pxi 6259 removing chassis ground

[Magna-PXI]

Hello, is there a procedure to remove chassis/edison ground from the PXI 6259?  Also, what could be the consequences for doing so?

[Seth_B.]

Why are you looking to remove the chassis ground from the PXI-6259?  The chassis ground is the ground basis for all operations and measurements and removing this connection could damage the board or lead to unexpected operations or inaccurate measurements.

[Magna-PXI]

Firstly, I am fairly new to NI and your product line.  I have inherited hardware.

Why would you rely on chassis ground as your measurement base?  This ground is noisey, whenever a large load across the building turns on, it will shift the ground slightly.  In my case for dyno operations, when the dyno is on, ground is very noisey causing all my measurements to bounce, especially when under hundreds of kilowatts.

I have isolated my sensors to using clean power through buffers, however, the PXI 6259 is negating this effort.

Why would the PXI 6259 provide Digital and Analog grounds if they are all the same ground as the power line that feeds the chassis? 

Is this a matter of me having the wrong board for the application?

[Seth_B.]

When conducting measurements, the chassis ground should only be used when measuring a floating source.  Otherwise, as you've pointed out, you get ground line noise coupled to your reading.  For Differential and Non-Referenced Single Ended (NRSE) measurements, the chassis ground connection is used as the reference for the control and bus interface circuitry, which is does not require as clean of a ground connection.  The Field Wiring and Noise Considerations for Analog Signals document explains the different measurement types and recommended ways of connecting them.  It is never recommended to use a Reference Single Ended (RSE) measurement with a grounded source, because you will pick up ground noise.

Additionally, for particularly dirty power, we recommend using an uninterruptable power supply (UPS) or other method to clean up the power line and ground before feeding them into the PXI chassis.  Alternatively, you could try a bank or channel-to-channel isolated board such as the PXI-6233 isolated M Series card.

When conducting measurements, the chassis ground should only be used when measuring a floating source.  Otherwise, as you've pointed out, you get ground line noise coupled to your reading.  For Differential and Non-Referenced Single Ended (NRSE) measurements, the chassis ground connection is used as the reference for the control and bus interface circuitry, which is does not require as clean of a ground connection.  The Field Wiring and Noise Considerations for Analog Signals document explains the different measurement types and recommended ways of connecting them.  It is never recommended to use a Reference Single Ended (RSE) measurement with a grounded source, because you will pick up ground noise.

Additionally, for particularly dirty power, we recommend using an uninterruptable power supply (UPS) or other method to clean up the power line and ground before feeding them into the PXI chassis.  Alternatively, you could try a bank or channel-to-channel isolated board such as the PXI-6233 isolated M Series card.