07-19-2011 09:56 AM
Hi clarksonphysics,
You are right that does not sound out of spec at all. What are these signals you are measuring? What other card and BNC breakout have you tried? Were you measuring the same signals with the different equipment?
Sorry for the barrage of questions I am just trying to figure out as much as I can about your system.
Regards,
Kyle S
07-19-2011 10:11 AM
The both signals are coming from a certain type of photogate call them photogate 1 and 2 such that when something is in front of them the voltage drops from around 5v to about a half of a volt. I have linked a few pictures of the signals I get from each individually in the original post. When I tried the other equipment it was the same model number for both the card and the breakout. When I used the other equipment it was the same with photogate 1 but not the same as 2 but the effect was still there and it was obvious it was the same problem. I have done more testing and it appears that the crosstalk does not happen until I specifically start monitoring the two channels in labview. So if I tell labview to look at channels 1 and 2 for a test, and then switch the inputs to 3 and 4 there will be no crosstalk until I run the next test in which case channel 3 and 4 will interfere with each other but 1 and 2 will not.
07-20-2011 09:10 AM
What happens if you were to ground channel 2 when reading from 1, do you still see the noise introduced on the input?
Regards,
Kyle S
07-21-2011 08:13 AM
If I have an input to channel 1 as a constant 5 volts and ground channel 2, channel 2 reads as 0 and channel 1 drops down to about a half of a volt down from 5.
07-21-2011 04:24 PM
Can you try hooking up a known voltage source that is not varying at all and doesn't have any inherent noise on it? Something like a 9 volt battery just to make sure the card isn't malfunctioning.
Regards,
Kyle S
07-25-2011 09:20 AM - edited 07-25-2011 09:20 AM
Attached is the measurement of a 9v battery.