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Manual - Stanford Research Systems

1. 20 fA 1 MO 10 11 20 Hz 10 Hz 5 fA 10 fA 0 040 20 fA 1MQ 10 12 10 Hz 10 Hz 5 fA 5 fA 0 040 20 fA 1MQ Frequency Compensation adjusted for flat frequency response typical values Average noise in the freq range below the 3 dB point but above the frequency where 1 f noise is significant Note The values listed above are typical for a 100 pF source capacitance and an infinite source resistance Significantly higher values of source capacitance or finite source resistance can degrade these specifications Proper use of the FREQ COMP adjustment and signal filters allows the user to alter the rated noise or bandwidth values The LOW DRIFT mode has a much lower bandwidth than the LOW NOISE and HIGH BW modes and should only be used for low frequency measurements viii Verifying Specifications To verify the specifications given for the SR570 current amplifier a few straightforward procedures should be followed First the unit must be warmed up for about 60 minutes Second for best performance the input current should produce an output voltage of about 1 V or less This eliminates problems with slew rate limiting in the various amplifier stages Finally care must be taken in selection of a current source for any measurement Since an ideal current source has infinite impedance any source used for measurements should have an impedance greater than the inverse of the sensitivity in ohms Most specifications liste
2. 2090 Rad Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Mylar Poly 50V 5 Rad Capacitor Mylar Poly 50V 5 Rad Capacitor Mylar Poly 50V 5 Rad Cap Monolythic Ceramic 50V 20 Z5U Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electro 100V 20 Rad Cap Mini Electro 100V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20
3. IOONO GNMDO turn the input offset current off and set LOW NOISE mode 140 PRINT 1 BSON1 BSLV 2500 turn the bias voltage on and set to 2 500 V 150 PRINT FI FLTT2 HFROI 1 LFRO14 put in a bandpass filter between 10 kHz and 300 kHz 160 END 12 Programming Examples Program Example 2 IBM PC Microsoft C via RS232 In this example the IBM PC s COM2 serial port is used to communicate with the SR570 The program asks the user to enter an SR570 command to send to the instrument Before running the program use the DOS MODE command to set up the serial port parameters e g MODE COM2 9600 n 8 2 Program written in Microsoft C to send commands to the SR570 current amplifier include lt stdio h gt include lt conio h gt include lt string h gt define BUFFER 0x2fd COM2 output status use Ox3fd for COM1 define OUT 0x2f8 COM output port use 0x3f8 for COMI define MASK 0x20 mask to pick out buffer empty bit void main void int i j char string 20 while 1 Loop forever use control C to exit printf input command string gets string Get command from user printf n j strlen string Append lt CR gt lt LF gt to the command string j 13 string j 1 10 for i 0 i lt j 1 i Send the command via RS 232 port one character at atime while inp BUFFER amp MASK 0 Wait until transmit buffer is empty outp OUT
4. Rad D 1 C 223 C 224 C 225 C 226 C 227 C 228 C 230 C 301 C 302 C 303 C 304 C 306 C 307 C 308 C 309 C 310 C 311 C 312 C 313 C 314 C 315 C 316 C 317 C 318 C 319 C 320 C 321 C32 C 323 C 324 C 325 C 326 C 327 C 328 C 330 C 401 C 402 C 403 C 404 C 405 C 406 C 407 C 408 C 409 5 0003 1 520 5 00232 520 5 00232 520 5 00192 542 5 00192 542 5 00008 501 5 00100 517 5 00159 501 5 00100 517 5 00100 517 5 00100 517 5 00008 501 5 00010 501 5 00022 501 5 00063 513 5 00065 513 5 00067 513 5 00023 529 5 00194 542 5 00194 542 5 00193 542 5 00193 542 5 00213 546 5 00213 546 5 00033 520 5 00033 520 5 00031 520 5 0003 1 520 5 00232 520 5 00232 520 5 00225 548 5 00225 548 5 00192 542 5 00192 542 5 00100 517 5 00100 517 5 00100 517 5 00017 501 5 00107 530 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00021 501 220U 470U 470U 22U MIN 22U MIN 22P 2 2U 6 8P 2 2U 2 2U 2 2U 22P 270P 001U 0033U 01U 033U 1U 47U MIN 47U MIN 2 2U MIN 2 2U MIN 4 7U 4 7U 47U 47U 220U 220U 470U 470U JU AXIAL 1U AXIAL 22U MIN 22U MIN 2 2U 2 2U 2 2U 47P 1 8 6P 22U 22U 22U 22U 82P Parts List Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Capacitor Ceramic Disc 50V 10 SL Capacitor Ta
5. SR570 and the device connected to the output were both connected to ground However this also means that the output is differential and cannot be used as a ground reference when attempting to trace noise in the SR570 circuitry Measurements of this type should be referenced to the input ground or the SR570 chassis APPENDIX B FRONT END AMPLIFIER On the high sensitivity scales since noise is dominated by DC current offset an op amp with a very low input current is used on all gain modes On intermediate sensitivity scales a low noise op amp is switched in for the LOW NOISE and HIGH BW modes to improve the AC response of the front end On the less sensitive scales where DC drift is dominated by drift in the offset voltage the low noise op amp is used in all gain modes On all scales the High BW mode is obtained by shifting some of the gain from the front end to the output stage Op Amp Allocation Table Scale Low Noise High BW Low Drift 1 mA V 100 pA V 10 pA V 1 pA V 100 nA V 10 nA V 1 nA V 100 pA V 10 pA V 1 pA V N NNN N RRR Re NNN WN RR RR mA R2 NUN ND ND ND ND K H 4 1 AD743 Low Noise 2 AD546 Low Input Current DYNAMIC RESERVE The term Dynamic Reserve comes up frequently in discussions about amplifiers It s time to discuss this term in a little more detail Assume the amplifier input consists of a full scale signal at fsig plus noise at some other frequency The traditional definit
6. 4 00190 407 4 00165 407 4 00030 401 4 00030 401 4 00030 401 4 00296 407 4 00165 407 4 00165 407 4 00030 401 4 00030 401 4 00317 407 4 00031 401 4 00030 401 4 00130 407 4 00272 407 4 00616 453 4 00030 401 4 00138 407 4 00138 407 4 00138 407 4 00138 407 4 00188 407 4 00021 401 4 00021 401 4 00021 401 4 00021 401 4 00021 401 4 00022 401 4 00022 401 4 00022 401 4 00022 401 4 00034 401 4 00034 401 4 00305 401 4 00027 401 4 00027 401 4 00032 401 4 00088 401 4 00032 401 200 200 10 10 845 42 2K 200 10 10 10 604 200 200 10 10 422 100 10 1 00K 221 49 9 10 10 0K 10 0K 10 0K 10 0K 4 99K 1 0K 1 0K 1 0K 1 0K 1 0K 1 0M 1 0M 1 0M 1 0M 10K 10K 43K 1 5K 1 5K 100K 51K 100K Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor 2W 1
7. 415 C 416 C 417 C 419 C 420 C 502 C 503 C 703 C 704 C 705 C 706 C 707 C 708 C 709 C 710 C711 C712 C713 C714 C715 C 716 C 717 C 718 C 719 C 720 C 801 C 802 C 803 C 804 C 805 C 806 C 807 C 808 C 809 C 810 C 811 C 822 C 823 C 824 5 00100 517 5 00100 517 5 00100 517 5 00002 501 5 00022 501 5 00022 501 5 00022 501 5 00022 501 5 00023 529 5 00023 529 5 00104 530 5 00233 532 5 00023 529 5 00023 529 5 00023 529 5 00234 551 5 00234 551 5 00100 517 5 00227 526 5 00227 526 5 00100 517 5 00023 529 5 00100 517 5 00100 517 5 00100 517 5 00023 529 5 00023 529 5 00100 517 5 00297 567 5 00297 567 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00225 548 5 00023 529 5 00100 517 5 00100 517 2 2U 2 2U 2 2U 100P 001U 001U 001U 001U 1U 1U 3 5 20P 22P 1U 1U 1U 1000U 1000U 2 2U 100U 100U 2 2U 1U 2 2U 2 2U 2 2U 1U 1U 2 2U 2 2U 50V RAD 2 2U 50V RAD 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U AXIAL 1U 2 2U 2 2U Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Cap Monoly
8. 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 Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 SOPPM Resistor Metal Film 1 8W 1 50PPM 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 D 9 Parts List R 817 4 00094 401 6 8K Resistor Carbon Film 1 4W 5 R 818 4 00079 401 4 7K Resistor Carbon Film 1 4W 5 R 819 4 00022 401 1 0M Resistor Carbon Film 1 4W 5 S0504 1 00026 150 28 PIN 600 MIL Socket THRU HOLE S0708 1 00570 150 16 PIN Socket THRU HOLE S0709 1 00570 150 16 PIN Socket THRU HOLE T1 6 00067 610 SR560 Transformer U 101 3 00116 325 78L05 Transistor TO 92 Package U 102 3 00385 340 74HC4053 Integrated Circuit Thru hole Pkg U 103 3 00430 340 AD7547JN Integrated Circuit Thru hole Pkg U 104 3 00091 340 LF412 Integrated Circuit Thru hole Pkg U 105 3 00402 340 74HC4052 Integrated Circuit Thru hole Pkg U 106 3 00296 340 OPA404 Integrated Circuit Thru hole Pkg U 107 3 00451 340 AD546 Integrated Circuit Thru hole Pkg U 108 3 00535 340 AD743JN Integrated Circuit Thru hole Pkg U 109 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 110 3 00385
9. Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N5822 Diode 1N4148 Diode 1N5822 Diode YELLOW LED T1 Package RED LED T1 Package KBP201G BR 81D Integrated Circuit Thru hole Pkg 1N5822 Diode 1N5822 Diode LM385BZ 2 5 Integrated Circuit Thru hole Pkg 1N5231B Diode MBR360 Diode MBR360 Diode 1N5822 Diode 1N4148 Diode D 4 Parts List D 803 D 04 DU105A DU105B K 101 K 102 K 103 K 104 K 105 K 106 K 107 K 201 K 301 N 701 N 702 P 101 P 102 P 103 P 104 P 701 P 702 PCI Q 501 Q 701 Q 702 Q 703 Q 801 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 117 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00523 335 3 00523 335 3 00523 335 3 00523 335 3 00523 335 3 00523 335 3 00523 335 3 00523 335 3 00523 335 4 00497 42 4 00501 425 4 00011 441 4 00799 441 4 00370 441 4 00326 441 4 00011 441 4 00011 441 7 00468 701 3 00021 325 3 00310 329 3 00887 325 3 00374 329 3 00376 329 4 00188 407 4 00188 407 4 00138 407 4 00188 407 4 00194 407 4 00194 407 4 00194 407 4 00188 407 4 00194 407 4 00194 407 4 00030 401 4 00030 401 4 00194 407 4 00030 401 4 00030 401 4 00030 401 4 00030 401 1N4148 1N4148 1N4148 1N4148 G6AK 234P ST U G6AK 234P ST U C C G6AK 234P ST UC G6AK 234P ST UC G6AK 234P ST U G6AK 234P ST U C C G6AK 234P ST UC G6AK 234P ST UC G6AK 234P ST U 1 5KX4 1 0MX5 10K 2M 50
10. Pkg U 501 3 00155 340 74HC04 Integrated Circuit Thru hole Pkg U 502 3 00045 340 74HC32 Integrated Circuit Thru hole Pkg U 503 3 00298 340 Z84C0008PEC Integrated Circuit Thru hole Pkg D 10 Parts List Gaaqqcqqqqqadcaqaqadca 8 8 Z onn F O D o 9 cu aqaqacqcqqqaqacaqaqcqaeca S 2 8 8 2 2 3 2 2 5 2 o0 F D G amp A AUS DO DIIS DONDE EES V ADD m unnm s aq o d 3 00081 341 3 00039 340 3 00158 340 3 00049 340 3 00277 340 3 00537 340 3 00411 340 3 00411 340 3 00411 340 3 00411 340 3 00411 340 3 00411 340 3 00411 340 3 00044 340 3 00384 329 3 00141 329 3 00067 340 3 00152 340 3 00239 335 3 00149 329 3 00141 329 8 00072 860 8 00072 860 3 00112 329 3 00307 340 3 00090 340 3 00446 340 3 00446 340 3 00446 340 3 00262 340 2K X8 100 74HC14 74HC154N 74HC74 74HC11 74HC373 74HC273 74HC273 74HC273 74HC273 74HC273 74HC273 74HC273 74HC244 LM350T LM337T CD4013 CD4051 HS 212 12 LM317T LM337T SR566 ASSY SR566 ASSY 7805 LM2940T 10 LF411 6N137 6N137 6N137 74HC86 Front and Rear Panel Parts List DI D2 D3 D4 D5 D6 D7 D8 D9 D 10 D11 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN STATIC RAM I C Integrated Circuit Thru hole Pkg Integrated Circuit Th
11. R 129 R 130 R 131 R 132 R 133 R 134 R 135 R 136 R 137 R 138 R 139 R 140 R 141 R 142 R 143 R 144 R 145 R 146 R 147 R 201 R 202 R 203 R 204 R 205 R 206 R 207 R 208 R 209 R 210 R211 R212 R 213 R214 R215 R 216 4 00398 407 4 00030 401 4 00030 401 4 00776 407 4 00136 407 4 00165 407 4 00139 407 4 00142 407 4 00204 407 4 00449 407 4 00192 407 4 00193 407 4 00022 401 4 00138 407 4 00141 407 4 00800 401 4 00164 407 4 00138 407 4 00132 407 4 00801 407 4 00164 407 4 00138 407 4 00132 407 4 00801 407 4 00030 401 4 00030 401 4 00141 407 4 00329 407 4 005 16 407 4 00164 407 4 005 16 407 4 00168 407 4 005 16 407 4 00168 407 4 00600 407 4 00168 407 4 00600 407 4 00600 407 4 00600 407 4 00600 407 4 00600 407 4 00030 401 4 00165 407 4 00030 401 499K 10 10 178 1 82K 200 10 0M 100K 750 4 99M 49 9K 499 1 0M 10 0K 100 20 0K 10 0K 1 10K 5 49K 20 0K 10 0K 1 10K 5 49K 10 10 100 402 14 3K 20 0K 14 3K 22 6K 143K 22 6K 15 8K 22 6K 15 8K 15 8K 15 8K 15 8K 15 8K 10 200 10 Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Res
12. R A A Hz noise For example a 100 MO resistor will produce a Johnson current noise of about 13 fA VHz It is important to remember that Johnson voltage noise is proportional to the square root of the measurement bandwidth Therefore using signal filters in a measurement will affect the actual value of noise measured in the circuit Shot noise Electric current has noise due to the finite nature of the charge carriers There is always some non uniformity in the electron flow which generates noise in the current This noise is called shot noise This can appear as voltage noise when current is passed through a resistor or as noise in a current measurement The shot noise or current noise is given by 1 2 rms 2q I f piss where q is the electron charge 1 6x107 Coulomb I is the RMS AC current or DC current depending upon the circuit and Af is the bandwidth Shot noise is usually not a problem in typical measurement setups For example a 1 uA current measured with a 100 kHz bandwidth will have only 180 pA of shot noise or 0 02 of the signal amplitude For very small currents shot noise will be more appreciable Take for instance a 1 pA current measured with a bandwidth of 100 Hz The shot noise will be 6 fA or 0 6 of the signal amplitude which might be important 1 f noise Every 100 resistor no matter what composition has the same Johnson noise However there is excess noise in addition to Johns
13. a metal box Inductive coupling An AC current in a nearby piece of apparatus can couple to the experiment via a magnetic field A changing current in a nearby circuit gives rise to a changing magnetic field which induces an emf d B dt in the loop connecting the detector to the experiment This is like a transformer with the experiment detector loop as the secondary winding q T p Noise Source Experiment Detector Cures for inductively coupled noise include 1 Removing or turning off the interfering noise source 2 Reduce the area of the pick up loop by using twisted pairs or coaxial cables or even twisting the 2 coaxial cables used in differential connections 3 Using magnetic shielding to prevent the magnetic field from crossing the area of the experiment 4 Measuring currents not voltages from high impedance detectors Resistive coupling or ground loops Currents flowing through the ground connections can give rise to noise voltages This is especially a problem with signal frequency ground currents Experiment Detector Noise Source In this illustration the detector is measuring the signal relative to a ground far from the rest of the experiment The experiment senses the detector signal plus the voltage due to the noise source s ground return current passing through the finite resistance of the ground between the experiment and the detector The detector and the experiment are
14. and listen only RS 232 interface lines are provided for remote instrument control These lines are optically isolated to reduce signal interference Digital noise is eliminated by shutting down the processor clock when not executing a front panel button press or an RS 232 command Internal sealed lead acid batteries provide up to 15 hours of line independent operation Rear panel banana jacks provide access to the internal Operation and Controls regulated power supplies or batteries for use as a voltage source Use this procedure as a guick orientation to the instrument s features and capabilities If you encounter problems read the detailed discussions on operation 1 Make sure that the correct line voltage has been selected on the rear panel power entry module 2 With the unit s power switch OFF hold the FILTER RESET key down and turn the unit ON This will return all instrument settings to their default state 3 Select a filter from the FILTER TYPE menu Then use the up down arrows of the FILTER FREQ menu to choose the filter 3 dB points 4 Ifan input offset current is desired choose a current level from the INPUT OFFSET menu with the up down arrow keys The current will be applied when the ON led is lit 5 When the bias voltage is off the amplifier input is a virtual null To set a bias voltage use the up down arrow keys of the BIAS VOLTAGE menu The test point will always reflect the selecte
15. attenuation of the signal that occurs when the filter capacitance forms a divider with the input capacitance of the multiplexers DG444 U205D U206C is used to bypass the filter sections entirely and U206A U206B is used to reset the filter stages by discharging them through R228 R329 U201 U305 is the second third gain stage with a fixed gain of 5 The input attenuator U205 U304 allows setting the gain of these stages to 1 2 or 5 under processor control OUTPUT STAGES The next gain stage consists of op amp U402 which is configured as a non inverting amplifier with a gain of 5 U401 is a DG444 that again serves to switch the input attenuation of this stage for overall gains of 1 2 or 5 Additionally output offset adjustment is provided by this stage U405B half of an AD7528 dual 8 bit DAC is used to provide a 5 volt offset voltage at the inverting input of U402 Following amplifier U402 is the other half of the 8 bit DAC U405A which along with op amp U404 forms a digital gain vernier This vernier is used in calibration to compensate for gain variances that occur with configuration changes such as input coupling and filter settings This DAC also provides the front panel uncal gain vernier function The final gain stage consists of U403 and output buffer U406 configured for a gain of 5 and with input attenuator U409 to select overall gains of 1 2 or 5 The LM6321 U406 provides the output drive c
16. filter 3dB point n ranges from 0 0 03Hz to 15 1 MHz See table below HFRO HFRQn Sets the value of the highpass filter 3dB point n ranges from 0 0 03Hz to 11 10 kHz See table below n filter frequency 0 0 03 Hz 1 2 0 1 0 3 Hz 3 4 1 3 Hz 5 6 10 30 Hz 7 8 100 300 Hz 9 10 1 3 kHz 11 12 10 30 kHz 13 14 100 300 kHz 15 1 Mz ROLD Resets the filter capacitors to clear an overload condition Other commands GNMDn Sets the gain mode of the amplifier n gain mode 0 Low Noise 1 High Bandwidth 2 Low Drift INVT n Sets the signal invert sense 0 non inverted 1 inverted BLNK n Blanks the front end output of the amplifier 0 no blank 1 blank RST Resets the amplifier to the default settings 11 Programming Examples PROGRAMMING EXAMPLES Program Example 1 IBM PC BASIC via RS232 In this example the IBM PC s COM2 serial port is used to communicate with the SR570 The program sets up the SR570 for a typical measurement 10 Example program to set up for a measurement This 20 program uses IBM Basic and communicates via the COM2 RS 232 port 30 40 50 setup COM2 for 9600 baud no parity 8 data bits 2 stop bits ignore cts dsr and cd 60 70 OPEN COM2 9600 N 8 2 CS DS CD AS 1 80 90 PRINT 1 clear COM2 100 110 PRINT 1 RST reset SR570 to the default settings 120 PRINT 1 SENS22 SUCM0 set the sensitivity to 20 wA V calibrated 130 PRINT FI
17. grounded at different places which in this case are at different potentials Cures for ground loop problems include 1 Grounding everything to the same physical point 2 Using a heavy ground bus to reduce the resistance of ground connections 3 Removing sources of large ground currents from the ground bus used for small signals Microphonics Not all sources of noise are electrical in origin Mechanical noise can be translated into electrical noise by microphonic effects Physical changes in the experiment or cables due to vibrations for example can result in electrical noise over the entire frequency range of the amplifier For example consider a coaxial cable connecting a detector to a amplifier The capacitance of the cable is a function of its geometry Mechanical vibrations in the cable translate into a capacitance that varies in time typically at the vibration frequency Since the cable is governed by Q CV taking the derivative we have c ydC dQ dt dt dt Mechanical vibrations in the cable which cause a dC dt will give rise to a current in the cable This current affects the detector and the measured signal Some ways to minimize microphonic signals are 1 Eliminate mechanical vibrations near the experiment 2 Tie down cables carrying sensitive signals so they cannot move 3 Use a low noise cable designed to reduce microphonic effects Thermocouple effects The emf created by junctions b
18. level is set by the up down arrows in the bias voltage section of the front panel The up arrow increases the voltage towards 5V and the down arrow decreases the voltage towards 5V To enable the bias voltage simply push the button directly below the bias ON LED The selected voltage can be monitored at the TEST point with a DC voltmeter whether the bias voltage is turned on or not Input Offset Current The SR570 can provide a DC current offset to suppress any background currents at the input The offset range can be changed from 1 pA to 5 mA both positive and negative in discrete increments Use the up down arrow keys in the Input Offset section to change the current level In addition to these fixed settings the user may specify arbitrary currents through the UNCAL feature To set an uncalibrated offset current the user must press both up and down buttons simultaneously lighting the UNCAL LED In this mode by pressing the up or down pushbuttons the user may reduce the calibrated current in roughly 0 1 increments from 100 down to 0 of the selected offset value In contrast to other front panel functions when in UNCAL the instrument s key repeat rate will start slowly and increase to a limit as long as either button is depressed Simultaneously pressing both Offset buttons once again will restore the unit to the previously calibrated current setting and turn off the UNCAL LED The sign of the current is set with the butto
19. the default settings will be restored Status The INPUT and OUTPUT overload LEDs indicate a signal overload This condition can occur when a signal is too large or the dynamic reserve is too low Reducing the sensitivity reducing the input signal and or switching to the HIGH BW setting should remedy this condition An INPUT overload indicates a voltage greater than 7V is present before the filter section while an OUTPUT overload indicates an overload after the filters The ACTIVE LED indicates communication activity via the SR570 s optoisolated RS 232 port The ERROR LED indicates that the SR570 has received an unknown or improperly worded command The error LED will remain lit until a valid command is issued Please refer to the Remote Programming section for further details on controlling the instrument via RS 232 The BLANK LED indicates that the optoisolated BLANK input on the rear panel of the SR570 is active The SR570 responds to a blanking input by internally grounding the amplifier signal path after the front end and before the first filter stage The TOGGLE LED indicates that the optoisolated TOGGLE input on the rear panel of the SR570 is active The SR570 responds to a toggle input by toggling the polarity of the INVERT function LINE FUSE 1A 100 120VAC or 1 2A 220 240VAC amp SRS STANFORD RESEARCH SYSTEMS MADE IN U S A WN S TTL HIGH TTL HIGH WRO TO TOGGLE TO BLANK INPUT CHARGER STATUS INPUT
20. the original packing materials are not available wrap the instrument in polyethylene sheeting or eguivalent and place in a strong box cushioning it on all sides by at least three inches of high density foam or other filler material USE IN BIOMEDICAL APPLICATIONS Under certain conditions the SR570 may prove to be unsafe for applications involving human subjects Incorrect grounding component failure and excessive common mode input voltages are examples of conditions in which the instrument may expose the subject to large input currents Therefore Stanford Research Systems does not recommend or approve the SR570 for such applications WARNING REGARDING USE WITH PHOTOMULTIPLIERS The front end amplifier of this instrument is easily damaged if a photomultiplier is used improperly with the amplifier When left completely unterminated a cable connected to a PMT can charge to several hundred volts in a relatively short time If this cable is connected to the inputs of the SR570 the stored charge may damage the front end op amps To avoid this problem always connect the PMT output to the SR570 input before turning the PMT on ACCESSORIES FURNISHED Power Cable Operating Manual ENVIRONMENTAL CONDITIONS OPERATING Temperature 10 C to 40 C Relative Humidity lt 90 Non condensing NON OPERATING Temperature 25 C to 65 C Non condensing WARNING REGARDING BATTERY MAINTENANCE Batteries used in this instr
21. while dead The internal battery charging circuitry of the SR570 will automatically charge dead batteries at a guick rate until they are approximately 80 charged The charge rate is then lowered to a level that is safe for maintaining the batteries During AC operation the batteries will be in this maintain charge condition indefinitely and will suffer no degradation from prolonged charging The sealed lead acid batteries used in the SR570 differ in this respect from nickel cadmium batteries which behave in exactly the opposite manner The sealed lead acid batteries will provide the longest service life if they are not allowed to discharge too deeply and if they are charged immediately after use Battery Care WARNING For safety reasons as with all rechargeable batteries the chemical recombination processes within the cells reguire that the batteries be allowed to vent non corrosive gases to the atmosphere Always use the batteries in an area with adeguate ventilation With all instruments powered by rechargeable batteries the user must take some precautions to ensure long battery life Understanding and following the precautions outlined below will result in a long operating life for the batteries in the SR570 The SR570 s internal lead acid batteries will have a variable service life directly affected by the number of discharge cycles depth of discharge and ambient temperature The user should follow these simple guideli
22. 0 200 10K 10K SR570 MAIN 2N3904 MTP25N05 MPS2907A MTP20P06 MTP5N05 4 99K 4 99K 10 0K 4 99K 5 11K 5 11K 5 11K 4 99K 5 11K 5 11K C Diode Diode Diode Diode Relay Relay Relay Relay Relay Relay Relay Relay Relay Res Network SIP 1 4W 290 Isolated Resistor Network SIP 1 4W 2 Common Pot Multi Turn Trim 3 8 Sguare Top Ad Pot Multi Turn Trim 3 8 Square Top Ad Pot Multi Turn Trim 3 8 Square Top Ad Pot Multi Turn Trim 3 8 Square Top Ad Pot Multi Turn Trim 3 8 Square Top Ad Pot Multi Turn Trim 3 8 Square Top Ad Printed Circuit Board Transistor TO 92 Package Voltage Reg TO 220 TAB Package Transistor TO 92 Package Voltage Reg TO 220 TAB Package Voltage Reg TO 220 TAB Package Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor D 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 R118 R119 R 120 R 121 R 122 R 123 R 125 R 126 R 127
23. 0012 306 3 00012 306 3 00012 306 3 00885 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00885 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00885 306 GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN YELLOW GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN YELLOW GREEN GREEN GREEN GREEN GREEN GREEN GREEN GREEN YELLOW LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectang
24. 340 74HC4053 Integrated Circuit Thru hole Pkg U111 3 00536 340 AD706 Integrated Circuit Thru hole Pkg U112 3 00195 340 CA3082 Integrated Circuit Thru hole Pkg U 113 3 00195 340 CA3082 Integrated Circuit Thru hole Pkg U 201 3 00382 340 OPA37 Integrated Circuit Thru hole Pkg U 202 3 00270 340 74HC4051 Integrated Circuit Thru hole Pkg U 203 3 00270 340 74HC4051 Integrated Circuit Thru hole Pkg U 204 3 00090 340 LF411 Integrated Circuit Thru hole Pkg U 205 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 206 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 301 3 00270 340 74HC4051 Integrated Circuit Thru hole Pkg U 302 3 00270 340 74HC4051 Integrated Circuit Thru hole Pkg U 303 3 00090 340 LF411 Integrated Circuit Thru hole Pkg U 304 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 305 3 00382 340 OPA37 Integrated Circuit Thru hole Pkg U 401 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 402 3 00297 340 LT1028 Integrated Circuit Thru hole Pkg U 403 3 00382 340 OPA37 Integrated Circuit Thru hole Pkg U 404 3 00090 340 LF411 Integrated Circuit Thru hole Pkg U 405 3 01017 340 TLC7528CN Integrated Circuit Thru hole Pkg U 406 3 00383 340 LM6321 Integrated Circuit Thru hole Pkg U 407 3 00087 340 LF347 Integrated Circuit Thru hole Pkg U 408 3 00143 340 LM393 Integrated Circuit Thru hole Pkg U 409 3 00371 340 DG444 Integrated Circuit Thru hole Pkg U 410 3 00143 340 LM393 Integrated Circuit Thru hole
25. 4 00032 401 4 00092 401 4 00056 401 4 00034 401 4 00034 401 4 0003 1 401 4 00192 407 4 00192 407 4 00192 407 4 00155 407 4 00787 407 4 00081 401 4 00081 401 4 00076 401 4 00081 401 4 00076 401 1 0M 249 15K 15K 2 87K 249 220K 10M 10M 768K 10 7K 17 8K 30 9K 174K 150K 21 5K 12 7K 8 25K 806K 1 0K 75 0K 249 249 2 15K 2 15K 3 32K 1 0M 100K 100K 56K 22 10K 10K 100 49 9K 49 9K 49 9K 150K 768 470 470 390 470 390 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1
26. 4 00148 407 12 1K R 224 4 00519 407 4 75K R 225 4 00135 407 1 50K R 226 4 00067 401 3 9K R 227 4 00067 401 3 9K R 228 4 00031 401 100 R 229 4 00305 401 43K R 301 4 00516 407 143K R 302 4 00164 407 20 0K R 303 4 00516 407 143K R 304 4 00168 407 22 6K R 305 4 00516 407 143K R 306 4 00168 407 22 6K R 307 4 00600 407 15 8K R 308 4 00168 407 22 6K R 309 4 00600 407 15 8K R 310 4 00600 407 15 8K R311 4 00600 407 15 8K R312 4 00030 401 10 R 313 4 00165 407 200 R 314 4 00030 401 10 R 315 4 00433 407 931 R 316 4 00030 401 10 R 317 4 00030 401 10 R 318 4 00296 407 604 R 319 4 00165 407 200 R 320 4 00165 407 200 R 321 4 00600 407 15 8K R 322 4 00600 407 15 8K R 323 4 00148 407 12 1K R 324 4 00519 407 4 75K R 325 4 00135 407 1 50K R 326 4 00067 401 3 9K R 327 4 00067 401 3 9K R 328 4 00030 401 10 R 329 4 00031 401 100 R 330 4 00065 401 3 3K R 401 4 00296 407 604 Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor Resistor D 7 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8
27. 6 C 827 C 828 C 829 C 830 C 831 C 832 D201 D 202 D 203 D 204 D 301 D 302 D 303 D 304 D 401 D 402 D 403 D 404 D 405 D 406 D 407 D 408 D 409 D410 D 501 D 502 D 503 D 505 D 701 D 702 D 703 D 704 D 705 D 706 D 707 D 708 D 709 D711 D712 D713 D 801 D 802 5 00100 517 5 00100 517 5 00023 529 5 00023 529 5 00023 529 5 00100 517 5 00100 517 5 00023 529 3 00368 301 3 00368 301 3 00203 301 3 00203 301 3 00368 301 3 00368 301 3 00203 301 3 00203 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00226 301 3 00004 301 3 00226 301 3 00009 303 3 00011 303 3 00062 340 3 00226 301 3 00226 301 3 00306 340 3 00198 301 3 00391 301 3 00391 301 3 00226 301 3 00004 301 Parts List 2 2U Capacitor Tantalum 35V 20 Rad 2 2U Capacitor Tantalum 35V 20 Rad 1U Cap Monolythic Ceramic 50V 20 Z5U 1U Cap Monolythic Ceramic 50V 20 Z5U 1U Cap Monolythic Ceramic 50V 20 Z5U 2 2U Capacitor Tantalum 35V 20 Rad 2 2U Capacitor Tantalum 35V 20 Rad 1U Cap Monolythic Ceramic 50V 20 Z5U 1N753A Diode 1N753A Diode 1N5711 Diode 1N5711 Diode 1N753A Diode 1N753A Diode 1N5711 Diode 1N5711 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148 Diode 1N4148
28. ACK BANANA JACK BANANA JACK D 14 Parts List 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 Z0 0 00325 032 0 00327 050 0 00328 050 0 00329 050 0 00330 050 0 00333 052 0 00334 052 0 00350 053 0 00355 050 0 00466 050 0 00523 048 0 00524 048 0 00666 050 0 00667 050 1 00124 178 1 00125 179 1 00126 176 1 00127 177 1 00194 171 4 00541 435 5 00027 503 6 00004 611 6 00050 612 6 00074 611 7 00201 720 7 00460 709 7 00462 709 7 00463 720 7 00464 720 7 00795 720 7 00796 720 9 00267 917 9 00792 917 2 520182 2 8 218 WHITE 8 18 RED 8 18 BLACK 5 1 2 18 6 22 1 3 4 22 2 1 4 24 20 18 RED 23 18 BLACK 5 5 8 18 8 1 4 18 23 18 WHITE 20 18 WHITE Termination Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 22 UL1007 Wire 22 UL1007 Wire 24 UL1007 Strip 1 4x1 4 Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1015 Strip 3 8 x 3 8 No Tin Wire 18 UL1015 Strip 3 8 x 3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin Wire 18 UL1007 Stripped 3 8x3 8 No Tin 4 PIN Connector Housing Plug 4 PIN Connector Housing Receptacle 062 DIAM Terminal Male 062 DIAM Terminal Female 28 CON DIL Cable Assembly Ribbon 130V 1200A Varistor Zinc Oxi
29. CHARGE MAINTAIN Operation and Controls SWITCHED AMPLIFIER POWER I ou lt 200mA 12VDC AMP GND 12VDC o9o c CHASSIS GND SWITCHES OPEN IF OFF OR 0 7VDC TTL INPUTS TOGGLE BLANK ee WARNING No v RS232 DCE G9600 BAUD Figure 3 SR570 Rear Panel REAR PANEL OPERATING SUMMARY The SR570 rear panel is pictured in Figure 3 Various interface and power connectors are provided along with fuses and charger status LEDs AC Power Input The power entry module contains the receptacle for the AC line cord and fuse The line fuse should be a 1 A slo blo for 100 120 VAC operation or a 1 2 A slo blo for 220 240 VAC operation Amplifier Power Output The 12 V 12 V and AMP GROUND banana jacks provide external DC power up to 200 mA for use as a bias source referenced to the amplifier s floating power supplies The CHASSIS GROUND banana jack is provided to allow the amplifier s ground to be referenced to the chassis If the unit is connected to an AC power source via a three prong grounding plug the chassis ground is connected to the AC line ground conductor Battery Charger Two 3 A slo blo fuses protect the battery supply and charging circuitry If these fuses are blown battery power will be unavailable and charging of the batteries will not be possible When both the positive and negative supply batteries are dead the red CHARGE LED will be on brightly and the batteries will be
30. D6 01 05 D6 01 05 D6 01 05 D6 01 05 74HC164 74HC164 74HC164 74HC164 74HC164 74HC164 74HC164 6J4 TRANSCOVER 4 40 HEX 4 40 KEP 3 16 X5 16 NYLN 4 40X3 16 M F 4 4 SPLIT 1 1 2 18 2 1 4 24 3 1 2 24 4 24 8 1 2 24 GROMMET2 4 SHOULDER 6 32X3 8PF 4 40X1 1 2PP 1 32 4 SHOULD F1404 4 40X3 8PF TO 220 4 40X1 2 PP 6 1 2 22 BL 4 24 BLK 1 8 ADHES TAPE FUSEHOLDER 8 18 8 SS BLACK RED GREEN WHITE Switch Momentary Push Button Switch Momentary Push Button Switch Momentary Push Button Switch Momentary Push Button Switch Momentary Push Button Switch Momentary Push Button 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 Power Entry Hardware Power Entry Hardware Nut Hex Nut Kep Spacer Standoff Tie Washer Split Parts List 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 Wire 24 UL1007 Strip 1 4x1 4 Tin Grommet Washer nylon Screw Flathead Phillips Screw Panhead Phillips Washer nylon Power Button Screw Black All Types Insulators Screw Panhead Phillips Wire 22 UL1007 Wire 24 UL1007 Strip 1 4x1 4 Tin Hardware Misc Hardware Misc Washer Flat BANANA JACK BANANA J
31. D703 are blocking diodes for the charging circuits while not charging and D707 and D708 are clamps to guard against battery polarity reversal U708 and U709 are LP365 micropower comparators that monitor the battery voltage A resistive divider chain sets the four trip points for each comparator D709 provides a stable 2 5 volt reference against which levels are compared For each battery three level indications are provided and are decoded by multiplexer U704 The trip level is 14 5 volts The trip outputs control the state of U703 and switch the battery charge voltage settings The low level is 11 3 volts and activates the front panel LOW BATT indicator R730 provides some level hysteresis for the low battery indication to prevent oscillation around the trip point The dead level is 10 7 volts and is used to disconnect the load from the batteries before they are damaged by an excessively deep discharge Q701 and Q703 are power MOSFET switches used to disconnect battery power from the amplifier Dead level hysteresis is provided by R724 R731 and D711 provide un interrupted battery power to the system RAM so that stored instrument settings are retained when the power is switched off POWER REGULATORS The 5 V and 10 V supplies are produced with three terminal regulators U801 and U802 respectively The 10 V supply is constructed of op amp U803 and Q801 a N channel MOSFET as the pass element The 10 V supply serves as the r
32. Frequency Hz APPENDIX C CAPACITANCE EFFECTS Feedback Capacitance All op amps have some parasitic capacitance associated with their inputs and output Together with the capacitance of the source being measured and the resistors in the amplifier circuit the parasitics affect the freguency response of the amplifier Typically this effect is manifested as overshoot or ringing in the sguare wave response of an instrument One way to compensate for these unwanted effects is to put a capacitor in the feedback loop of the op amp The value of this capacitor is chosen to optimize the freguency response of the circuit In the SR570 we have implemented a variable feedback capacitance across the amplifier which can be controlled from the instrument s front panel To get the best freguency response the FREO COMP can be adjusted to give a clean sguare wave output with a sguare wave input It is important that the source resistance and capacitance be the same for the adjustment procedure as it will be for the actual measurement to get the best results CG FREQ COMP Current Source I Input Capacitance One of the most important differences between using a current amp instead of a voltage amp is the effect that input capacitance has on the noise performance of the instrument In the figure above we see that in the traditional configuration of a current amplifier with a virtual null at the input and an essentially infi
33. INSPECT THE BATTERIES Batteries used in this instrument are sealed lead acid batteries With usage and time these batteries can leak Always use and store this instrument in the feet down position To prevent possible damage to the circuitboard it is recommended that the batteries be periodically inspected for any signs of leakage PROGRAMMING DETAILED COMMAND LIST REMOTE PROGRAMMING Introduction The SR570 is eguipped with a standard DB 25 RS 232 connector on the rear panel for remote control of all instrument functions The interface is configured as listen only 9600 baud DCE 8 data bits no parity 2 stop bits and is optically isolated to prevent any noise or grounding problems The ERROR LED on the front panel will light if the SR570 receives an unknown or improperly worded command The LED will remain lit until a proper command is received Data are sent to the instrument on pins 2 and 3 which are shorted together The data flow control pins 5 6 8 20 are shorted to each other The ground pins 1 amp 7 are connected to each other but optically isolated from the amplifier circuit ground and the chassis ground Command Syntax The following is a list of commands used to program the SR570 All RS 232 commands consist of four letter codes followed in most cases by an integer value n Commands must end with a carriage return and line feed lt CR gt lt LF gt 10 Sensitivity control commands SENS n Se
34. MODEL SR570 Low Noise Current Preamplifier RS Stanford Research Systems 1290 D Reamwood Avenue Sunnyvale California 94089 Phone 408 744 9040 Fax 408 744 9049 email infor thinkSRS com www thinkSRS com Copyright O 1997 2005 2015 by SRS Inc All Rights Reserved Revision 1 7 08 2015 Table of Contents Condensed Information Safety and Use Accessories Furnished Environmental Conditions Symbols Specifications Verifying Specifications Abridged Command List Operation and Controls Introduction Overview Ouick Start Instructions SR570 Block Diagram Front Panel Operation Power Input Defaults Bias Voltage Input Offset Current Invert Filters Gain Mode Sensitivity Output Filter Reset Status Rear Panel Operation AC Power Input Amplifier Power Output Battery Charger Blanking Input Toggling Input RS 232 Interface Battery Care and Usage Recharging Battery Care ANNAA HB FF ss m 9My0ocece N ee O lt J lt J J oo SR570 Low Noise Current Preamplifier Programming Remote Programming Introduction Command Syntax Detailed Command List Sensitivity Control Input Offset Current Control Bias Voltage Control Filter Control Other Commands Programming Examples BASIC Microsoft C SR570 Circuitry Circuit Description Front End Filters and Gain Output Stages Overload Detection Microprocessor Battery Charger and Preregs Power Regulators Rear Panel Inter
35. OLTAGE SELECTION When the AC power cord is connected to the unit and plugged into an AC outlet the unit automatically switches the amplifier power source from internal battery operation to line operation The internal batteries are charged as long as AC power is connected The SR570 operates from a 100V 120V 220V or 240V nominal AC power source having a line freguency 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 is visible Conversion to other AC input voltages reguires a change in the fuse holder voltage card position and fuse value Disconnect the power cord open the fuse holder cover door and rotate the fuse pull lever to remove the fuse Remove the small printed circuit board and select the operating voltage by orienting the printed circuit board so the desired voltage is visible Push the card firmly into its slot Rotate the fuse pull lever back to its normal position and insert the correct fuse into the fuse holder LINE FUSE Verify that the correct line fuse is installed before connecting the line cord For 100V 120V use a 1 Amp fuse and for 220V 240V use a 1 2 Amp fuse LINE CORD The SR570 has a detachable three wire power cord for connection to an AC power source and to iii a protective ground The exposed metal parts of the instrument are connected to
36. Resistor Carbon Film 1 4W 5 Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM Resistor Metal Film 1 8W 1 50PPM 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 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 D 8 Parts List Parts List 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 723 R 724 R 725 R 726 R 727 R 728 R 729 R 730 R 731 R 801 R 802 R 803 R 804 R 805 R 806 R 807 R 808 R 809 R 810 R 811 R 812 R 813 R 814 R 815 R 816 4 00022 401 4 00169 407 4 00042 401 4 00042 401 4 00376 407 4 00169 407 4 00058 401 4 00035 401 4 00035 401 4 00612 407 4 00278 407 4 00576 407 4 00386 407 4 00614 407 4 00155 407 4 00363 407 4 00383 407 4 00615 407 4 00207 407 4 00021 401 4 00203 407 4 00169 407 4 00169 407 4 00582 407 4 00582 407 4 00309 407 4 00022 401 4 00032 401
37. SR and CD are tied to DTR See the Remote Programming section for more info BATTERIES AND P E M The batteries used in the SR570 are of sealed lead acid construction There are three 12 volt 1 9 amp hour batteries two of which serve as the positive power supply and one of which serves as the negative power supply Powering the SR570 alone battery life should be 10 15 hours The batteries should last for more than 1000 charge discharge cycles provided the guidelines under the usage section are followed Two 3A slo blo fuses on the rear panel protect the battery supplies and amplifier against excessive currents The power entry module P E M contains the AC line fuse RFI filter and voltage selection card To change the operating voltage of the unit the voltage selector printed circuit card must be pulled out and reinserted into the P E M with the desired operating voltage visible FRONT PANEL The front panel contains the pushbuttons LED indicators and serial shift registers The front panel pushbuttons are decoded in a 3 x 5 matrix fashion The front panel LEDs are controlled by shift registers U1 through U7 which allow the 7 eight bit control bytes to be serially shifted in one bit at a time The red overload LEDs are controlled directly from the output of the overload comparator The LINE LOW BATT BLANK and TOGGLE LEDs are also controlled directly from their respective main board circuits The FREQ COMP
38. W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM R 402 R 403 R 404 R 405 R 406 R 407 R 408 R 409 R 410 R411 R 412 R 413 R 414 R 415 R 416 R 417 R 418 R 419 R 420 R 421 R 422 R 423 R 424 R 425 R 426 R 427 R 428 R 429 R 430 R 431 R 432 R 433 R 434 R 435 R 436 R 437 R 440 R 441 R 501 R 502 R 503 R 701 R 702 R 703 4 00165 407 4 00165 407 4 00030 401 4 00030 401 4 00325 407
39. apability for the 50 ohm output OVERLOAD DETECTION The overload detectors constantly monitor the I to V amplifier output front end output filter 1 output U402 after the second filter output and final stage output for excessive signal levels Comparators U408 and U410 compare both positive and negative signal excursions against a 5 volt reference and light the front panel output or input overload indicators if any levels are excessive MICROPROCESSOR The system processor U503 is a CMOS Z80 processor running at 4 MHz The system clock consists of Schmitt trigger U506A and an R C network The oscillator is designed so that latch U508A can shut down the clock oscillator completely thereby disabling all digital circuits in the amplifier so that no digital noise will be present The processor and clock only run when a front panel key is pressed and instrument settings are to be changed or while there is activity on the RS 232 port The SR570 uses a 8 K x 8 CMOS EPROM U504 containing system firmware and calibration bytes along with a2 K x 8 CMOS RAM U505 which is battery backed up at all times to retain instrument settings U507 generates port strobes for system IO and U510 provides a buffered data bus The buffered data bus is active only during IO instructions to keep digital noise in the amplifier to a minimum while the processor is running U601 through U607 are control latches providing the 56 DC control lines tha
40. ayed by three indicator LEDs LOW NOISE HIGH BW and LOW DRIFT For a given gain setting the LOW NOISE mode allocates gain toward the front end in order to quickly lift low level signals above the instrument s noise floor The LOW DRIFT mode allocates the gain just as the LOW NOISE mode except the front end op amp is switched to one with a very low input bias current for high sensitivity settings The HIGH BW setting allocates more gain toward the output stages after the filters Since smaller values of feedback resistance are needed for the front end gain the bandwidth of the amplifier is increased over that of the other two settings This also prevents signals which are attenuated by the filters from overloading the amplifier See Appendix B for further details of op amp selection for the different gain modes Operation and Controls Sensitivity The instrument s sensitivity is increased or decreased using the SENSITIVITY section pushbuttons Sensitivity settings from 1 pA V to 1 mA V are available and are displayed as the product of a factor 1 2 or 5 and a multiplier x1 x10 x100 with the appropriate units In addition to these fixed settings the user may specify arbitrary sensitivities through the UNCAL feature To set an uncalibrated or arbitrary sensitivity the user must press both up and down buttons simultaneously lighting the UNCAL LED In this mode by pressing the up or down pushbuttons the user may reduce the ca
41. banana plug connectors Two configurable low or high pass filters 6 or 12 dB octave The 3 dB point of each filter is settable in a 1 3 10 sequence from 0 03 Hz to 1 MHz for lowpass filters and 0 03 Hz to 10 kHz for highpass filters Long time constant filters may be reset with a front panel button Most of the gain is allocated in the front end of the instrument to decrease the magnitude of Johnson noise at the output Front end gain is reduced to increase the amplifier s frequency response A very low input bias current amplifier is used for more accurate measurements on the higher sensitivity ranges 0 5 of output 10 mV 50 mV High BW 25 C 100 pA V 1 mA V sensitivities See Table 1 5 V into a high impedance load 50W output impedance 2 V peak to peak at 1 MHz 12 VDC 200 mA referenced to amplifier ground Listen only 9600 Baud DCE 8 bit no parity 2 stop bits All instrument functions may be controlled PC compatible serial connector Optically isolated TTL inputs to set gain to zero blanking or to invert gain polarity toggling 0 to 50 C 100 120 220 or 240 VAC 50 60 Hz from line Internal batteries provide up to 15 hours between charges Batteries are charged while connected to the line Line power required is 30 watts while batteries are charging and 6 watts once fully charged 8 3 x 3 5 x 13 0 Rack mounting hardware available 15 Ibs including batteries 1 year v
42. charging at a fast rate When the batteries approach a fully charged condition the charging current will be reduced to a trickle charge to maintain the batteries Because the batteries charge at different rates the indicators on the rear panel can reflect the charge status of the positive and negative batteries independently When one set of batteries switches to the MAINTAIN mode the red CHARGE LED will be reduced to half brightness and the yellow MAINTAIN LED will turn on at half brightness When both batteries switch to MAINTAIN the red CHARGE LED will turn off and the yellow MAINTAIN LED will be on full brightness Operation and Controls Blanking Input The BLANK input accepts a TTL level signal and grounds the amplifier signal path after the front end for as long as the input is held high The response time of the blanking input is typically 5 us after the rising edge turn on and 10 us after the falling edge turn off Toggling Input The TOGGLE input accepts a TTL level signal and toggles the invert function as long as the input is held high The response time of the toggling input is typically 5 us after the rising edge turn on and 10 us after the falling edge turn off The Toggle input can be used for synchronous detection of an AC signal If the signal is toggled at the freguency of interest in phase with the signal being measured with a TTL sguare wave then a DC component will be produced that is proport
43. d above were measured with an input capacitance of 100 pF Higher input capacitance will lead to a decrease in performance Lets look at a simple example to illustrate some of these principles To test the gain and freguency response of the instrument at 1 nA V sensitivity we might use a 1 V RMS sine wave across a GO resistor and through 1 meter of coax cable into the amplifier front end The cable itself has about 100 pF of input capacitance to ground Any other sources of capacitance will only increase this value and degrade the noise performance of the instrument The 1 GO resistor while a good current source at DC will be less accurate at higher freguencies due to capacitance of the resistor A typical resistor will have about 0 1 pF capacitance which will provide a parallel impedance of 1 GO at about 1 6 kHz Since this effect provides an alternate path for current the actual current to the amplifier will be increased and may be misinterpreted as a peaking in the frequency response of the amplifier near 1 kHz These are only a few examples of what can go wrong when making a measurement It is very important that the current source be completely characterized before performing specification verification ix Specifications Keep in mind the following items when trying to verify specifications or when making sensitive measurements 1 Make sure the source impedance is greater than the inverse of the sensitivity e g wi
44. d bias voltage but the bias will only be applied when the ON led is lit 6 Set the sensitivity and gain mode to the desired settings for the the amplitude of the signal to be measured 7 Adjust the FREQ COMP pot near the input BNC to compensate the amplifier s frequency response for any input capacitance An external square wave signal from the source under test can be used for precise calibration 8 Connect the signal to be measured to the INPUT BNC The signal will be converted to a voltage filtered and amplified The amplifier output voltage can be accessed from the OUTPUT BNC connector Operation and Controls Front End Input Amplifier Filter 1 PAP LPF N Offset Current 0 03Hz 1MHz Bias Voltage GND Signal Filter 2 Output Buffer Amplifier Amplifier 7 HPF TEN Output r 7 0 03Hz 1MHz 500 9 GND Microprocessor G Blank Gyn Toggle Input Output Strobes amp Latches Power Supply Ext Power Amp Ground Qptolsolated RS 232 Interface Chassis Ground Figure 1 SR570 Block Diagram Operation and Controls ODEL SR570 LOW NOIS GAIN MOD LOW NOISE HIGH BW LOW DRIFT TTL CONTROL BLANK TOGGLE INTERFACE ERROR Figure 2 SR570 Front Panel FRONT PANEL OPERATING SUMMARY The operation of the SR570 Low Noise Preamplifier has been designed to be as simple and intuitive as possible The effect
45. d without the bias Op amp input offset voltages can be nulled with pots P101 and P102 To null out the offset for U108 Low Noise input attach a shielded open to the input of the SR570 and select the 1 mA V sensitivity The unit should otherwise be in the default start up mode Adjust pot P102 to give 0 volts at U108 pin 6 To adjust the Low Drift mode op amp repeat the procedure as above with Low Drift mode 17 and 1 pA V sensitivity selected adjusting P101 to give 0 volts at U107 pin 6 FRONT END REPLACEMENT The most commonly damaged components are the front end input op amps U107 Analog Devices AD546 and U108 Analog Devices AD743 Both are located under the metal shield near the front of the PCB If the unit is constantly overloaded or doesn t amplify any signals chances are one of these op amps has been damaged Switching between gain modes while referring to the op amp allocation table in Appendix B should determine which device needs to be replaced When replacing an op amp make sure that all eight pins make firm contact in the socket and that the orientation for pin 1 is observed match the notch on the IC with the notch on the socket After replacement the op amp input offset voltage should be nulled out using either P101 or P102 cf Calibration BATTERY REPLACEMENT After three to five years or about 1000 charge discharge cycles the sealed lead acid batteries degrade When the battery op
46. de Nonlinear Resistor 01U Capacitor Ceramic Disc 50V 20 Z5U 1A 3AG Fuse GB1219 36 Battery 3A 3AG Fuse SR500 32 Fabricated Part SR570 Lexan Overlay SR570 Lexan Overlay SR570 4 amp 5 Fabricated Part SR570 6 Fabricated Part BATTERY PAN Fabricated Part BATTERY RETAINR _ Fabricated Part GENERIC Product Labels EC WARNING Product Labels Miscellaneous and Chassis Assembly Parts List R 124 R 128 U 504 Z0 Z0 Z0 Z0 Z0 4 00857 458 4 00864 458 3 00305 342 0 00150 026 0 00179 000 0 00180 000 0 00185 021 0 00204 000 1 0G 5W 200PPM 500M 3 4 WATT 27C64 255 4 40X1 4PF RIGHT FOOT LEFT FOOT 6 32X3 8PP REAR FOOT Resistor Metal Oxide Resistor Metal Oxide EPROM PROM I C Screw Black All Types Hardware Misc Hardware Misc Screw Panhead Phillips Hardware Misc D 15 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 Z0 0 00248 026 0 00315 021 0 00326 026 0 00471 021 7 00122 720 7 00217 735 7 00259 720 7 00260 720 7 00465 720 7 00466 720 10 32X3 8TRUSSP 6 32X7 16 PP 8 32X1 4PP 4 40X1 PP DG535 36 PS300 40 SR560 28 SR560 27 SR570 7 SR570 8 Screw Black All Types Screw Panhead Phillips Screw Black All Types Screw Panhead Phillips Fabricated Part Injection Molded Plastic Fabricated Part Fabricated Part Fabricated Part Fabricated Part D 16 Parts List
47. e and always use the shortest possible cable length Above the input BNC is the FREO COMP adjustment potentiometer This feature allows the user to compensate for any input capacitance by varying the capacitance across the front end amplifier feedback resistor In this way the amplifier bandwidth can be easily adjusted to compensate for source capacitance by measuring a sguare wave signal from the source of interest and using FREO COMP to optimize the output waveform See Appendix C for further discussion of the effects of source capacitance Defaults Any changes made to the front panel settings of the SR570 will be stored even when power is turned off as long as the batteries are hooked up To reset the SR570 to its default settings simply turn the power off and while depressing the FILTER RESET button turn the power on Alternatively removing Operation and Controls the batteries from an SR570 with no AC power connected will reset the unit to the default state The default settings are Sensitivity 1 uA V calibrated Invert off Input Offset 1 pA calibrated off Bias 0 V off Filters none Hi Freq 0 03 Hz Lo Freq 1 MHz Gain Mode Low Noise Bias Voltage In the default configuration the SR570 is a virtual null at the input BNC The bias voltage provides a variable 5V to 5V voltage 12 bit 1 22 mV resolution at the input This voltage can be used to bias a photodiode or similar device The voltage
48. eference for the 10 V supply through divider R809 and R810 The power output banana jacks on the rear panel J801 and J803 are connected to the pre regulated voltages after the power switch and before the regulators This output can provide up to 200 mA of power for use as an external bias source etc Under some conditions these jacks may be used to supply the unit with external DC power U506C and U506D generate the TTL level input to the processor to indicate when the unit is operating on the AC line Capacitors C801 through C811 are logic supply bypass capacitors distributed throughout the printed circuit board REAR PANEL INTERFACES Three optically isolated rear panel interfaces are provided on the SR570 The blanking input accepts a TTL level signal and opens the amplifier signal path before the front end differential amplifier for as long as the input is held high The toggling input also accepts a TTL level signal and toggles the invert status of the I to V amplifier output signal before the front end differential amplifier for as long as the input is held high The response time of both the blanking and toggling inputs is typically 5 us after the rising edge turn on and 10 us after the falling edge turn off The RS 232 interface allows calibration and control of the instrument at 9600 baud Data in and out on the connector are tied together 16 echoing data back to the sender Hardware handshaking lines CTS D
49. eration time shortens or if the unit stays very warm for more than a day after it is plugged into the line the batteries may require replacement The three batteries are a standard size which are available from several different distributors All are 12 VDC with a charge capacity of about 2 0 Amp hours and measure 7 02 X 1 33 X 2 38 Two of the batteries are wired in parallel to provide the high current required for the positive supply Take care to observe battery polarities when replacing FUSE REPLACEMENT There are three fuses on the back panel of the instrument The fuse located inside the power entry module will blow if the unit draws excessive line current The replacement should be a standard 1A slo blo fuse The other two fuses are in line with the batteries and are rated at 3 A These fuses will blow if the rear panel 12 VDC supplies are shorted or if excess current flows to or from the batteries 18 APPENDIX A Amplifier Noise Sources Input noise The input noise of the SR570 current amplifier varies depending upon the sensitivity setting On the 1 mA V setting the noise is dominated by the voltage noise of the op amps in the circuit Typically this figure is about 100 nV VHz which when divided by the 1 kQ feedback resistor gives a current noise of 100 pA VHz On the other hand the noise on the higher sensitivity ranges is dominated by the Johnson noise of the feedback resistor On the 1 nA V
50. etween dissimilar metals can give rise to many microvolts of slowly varying potentials This source of noise is typically at very low freguency since the temperature of the detector and experiment generally changes slowly This effect is large on the scale of many detector outputs and can be a problem for low freguency measurements especially in the mHz range Some ways to minimize thermocouple effects are 1 Hold the temperature of the experiment or detector constant 2 Use a compensation junction i e a second junction in reverse polarity which generates an emf to cancel the thermal potential of the first junction both held at the same temperature A 4 A few words about Baluns To reduce the effects of ground loops the SR570 has a balun BALanced UNbalanced common mode choke connected to the output stage This may be thought of as two wires wrapped about a magnetic core forming a pair of inductors One wire carries the output signal and the other the return forming essentially a differential signal which can pass through the balun with little to no attentuation over the SR570 s bandwidth Non differential common mode signals like ground loop pickup however are effectively blocked by the balun The degree of rejection varies with freguency and is determined by the choke inductance and the resistance of the windings The presence of the balun effectively breaks the ground loop which would have occurred if the
51. faces Batteries and P E M Front Panel Calibration amp Repair Calibration Front end Replacement Battery Replacement Fuse Replacement Appendices A Amplifier Noise Sources Input Noise Noise Sources Johnson Noise Shot Noise 10 10 10 10 10 11 11 11 12 13 SR570 Low Noise Current Preamplifier 1 f Noise Total Noise External Noise Sources Capacitive Coupling Inductive Coupling Ground Loops Microphonics Thermocouple Effects Baluns B Gain Allocation Front end Amplifier Op Amp Allocation Dynamic Reserve C Capacitance Effects Feedback Capacitance Input Capacitance Component Parts List Main Circuit PC Board Front amp Rear Panel PC Boards Miscellaneous Parts A 1 A 2 A 2 A 2 A 2 A 3 Schematic Circuit Diagrams Sheet No Input Stage Filter and Gain 1 Filter and Gain 2 Output Stage Microprocessor Section Digital I O amp Front Panel Control Battery Charger amp Preregulators Power Regs amp Rear Panel Conn Front Panel Rear Panel 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 ii SR570 Low Noise Current Preamplifier Safety and Preparation for Use WARNING Dangerous voltages capable of causing death are present in this instrument Use extreme caution whenever the instrument covers are removed 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 LINE V
52. he filter cutoff frequencies are controlled by the up down arrows in the FILTER FREQ section When the FILTER TYPE section is configured solely as high pass or low pass i ii iv and v the cutoff frequency is illuminated by one of sixteen LEDs in the range from 0 03 Hz to 1 MHz High pass filters are not available for the four highest freguency settings When the filter section is configured as band pass iii the cutoff freguencies are illuminated by two LEDs The lower freguency setting marks the cutoff for the high pass filter and the higher setting is the cutoff for the low pass filter To change the values of the bandpass cutoff freguencies use the up arrow button to change the lowpass cutoff and the down arrow to change the highpass cutoff If the displayed freguency is already at the highest or lowest possible choice then pushing the button again will cause the freguency to wrap around to the opposite extreme freguency In this case the two cutoffs can be set to the same freguency to provide a narrow bandpass The highpass frequency can never exceed the lowpass freguency When both filters are removed from the signal path vi all FREO LEDs are extinguished and the NONE LED is lit Gain Mode The allocation of gain throughout the instrument is set using the GAIN MODE pushbutton The gain mode feature controls the tradeoffs between dynamic reserve bandwidth and noise in the amplifier circuits The Gain Mode is displ
53. i Specifications Low Noise Mode High Bandwidth Mode APMRWRRU VINT MIS VT GaSe E Pe SAT We 3 I LEW 1 100 104 108 10 1 100 104 108 10 Freguency Hz Gain Nominal Gain dB Gain Nominal Gain dB Freguency Hz Amplifier Bandwidth for several sensitivity settings typical Low Noise Mode High Bandwidth Mode Current Noise Amps IHz Current Noise Amps IHz 100 1000 100 Frequency Hz Frequency Hz Current Noise as a function of Frequency for several sensitivity settings typical Note The amplifier bandwidth and noise data were taken with the front panel frequency compensation adjusted for flat frequency response over the widest frequency range with an input capacitance of 100 pF Either the bandwidth or the noise specification can be improved at the expense of response flatness vii Specifications Table 1 Temperature Coefficient Bandwidth 3 dB 1 Noise NHz Low Drift 11 28 C DC Input Sensitivity A V High BW Low Noise Low Noise High BW input offset C Impedance 10 3 1 0 MHz 1 0MHz 150pA 150 pA 0 01 9o 20 nA IO 10 4 1 0 MHz 500kHz 60pA 100 pA 0 01 2 nA 1Q 10 5 800 kHz 200kHz 2pA 60 pA 0 01 200 pA 100 Q 10 6 200 kHz 20 kHz 600 fA 2 pA 0 01 20 pA 100 Q 10 7 20 kHz 2 kHz 100 fA 600 fA 0 01 2 pA 10 KQ 10 8 2 kHz 200 Hz 60 fA 100 fA 0 01 400 fA 10 kQ 10 9 200 Hz 15 Hz 10 fA 60 fA 0 025 40 fA 1 MQ 10 10 100 Hz 10 Hz 5 fA 10 fA 0 025
54. ion of dynamic reserve is the ratio of the largest tolerable noise signal to the full scale signal expressed in dB For example if full scale is 5 uA then a dynamic reserve of 60 dB means noise as large B 1 as 5 mA 60 GB greater than full scale can be tolerated at the input without overload The problem with this definition is the word tolerable Clearly the noise at the dynamic reserve limit should not cause an overload anywhere in the instrument This is accomplished by adjusting the distribution of the gain To achieve high reserve the input signal gain is set very low so the noise is not likely to overload This means that the signal at the filter section is also very small The filters then remove the large noise components from the signal which allows the remaining component to be amplified to reach full scale There is no problem running the input amplifier at low gain However large noise signals almost always disturb the measurement in some way The most common effect of high dynamic reserve is to generate noise and drift at the output This comes about because the output amplifier is running at very high gain and front end noise and offset drift will be amplified and appear large at the output The noise is more tolerable than the DC drift errors since increasing the time constant of the filters will attenuate the noise Lastly dynamic reserve depends on the noise frequency Clearly noise at the signal frequency wi
55. ional to the signal amplitude This is the basic principle of operation of lock in amplifiers The modulated signal is then passed through a low pass filter and the DC signal is measured at the output RS 232 Interface The RS 232 interface connector allows listen only communication with the SR570 at 9600 baud DCE Communication parameters should be set to 8 data bits no parity 2 stop bits Data sent must be delimited by lt CR gt lt LF gt All front panel functions excluding power and toggling are available over the RS 232 interface For more information on programming and commands see Appendix A Remote Programming BATTERY CARE AND USAGE The SR570 can be powered from either an AC power source or from three 12 V 1 9 Amp hour maintenance free sealed lead acid rechargeable batteries Integral to the SR570 is an automatic battery charger along with battery protection and charge indication circuitry Recharging During battery operation the front panel LOW BATT LED will light when the batteries are low and reguire charging For the longest battery life the batteries should be immediately charged by plugging the unit into AC power whenever the LOW BATT indicator is lit Internal protection circuitry will disconnect the batteries from the amplifier if the unit is operated for too long in the low battery condition This protects the batteries from permanent damage which could occur if they were to remain connected to a load
56. istor Resistor Resistor Resistor Resistor Resistor Resistor D 6 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Metal Film 1 8W 1 50PPM Carbon Film 1 4W 5 Parts List Parts List R217 4 00325 407 845 R218 4 00030 401 10 R219 4 00030 401 10 R 220 4 00296 407 604 R 221 4 00165 407 200 R 222 4 00165 407 200 R 223
57. librated sensitivity in roughly 1 increments from 100 down to 0 of the selected sensitivity In contrast to other front panel functions when in UNCAL the instrument s key repeat rate will start slowly and increase to a limit as long as either sensitivity button is depressed Simultaneously pressing both sensitivity buttons again will restore the unit to the previously calibrated sensitivity setting and turn off the UNCAL LED Output The output of the instrument is an insulated BNC with a 50 ohm output impedance In most applications the instrument will be used to drive high impedance loads e g voltmeters or oscilloscopes Therefore the instrument s gain is calibrated for high impedance loads When driving a 50 ohm load the gain of the amplifier is reduced by a factor of two The shields of the two front panel BNCs are connected together and form the amplifier s floating ground In addition a balun is used at the output to reduce common mode noise See the end of Appendix A for more details about the output balun Filter Reset If an overload occurs with filter settings of long time constants the FILTER RESET pushbutton will speed the SR570 s recovery from overload The filters will be discharged by momentarily grounding the filter capacitors The FILTER RESET button is also used to return the unit to its default settings Simply hold down the Operation and Controls FILTER RESET button while turning on the power and
58. ll make its way to the output without attenuation So the dynamic reserve at fsig is 0 dB As the noise frequency moves away from the signal frequency the dynamic reserve increases Why Because the filters after the front end attenuate the noise components The rate at which the reserve increases depends upon the filter time constant and rolloff The reserve increases at the rate at which the filter rolls off When the noise frequency is far away the reserve is limited by the gain distribution and overload level of each gain element In the SR570 decreasing front end gain to increase dynamic reserve can only be accomplished by decreasing the value of the input op amp s feedback resistor Thus the high dynamic reserve mode is also a high bandwidth mode due to a smaller time constant between the input capacitance and the feedback resistor On the other hand a smaller resistor means that even though the Johnson noise is less the extra gain of 10 at the output makes the noise greater So when making a measurement it is important to keep in mind the tradeoff between high dynamic reserve bandwidth and low noise performance The dynamic reserve is a function of freguency and depends on the amplifier configuration sensitivity filters and gain mode setting The figure below shows the dynamic reserve for a SR570 set to sensitivities of 20 LA V 50 uA V and 100 u A V with the high pass filter set to 100 Hz and the low pass filter se
59. n directly below the POS and NEG LEDs A positive offset current is defined to be a current that will produce a positive output voltage with no signal connected to the input BNC and INVERT not selected The button below the input offset ON LED turns the offset on and off The current level can be adjusted whether the offset current is turned on or not Invert The INVERT pushbutton allows the user to invert the output of the instrument with respect to the input A positive current will give a negative voltage and visa versa The INVERT LED displays the output sense relative to the input unless the TOGGLE feature is being used Filters The SR570 contains two identical 1st order R C filters whose cutoff frequencies and configuration high pass or low pass are controlled from the front panel The maximum bandwidth of the instrument is 1 MHz The FILTER CUTOFFS can be configured in the following six ways i high pass filter at 6 dB octave ii high pass filter at 12 dB octave iii high pass filter at 6 dB octave and low pass filter at 6 dB octave band pass iv low pass filter at 6 dB octave v low pass filter at 12 dB octave vi no filters in the signal path Filter settings are chosen by the FILTER TYPE pushbutton Each time the FILTER TYPE pushbutton is pressed the instrument configures the two R C filters in the progression shown above LEDs give a visual indication of the filter configuration T
60. nes below to ensure longest battery life AVOID DEEP DISCHARGE Recharge the batteries after each use The two step fast charge trickle charge operation of the SR570 allows the charger to be left on indefinitely ALWAYS recharge the batteries immediately after the LOW BATT indicator LED on the SR570 comes on Built in protection circuitry in the unit removes the batteries from the load once a dead battery condition is detected Avoiding deep discharge will provide the longest battery life upwards of 1 000 charge discharge cycles DON T LET THE BATTERIES SIT IDLE If the batteries are left for an extended period of time without charging they may become irreparably damaged An SR570 in storage should be topped off every three months with an overnight charge to maintain its batteries in peak condition Operation and Controls AVOID TEMPERATURE EXTREMES When using battery power operate the SR570 at or near room temperature Operating at lower temperatures will reduce the capacity of the batteries At low temperatures more time is reguired to recharge the batteries to their rated capacity Higher temperatures accelerate the rate of reactions within the cell reducing cell life KEEP THE BATTERIES COOL When not in use the SR570 should be stored in a cool dry place with the batteries fully charged This reduces the self discharge of the batteries and ensures that the unit will be ready for use when needed
61. nite input resistance any voltage noise that appears at the input to the op amp will also appear at the output without any gain On the other hand if we introduce some capacitance from the input to ground say coaxial cable capacitance about 100 pF m then we have gain for the op amp input voltage noise Let s look at the effect that input capacitance would have on a typical measurement If we make a measurement on the 1 nA V scale then the feedback resistor in the low noise mode is I GW The bandwidth of this sensitivity range without any filters in the circuit is about 20 Hz If we use one meter of coax cable at the input then we have about 100 pF of input capacitance which at 20 Hz is about 80 MW to ground Therefore the input voltage noise of the op amp is amplified with a gain of around 13 Even more important is that this gain increases with increasing values of input capacitance Incidentally the FREQ COMP capacitor mentioned above also has the effect of limiting the ultimate value of noise gain in the circuit to the ratio of the input capacitance to the feedback capacitance There are a few straightfoward precautions that can be taken to minimize the effects of input capacitance 1 Place the amplifier as close as possible to the signal being measured and use the shortest cable length necessary to connect them 2 Use high quality low noise coaxial cables 3 Reduce any stray capacitance to ground at the
62. ntalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Ceramic Disc 50V 10 SL Capacitor Mylar Poly 50V 5 Rad Capacitor Mylar Poly 50V 5 Rad Capacitor Mylar Poly 50V 5 Rad Cap Monolythic Ceramic 50V 2090 Z5U Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Cap Mini Electro 100V 20 Rad Cap Mini Electro 100V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Electrolytic 16V 20 Rad Capacitor Ceramic 50V 80 20 Z5U AX Capacitor Ceramic 50V 80 20 Z5U AX Cap Mini Electrolytic 50V 20 Radial Cap Mini Electrolytic 50V 20 Radial Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL Capacitor Variable Misc Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad Capacitor Ceramic Disc 50V 10 SL D 2 Parts List C410 C 411 C 412 C 413 C 414 C
63. of each keypress on the front panel is reflected in the change of a nearby LED All front panel functions except power can be controlled through the rear panel RS 232 interface Power The SR570 is turned on by depressing the POWER switch When disconnected from AC power the unit will operate for approximately 15 hours on internal sealed lead acid batteries Up to 200 mA of unregulated battery power is available at the rear panel banana jacks as long as the power switch is in the ON position Battery life will be reduced when the unit is providing external power through the rear panel jacks When operating on batteries the front panel LINE indicator will not be lit As the batteries near depletion the LOW BATT LED will light indicating that the unit should be connected to AC power to charge the batteries When connected to an AC power source amplifier power is derived from regulated line power and the internal batteries are automatically charged When operating on AC power the front panel LINE indicator is on to indicate the source of amplifier power Charging status is indicated on the rear panel by the CHARGE and MAINTAIN LED indicators Input An insulated BNC is provided to connect the signal of interest to the amplifier Care should be taken in choosing a cable to connect to the amplifier input Both cable capacitance and dielectric guality will affect sensitive measurements Whenever possible use low noise coaxial cabl
64. on noise which arises from fluctuations in resistance due to the current flowing through the resistor For carbon composition resistors this is typically 0 1 u V 3 u V of rms noise per Volt of applied across the resistor Metal film and wire wound resistors have about one tenth the noise This noise has a 1 f spectrum and makes measurements at low freguencies more difficult Other sources of 1 f noise include vacuum tubes and semiconductors Total noise All intrinsic noise sources are incoherent The total random noise is the sguare root of the sum of the sguares of all the incoherent noise sources External noise sources In addition to the intrinsic noise sources discussed previously there are a variety of external noise sources within the laboratory Most of these noise sources are asynchronous i e they are not related to the signal freguency Examples include lighting fixtures motors cooling units radios computer screens etc These noise sources affect the measurement by increasing the reguired dynamic reserve or lengthening the time constant Some noise sources however are related to the signal and if picked up in the measurement will add or subtract from the actual signal and cause errors in the measurement Typical sources of synchronous noise are ground loops between the experiment detector and amplifier and electronic pick up from the experimental apparatus Many of these noise sources can be minimized wi
65. output of the circuit being measured 4 If the amplifier must be placed a large distance from the circuit under test then use triaxial cable with both a guard and a shield to reduce the capacitance to ground Parts List Main Circuit Board Parts List B 401 C 101 C 102 C 103 C 104 C 105 C 106 C 107 C 108 C 109 C 110 C 111 C 112 C 113 C 114 C 115 C 116 C 117 C 118 C 119 C 120 C 201 C 202 C 203 C 204 C 205 C 206 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 C222 6 00137 601 5 00100 517 5 00100 517 5 00225 548 5 00225 548 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00100 517 5 00225 548 5 00225 548 5 00100 517 5 00100 517 5 00016 501 5 00015 501 5 00011 501 5 00215 501 5 00019 501 5 00225 548 5 00225 548 5 00100 517 5 00100 517 5 00100 517 5 00010 501 5 00022 501 5 00063 513 5 00065 513 5 00067 513 5 00023 529 5 00194 542 5 00194 542 5 00193 542 5 00193 542 5 00213 546 5 00213 546 5 00033 520 5 00033 520 5 00031 520 15MH 22U 22U 1U AXIAL 1U AXIAL 2 2U 2 2U 2 2U 2 2U 2 2U 2 2U 2 2U 2 2U 1U AXIAL 1U AXIAL 2 2U 2 2U 470P 39P 27P 20P 68P 1U AXIAL 1U AXIAL 2 2U 2 2U 2 2U 270P 001U 0033U 01U 033U 1U 47U MIN 47U MIN 2 2U MIN 2 2U MIN 4 7U 4 7U 47U 47U 220U Inductor Capacitor Tantalum 35V 2090 Rad Capacitor Tantalum 35V
66. pot P1 is mounted on the front panel printed circuit board and is used to control the main amplifier feedback capacitance CALIBRATION AND REPAIR CALIBRATION Six pots exist which may be used to calibrate various voltages on the SR570 Two are used to adjust the battery voltages while the rest are used to null out offsets in the front end amplifier stage The bottom panel of the SR570 must be removed to access the pots Pots P701 and P702 adjust the battery voltage levels The batteries must be disconnected to make these adjustments To adjust the positive supply voltage adjust P701 while measuring the voltage at U701 pin2 For the negative supply adjust P702 while measuring U702 pin 3 The recommended voltages are 14 0 V and should have been set at the factory Pots P103 and P104 are used to ensure that the applied input bias voltage is completely subtracted from the front end output P104 should be adjusted first Turn off the SR570 Using an ohmmeter measure between U107 pin 3 and U105 pin 4 and adjust P104 so that the resistance is egual to that measured across R105 Turn on the SR570 Select a 1 mA input offset current and 1 mA V sensitivity from the front panel The SR570 should otherwise be in its default start up state Low Noise no filters etc seep 4 Measure the voltage at U106 pin 1 Now select a 3V bias from the front panel Adjust P103 until the output at U106 pin 1 is the same as that measure
67. r BNC Connector Male Connector BNC Connector BNC Connector D Sub Right Angle PC Female Resistor Network SIP 1 4W 2 Common Resistor Network SIP 1 4W 2 Common Resistor Network SIP 1 4W 2 Common Resistor Network SIP 1 4W 2 Common Resistor Network SIP 1 4W 2 Common Pot Multi Turn Trim Mini Printed Circuit Board 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 Film 1 4W 5 Resistor Carbon Film 1 4W 5 Resistor Carbon Film 1 4W 5 Switch Switch Switch Switch Switch Switch Switch Switch Switch D 13 Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button Momentary Push Button 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 3 00303 340 3 00303 340 3 00303 340 3 00303 340 3 00303 340 3 00303 340 3 00303 340 0 00014 002 0 00017 002 0 00042 010 0 00043 011 0 00077 030 0 00079 031 0 00089 033 0 00096 041 0 00109 050 0 00122 053 0 00126 053 0 00128 053 0 00136 053 0 00153 057 0 00194 043 0 00195 020 0 00202 021 0 00231 043 0 00237 016 0 00240 026 0 00243 003 0 00259 021 0 00268 052 0 00277 053 0 00299 000 0 00312 000 0 00314 040 0 00321 035 0 00322 035 0 00323 035 0 00324 035 D6 01 05 D6 01 05
68. ru 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 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 Integrated Circuit Thru hole Pkg Integrated Circuit Thru hole Pkg Relay Voltage Reg TO 220 TAB Package Voltage Reg TO 220 TAB Package SRS sub assemblies SRS sub assemblies 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 LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular D 11 D12 D 13 D 14 D15 D 16 D17 D18 D19 D 20 D21 D22 D 23 D 24 D 25 D 26 D27 D 28 D 29 D 30 D31 D 32 D 33 D 34 D 35 D 36 D 37 D 38 D 39 D 40 D 41 D 42 D 43 D 44 D 45 D 46 D 47 D 48 D 49 D 50 D51 D 52 D 53 D 54 D55 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 00012 306 3 0
69. scale the 1 GQ resistor alone produces an input current noise of 4 pA NHz while the 100 nV NHz of amplifier voltage noise gives an input current noise of about 0 1 fA NHz Therefore all the possible sources of noise must be considered in order to calculate a noise figure for a current amplifier Noise Sources There are two types of noise we have to worry about in laboratory situations intrinsic noise and external noise Intrinsic noise sources like Johnson noise and shot noise are inherent to all physical processes Though we cannot get rid of intrinsic noise sources by being aware of their nature their effects can be minimized External noise sources are those found in the environment such as power line noise and broadcast stations The effect of these noise sources can be minimized by careful attention to grounding shielding and other aspects of experimental design We will first discuss some sources of intrinsic noise Johnson noise Every resistor generates a noise voltage across its terminals due to thermal fluctuations in the electron density within the resistor itself These fluctuations give rise to an open circuit noise voltage 1 2 V rms 4k TRAf TM where k Boltzmann s constant 1 38x10 J K T is the temperature in Kelvin typically 300 K R is the resistance in Ohms and Af is the bandwidth of the measurement in Hz Using this formula the Johnson current noise is given by 10 1 2 rms 21 27x10
70. string i Output the next character to COM2 j j 13 CIRCUIT DESCRIPTION LOW NOISE Current to Voltage FRONT END The current signal to be amplified is connected to BNC J104 Relays K103 K104 amp K105 choose the sensitivity range Resistors R132 R135 serve to protect the inputs to the amplifier and to limit the maximum noise gain due to input capacitance The value of resistance is chosen to produce less than a 0 1 error in the voltage output Resistors R124 R127 are the feedback resistors that control the gain of the main amplifier circuit Switch U109 and resistors R121 R123 can multiply the effective feedback resistance by 1 or 10 to double the number of sensitivity ranges Capacitors C117 C120 can be used to limit the bandwidth of the amplifier circuit The FREO COMP pot on the front panel controls the fraction of voltage that is fed back through the capacitors to the amplifier inputs providing a variable feedback capacitance Relays K106 amp K107 choose between the two main amplifier op amps U107 amp U108 Voltage regulator U101 provides a 5V source for both the bias voltage and input offset current U111B is used as an inverter to create a 5V source U102 switches the noninverting input of U107 amp U108 between ground and a selected bias voltage and controls the sign of the bias and offset The 12 bit DAC U103 allows processor control of both bias and offset levels U110 U111A and R136 R143 generate
71. t configure all of the instrument s hardware U608 is an input buffer that takes data from the front panel and RS 232 and provides a processor input indicating line operation 15 BATTERY CHARGER AND PRE REGULATORS The 17 volt AC line transformer provides unregulated power for both amplifier operation and battery charging Diode bridge D706 and filter capacitors C706 and C707 generate unregulated DC voltages that are pre regulated to 12 VDC by U706 and U707 to take the place of the batteries when the instrument is operating on AC line power Relay U705 switches the amplifier from battery to pre regulated AC whenever the AC line cord is plugged in D712 D713 and C709 C710 provide unregulated DC to charge the batteries U701 and U702 operate as AC regulators limiting peak battery charging voltage As there are two positive batteries and one negative battery U701 is a LM350 regulator that provides twice the current of the LM337 negative battery regulator Charging is controlled by changing the set voltage of the regulators based on battery charge status Flip flop U703 determines whether the charge regulators will be set to 15 5 volts for a quick charge or 13 8 volts for a trickle or maintain charge by grounding the bottom of P701 and P702 C712 and R704 insure that the charger always powers up in the quick charge mode P701 and P702 are provided to adjust the open circuit trickle charge voltage to 13 8 volts D701 and
72. t to 1 kHz for a bandpass from 100 Hz to 1 kHz The dynamic reserve characteristics are shown for both High Bandwidth and Low Noise gain modes The Low Drift mode has the same dynamic reserve as the Low Noise mode There are several features to note In the bandpass region between 100 Hz and 1 kHz the dynamic reserve is near 0 dB The dynamic reserve is 3 dB at the filter freguencies of 100 Hz and 1 kHz The dynamic reserve rises by 6 dB oct or 20 dB per decade as the signal moves away from the pole freguency since each RC filter attenuates the signal If a faster rolloff for interfering signals was reguired a 12 dB octave HP or LP filter could be used The DR rises to a maximum which depends on the gain distribution in the amplifier circuit The plot gives the DR for a 1 2 5 seguence of sensitivities on two different gain modes It turns out that between 20 pA V and 100 A V the curves are exactly the same for any other 1 2 5 seguence Below 20 pA V the maximum DR increases by 20 dB for all gain modes over those in the plot Above 100 A V the Low Noise curves are the same as in the plot and the High Bandwidth curves are the same as the Low Noise Keep in mind that the amplifier bandwidth may limit the DR at the higher freguencies on some sensitivities Dynamic Reserve vs Freguency 40 DC mm mwy Iter F 30 kJ oO gt o 20 oO c 2 E S 10 gt Q 0 ww ft 6 dB octave 20 dB decade due to filters
73. th a sensitivity of 1 nA V use a source impedance greater than 1 GO 2 If using a voltage source and a big resistor to source the current use several smaller resistors in series instead of one larger value to reduce the shunting capacitance 3 Adjust the FREQ COMP pot on the front panel to optimize frequency response for the source character istics and for the sensitivity selected 4 Use short lengths of high quality coaxial cable to connect to the amplifier input 5 Keep the amplifier output below 1 VRMS to avoid slew rate limiting at high frequencies 6 Ground the chassis green connector on back but do not connect the chassis to the amplifier ground white connector 7 Forlow level measurements disconnect the power cord and use the internal batteries Abridged RS 232 Command List Command Syntax All RS232 commands consist of four letter codes followed in most cases by an integer value n Commands must end with a carriage return and linefeed lt CR gt lt LF gt The SR570 RS232 interface is configured as listen only 9600 baud DCE 8 data bits no parity 2 stop bits and is optically isolated to prevent any noise or grounding problems Sensitivity control commands SENS n Sets the sensitivity of the amplifier n ranges from 0 1 pA V to 27 1 mA V SUCM n Sets the sensitivity cal mode 0 cal 1 uncal SUCVn Sets the uncalibrated sensitivity vernier 0 lt n lt 100 percent of full scale Inp
74. th a voltage preamplifier The answer is twofold First to get a large voltage from a small current large resistors are necessary In combination with cable capacitance and other stray capacitance this can lead to unacceptable penalties in freguency response and phase accuracy Current amplifiers have much better amplitude and phase accuracy in the presence of stray capacitance Secondly using resistive terminations forces the current source to operate into possibly large bias voltages a situation that is unacceptable for many sources and detectors Current amplifiers can sink current directly into a virtual null or to a selected DC bias voltage Overview The SR570 is a low noise current preamplifier providing a voltage output proportional to the input current Sensitivities range from 1 mA V down to 1 pA V The general architecture is diagrammed in figure 1 on the following page The DC voltage at the input can be set as a virtual null or biased from 5V to 5V An input offset current from 1pA to 1 mA may also be introduced The user can choose between low noise high bandwidth and low drift settings and can invert the output relative to the input Two configurable R C filters are provided to selectively condition signals in the freguency range from DC to 1 MHz The SR570 normally operates with a fully floating ground with the amplifier ground isolated from the chassis and the AC power supply Input blanking output toggling
75. th good laboratory practice and experiment design There are several ways in which noise sources are coupled into the signal path Capacitive coupling An AC voltage from a nearby piece of apparatus can couple to a detector via a stray capacitance Although Cstray may be very small the coupled noise may still be larger than a weak experimental signal This is especially damaging if the coupled noise is synchronous at the signal freguency Stray Capacitance We can estimate the noise current caused by a stray capacitance by dV stray dt stray noise where is 2z times the noise frequency Vnoise is the noise amplitude and Cstray is the stray capacitance For example if the noise source is a power circuit then f 60 Hz and V noise 120 V Cstray can be estimated using a parallel plate equivalent capacitor If the capacitance is roughly an area of 1 cm separated by 10 cm then Cstray is 0 009 pF The resulting noise current will be 400 pA at 60 Hz This small noise current can be thousands of times larger than the signal current If the noise source is at a higher frequency the coupled noise will be even greater Cures for capacitive noise coupling include 1 Removing or turning off the noise source 2 Keeping the noise source far from the experiment reducing Cstray Do not bring the signal cables close to the noise source 3 Installing capacitive shielding by placing both the experiment and detector in
76. the input offset current by providing a constant voltage with respect to the bias voltage across the offset resistors R128 R131 U110 which can switch between x1 and x10 modes and relays K101 amp K102 choose the input offset range U106A and R104 R105 R108 R109 are part of a differential amplifier circuit that gives an output voltage that is referenced to ground regardless of the value of bias voltage Potentiometer P103 can be used to calibrate any offset in the differential amplifier while P104 balances any offset created by the INVERT function U105 controls the blank toggle amp invert features by flipping the polarity of the signal into U106A for inverting amp toggling and providing open circuits for blanking CONFIGURABLE FILTERS AND GAIN The two filter stages in the SR570 each consist of 16 R C filters which can be configured as either high pass or low pass by a relay In the following description part references in parentheses refer to filter two Relay K201 K301 selects either the high pass or low pass configuration for all of the sixteen filters The output of one R C section is selected by multiplexer U202 or U203 U301 or U302 and passed on to non inverting buffer U204 U303 Approximately 80 pF input capacitance of the multiplexers is included in the calculation of the R C time constants of the filters The four highest freguency stages are not available as high pass filters because of unacceptable
77. the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground CONNECTION TO OTHER INSTRUMENTS All front panel BNC shields are isolated from the chassis ground and the power outlet ground via a 1MQ resistor Do not apply any voltage to either the shields or to the outputs The outputs are not protected against connection to any potential other than circuit ground VENTILATION Always ensure adequate ventilation when operating the SR570 The unit will generate heat while charging batteries POWER UP All instrument settings are stored in nonvolatile memory battery backed up RAM and are retained when the power is turned off They are not affected by the removal of the line cord If the power on self test passes the unit will return the settings that were in effect when the power was last turned off If an error is detected or if the backup battery is exhausted the default settings will be used Additionally if the FILTER RESET key is held down when the power is turned on the instrument settings will be set to the defaults shown below Sensitivity 1 A V calibrated Invert off Input Offset 1 pA calibrated off Bias 0 V off Filters none Hi Pass Freq 0 03 Hz Lo Pass Freq 1 MHz Gain Mode Low Noise SR570 Low Noise Current Preamplifier REPACKAGING FOR SHIPMENT The original packing materials should be saved for reshipment of the SR570 If
78. thic Ceramic 50V 20 Z5U Cap Monolythic Ceramic 50V 20 Z5U Capacitor Variable Misc Capacitor Ceramic Disc 50V 10 NPO Cap Monolythic Ceramic 50V 20 Z5U Cap Monolythic Ceramic 50V 20 Z5U Cap Monolythic Ceramic 50V 20 Z5U Capacitor Electrolytic 35V 2090 Ax Capacitor Electrolytic 35V 2090 Ax Capacitor Tantalum 35V 2090 Rad Capacitor Electrolytic 35 Capacitor Electrolytic 35 V 2090 Rad V 2090 Rad Capacitor Tantalum 35V 2090 Rad Cap Monolythic Ceramic 50V 2090 Z5U Capacitor Tantalum 35V 2090 Rad Capacitor Tantalum 35V 2090 Rad Capacitor Tantalum 35V 2090 Rad Cap Monolythic Ceramic 50V 20 Z5U Cap Monolythic Ceramic 50V 2090 Z5U Capacitor Tantalum 35V 2090 Rad Capacitor Non polarized Electrolytics Capacitor Non polarized Electrolytics Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V Capacitor Ceramic 50V 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U 80 20 Z5U AX AX AX AX AX AX AX AX AX AX AX Cap Monolythic Ceramic 50V 20 Z5U Capacitor Tantalum 35V 20 Rad Capacitor Tantalum 35V 20 Rad D 3 C 825 C 82
79. ts the sensitivity of the amplifier according to the following table 24 25 26 SUCM n SUCVn scale 1 2 5 pA V 10 20 50 pA V 100 200 500 pA V 1 2 5 nA V 10 20 50 nA V 100 200 500 nA V 1 2 5 pA V 10 20 50 uA V 100 200 500 LA V27 1 mA V Sets the sensitivity cal mode 0 cal 1 uncal Sets the uncalibrated sensitivity vernier O lt n lt 100 percent of full scale Input Offset Current control commands IOON n Turn the input offset current on n 1 or off n 0 IOLV n Sets the calibrated input offset current level according to the following table 27 28 29 scale 1 2 5pA 10 20 50 pA 100 200 500 pA 1 2 5nA 10 20 50 nA 100 200 500 nA 1 2 5 pA 10 20 50 pA 100 200 500 pA 1 2 5mA IOSN nSets the input offset current sign 0 neg 1 pos IOUC n IOUV n Sets the input offset cal mode 0 cal 1 uncal Sets the uncalibrated input offset vernier 1000 n lt 1000 0 100 0 of full scale Bias Voltage control commands BSON n BSLV n Turn the bias voltage on n 1 or off n 0 Sets the bias voltage level in the range 5000 n x 5000 5 000 V to 5 000 V Filter control commands FLTT n IB ABWNrF LFRO n Sets the filter type according to the following table filter type 6 dB highpass 12 dB highpass 6 dB bandpass 6 dB lowpass 12 dB lowpass none Sets the value of the lowpass
80. ular LED Rectangular LED Rectangular LED Rectangular LED Rectangular D 12 Parts List Parts List D 56 D 57 D 58 D 59 D 60 D 61 D 62 D 63 D 64 D 65 D 66 D 67 J4 J5 J 104 J 401 J 601 J 805 J 806 JP801 N1 N2 N3 N4 N5 Pl PC2 Ol Q2 Q3 RI R2 R3 R4 R5 SWI SW2 SW3 SW4 SWS SW6 SW7 SW8 SW9 3 00884 306 3 00885 306 3 00885 306 3 00012 306 3 00884 306 3 00884 306 3 00884 306 3 00004 301 3 00004 301 3 00004 301 3 00004 301 3 00004 301 1 00139 130 1 00197 101 1 00073 120 1 00073 120 1 00139 130 1 00073 120 1 00073 120 1 00016 160 4 00288 425 4 00288 425 4 00288 425 4 00298 425 4 00298 425 4 00802 452 7 00469 701 3 00022 325 3 00022 325 3 00021 325 4 00057 401 4 00057 401 4 00059 401 4 00026 401 4 00803 401 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 2 00031 201 RED YELLOW YELLOW GREEN 1N4148 1N4148 1N4148 1N4148 1N4148 28 PIN DIL TEFLON TEST JAC INSL INSL 28 PIN DIL INSL INSL RS232 25 PIN D 470X9 470X9 470X9 470X5 470X5 2 0K SR570 FP 2N3906 2N3906 2N3904 220 220 22K 1 3K 910 D6 01 05 D6 01 05 D6 01 05 D6 01 05 D6 01 05 D6 01 05 D6 01 05 D6 01 05 D6 01 05 LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular LED Rectangular Diode Diode Diode Diode Diode Connector Male Vertical Test Jack Connector BNC Connecto
81. ument are sealed lead acid batteries With usage and time these batteries can leak Always use and store this instrument in the feet down position To prevent possible damage to the circuitboard it is recommended that the batteries be periodically inspected for any signs of leakage Specifications Symbols you may find on SRS products Description Alternating current Caution risk of electric shock Frame or chassis terminal Caution refer to accompanying documents Earth ground terminal On supply Off supply Specifications Input Input Input Impedance Input Offset Maximum Input Noise Sensitivity Freguency Response Grounding Filters Signal Filters Filter Reset Gain Allocation Low Noise High Bandwidth Low Drift Output Gain Accuracy DC Drift Maximum Output Slew Rate Limit Rear Panel Interface RS 232 External Gating General Operating Temperatures Power Dimensions Weight Warranty Virtual null or user set bias voltage 5V to 5V See Table 1 b5 mA full scale adjustable dc offset current See graphs on next page 1 pA V to I mA V in a 1 2 5 sequence Vernier sensitivity in 1 steps Flat to 0 5 dB up to 1 MHz 1 mA V sensitivity Frequency response can be adjusted from the front panel to compensate for the effects of source capacitance at the input Amplifier ground is fully floating Amplifier and chassis grounds may be connected together at rear panel
82. ut Offset Current control commands IOON n Turns the input offset current on n 1 or off n 0 IOLV n Sets the calibrated input offset current level n ranges from 0 1 pA to 29 5 mA IOSN n Sets the input offset current sign 0 neg 1 pos IOUC n Sets the input offset cal mode 0 cal 1 uncal IOUV n Sets the uncalibrated input offset vernier 1000 lt n 1000 0 100 0 of full scale Bias Voltage control commands BSON n Turns the bias voltage on n 1 or off n 0 BSLV n Sets the bias voltage level in the range 5000 lt n 5000 5 000 V to 5 000 V Filter control commands FLTT n Sets the filter type 026 HP 1 12 HP 2 6 BP 3 6 LP 4 12 LP and 5 none LFRQ n Sets the value of the lowpass filter 3dB point n ranges from 0 0 03Hz to 15 1 MHz HFRQ n Sets the value of the highpass filter 3dB point n ranges from 0 0 03Hz to 11 10 kHz ROLD Resets the filter capacitors to clear an overload condition Other commands GNMD n Sets the gain mode of the amplifier 0 low noise 1 high bw 2 low drift INVT n Sets the signal invert sense 0 non inverted 1 inverted BLNK n Blanks the front end output of the amplifier 0 no blank 1 blank RST Resets the amplifier to the default settings INTRODUCTION Why use a Current Amplifier Many people wonder why current amplifiers are necessary Why not simply terminate a current source with a resistor and amplify the resulting voltage wi

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