Aperture Time and Resolution

For DC voltage, DC current, resistance, and temperature measurements, the DMM provides two ways to set integration time, both of which affect the measurement resolution. These are in the number of power-line cycles (NPLCs) and aperture (in seconds).

NPLC Mode

Using NPLCs sets the number of power-line cycles during which the DMM’s analog-to-digital (A/D) converter samples the input signal for a measurement. The DMM automatically detects the AC line frequency, using it and the NPLC selection to set integration time. Use a larger NPLC value for better resolution. Use a smaller value for faster measurements. To obtain normal mode (line-frequency noise) rejection, you must select NPLC mode, with an integral number of power-line cycles (e.g., 1, 10, or 100 NPLC).

Aperture Mode

Aperture is the period, measured in seconds, during which the DMM’s analog-to-digital (A/D) converter samples the input signal for a measurement. A longer aperture yields better resolution; a shorter aperture provides for faster measurements. This mode allows the user to set a specific integration time, not based on power-line frequency. Use aperture, instead of NPLC, only if you need precise control over the DMM’s integration time.