Offset Nulling

Offset Nulling

Offset nulling consists of measuring the corresponding zero reading in a measurement path and subtracting this value from subsequent samples.

The way you connect the leads to obtain the zero reading depends upon the type of measurement you are taking.

To perform offset nulling, complete the following steps:

1. Disconnect the DUT from the leads that are connected to the DMM.
2. If you are measuring DC voltage, inductance, or resistance, short the input leads to obtain the corresponding zero reading. If you are measuring DC current or capacitance, leave the leads unconnected (open circuit) to obtain the corresponding zero reading. In a switching system, you can make the open-circuit or short-circuit measurement with channels dedicated as short or as an open. NI recommends using cables and switches with low thermal voltages and low-path resistance to minimize the offset introduced by the measurement path. Refer to Thermal Voltages for more information.
3. Record the value of the measurement.
4. Connect the leads to the DUT, and subtract the value measured in step 3 from all subsequent measurements.

The subtraction operation can be performed programmatically with the ADE, and the DMM SFP has an offset nulling feature.

For capacitance and inductance measurements, NI recommends using OPEN/SHORT compensation rather than offset nulling to remove offset errors. OPEN/SHORT compensation performs a fixture/cable characterization at the test frequency to compensate for offset and gain errors, while offset nulling only performs an arithmetic subtraction of the offset present in the fixture/cable.

For resistance measurements in the ranges ≤10 kΩ, you can enable offset compensated ohms, which removes offsets in the measurement path much better than offset nulling alone.