Strain Gauge Input Configuration Diff or NRSE

[Jim_Browne]

Hello,

Hopefully simple question here...

I have a USB-6225 with two SCB-68 breakout boxes.  We are acquiring full-bridge strain gauges with a separate excitation source (Tektronix precision PSU).  For a previous phase of work, we were using the 16 available DIFF channels on the two SCB-68's. 

However, we now want to add two more channels which would exceed what we have available on the breakouts.  The 6225 has plenty of available channels, however, if we used NRSE or RSE acquisition. 

So my question is, with excitation being supplied by an external PSU, can I use NRSE inputs to acquire the signal from my full-bridge gauges?  

Thanks!

[fromm8]

           Hi Jim

-          I was checking the specifications for the USB-6225, and you have 40 differential channels available (specifications: first page) and right now you are using 16.

-          https://www.ni.com/docs/en-US/bundle/pci-pxi-usb-6225-specs/page/specs.html

-          Why do you not have more available diff channels?

          Regards

[Jim_Browne]

Thanks for the reply.

The issue is the number of inputs on the SCB-68 breakout box.  In theory, the 68 pin connector (1) on the DAQ supports AI's 16-79, but attaching the SCB-68 seems to only allow access to 16 of them (8 DIFF). 

Its a bit of time issue right now, and I wish I had discovered this problem earlier.  I have done some searching on other breakouts, but it is not clear which one supports the other 64 inputs available on the the unit's second mass connector.  Short of cutting open the 68 pin cable and hard-wiring each channel (wasting a cable), I'm trying to see if I can use the single-ended inputs instead.  

A solution to either problem works for me!

[fromm8]

Hi Jim

Please check this article about compatible devices and cabling for the NI SCB-68.

Compatible Devices and Cabling for the NI SCB-68/SCB-68A Terminal Block

If you have the correct cables, then you know that * You can only use direct feedthrough mode on Connector 1 of M Series NI 6225/6255 devices

You can find information about direct feedthrough mode in the manual (page 5):

Using the SCB-68 in Direct Feedthrough Mode

Regards