CMRR vs. Frequency Sweeps

Created on 2011-08-23 23:46:00

Question: How do I make a CMRR vs. frequency sweep?

Answer: APx500 has single-frequency CMRR and CMRR IEC measurements, but no measurement labeled CMRR Sweep. However, to do a CMRR vs. Frequency sweep, simply select the Stepped Frequency Sweep measurement and set the Configuration in the Output Settings dialog of Signal Path Setup to one of the CMRR modes, as shown below.

Configuration in the Output Setting dialog.

If the instrument is not in the APx525 Family, read the additional comments below:

The APx515 has CMRR but not CMRR IEC. However, the CMRR IEC test can be done by making one XLR barrel adapter with a 10 Ω resistor in series with pin 2 (and the other pins wired direct), and another with a 10 Ω resistor in series with pin 3. The CMRR test is then run three times, following the procedure above. The first time it is run with no adapter, the second time it is run with the pin 2 resistor adapters inserted in series between the Analog Output and the XLR connecting cable, and the third time it is run with the pin 3 resistor adapter inserted in series. The worst ratio of the three is reported as the measurement result.

The APx585 does not have CMRR tests or settings. However, CMRR can be measured by modifying the femal end of an XLR cable so that pin 2 connects to both signal conductors and pin 3 connects to none (and pin 1 connects to ground). This can be combined with the 10 Ω resistors explained above for the CMRR IEC test.Use Level and Gain for single frequency CMRR measurements, or Stepped Frequency Sweep for CMRR vs. Frequency.