Problem with AI acquire waveforms.vi

[lyn]

I'm using AI acquire waveforms.vi to acquire 2 waveform.

ACH0 : a 50Hz sinewave
ACH1 : some spikes

when i display the 2 waveforms, the spike seems to be superimposed with the sinewave. Why is this so? can i separate the two waveform without making any changes to the original waveform? i need the 2 input waveforms to be synchronised.

I had tried to acquire the 2 waveforms one after another in sequence(AI acquire waveform.vi), however they are not synchronised.

pls advise.

thks & best regards
lyn

[markwysong]

As far as acquisition goes, it looks like you have the right code. You have separated the waveforms into graphs properly as well.

I may need a little clarification on your signals. When you say "spike is superimposed with the sine wave", what do you mean? I'm assuming that you mean that you have two inputs -- a sine wave, and spikes on an otherwise 0 volt signal. Is this correct?

Mark

[lyn]

the first wavefrom should be a +/-10V sinewave only and the second waveform should be only a constant dc voltage with spikes (abt 20usec width).
The problem we are facing now is that the second waveform of the acquire waveforms have a scaled down sinewave(abt 3-4V) with the spikes riding on it. how to get rid the scaled down (abt 3-4V) sinewave. How to acquire just the spikes in the second waveform only while at the same time synchronizing the spike waveform to the sinewave in the first waveform.

thk,lyn

[markwysong]

Which card are you using for your acquisition, and how is it set up (differential, single-ended)? I'm wondering about the ground signal not being hooked up properly.....

As mentioned before, your code for obtaining the signal and displaying it are correct. The signals should pretty much be synched (offset only by the interchannel delay, which is extremely small--on the order of nanoseconds).

The only other thing I can think of is that the input impedance of these cards is very high, and you will get crosstalk between channels if there is not sufficient impedance on the input line. In looking at your data, however, I don't believe this is the case, because your spike "sine wave" is out of phase with your first channel, which would no
t be indicative of this crosstalk. Now that I think about it, not connecting the ground correctly should have about the same effect....

Can you verify on an oscilloscope that your spike signal indeed is not imposed on a sine wave?


Mark

[lyn]

I'm using PCI 6025E for my acquision. I'm not sure if I'm using the correct setup but the current setup is RSE(single- ended). how do i know if the ground signal is being hooked up properly?

I've verified that the spike signal is not superimposed on a sine wave on a scope. Just by acquiring the spike signal alone without the 50hz reference sine wave(just one channel), the output is a clear waveform of spikes. Why is the spike signal riding on a sine wave when acquired together with the reference 50 hz sine wave?

I don't have this problem when i acquire the 50 hz sine wave and the spike signal individually by 2 separate acquire waveform.vi. But if i do this, the 2 signals will not be synchronised. Hence, i changed to use acquire waveform
s.vi. Though synchronised, the spike waveform is riding on an unwanted sinewave. What have gone wrong? How should I solve this problem?