Analog signal varying

[balajikasthuri]

"Hi,

I have connected an unground(isolated) anolog output of a tachometer to ACH0 and ACH8(Chanel 0) of PCI6014 in differential mode. I have connected a 100 K bias resistors from ACH0 and ACH8 to AIGND. I am able to measure the analog values through labview (and MAX)correctely as long as I keep pressing the resistors across the terminal board with my hand . Once I remove my hand, I measure my values correctly for few seconds, but later my readings jump erratically before returning to normal. This cycle of normal readings and disturbance keeps continuing through out my experiment.
Could any one help."

[Ben]

THis sounds like a weird problem!

If i understand you correctly, you say as long as you press on resistor, everything is fine!

If this understanding is correct, it sounds like you have a mechanical connection issue. Re-check ALL of your conncetions. Not only the resitor leads and tach leads but also the cables to your terminal block.

If checking and re-doing all of your connections does not help then you may have a bad teminal block. I have seen cracked traces act this way.

Ben

[balajikasthuri]

Thanks Ben,

I found out the solution for this problem.It was actually the earth wiring which had a loose connection.

thanks,