Series 3700A System Switch/Multimeter Reference Manual
Section 8: Theory of operation
3700AS-901-01 Rev. D/June 2018
8-17
1. For 10
MΩ
and 100
MΩ, V
measurement
is made on Input HI. Input Sense HI is unused.
2. Default condition for 4-wire is
dmm.opendetector=dmm.ON
.
3. For
dmm.drycircuit=dmm.ON
, I
OPENLEAD
is disabled, but
print(dmm.opendetector)
returns
1.0.
4. Additional cable and Series 3700A card capacitance can increase settling times, resulting in
additional measurement uncertainty. Keithley Instruments recommend the use of Teflon or other
low-dielectric absorption wire insulation for these measurements.
4-wire dry-circuit open lead detection
The Series 3700A dry-circuit resistance measurement circuitry was designed for low power, low
glitch, and low open voltage applications such as GMRR head testing and air bag / squib testing that
require low energy resistance sourcing. For this reason,
dmm.opendetector = dmm.ON
is disabled
when
dmm.drycircuit = dmm.ON
. The I
OPENLEAD
current pulse would exceed the dry-circuit
voltage application.
The follow schematic provides a simplified view of the Series 3700A 4-wire dry-circuit open lead
detection.
Figure 116: Simplified Dry-Circuit open V-clamp feedback loop schematic
Dry-clamp open lead detector (dry-circuit)
A hardware detector is used to detect an open input lead. The hardware detector uses an internal
circuit to monitor the voltage on the V
DRY-CLAMP
terminal. The circuit will stop the A/D in less than
100 µs and return an overflow reading if the voltage is greater than 1 V.
