NI 9237 Internal Excitation Drops When Load Connected

Updated Dec 28, 2018

Reported In

Hardware

  • NI-9237

Driver

  • NI-DAQmx

Issue Details

  • When I connect a load to my module, I observe the excitation drop immediately. I am measuring this drop with a multimeter and configuring the excitation in NI MAX. Is my module broken?
  • I cannot read more than 3 Volts in my 9237 module when I connect my four bridges to the terminals. Why is the module not suplying the 10 Volts I request in my DAQmx task?

Solution

This is expected behavior: The maximum power that can be supplied by the 9237 is 150mW as stated on page 6 of the 9237 Datasheet. The card will adjust the excitation level if the resistance of the load is too small to meet this requirement. Use the equation below to unsure that you are not exceeding the power limits of this card. 

If you find you are exceeding this power limit, consider either using a lower excitation voltage or using external excitation if your sensor requires it. 

Additional Information

It is possible that you may see that the card is providing power above this 150mW limit and the excitation voltage does not drop low enough. It is not recommended that you continue operating at this level because you risk damaging the device or decreasing performance over time. You should verify your system requirements using the equation above to determine if external excitation makes sense for your application. 

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