What Does the Millivolts per Volt Unit for a Bridge-Based Sensor Mean?

Updated Dec 16, 2019

Reported In

Hardware

  • CompactDAQ Chassis
  • C Series Strain/Bridge Input Module

Driver

  • NI-DAQmx

Other

  • Strain gauges
  • Load cells
  • Force transducers
  • Pressure transducers
  • Torque transducers

Issue Details

  • I have a bridge-based sensor and its rated output is given in mV/V. What does this mean?
  • How can I make sure that my bridge sensor voltage output level is within the range of the DAQ device that I am using?

Solution

Bridge-based sensors typically specify rated output (R.O.) in millivolts per volt (mV/V), where mV/V is the ratio of output voltage to the excitation voltage required for the sensor to work. These sensors are strain gauge based sensors that provide a voltage output that is proportional to the excitation voltage. This unit of measurement enables the bridge sensor readings to remain fixed regardless of any fluctuations in the excitation voltage.

For example, a sensor with a nominal rated output of 2 mV/V excited with 5 V will provide a nominal voltage output of 10 mV, whereas a 10 V excitation will derive in a nominal voltage output of 20 mV. 

Note: If you are using a module that takes ratiometric measurements like NI-9237, it will measure and show a mV/V value, in this case 2mV/V. 

Additional Information

  • Bridge sensors are a common type of pressure measurement. Bridge sensors are made of a strain gauge and a diaphragm with a change in pressure casuing a corresponding resistance change. This mechanism allows pressure to be accurately measured in DAQ systems.
  • Remember to check the power requirements of the sensor to identify if you will need an external power supply or not. The power requirements of your module is specified in the specifiactions of the device. For example, for the NI-9237, the analisys is explained in the following document and it should be similar for other modules: When Should I Provide an External Voltage to NI 9237 Module?

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