Strain gauge wiring

[Casperloo]

I am connect a half bridge setting to SCXI-1314 terminal block. If I wire the output end to S- (negative output) instead of S+, is my result just the negative of the real value? Or it is not correct?

[RavensFan]

I doubt that is correct.

Half bridges (and 1/4 bridges) have their terminals pretty well defined.  Look at the manual for your SCXI DAQ device.

http://www.ni.com/pdf/manuals/372583e.pdf

[Casperloo]

The data we got seems pretty good.

I see the manual. Only S+ is connected. But I also see the block diagram (http://www.ni.com/pdf/products/us/4scxisc286_ETC_196.pdf). It seems both S+ and S- go to the SCXI-1520 amplifier. I just want to know where S- is connected.

Thanks

[RavensFan]

It does go to the amplifier.  But if you look closely at the manual for a full bridge configuration.  For a half bridge, that input is not used.  And if you connected to S- instead of S+ in a half bridge configuration, then you didn't complete your Wheatstone bridge properly.

[Casperloo]

So if I connect to S-, what will I get?  Shall I get anyting?

When I load the structure with the strain gauge, the reading changes and increases with the loading. It seems they work well.

The reason I want to make this clear is that I will make some new strain gauges. I am not sure to change the current connection method.

The cable of the strain gauge is connected to a 8 pin plug first, then the plug goes to a patch pannel, then goest to SCXI 1314.

The wire order of the plug and the connecting cable between the pannel and the scxi may has something wrong.

Do you know anyway I can check them and find the right order?

I am curious that our S- is actually S+,  and P- is actally P+.

For Pore pressure transducers, the order seems good. ( if we switch P+ and P-, S+ and S-, this will not affect pore pressure transducers. it is a full bridge configuration.)

Thanks

[RavensFan]

I have no idea.  Perhaps you will see something.  Maybe it depends on if any of your legs of the bridge are grounded and you are somewhat completing your circuit in a different manner.  If your S+ input is open, then you might be referencing your S- input to a floating terminal  Whether you are reading correctly or wrongly might be just pure luck.  Maybe you see some changes, but perhaps they are just wrong.  I don't think your S- is actually S+.

Why don't you try connecting your gages just like it shows in the manual that way you can be sure you are connecting them correctly?