Having Problem In Differential Measurement On My UUT

[NormanSim]

Hi, I having problem using PCI-6025E for differential measurement on my UUT (an audio product, BTL output). I had switch to differential mode in MAX. Measurement connection positive (ACH0), negative (ACH8). I able to get the RMS value and freq of the measurement however the waveform is not uniform (unable to get beautiful sinewave). When I use Scope to measure the UUT output, I able to get uniform sinewave. I also tried to replaced the DAQ board however in vain. May I know what can be wrong in my measurement? Thank you in advance......... Best Regards, Norman

[devchander]

A lot of reasons may be causing this problem.

To start with, what is the frequency of your sine wave?? and at what sampling rate are you reading it on your DAQ??

remember Nyquist criterion.

To get a very good representation of your sine wave, ideally keep your AI channel's sampling rate at least 10 times the frequency of your sine wave.

Ex: Measure a sine wave of freq 10 Hz on a AI channel at a sampling rate of 100Hz or more

If you are already following this and still observe this problem, connect in single ended mode and see if it helps

Message Edited by devchander on 05-29-2006 03:41 AM

[NormanSim]

Hi Devchander, Thank you for the reply. The measurement signal is 1KHz, 3VRMS. The sampling rate I'm using is 40000 scans/sec. As the output signal ground cannot be common, I can only use Differential mode. However, if I use a Transformer, input signal at Primary side and connect the Secondary to DAQ. And by using RSE, I can measure the signal. Thanks & Regards, Norman

[AnalogKid2DigitalMan]

Have you tried the bias resistors required for differential operation as outlined in the manual for the 6025?