channel-to-channel isolation during NI9205/9206 differential configuration mode

[NCLbingji]

As stated in the datasheet of NI9206

/*****************************************************************

Maximum Voltage

Connect only voltages that are within the following limits.

AI to COM, PFI0 to COM, and DO to COM................±30 VDC

Isolation Voltages

Channel-to-channel...........................None

Channel-to-earth ground

urement Category I

U.S. (UL 61010-1) ...............600 VDC, Meas

**********************************************************************************/

I don't know if I get this right.

COM actually means the common ground for MUX, PGIA and Front end ADC. COM to earth ground is 600VDC max. No matter to use differential or ,RSE or NRSE configuration, AI to COM must be within ±30 VDC. For example, COM is connected to 400VDC referenced to earth ground. By using differential configuration, (AI0+, AI0-) can mearsure between ±5 VDC(scale range) in the range from 370VDC to 430VDC(decided by COM=400VDC). It is also the same for other differential input pairs, (AI1+, AI1-)........(AI7+, AI7-).

If so, this also means I can not by using one NI9206 to measure both ±5 VDC(scale range) and 95VDC-105VDC(scale range).

Thank a lot for all your help.

Regards

Bing 

[Seth_B. · Accepted solution]

You are correct, if COM is at 400 VDC, then none of the inputs can be outside of 380VDC to 430 VDC.  As a result, measuring ±5VDC would damage the module.  In order to do something like this, you will need a channel-to-channel isolated module.

Regards,