SRS Labs Lock-In Amplifier, SR530 Circuit Description, Calibration and Repair, Appendix B RS232

Circuit Description
Introduction	34
Signal Amplifier	34
Current Amplifier	34
Notch Filters	34
Bandpass Filter	34
Reference Oscillator	35
PSD, LP Filters and DC Amplifier	35
Analog Output	36
A/D's	36
D/A's	36
Expand	36
Front Panel	36
Microprocessor Control	36
RS232 Interface	37
GPIB Interface	37
Power Supplies	37
Internal Oscillator	37
Calibration and Repair
Introduction	38
Multiplier Adjustments	38
Amplifier and Filter Adjustments	38
CMRR Adjustment	38
Line Notch Filter Adjustment	39
2xLine Notch Filter Adjustment	39
Repairing Damaged Front-End	39
Appendix A: Noise Sources and Cures
Johnson Noise	40
'1/f' Noise	40
Noise Spectrum	40
Capacitive Coupling	41
Inductive Coupling	41
Ground Loops	42
Microphonics	42
Thermocouple Effect	42
Appendix B: RS232
Simplest Case Using the RS232	43
Using Control Lines	43
Baud Rates	43
Stop Bits	44
Parity	44
Voltage Levels	44
'Eavesdropping'	44
Appendix C: GPIB
Introduction to the GPIB	45
Bus Description	45
Appendix D: Program Examples
Program Description	46
IBM PC, Microsoft Basic, via RS232	46
IBM PC, Microsoft Fortran, via RS232	47
IBM PC, Microsoft C, via RS232	49

ii

IBM PC, Microsoft Basic, via GPIB	51
HP-85, HP Basic, via HPIB	53
Documentation
Parts List, Oscillator Board	55
Parts List, Main Board	56
Parts List, Front Panel Board	70
Parts List, Quad Board	73
Parts List, Miscellaneous	77
Schematic Diagrams	79