Keithley 3720-ST

Series 3700A System Switch/Multimeter Reference Manual Section 8: Theory of operation
3700AS-901-01 Rev. D/June 2018 8-19
• I
SOUR
open voltage with dmm.opendetector. A hardware detector is used to continuously detect
for open input lead. The hardware detector uses a comparator circuit to monitor the voltage on
the ohm I
SOUR
V
OPEN-HI-LEAD
terminal. If during a measurement cycle, the input voltage on
I
SOUR
V
OPEN -HI-LEAD
terminal is greater than 7.1 V, the A/D will stop in less than 100 µs and return
an overflow reading. The following table notes timing with dmm.opendetector = dmm.ON.
The thermocouple open detection times are listed in the following table.
I
ON
source
settle
(ms)
I
OPENLEAD
measure
(ms)
Phase
internal
DMM
comm. (ms)
I
off
source
settle
(ms)
Line
freq
(Hz)
T/C measurement
time (ms)
Internal DMM comm.
(ms)
1.0
0.8
0.4
1.0
60
min
max
0.06
0.0083
250
50
0.010
240
1. Default condition is dmm.opendetector=dmm.ON or 1.
2. For dmm.transducer=dmm.TEMP_THERMISTOR, dmm.TEMP_THREERTD, and
dmm.TEMP_FOURRTD, I
OPENLEAD
phase is disabled, but print(dmm.opendetector) returns 1.0.
3. dmm.opendetector is a common remote command, shared with fourwireohms. To enable or
disable dmm.opendetector for either function, the appropriate function must be selected before
applying the new dmm.opendetector state. For example, to disable thermocouple open
detection, send dmm.func="temperature" then dmm.opendetector=0.
The following figure is a schematic representation of the Series 3700A open thermocouple detection.
Figure 117: Thermocouple Open Detector drawing