Strain gauge as voltage inputs

[Setu]

Hi All,

I am just a little confused and need some clarification.

I have set up a strain guage bridge in quarter bridge configuration. That is, only one arm of the bridge is active and the other three arms are just 1% tolerance resistors. I supply my own excitation and I have wired the sense terminal into the analogue input terminal of the SCXI 1100 module. I read this channel as simple voltage input. Then I use the "Convert Strain Gauge Reading.vi" to convert the voltage to strain. Now here are my questions:

1. I want to confirm if I should be selecting the quarter bridge I configration for "Convert Strain Gauge Readings.vi"
2. Is there anything else I should be aware of? EG: The tolerance of resistors?

Because I will be
designing for close to 90 strain gauges, I want to make sure that this WILL work before I build my circuits.

Thanks to anyone who can help!

Regards,
-
Setu.

[chutla]

Greetings!

It sounds like you have things pretty well set up. As far as resistor tolerances are concerned, your measurements are never going to be any better than the worst case tolerance. Do you have an independent means of testing a single strain gauge before you start mass producing them? You can probably do any final calibration in Labview.
One final thought. Are you using a differential mode on your daq cards? You might want to experiment with differential, NRSE, NRE modes, for the lowest noise system.
Also, be sure your excitation signal is not sufficient to actually heat up the resistors. In other words, pay attention to the POWER rating of the resistors as well as their values. It's worth a day or two on the bench to check this out!


Good luck!

Eric

[Setu]

Hi Eric,

Thanks for the input, i really appreciate it.

"Do you have an independent means of testing a single strain gauge before you start mass producing them? You can probably do any final calibration in Labview."
Yes that is what I am doing at the moment. We have a very accurate strain gauge reader that I using to verify the labview readings. Apparantely the readings differ quite a bit, but that could be due to the wrong settings on the strain reader. I will try again next week.

"You might want to experiment with differential, NRSE, NRE modes, for the lowest noise system."
I will be using the SCXI system, so the only option I have is differential!

"Also, be sure your excitation signal is not sufficient to actually heat up t
he resistors."
Ahh... didn't think of that! Thank you.

I will keep you updated. Bye for now.

Regards,
-
Setu.