Strain gauge Measurement

[Nick]

Hello All,
I am using SCXI 1520 using Terminal Block 1314 for Strain Gauge
Measurement.
We have got a Strain Gauge of 120 Ohm with the NI Hardware which was
connected to CH02(One of the 8 channels provided), Now my problem is
that if I connect the Strain Gauge to some other channel(except Channel
2) I am not able to get any readings , and if I reconnect it back to
Channel 2 it gives prorper results.
I have connected the strain Gauge in
a Quarter bridge Configuration(obviously for a Single Strain Gauge) as
per the circuit diagram provided correctly.

I have Pentium -4 , 256MB RAM, Win XP SP2 machine.

Could anybody please try to explain where I am going wrong.

With Regards
Sandeep

[Justin_M]

Sandeep,

It sounds like you might have a problem with the quarter bridge completion resistors.  The SCXI-1314 includes a factory installed and socketed 350 Ohm quarter-bridge completion resistor for each channel.  Because you are using a 120 Ohm strain guage, you'll need to make sure that you use a 120 Ohm completion resistor.  I'm guessing that channel 2 of your 1314 has a 120 Ohm resistor installed, and the other channels probably still using the default 350 Ohm resistors.  Try replacing a completion resistor on one of the other channels with a 120 Ohm resistor, or switch it with the channel 2 resistor (they should be labeled QTR0, QTR1, etc. on the 1314 board).

-Justin M

[Alankar]

Thank you Justin

Yes you are correct, I got the solution 1314 has 350 Ohm Completion resistors and only Chaneel 2 is installed with a 120 Ohm completion resistor.

So, it was for quarter bridge but if I want to measure strain with full bridge (with 120 Ohm Starin Gauges)then I need not to change the cpmpletion resistors because we wont be using them I just want to ask will it work??

[Justin_M]

That is correct.  The full-bridge configuration will not use the completion resistors, since you are building the entire bridge with strain guages (In the Getting Started with SCXI Manual, see figure 4-10 on page 4-18).  That should work just fine.