My strain gauges (full Wheatstone bridge) give me a constant negative voltage

[balaclava]

Hi, I'm currently trying to calibrate strain gauges to work with a one-axis tribometer...I'm using XP, LabVIEW 8.5.1, have the latest version of NIDAQmx and SignalExpress 2.5.1.  Right now the strain gauges are hooked up to a SC-2043-SG signal conditioning board, which in turn is hooked up to a PCI 6251.

The problem right now is that while the computer recognizes the device and is getting output from it, I'm getting a constant negative voltage (-10.2 V or something like  that).  My configuration for the SC-2043-SG is as follows:

Custom voltage w/ excitation

-External excitation (can't switch to internal excitation source- apparently it doesn't exist even though I've set the switch on the board to INT)

-Full Wheatstone bridge

-Differential terminal configuration

-Not using ex for scaling

-Ex value is 1m

-Channel is ai0

I've currently got this set up in SignalExpress 2.5.1 and have been generating VIs from the task that I've made there.

Another odd thing is that the gauges don't seem to respond to when I put pressure on them.

So what I mainly need to know is

1) Do I have bad gauges?

2) Do I have an incorrect configuration?

I guess on a side note I've noticed that when I set the terminal configuration to RSE, the values oscillate around 0.08V.  Should I use that instead and calibrate it from there, so that at least the configuration reads 0 by default?

[Nathan_R]

Hi balaclava,

Since the SC-2043-SG is an older signal conditioning board is does not support programmatic control of its excitation or settings. This is why there is no internal excitation available to select in your DAQmx task. These setting must be configured on the SC-2043-SG using the on-board jumpers.

You will want to set the jumpers for internal power and excitation and set for full bridge gauges. More information on all of the jumper settings can be found in the SC-2043-SG User Manual. Also page 30 of the manual shows how to connect a full bridge sensor.

Once you have the SC-2043-SG configured correctly it then does the bridge signal conditioning and provides the DAQ card with a voltage signal referenced to AI Sense. You can measure this signal using a normal analog input voltage task with the terminal configuration set to NRSE or RSE. It does not provide the DAQ card with a differential signal.

Please let me know if you have any questions and take care.

Thanks,

[balaclava]

Followed what you said and set the terminal configuration to NRSE- works like a charm now, thanks.