Can I Adjust the Range on the NI-9237 to Maximize Resolution?

Issue Details

• I have a NI-9237 and want to know if I change the range then does it fit ADC bits of resolution to the range that I specify?
• I have a sensor that is only 2 mV/V and the but the NI-9237 has a 25 mV/V range, can I scale the range of the NI-9237 to fit the sensor?

Solution

The NI 9237 only has one input range, so changing the values of Analog Input Maximum and Analog Input Minimum does not affect resolution. If you set the maximum or minimum to a narrower range, DAQmx will coerce the values to +/-25 mV/V to indicate that this is the closest supported range. Reading the maximum and minimum properties with a property node will return the coerced values. For example, setting the minimum to 0 mV/V and the maximum to 2 mV/V will not return an error it will be coerced to a maximum of 25 mV/V. If you set maximum and minimum to a wider range, DAQmx will return an error since you are asking it to do something the module can't handle. For example, setting the minimum to 0 mV/V and the maximum to 30 mV/V will return Error -200077 that the requested value is not a supported value for the property.
 

Additional Information

The NI-9237 is a ratiometric measurement device, meaning that it measures the ratio between the sensor output and the excitation voltage provided. The following link on Bridge Sensor Scaling provides more information on ratiometric measurements. The module has both internal and external excitation options. The external excitation still needs to be routed through the module for an accurate ratiometric measurement. The excitation ranges are specified in the datasheet, note that the internal excitation has a maximum power of 150 mW. Full bridge sensors with a nominal resistance of  350 Ω or less requiring 10 V excitation will require an external excitation source.