Solution
Errors in your PXIe-4311 measurement can occur when using the module with the TB-4309 ST without connecting the proper signal ground reference.
The PXIe-4311 is a 32-channel, high-speed analog input module. It is non-channel isolated, meaning all channels share the same ground reference.
The TB-4309 screw terminal (ST) block does not expose dedicated ground terminals, therefore you must connect the PFI_GND terminal on the TB-4309 ST as a signal ground for all PXIe-4311 channel (AI+ and AI-) connections. In your setup, this can look like connecting your device’s or system’s ground to PFI_GND.
Removing the PFI_GND connection will leave the common mode voltage source floating and may introduce measurement errors. The following figure illustrates the grounded source PXIe-4311 block diagram with TB-4309. See PXIe-4311 User Manual: Block Diagram for more details.
The PFI_GND connection is important to be aware of especially if transitioning your system from the PXIe-4309 to the PXIe-4311, as the PXIe-4309 analog input module is a channel-isolated and does not require the signal ground reference.