signal distortion in Voltage Measurement

[Laura F.]

Hi venkatgill,

The default settings on the SCB-68 should be fine for you.  The onboard CJC temperature sensor is disabled (which you want).  To connect to differential channel 6, you would connect the positive lead of your signal to pin 25 and the negative lead of your signal to pin 58.  Try inputting a signal and reading it in with the test panels in MAX.

Thanks!

Laura

[venkatgill]

Hello Laura,

I have done the test specified by you earlier i.e generating signal from DAQ and rotuing it back using input channel. It worked well and DAQ succesfully measured the output without any distortions as shown before.

I think this concludes that the DAQ card and the connector block CB-68LP works fine. I am sure that the transducer is fine and the original signal is from Power supply panel which is good. I want to know if there are any other constraints which can effect the signal this way. There are no inductive current switches in the process. Will this happen because of lack of proper grounding?

Is this the same procedure for measuring current across a resistive load?

[Laura F.]

Hi venkatgill,

I am glad to hear that your test went well.  So I think the next troubleshooting steps are:

1.  Input a DC voltage signal and read it with test panels in MAX.  Watch for the spikes you saw in your sinusoidal signal.  Try different input configurations.  You can read about recommended input configurations in this tutorial about grounding.  Note that you do not want to use reference single ended (RSE) if your signal source is grounded. 

2.  If you use all recommended input configurations and do not see any spikes, try the same test with your sinusoidal signal you were using earlier. 

3.  If no spikes are present, move on to the LabVIEW example you were using before and try both the DC and sinusoidal signals.  For that example your signals need to be connected in differential mode. 

4.  If you are seeing the spikes, try the other input configurations.  To change the input configuration programatically you will want to use a DAQmx Channel Property node. I am attaching that example you are using that I modified slightly so you can change the input configuration.  Use only the recommended input configurations.  Make sure your sampling rate in the program is at least 10 times larger than the frequency of the signal. 

Hopefully one of these steps will help you narrow down where the problem lies.  You may also want to try a different function generator if you have one available. 

Thanks,

Laura