Strain gauges wiring

[david@hv]

Hi, 

We have bought a chassis National Instrument, a module NI 9237 (strain gauge measurement) with a D-SUB.
We have strain gauges to measure micro-strain.
Those sensors have 3 wires (RED, WHITE, BLACK picture 1). We have a problem with the wiring of our strain gauges. We do not know how to plug it to obtain results. We do not have any information about the strain gauges.

1) Have you ever worked with this kind of sensors?

2) Are they standard or special sensors?

We have tried several wiring. Firstly we have tried the one witch is proposed in the Labview DAQ assistant but it does not work (picture 2 ).

3) The resistor called RL, should it be simulated, created or are they already in the module?

4) R3 and  R4 are they included in the module or should we add those?

5) What is the best plug-in to have a half bridge? Full bridge?

Do not hesitate to give us additional questions if you need anymore info.

Thank you very much

[Alain_S]

Did you measure the electrical resistence between the different wires?

I would do that first and then try to figure out how the strain gauges are connected.

[david@hv]

Thank you Alain.

We have measured the resistance between all the wires.

We obtain :

         black - red     350  Ohm

         white - red     350  Ohm

         black - white  0   Ohm

We would like to know how this sensor work, because usually strain gauges have only two wires. After we will be able to find the right wiring for our application.

[neil84]

Hi,

According to the picture, it seems that there is two strain gauges in the same sensor with one common wire, but your last answer idicates other think: two parallel strain gauges. could you do an extra test? what resistances do you measure if you deform the strain gauge?

[david@hv]

Hi Neil84,

thank you for your answer.

Unfortunatly we don´t have an accurate tool to measure this type of resistance. With our measuring tool there is no variation.

But we have tried a new wiring. An half bridge with too sample (so 2 strain gauges), but without pluging the withe wire. Now it works, we detect something on labview. We will make some additional tries to verifie our results.

Your answer is interresting because we would like to understand how does it work. We will try a new wiring with only one sensor and try to know if it is composed of two strain gauges according to your opinion.

thank you

[RavensFan]

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neil84 wrote:

Hi,

According to the picture, it seems that there is two strain gauges in the same sensor with one common wire, but your last answer idicates other think: two parallel strain gauges. could you do an extra test? what resistances do you measure if you deform the strain gauge?

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No.  It would be a single gage.  The third wire is to compensate for lead wire resistance.  The red wire is on one side of the gage.  The white and black wires are tied together on the other side of the gage.

This module is designed for full bridge or half bridge strain gage setups.  With only a single gage, you need a quarter bridge setup.

I would look at this link for some more information. http://digital.ni.com/public.nsf/websearch/C918C9BACB7716F6862574CB003F7AE8?opendocument&Submitted&&...

Also this http://zone.ni.com/devzone/cda/tut/p/id/3642 and this http://zone.ni.com/devzone/cda/tut/p/id/4172 to learn more about strain gages.