Auto Zero

Auto Zero

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

Notes  The NI 4050 does not support Auto Zero. 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 calibration, either self-calibration or external 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 performs an Auto Zero and stores the value for use in subsequent measurements, as long as Auto Zero ONCE remains selected. If you disable Auto Zero ONCE, the DMM restores the Auto Zero offset from the previous calibration.

Note  The NI 4060/4065 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.