Shunt calibration CDAQ

[dengrodrigo]

Hi:

  I’m using C-DAQ NI 9237 module with Signal Express and I have the following doubts: 1)      How can I perform a shunt calibration using a ¼ Wheatstone bridge? I’m using module NI 9945 and I don’t have any way to perform the shunt.2)      Concerning the half and full Wheatstone bridge the shunt calibration is possible using module NI 9949. Is the precision resistor of 100kOhm internal to the module? Can I connect an external precision resistor to pins 1 and 10 of the module? 3)      If the precision resistor is internal how can I activate the resistor? I suppose that is just short-cut pin 1 to pin 10. Is that right?  Regards, Diogo Ribeiro.

[dengrodrigo]

Hi again:

Does anyone can share his experience concerning the shunt calibration using Signal Express?

I'm having a lot of difficulties in performing it! I also can't find any technical document concerning this issue for the CDAQ users.

Thanks again.

Regards,

Diogo Ribeiro.

[John_P1]

Hi Diogo,

Thanks for posting!   To answer your questions:

1. The 100 kOhm shunt resistor is internal on the 9237 (connected to a switch across pins 1 and 10).  The 9945 accessory performs the 1/4 bridge completion and the circuit containing the shunt resistor is wired across R3 internally.  Running the calibration in Signal Express will automatically connect/disconnect the shunt as necessary.
2. To perform the shunt calibration on the 9949, you would use jumper cables to connect the Shunt Calibration pins (1 and 10) across the desired resistor (you can specify the resistor used in software).
3. Again, the driver will automatically connect and disconnect the shunt resistor during the calibration process.  You can provide your own external shunt resistor on the 9949, but you would have to make the measurements and scale the data yourself in software.  I would recommend that you let the driver handle this.

I hope this answers your questions, if you have any others please let me know.

-John