NI-9250 Input impedance

[CHA_1]

The NI-9250 specification states a 50 ohm impedance AI- to chassis. 

I use the device with BNC-connector and it is clear, from documentation, that AI- is the shield of the BNC-connector. But where can I find a defined connection/point/terminal of the chassis?
I have not been able to measure the claimed 50ohm anywhere. 
Between where can I find the stated 50 ohm?

[santo_13]

Chassis connection is indirectly referring to the GND plane of the card and electrically when inserted into the cRIO/cDAQ chassis, you will be able to measure 50ohm between the AI- and any exposed metal portion of the chassis or chassis screw.

[CHA_1]

No, 50 ohms can not be measured from AI- to ANY point of the NI9250 (chassie, DSUB-sockets, Earth screw etc).

It is more like 2.2 Mohms

Can anyone please explain the by NI stated 50 ohms between AI- and Chassie. Or is the NI-9250 specification wrong?

[Henrik_Volkers]

What do you measure (using a DMM) between both AI-  after configuration while the task is running? 

[CHA_1]

DC resistance using a DMM Fluke 789. NI-9250 switched off, nothing else than DMM is connected.

Both AI- and chassie are defined by marking on the product. Definitely not 50 ohms between them.

[Henrik_Volkers · Accepted solution]

That's why I wrote, measure while configured and task is running 😉

[CHA_1 · Accepted solution]

Thanks. 50 ohms confirmed when the device is active/ready (power on).