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 300µStrain 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: 01/14/2009 Document ID: 4DAFURLX |
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