Keithley DMM7510

Model DMM7510
7½ Digit Graphical Sampling Multimeter Reference Manual Section 4: Measure consideratio
ns
DMM7510-901-01 Rev. B / May 2015 4-5
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
REF
), as shown in the figure below.
Basic circuit theory dictates that I
REF
is equal to the I
DUT
. Because the voltmeter of the Model
DMM7510 (V
MEAS
) has high input impedance (>10 GΩ), current through the voltmeter branch is
insignificant and can be discounted. Therefore, as shown in the following figures, I
REF
= I
DUT
.
Figure 136: 2-wire ratiometric resistance measurement method schematic