SRS Labs SR850 - Manual (Page 227)

7-9
Performance Tests
3. Common Mode Rejection
This test measures the common mode rejection of the lock-in.
Setup
We will use the internal oscillator sine output to provide the signal.
Connect the Sine Out to both the A and B inputs of the lock-in. Use equal length cables from A and B to a
BNC TEE. Connect the cable from the Sine Out to the TEE. Do not use any termination.
Procedure
1) {PRESET} (Turn the lock-in off and on with the [
←
] key pressed)
2) Press the keys in the following sequence:
[REF/PHASE]
<Ref. Frequency>
[1] [0] [0] [ENTER]
[DISPLAY/SCALE]
<Type and Trace>
Highlight the trace number.
Use the knob to select trace 3 (R) for the top display.
[INPUT/FILTER]
<Coupling>
Select DC.
3) The value of R should be 1.000 V (within 2%).
4) Press
[INPUT/FILTER]
<Source>
Select A-B.
[GAIN/PHASE]
<Sensitivity>
Use the knob to select 200 µV.
5) Record the value of R.
6) This completes the CMRR measurement test. The common mode rejection is 20log(1.0/R) where R is
in Volts. Enter the results of this test in the test record at the end of this section.