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
