NI 4065 DMM Measurement Cycle

The NI 4065 measurement cycle is made up of three measurement phases: switch time, settling time, and aperture time. Refer to the figure below for relative timing of these phases. The aperture time is the length of time the signal of interest is being measured. Generally the settle and aperture times are selected by the device driver based on the specified resolution. These values can also be independently controlled. Refer to Configuring Measurement Timing for more information.

The internal switch time is required to configure the analog circuitry of the NI 4065 for the next measurement. This time is not user programmable.

During resistance measurements, the signal is measured with an applied current source. The AC measurement cycle contains the same phases, but the minimum signal measurement time is based on the minimum frequency required of the measurement. For example, for a minimum frequency of 50 Hz with a 5½ digit resolution, an aperture time of 10x the period of the 50 Hz signal is required, or in this example, 200 ms.

When Auto Range is selected, the Auto Range measurement phase occurs before the signal measurement phases. After the correct range is identified, signal measurements use the selected range.

Note  When using Auto Range, keep in mind that longer apertures significantly slow down Auto Ranging because multiple measurements are made to find the best range possible. For best measurement speed, manually select the desired range.