5: Source-measure considerations 2470 High Voltage SourceMeter Instrument
5-22 2470-901-01 Rev. A / May 2019
Calculate accuracy of a resistance measurement made by
sourcing I and measuring V
This example shows how to use the summation method to calculate the accuracy of a resistance
measurement made by sourcing current and measuring voltage. With this method, the accuracy of
the source and measurements are found separately and then added together.
Device to be measured = 20 Ω resistor using 100 mA test current
Current source accuracy:
Current output = 100 mA on 100 mA range
Accuracy specification = ± (0.025% of output + 15 µA)
= ± {(100 mA x 0.00025) + 15 µA}
= ± {25 µA + 15 µA}
Voltage measure accuracy:
Input signal = (20 Ω x 100 mA) = 2 V
Accuracy specification of 2 V range = ± (0.012% of output + 300 µV)
= ± {(2 V x 0.00012) + 300 µV}
= ± {240 µV + 300 µV}
Total measurement uncertainty = 0.04% + 0.027% = 0.067%
For higher accuracy measurements when using SMU Instruments, use the source readback function
to actually measure the source output. Use the measured source value to calculate the resistance. To
calculate the total accuracy from this example using source readback, add the current and voltage
measurement accuracy specifications.
Current measure accuracy:
Input signal = 100 mA on 100 mA range
Accuracy specification of 100 mA measurement range = ± (0.025% of reading + 6 µA)
= ± {100 mA x 0.00025) +6 µA}
= ± {25 µA + 6 µA}
= ±31 µA
Total measurement uncertainty using source readback = ± (0.031% + 0.027%) = ±0.058%
Notice the total uncertainty of 0.058% when measuring the output of the current source is much better
than using the current source output specification to calculate the total error (±0.067%).
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