Differential Measurement

[NormanSim]

Hi There,

I having some problem with differential measurement.

My UUT (Audio Set) output is BTL signal. When I connect this BTL (Mono Bridge Tied Load) signal to scope, the output is perfect.

However when I use Differential mode of my 6025E DAQ board, I cannot get the correct measurement.

I check my DAQ board (differential mode) using an ocsillator and it is working fine.

May I know what can be the possible problem with my set up?

Thank you in advance,

Best Regards,

Norman

[Dennis_Knutson]

When you measure the signal with the scope, are you doing a differential measurement with two separate scope probes, are you referencing it to ground with the probe's ground clip, or is the probe's ground clip unconnected? Maybe you should try RSE or NRSE with the DAQ board.

[NormanSim]

Hi, I using scope without AC Ground, I'm not using differential probe. My UUT output audio signal is BTL type, so I must use differential mode to check. Thanks & Regards, Norman

[johnsold]

Norman,

I think the suggestion was not that you do not need a differntial measurement, but that the input circuitry of the A/D board must be properly connected, particularly to provide a path for the input bias currents. Look at the instructions for how to wire and connect the inputs of your board. If you are capacitively coupling to your amplifier and not providing a DC path to ground at both of the inputs, you will have problems.

Lynn