Digital Multimeter Measurement Defaults

This tutorial recommends tips and techniques for using a National Instruments digital multimter (DMM) to build the most accurate measurement system possible. In this tutorial, you learn how the NI 4070 can operate as both a 6½ digit digital multimeter and a fully isolated, high-voltage digitizer, capable of acquiring waveforms at sample rates up to 1.8 MS/s at ±300 V input. This section of the tutorial covers the NI 4070 default measurement settings.

For more information return to the Complete Digital Multimeter Measurement Tutorial.

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The following table lists the default measurement settings for the NI 4070 Digital Multimeter.

Function	Aperture	AutoZero	ADC Calibration	DC Noise Rejection
DC 6½ digits	100 ms	ON	ON	High-Order
DC 5½ digits	500 µs	ONCE	OFF	Second-Order
DC 4½ digits	20 µs	ONCE	OFF	Second-Order
DC AutoRange	500 µs	N/A	OFF	Second-Order
AC	Max (DC or 4/(minFreq))	OFF	OFF	N/A
AC AutoRange	Max (500 µs or 4/(minFreq))	OFF	OFF	N/A
Frequency	2/(minFreq)	N/A	N/A	N/A
Period	2 x (the maximum period)	N/A	N/A	N/A

By default, the Aperture time, AutoZero, ADC Calibration, DC Noise Rejection settings for a measurement are chosen by the driver based on the configured measurement and resolution. These values were chosen to ensure accuracy for 6½ digit measurements while not sacrificing performance at lower resolutions. For AC, excluding AutoRange, the aperture is expressed as Max (DC or 4/minFreq). minFreq, or minimum frequency, is a user programmable parameter with a default value of 20 Hz. Therefore, the aperture default is 200 ms.

The same applies for other user selectable values of minFreq. For example, if a minFreq of 1 kHz is selected then 4/minFreq = 4/1 kHz = 4 ms. In this case 4 ms would be used as the AC aperture for resolutions <6 digits. For resolutions >6 digits, 100 ms would be used.

Default Settle Times

Function	Settle Time
DC V (100 mV-10 V)	1 ms
DC V (100 V, 300 V)	2 ms
DCV AutoRange	2 ms
Resistance <10 kW	1 ms
Resistance 10 kW	5 ms
Resistance 100 kW	25 ms
Resistance 1 MW	100 ms
Resistance > or = 10 MW	250 ms
Resistance AutoRange	50 ms
AC V DC coupled	3 µs
AC V AC coupled	1 s
Frequency/Period	500 ms
DC I	100 µs
AC I	3 µs
Diode	10 ms

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