6-7
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 [Setup] key pressed)
2) Press the keys in the following sequence:
[Freq]
Use the knob to adjust the frequency to 100.0 Hz.
[Channel 1 Display]
Set the Channel 1 display to R.
3) The value of R should be 1.000 V (within 2%).
4) Press
[Couple]
Select DC coupling.
[Input]
Select A-B.
[Sensitivity Down]
Set the sensitivity to 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.
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