3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Connector BNC Line Cord Integrated Circuit Thru hole Pkg Fabricated Part Fabricated Part Lexan Overlay LAYOUT I6T2OHtZ LM340 5 ESTOHDL 9262 v4 OZOPIHPL lt VCO u 1 24 Dn lt 0 U13 us c P2 R25 R99 LHOO70 TL CD POT AH P 19 20
3. binary counter and the flip flop 2 2 U14 are used to divide by 215 to generate a 1 000 second gate In order to eliminate one count flicker in the result the count latch 1 2 U14 15 set by a falling edge of the wave form which 15 to be counted When the count latch 15 set the reset to the time base counters 15 released starting the one second count period Also the reset to U15 the four decade counter latch display driver 1s released to begin the count The count accumulates for 1 second when the falling edge of the Q output from 2 2 U14 sets 1 2 U13 high The Q output of 1 2 U13 stays high for about 1 2 clock period 15us asserting the Latch Enable input on U15 to transfer the counter contents to the latch for display Then 1 2 U13 is reset and 2 2 Ul3 is clocked high asserting the Q bar output to reset the count latch The entire count cycle begins with the next falling edge from the opto pick off comparator If the wheel stops so there are no more pulses to count the reset to 15 will be asserted indefinitely After a few seconds R36 will charge C13 to assert the Disp Sel to 15 causing the contents of the counters which are zero to be displayed instead of the contents of the latches which contain the last count U15 multiplexes the display information to the 4 digit common cathode LED Each of the digits are selected in sequence by U15 saturating one of the display driver transistors Q2 Q5 POWER SUPPLIES The
4. chopper wheel design This second signal provides a signal at f 6 with known phase which 15 used to synthesize other reference outputs Logic signals at f amp 1 6 are generated by the dual comparator U6 The 1 2 of U6 compares the photo current signal to a fixed voltage of about 3 6VDC in order to generate f The 2 2 of U6 compares the photo current signal to the peak value of the photo current signal less two diode drops Comparing to the peak voltage compensates for variations in LED amp phototransistor sensitivity Both comparators have about 0 2V of hysteresis to prevent multiple edges on logic transitions FREQUENCY SYNTHESIS The outer row frequency f is measured directly by one of the phototransistors The difference between the outer amp inner row frequencies f 6 is measured by the other phototransistor The other frequencies are synthesized from these two references by a phase lock loop circuit Name Frequency Description f f outer row Sf Sf 5 x outer row finner 5f 6 inner row Tam 11f 6 outer row inner row faitt f 6 outer row inner row The Dual 1 4 Multiplexer U17 15 used to pass f or f 6 to the right hand reference output BNC per the setting of the REFERENCE MODE switch SW U17 also selects f of f 6 as a source to the PLL frequency synthesizer circuit To generate 51 6 the frequency of the inner row of slots U17 selects 1 6 as the input to the phase detector of U12 a CMOS phase lock loop T
5. phase measurement will not drastically affect the lifetime Source Chop at f Use outer row of slots Chopper Wheel Chopper Controller c When a small diameter beam is chopped by a blade the light intensity vs time is a square wave I t Io sin wt 1 3 sin 3wt 1 5 sin 5wt Providing that the optical media 15 not saturated by the light beam the media will respond linearly to each Fourier component In this case we are interested in the response at the 5th harmonic for which the chopper controller has a reference signal output at 5f To use this feature set the REFERENCE MODE switch to the center position and use the left BNC reference output as the reference input to the lock in amplifier figure 6 The lock in will now detect the response from the experiment at the 5th harmonic of the chop frequency up to 20kHz Note that the Experiment Sy Detector Lock In Amplifier Lock at5f to 20 kHz Figure 6 Single Beam with Effective Chop Frequencies to 20 kHz Ampli f the n rj codi vs Beam Size Beam Intensity vs Time 4 fee Slot Aperture L 4 6 mm for the 30 Slot Wheel Minimum at 2L 5 Amplitude as 1 2 0 2 0 3 0 0 0 0 5 1 0 1 5 Beam Size b mm Figure 7 Amplitude of the 5th Harmonic vs Beam Size The amplitude of the 5th harmonic vs beam size 15 plotted in figure 7 If your beam is much larger than 0 5mm you may wish to pa
6. to the wheel Then firmly tighten all three screws Handle blades carefully as they are easily bent BASEPLATE REMOVAL The baseplate of the unit may be removed to allow for pole mounting Use an allen wrench to remove the 6 32 bolt from the bottom of the baseplate Figure 4 30 25 Slot and 6 5 Slot Chopper Blades APPLICATIONS SINGLE BEAM EXPERIMENT In this application a single optical beam 15 could be used in which case the reference from chopped by the outer row of slots and the the left BNC would be used In either case the reference output from the right BNC is used to REFERENCE MODE switch is in the up lock the lock in amplifier to a chop frequency position figure 5 Note that the inner row of slots Source Chop at f _ pad gt Detector Use outer row of slots Experiment Chopper Whee Lock In Amplifier fe mme ool boo Chopper Controller PP 4 Reference Input Figure 5 Single Beam Experiment SINGLE BEAM EXPERIMENT WITH EFFECTIVE CHOP FREQUENCIES TO 20 KHZ In certain situations very high chop frequencies are desirable For example you can infer the lifetime of a fluorescent decay by measuring the phase shift between the light which excites the material and the fluorescent decay output tang 2nf where is the observed phase shift f 1s the chop frequency and t 1s the lifetime Accuracy is improved by using a chop frequency f 1 2nt so that small errors in the
7. 03 0 00209 021 SR540 PARTS LIST 10K 5 6K 1 2K 100 1 0K 22K 1 0K 1 0M 470 56V 500A SPDT SPDT SR540 RXEO030 CD4066 LM324 CD4066 LH0070 0H LM393 7815 LM317T 7805 74HCU04 74HC4020 CD4046 74HC73 74HC73 74C926 74HC153 74 191 32 768 KHZ 2607 FOOT 3 8 6 32 KEP 4 3 8 X3 32 4 18 RED 4 24 5 24 7 1 4 24 4 40X 2 6VMAS 6 32X3 8PP TO 5 4 40X3 8PP Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Varistor Zinc Oxide Nonlinear Resistor Switch On Off On Toggle Right Angle Switch On Off On Toggle Right Angle Transformer Thermistor various Voltage Reg TO 220 TAB Package Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Voltage Reg TO 220 TAB Package Voltage Reg TO 220 TAB Package Voltage Reg TO 220 TAB Package Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg
8. 10P 47 1N4148 1N4148 15 Capacitor Tantalum 35V 20 Rad Connector Misc Misc Parts Optical Switch Optical Switch Printed Circuit Board Hardware Misc Hardware Misc Screw Allen Head HEX HEAD Knobs Screw Black All Types Wire Other Glue Screw Panhead Phillips Fabricated Part Chemically Etched Part Machined Part Machined Part Machined Part Chemically Etched Part Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Cap Mini Electrolytic 50V 20 Radial Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 50V 20 Rad Capacitor Electrolytic 50V 20 Rad Cap Monolythic Ceramic 50V 20 Z5U Capacitor Electrolytic 50V 2096 Rad Hardware Misc Capacitor Mylar Poly 50V 5 Rad Capacitor Tantalum 35V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 50V 20 Rad Capacitor Tantalum 35V 20 Rad Cap Monolythic Ceramic 50V 20 Z5U Capacitor Tantalum 35V 20 Rad Cap Mini Electrolytic 50V 20 Radial Capacitor Mylar Poly 50V 5 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Diode Diode R 17 18 R19 R 20 R21 R 22 R 23 R 24 25 R 26 28 29 R 31 R 32 R 34 R 35 R 36 R 37 3 00001 301 3 00001 301 3 00203 301 6 00002 611 1 00030 100 1 00031 133 4 00271 445 4 00019 443 7 00054 701 7 005
9. 58 701 3 01860 325 3 01860 325 3 01860 325 3 01860 325 3 00020 325 4 00273 401 4 00305 401 4 00773 402 4 00031 401 4 00034 401 4 00034 401 4 00188 407 4 00187 407 4 00193 407 4 00061 401 4 00034 401 4 00048 401 4 00078 401 4 00021 401 4 00272 407 4 00188 407 4 00021 401 4 00059 401 4 00614 407 4 00037 401 4 00131 407 4 00094 401 4 00090 401 4 00054 401 4 00035 401 4 00021 401 4 00034 401 4 00032 401 4 00032 401 4 00057 401 4 00057 401 4 00032 401 4 00034 401 1N4001 1N4001 1N5711 25A 3AG 4P4C 16 PIN SRA 2 0K 20K SR540 SR540 LED MPSAI3 MPSAI3 MPSAI3 MPSAI3 PN2222 5 6K 4 3K 2 2 100 10K 10K 4 99 4 53 499 240K 10K 2 2K 39K 1 0K 221 4 99 1 0K 22K 174K 1 00 6 8K 560 200K 10M 1 0K 10K 100K 100K 220 220 100K 10K 16 SR540 PARTS LIST Diode Diode Diode Fuse Connector Misc Connector Male Right Angle Pot Multi Turn Side Adjust Pot 10 Turn Panel Printed Circuit Board Printed Circuit Board Transistor TO 92 Package Transistor TO 92 Package Transistor TO 92 Package Transistor TO 92 Package Transistor TO 92 Package Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Comp 1 2W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 5W 1 Resistor Metal Film 1 5W 1 Resistor Metal Film 1 8W 1 SOPPM Resi
10. 5Q This 15 just equal to the real resistance of the cable and motor windings With this arrangement the speed of the motor will not be affected by load variations which normally would change the current and so change the voltage that 1s applied to the motor This improves frequency stability of the chopper and 12 4 kHz Set the FREQUENCY ADJUST dial to 7 5 and use a small screwdriver to adjust the MOTOR CAL pot so that the four digit display shows 3000 10 Hz improves the linearity of the speed vs control voltage characteristic OPTICAL PICK OFFS There are two slotted optical switches which detect slots 1n the chopper wheel Each optical switch uses an infrared LED and a phototransistor If the light passes through a slot to the phototransistor its collector current will be several milliamps The collectors of the photo transistors are connected together summing their currents The common collector is held at 3 0VDC by 4 4 of U3 The current 15 sensed by R15 so that the output of 4 4 U3 will swing by volt mA of collector current Radiated noise at the chop frequency is greatly reduced as all lines going to the chopper head are held at constant voltage The waveform at pin 14 of U3 looks like this f 6 The current from one of the optical switches 15 just a square wave at the frequency of the outer row of slots The outputs from the second photo transistor places a pulse top of every sixth pulse per the
11. MODEL SR540 OPTICAL CHOPPER d 5 RS Stanford Research Systems MODEL SR540 OPTICAL CHOPPER Copyright 1986 1988 1995 1997 Stanford Research Systems Inc All Rights Reserved Rev 2 6 06 2009 Stanford Research Systems Inc 1290 D Reamwood Ave Sunnyvale CA 94089 USA 408 744 9040 TABLE OF CONTENTS Symbols Used unida 2 DPECIHCAUONS EE 3 Safety amp Preparation for Use 4 Quick Start Instruction 5 Operating Instructions MEU O sera S E 6 Prequency of Operation aa 6 Chanoine EE 6 Baseplate Removal sn eu 6 Applications Incl Beam creator toa 7 single Beam Chopping to 20 KHZ Dual Beam 10 Detection at Sum amp Difference Frequencies 11 Variable Aperture csset tete 11 EE 12 Circuit Description Motor Speed EE 12 Optical PICK 12 Eregueney Synthesis Ae 13 Fregene E 13 POWCIOSUDDIIES 14 CH EC GE 15 E OU nee ee ne o yee EN 19 EE NET A o 21 Symbols you may find on SRS products Symbol d ep Alternating current Caution risk of electric shock Frame or chassis terminal Caution refer to accompanying documents On supply Off supply Earth ground terminal Chop Frequency Frequency Stability Long Term Frequency Drift Phase Jitter Freque
12. e Voltage Selected Open the cover on the power entry module using a small screwdriver pull the voltage selector card straight out using long nose pliers orient selector card so that the desired voltage 15 readable at the bottom orient the indicator pin to point up when desired voltage is readable at the bottom figure 2 insert voltage selector card into housing printed side facing left and edge containing desired voltage first replace cover and verify that the indicator pin shows the desired voltage Power Entry Module Figure 2 Voltage Selector Card LINE FUSE Verify that the correct line fuse is installed before connecting the line cord For 100V and 120V use a 1 4 Amp fuse and for 220V and 240V use a 1 8 Amp fuse LINE CORD This instrument has a detachable three wire power cord with a three contact plug for connection to both the power source and protective ground The protective ground contact connects to the accessible metal parts of the instrument To prevent electrical shock always use a power source outlet that has a properly grounded protective ground contact OPERATE ONLY WITH COVERS IN PLACE To avoid personal injury do not remove the product covers or panels Do not operate the product without all covers and panels in place KEEP HANDS CLEAR OF CHOPPER BLADE Quick Start Instructions Make sure the correct line voltage is selected the correct fuse is installed and the power switch is off
13. gnal Out Figure 8 Dual Beam Experiment DETECTION AT THE SUM amp DIFFERENCE FREQUENCIES Certain applications require detection at the sum or difference frequency of two chopped beams In figure 9 a source beam is split into two One of the beams 15 chopped by the outer row of slots on the wheel the other 15 chopped by the Chop at f Source Chopper Controller Jam inner row By placing the REFERENCE MODE switch in the down position the sum frequency is available at the left reference BNC and the difference frequency 15 available at the right BNC Nonlinear Optical pum E Material focus Detector Chopper Wheel Lock In Amplifier sum Figure 9 Sum and Difference Frequency Detection VARIABLE APERTURE In some situations one must reduce the duty cycle of a chopped optical beam This can be done with the SR540 by mounting two identical blades and staggering their position relative to each other The minimum slot aperture 15 about 0 5mm below which the slotted optical detector will fail to detect the outer row of slots This corresponds to a 10 duty cycle on the 30 slot 11 blade and a 2 duty cycle on the 6 slot blade For duty cycles less than 20 you should select the pulse mode reference level on the lock in Since the f 6 notch 15 obscured when two blades are mounted only the f amp 5f reference outputs will work finner gt fsum and will not work Y
14. he output of the phase detector 15 filtered by R23 R24 and C3 The quad analog switch U4 will also switch in C2 or Cl if the 400Hz or 40Hz MAX FREQ SLOTS ranges are selected at SW2 The filtered output of the phase detector controls the VCO frequency The maximum 13 frequency of the VCO 15 set by R22 U4 increases the maximum frequency by switching in R20 or R21 when the 400 Hz or 4KHz ranges are selected The output frequency of the VCO is divided by 18 which is programmed to divide by 5 or 11 per the setting of the REFERENCE MODE switch SW1 To generate 5f 6 U18 loads 10 when the counter reaches 15 to divide by 5 In order for the frequencies at the input of the phase comparator to be equal the VCO must run at 5xf 6 The same circuit 1s used to generate 5f however the multiplexer U17 selects f not f 6 as the input to the phase detector To generate 111 6 the sum frequency f 6 1s selected as the input to the phase detector and U18 is programmed to divide by 11 by presetting to 4 when the counter reaches 15 In all cases the output of the VCO 15 passed to the left reference output BNC This output 1s always a square wave FREQUENCY DISPLAY The four digit frequency display always shows the frequency f of the outer row of slots independent of the reference mode which has been selected The time base for the counter is a 32 768Hz crystal oscillator which 15 sustained by a hex inverter U11 14 stage
15. ncy Display Frequency Control VCO Reference Modes Dimensions Power Warranty SPECIFICATIONS 4 Hz to 400 Hz with 6 slot blade 400 Hz to 3 7 kHz with 30 slot blade 250 ppm C typical lt 2 100 Hz lt f lt 3700 Hz 0 2 rms from 50 Hz to 400 Hz 0 5 rms from 400 Hz to 3 7 kHz 4 digit 1 Hz resolution 1 Hz accuracy 10 turn pot with 3 ranges 4 Hz to 40 Hz 40 Hz to 400 Hz 400 Hz to 3 7 kHz 0 to I0 VDC Control voltage overrides frequency dial Switch Left BNC Right BNC up T inner f middle 5xf f down f f inner zu f inner Controller dol Chopper Head 2 8 x 2 1 x 1 0 Blade Diameter 4 00 100 120 220 240 VAC 50 60 Hz 12 Watts Electronics One year parts and labor on materials and workmanship Chopper Motor Ninety days parts and labor on materials and workmanship SAFETY AND PREPARATION Figure 1 Power Entry Module Voltage Selector Card Orientation This instrument may be damaged if operated with the LINE VOLTAGE SELECTOR set for the wrong ac input source voltage or if the wrong fuse is installed LINE VOLTAGE SELECTION The SR540 operates from a LOOV 120V 220V or 240V nominal ac power source having a line frequency of 50 or 60 Hz Before connecting the power cord to a power source verify that the LINE VOLTAGE SELECTOR card located in the rear panel fuse holder is set so that the correct ac input voltage value 15 visible figure 1 To Chang
16. ou may observe the duty cycle of the chopped beam on the f output CALIBRATION Only one adjustment is required to calibrate the SR540 Chopper Controller The adjustment pot located on the rear panel is used to match the controller to the motor Mount the 30 slot blade and set the MAX FREQ SLOT switch to CIRCUIT DESCRIPTION MOTOR SPEED CONTROL The output of US a precision 10 000VDC reference is attenuated by P2 the ten turn potentiometer to control the motor speed The set voltage can be overridden by a voltage at the CONTROL VOLTAGE input The speed control voltage 1s buffered by 2 4 of U3 and attenuated by R8 R9 and RIO U2 a quad analog switch selects the attenuation factor to provide full scale voltages of 10 0 5 0 or 0 5VDC per the setting of the MAX FREQ SLOTS switch The 3 4 of U3 1 used to amplify this voltage by about x2 6 The MOTOR CAL pot 1s used to adjust the gain of this amplifier to compensate for variations between motors The output of the amplifier 1s buffered by UI to drive the motor R4 senses and limits the motor current to 200mA by turning on Ql The 1 4 of U3 feeds back a voltage equal to the voltage applied to the motor minus 4 7 times the voltage across RA Since the feedback voltage goes down when current 1s increased the voltage applied to the motor will go up hence the output behaves like a negative resistance connected to a voltage source The negative resistance is about x 4 7 1
17. power transformer primary is tapped for operation at 100 120 220 or 240VAC The power entry module does the required switching Full wave bridge rectifiers are used to rectify the 7 5 VAC and 30VAC to 8 5VDC and 40VDC The unregulated 40VDC is used by Ul the motor driver transistor and by US to provide regulated 30VDC The 30VDC 1s the DC supply to U7 a 15VDC regulator U9 regulates the 8 5 VDC to 5 0VDC 14 SR540 PARTS LIST Motor and Motor related Parts List 5 00102 517 1 00030 100 7 00055 700 3 00173 309 3 00173 309 7 00056 701 0 00000 000 0 00000 000 0 00146 025 0 00147 004 0 00150 026 0 00151 055 0 00205 058 0 00222 021 7 00057 720 7 00058 716 7 00059 721 7 00060 721 7 00061 721 7 00062 716 4 70 AP4C 12VDC MOC70U2 MOC70U2 SR541 UNDECIDED PART UNDECIDED PART 6 32X3 8H 1 4 20X1 4 40X1 4PF DC 44 4C 6 EPOXY GLUE 6 32X 1 4PP SR540 1 SR540 10 SR540 2 SR540 3 SR540 6 SR540 9 Main Board and Chassis Assembly Parts List CX2 3 00062 340 3 00062 340 5 0003 1 520 5 00033 520 5 00192 542 5 00100 517 5 00127 524 5 00 128 509 5 00023 529 5 00038 509 0 00772 000 5 00064 5 13 5 00100 517 5 00030 520 5 00038 509 5 00100 517 5 00023 529 5 00100 5 17 5 00192 542 5 00064 513 5 00003 501 5 00017 501 3 00004 301 3 00004 301 KBP201G BR 81D KBP201G BR 81D 220U 470 22U MIN 22 2 20 4700 JU 10U 1 5 WIRE 0047U 2 20 22000 100 220 JU 2 20 22U MIN 0047U
18. ss the beam through an aperture or bring it to focus at the chopper blade amplitude of the 5th harmonic term will depend on beam size For a beam with diameter b using the 30 slot wheel with a slot aperture L the amplitude of the nth harmonic is given by a 4 L cos 1 b L nt b 2 DUAL BEAM EXPERIMENTS In this arrangement the output from a single source 15 split in two and chopped at two different frequencies by the same chopper wheel figure 8 One of the beams passes through the experiment while the other beam a reference beam passes through a control arm The beams are recombined and sent to the same detector Two lock in s are used to detect the two signals which are at different frequencies The signal at f corresponds to the control arm the signal at Chop at f Source Chop at f inner Chopper Wheel Ex oo Chopper Controller Control Arm D Experimental Arm Amplifiers finner 15 the response from the experimental arm If the detected signal in the experimental arm is ratioed to the detected signal in the control arm then effects due to changing source intensity and detector efficiency are removed Also note that each beam passes through one beam splitter reflects off one beam splitter and reflects off one mirror so that effects due to these components are cancelled in the ratio output Detector Signals at f and f inner Lock In Normalized Si
19. stor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 SOPPM Resistor Metal Film 1 8W 1 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 5W 1 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 SOPPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 18 X TI Z0 ZO 20 20 20 20 20 20 20 20 Z0 4 00034 401 4 00273 401 4 00024 401 4 00031 401 4 00021 401 4 00059 401 4 00021 401 4 00022 401 4 00081 401 4 00355 435 2 00012 206 2 00012 206 6 00014 610 4 00766 431 3 00257 329 3 00074 340 3 00098 340 3 00074 340 3 00188 340 3 00143 340 3 00114 329 3 00149 329 3 00112 329 3 00051 340 3 00169 340 3 00072 340 3 00048 340 3 00048 340 3 00170 340 3 00166 340 3 00171 340 6 00015 620 0 00002 008 0 00009 000 0 00025 005 0 00048 011 0 00089 033 0 00103 040 0 00127 050 0 00128 053 0 00129 053 0 00134 053 0 00149 020 0 00153 057 0 00155 002 0 00185 021 0 00207 0
20. ting frequency is influenced by several factors 1 Avoid low frequency operation below 100Hz In general phase jitter background noise and lock in amplifier noise all degrade at low frequencies Avoid high frequency operation Motor lifetime will be reduced if the unit 1 operated for extended periods above 2KHz Avoid known noise frequencies For example the line frequency and all its even and odd harmonics should be carefully avoided Avoid using the bottom 10 of the frequency control dial The phase jitter DIAMETER 4 DIAMETER 4 APERTURE 170 APERTURE 124 APERTURE 84 APERTURE 62 of the reference outputs will degrade at the low end of the range so switch to the next lower MAX FREQ SLOTS range 5 Always use the correct wheel as indicated by the MAX FREQ SLOTS switch Using the wrong wheel will seriously degrade the performance of the synthesized reference outputs left BNC For frequencies from 4Hz to 400 Hz use the 6 5 slot blade from 400Hz to 3 7kHz use the 30 25 slot blade CHANGING BLADES The chopper blade figure 4 may be replaced by removing the three flat head screws which hold the outside hub to the wheel When replacing the blade be sure to insert the blade between the slotted optical detectors before placing it on the wheel Secure the blade by sandwiching it between the wheel and outer hub Install and loosely tighten the three flat head screws which hold the hub
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