Auto Zero

NI Digital Multimeters Help (NI-DMM 18.1)

Edition Date: March 2018

Part Number: 370384V-01

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Auto Zero is a method used to compensate for internal DMM offsets.

Notes For NI 4065 devices, Auto Zero is always ON. Auto Zero is an integral part of the signal measurement phase and adds no extra time to the overall measurement.

When Auto Zero is enabled, the internal DMM input is connected to its input LO and measured. The subsequent input signal is measured, and the Auto Zero value subtracted from it. Thus, any offsets in the measurement path or ADC are subtracted from the signal, correcting for the offsets. You can disable Auto Zero before initiating or reading a measurement; it remains disabled until you enable it again.

When you disable Auto Zero, the DMM restores the Auto Zero value from the previous self-calibration.

If you find the offset to be unacceptable, you can either subtract it algorithmically in a later process, such as by shorting the inputs and recording it, or you can run self-calibration, which calculates and stores new Auto Zero offsets. To maintain stable offset performance in high resolution modes (for example, 6½ or 7½ digit resolution) you should enable Auto Zero.

You can also enable Auto Zero ONCE. Auto Zero ONCE is equivalent to Auto Zero ON if you perform a single point acquisition with the Number of Averages set to 1. If you are performing a multiple point acquisition, enabling Auto Zero ONCE will cause the DMM to perform Auto Zero only during the first measurement cycle for each acquisition. Using Auto Zero ONCE can reduce total acquisition time.

Note  The NI 4065 does not support setting Auto Zero to ONCE.

NI recommends using Auto Zero ONCE only for multiple measurements taken on the same range. If you enable Auto Zero ONCE for an Auto Range measurement, Auto Zero ON is used to ensure that the correct Auto Zero value is applied to each range.

Related Topics

Configuring Auto Zero

Self-Calibration

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