5B38 measuring 3.33 V

[Tom_SAVU]

I am measuring strain from a full bridge using a 5B38 module (3.33 V excitation), a 5B08 backplane and a PCI-6024E board. The board is configured in NRSE mode, DC coupling. The problem is that, when no load is applied to the strain gages, the board is measuring arround 3.33 V (approx. the excitation voltage).

Can anybody tell me which could be the problem.

Thank you !

[Jeffrey_P]

It sounds to me as though there is something in the physical connections of the strain gauge to the module.  I would verify the connections with the picture that I am attaching to this post.  Also, I would ensure that there are no bridge connections left-over from old half or quarter bridges that are bridging the module terminals.  Also, I would verify that the strain gage itself is still good.  You could try a different strain gage or verify the resistors are still good.  Another thing to verify that the ohm rating of the strain gage matches up with the range for the module.

Hope this is helpful!

Jeff P.

National Instruments Applications Engineer

[Tom_SAVU]

Dear Jeff,
Thanks, you were right. I replaced the bridge and now I have only 0.02V when the cell is not loaded.
Happy New Year !
Tom