Resistance Measurements

NI power supplies and SMUs can make resistance measurements because they can both generate and measure test voltages and currents. Because they can operate as precision current sources at high current levels, these devices are well suited to measure low resistance values.

To measure a resistance with an NI power supply or SMU, select a test current that creates a voltage drop within module capabilities. After the channel output is enabled and settled, use the niDCPower Measure Multiple VI or the niDCPower_MeasureMultiple function to measure the actual current being delivered to the resistor as well as the measured voltage across the resistor. To determine the accuracy of a resistance measurement, the accuracy specifications of both current and voltage measurements for the power supply or SMU should be taken into account. For channels with remote sense capabilities, enabling this feature results in a more accurate voltage measurement at the resistor terminals.

Compensation for Offset Voltages

When measuring low-value resistances, thermal voltages may introduce significant offsets into the resistance measurement path. If an offset voltage exists in series with the resistance to be measured, as in the following figure, taking a second measurement at a different current output setpoint allows the offset to be accounted for in the resistance calculation.


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The two test currents, I1 and I2, create voltage drops of V1 and V2, respectively. Thus, the following two equations can be derived:

  • V1 = I1R + VOS
  • V2 = I2R + VOS

Rearranging these two equations allows you to calculate the unknown resistance, R, without measuring VOS. Assuming the currents I1 and I2 are different, the following equation can be derived:

R = (V2 - V1) / (I2 - I1)

For the best signal-to-noise performance, test currents of opposite polarity should be used (for example, +100 mA and -100 mA). If currents of opposite polarity are not feasible, the next best solution is to use test currents that are as far apart as possible. For example, if your first current is 1 A, you could choose a second test current of 10 mA.