Calibration?

[Katie734]

Hello I'm having difficulties with our signal and think it may be the calibration of the DAQ. I've attached a photo of what 
our data is looking like when the input isn't attached. For whatever reason the 
noise stays around -9.5 or 9.5 volts every time we run the simulation. We are not sure why when nothing is attached it is reading 9.5, but it is causing problems, and need to make sure when nothing is attached it reads in closer to 0. Any advise on what may be going wrong?

Thanks, 

[JÞB]

What is the DAQ device, How is the input configured?

[SnowMule]

Looks like a period of about .017 sec ... which is awfully close to the period of 60Hz ...

Look at the neutral and ground lines on anything connected to mains voltage.  Ground the cabinets, shield the DAQ/sensors from big-power stuff ... computers, CRT monitors, motors/drivers, etc. 

You're just picking up line noise.  Shielding is your friend here.

[Katie734]

The DAQ is a BNC 2090A. The DAQ is triggered by a seperate device, and records 500 samples. 

[RavensFan]

If you have nothing connected, then you are just picking up a voltage that tends to float to one extreme for another.  You can't ever accurately measure "nothing".  You should connect the wires together and you should see zero volts then, with far less 60Hz noise.

[Henrik_Volkers]

The main cause of a floating input high voltage reading is the input bias current. Short cut the input and read the voltage , now measure a 1Meg Resistor in voltage mode and you can calculate the bias current and check it against the spec of your device.