Keithley DMM7510 Reference Manual page 133

Section 2: General operation Model DMM7510 7½ Digit Graphical Sampling Multimeter Reference Manual
Sense current is negligible, therefore
Measure resistance is
Open lead detection
When 4-wire measurements are made, erratic readings can occur if the Sense HI, Sense LO, or both
terminals are open. This can be caused by broken test leads.
To prevent erratic readings from open leads, you can enable the open lead detector feature. When
open lead detection is enabled and the range is 1 Ω to 1 MΩ ranges, the instrument pulses a 1 ms
negative current on the Sense HI and Sense LO terminals. If the signal at either terminal is less than
–10 mV, the display reads "OverflowΩ". If the signal is more than –10 mV, the current pulse is
automatically shut off, and the 4-wire measurement continues. For the 10 MΩ to 1 GΩ ranges, only
the Sense LO terminal is pulsed with a negative current, which minimizes settling time and device-
under-test noise.
When open lead detection is enabled, there is minimal impact on reading rates and an increase in
measurement reliability and integrity.
Open lead detection reduces the reading rate by 2 ms while Sense HI and Sense LO are measured.
Also, for measurements made through long capacitive cables or switch cards, the open lead detection
pulse current can increase settling time and decrease accuracies, especially for the 10 kΩ to 1 MΩ
ohm ranges.
Two-wire local sense connections
Two-wire connections are shown in the following figures.
Two-wire local sense connection drawings
Figure 68: Two-wire DUT connections to rear panel
2-106 DMM7510-901-01 Rev. B / May 2015