Resistance

NI Digital Multimeters Help (NI-DMM 18.1)

Edition Date: March 2018

Part Number: 370384V-01

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The DMM can make resistance measurements using a constant-current technique. A current is supplied to the resistance under test, and the DMM measures the resulting voltage as represented in the following figure.

With a known current and voltage, the DMM can determine resistance using Ohm's Law, as follows:

VM = IsRT

where RT is the sum of all resistances

RT = Rx + RLEAD + RLEAD

Therefore, the value of Rx = VM/Is if RLEAD is small or negligible compared to Rx.



The NI 4080/4081/4082 and NI 4070/4071/4072 generate a highly-stable current source, Is. The table below lists the value of this current by range:

Range Test Current1 Maximum Test
Voltage (Vt)
Offset Compensated
Ohms Available?
100 Ω1 mA 100 mVYes
1 kΩ 1 mA 1 VYes
10 kΩ 100 µA 1 VYes
100 kΩ10 µA1 VNo
1 MΩ10 µA 10 VNo
10 MΩ 1 µA10 VNo
100 MΩ1 µA || 10 MΩ*10 VNo
5 GΩ1 µA || 10 MΩ*10 VNo
1-10% to 0% tolerance
*Refer to Measuring on the 100 MΩ Range.

Every time you run self-calibration, the current source recalibrates to an ultra-high stability 10 kΩ reference resistor. While the absolute tolerance of the current is ±5%, the recalibration process identifies the value to a sub-ppm precision level. The calculated value of resistance is corrected to the precision of the ultra-stable reference resistor, assuring accurate measurements.



The NI 4065 generates a highly-stable current source, Is. The table below lists the value of this current by range:

Range Test Current1 Maximum Test
Voltage (Vt)
100 Ω1 mA 100 mV
1 kΩ 1 mA 1 V
10 kΩ 100 µA 1 V
100 kΩ10 µA1 V
1 MΩ5 µA 5 V
10 MΩ 500 nA5 V
100 MΩ500 nA || 10 MΩ*5 V
1-10% to 0% tolerance
*Refer to Measuring on the 100 MΩ Range.


The DMM has two modes of resistance measurement: 2-wire and 4-wire. Each mode applies the same precision current to the circuit, but the difference between 2-wire and 4-wire resistance measurements is how the voltage measurement is made.

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