Ratiometric Method - Keithley DMM7510 Reference Manual

Model DMM7510 7½ Digit Graphical Sampling Multimeter Reference Manual Section 4: Measure considerations

Ratiometric method

For the 10 MΩ through 1 GΩ ranges, the ratiometric method is used to measure resistance. Test
current for this method is generated by a 6.9 V voltage source through a 10 MΩ reference resistance
(R ), as shown in the figure below.
REF
Basic circuit theory dictates that I is equal to the I . Because the voltmeter of the Model
REF DUT
DMM7510 (V ) has high input impedance (>10 GΩ), current through the voltmeter branch is
MEAS
insignificant and can be discounted. Therefore, as shown in the following figures, I = I .
REF DUT
Figure 136: 2-wire ratiometric resistance measurement method schematic
DMM7510-901-01 Rev. B / May 2015 4-5