Offset Nulling (Bridge Balancing)

When you install a bridge-based sensor, the bridge probably will not output exactly 0 V when not under load. Slight variations in resistance among the bridge legs generate some nonzero initial offset voltage. Use the DAQmx Perform Bridge Offset Nulling Calibration VI/function or the DAQ Assistant to perform an offset nulling calibration, which performs bridge balancing in a few different ways. Refer to the device documentation to determine the offset nulling methods your device provides.

Software Compensation (Initial Bridge Voltage)

This method of bridge balancing compensates for the initial voltage in software. With this method, NI-DAQmx measures the bridge while not under load. NI-DAQmx then uses this measurement as the initial bridge voltage when scaling readings from the bridge. This method is simple, fast, and requires no manual adjustments. The disadvantage of the software compensation method is that the method does not remove the offset of the bridge. If the offset is large enough, it limits the amplifier gain you can apply to the output voltage, thus limiting the dynamic range of the measurement.

Offset Nulling Circuit

The second bridge balancing method uses an adjustable resistor, or potentiometer, to electrically adjust the output of the bridge to 0 V.

Hardware Nulling Compensation

The third method, like the software compensation method, does not affect the bridge directly. A nulling circuit adds an adjustable DC voltage, positive or negative, to the output of the instrumentation amplifier to compensate for initial bridge offset.