I have a PXI-6133 that I am using, and the limits are +-35V on the input terminals, and +-36V channel to earth. My question is what happens if voltages exceed these limits. Are there Zener diodes or varistors across the inputs to clip excess voltage? Will the input stage be damaged?
Channel to earth means channel to PXI chassis, I presume. I have the PXI-1000B, which I intend to disconnect from line power during data acquisition to prevent ground loops. Data is transmitted by MXI fiber optic link to the computer. Should I operate in floating source mode always, where the common (coax shield) is connected to AIGND through 5 kohm and 0.1 uF (as in the BNC-2110)? Many signals are floating sources anyway, e.g., Pearson current monitors. Some are voltage dividers that are referenced to the experiment ground. This ground jumps in potential when a high energy capacitor is discharged across a load. The ground may jump to +50 volts. I think I should connect the common to the AIGND through the BNC-2110 impedance (FS mode) so that AIGND may follow the (-) input somewhat, stay within 36 V of AIGND.
What is the connection between AIGND and the PXI chassis? How will this affect the data on the other input channels?
The maximum working voltage for all analog input channels on the PXI-6133 is +-11 V. If voltages go above that value, the board has over voltage protection of up to +-36 V and anything greater than that will start breaking things on the board.
We don't support/recommend raising Ground on the chassis mainly due to safety reasons. I do recommend using an SCXI-1125 which provides 300 Vrms of working isolation and lowpass filtering for each analog input channel and it has up to 8 channels. Here is a link to the product information.