Why do I see Voltage Offsets in NI 9237 Acquisitions when Connecting Additional Strain Sensors?
Hardware: CompactRIO>>Analog Input Modules>>NI 9237
Problem: While measuring strain from a channel on the NI 9237, if an additional strain sensor is inserted into an available channel on the module it may cause other channels to see an offset. How can I correct this offset?
Solution:
The voltage offset that occurs is expected behavior when the NI 9237 module is used in half-bridge mode. When in half-bridge mode, additional loading of the excitation internal/external source can cause small changes in the excitation voltage at the remote half bridge which are different from the small excitation voltage changes in the module's half-bridge completion network. The amount of offset incurred will depend on the excitation voltage level. However you will typically see a range of 40 to 300uStrain offsets. To correct for this offset, National Instruments recommends performing bridge calibrations on all channels when a new sensor is inserted to adjust for slight changes in offsets. Refer to the NI 9237 Product Page or the Devzone Tutorial: Measuring Strain with Strain Gauges for more information on performing bridge calibrations.
When the NI 9237 module is used in full-bridge mode, this effect is not seen since both halves of the bridge are remote and see the excitation voltage at the same point.
Related Links: Devzone Tutorial: Measuring Strain with Strain Gauges Product Page: NI 9237
Attachments:
Report Date: 09/11/2007
Last Updated: 12/12/2007
Document ID: 4DAFURLX
