shunt calibration using CDaq 9237

[lopez]

I am looking for help in determining the correct location for the shunt resistor and if I need to physicaly wire it when using a Quarter Bridge (type 1) strain guage.  I have the 9445 bridge completion accessory.

I thought the shunt would be located at R1 or R2 based on the wiring diagram shown in the MAX "new task" set up help screen, but the note on the calibration wizard says R1 and R2 are disabled for half and quarter bridge configurations.

I have tried applying the shunt calibration to R1, R2 and R3, but the only difference seems to be a sign switch on the actual strain reading.  Further, not engaging the shunt resistor gives about the same reading as with it.

Thanks

Alfonso

[Erik_J]

Hi Alfonso,

You should be able to put your strain gauge across pins 0 and 1 (EX+ and IN+) on the 9945 to get a strain reading.  All other quarter bridge circuitry should be taken care of inside the 9945.

I hope this helps!

Regards,
Erik

[lopez]

Eric,

I have the strain guage wired as you say.  I am trying to do a software calibration within MAX.  It asks for the location of the shunt resistor (R1, R2, R3 or R4).

The diagram for the quarter bridge type I shows the strain guage is R4. I need to determine if the shunt resistor is R1 or R2.

I am having trouble getting different strain readings when appying the shunt resister vs. not applying it.

Thanks

[Erik_J]

Hi lopez,

R₃ is the quarter-bridge completion resistor (dummy resistor), and is the resistor that you will need to select to shunt across.  Please select R₃ as your shunt resistor and let me know if you experience any more difficulties.

Regards,
Erik