Section 8: Theory of operation
Series 3700A System Switch/Multimeter Reference Manual
8-16
3700AS-901-01 Rev. D/June 2018
dmm.opendetector open voltage
With
dmm.opendetector = dmm.ON
, a separate -1.5 A I
OPENLEAD
SHI and a separate SLO current
source will pulse on and off before the start of each measurement while I
SOUR
remains enabled. The
A/D will monitor SHI for 2 ms, then switch to SLO for an additional 2 ms. During either phase, if the
input voltage exceeds the above table, the A/D will stop in less than 100 µs and return an overflow
reading. If there are no open leads detected during the I
OPENLEAD
phase, the I
OPENLEAD
is disabled and
standard 4-wire is enabled.
V
MEAS
with open input:
If Sense HI is disconnected, V
MEAS
will droop less than
–1V, causing an A/D overflow.
V
MEAS
with valid connections:
For valid connections, INPUT Sense HI, V
MEAS
, will dip during the 4 ms I
OPENLEAD
phase. The amount
of the voltage dip is the sum of I
OPENLEAD
and the range I
SOUR
and R
DUT
load. For example, if
measuring a 100
kΩ
on the 100
kΩ
range, the
V
MEAS
across the 100
kΩ will be 0.85 V (10 A to
1.5 µA) × 100
KΩ
during I
OPENLEAD
and 1 V during measurement phase.
The tables below note timing with
dmm.opendetector = dmm.ON
.
Range
SHI and SLO
IOPENLEAD
phase (ms)
1
SHI settling
time (ms)
Line frequency
(Hz)
SHI measurement time
(ms)
1-10
kΩ
4.0
0.5
60
min
max
0.0083
250
50
0.010
240
100
kΩ
4.0
2.0
60
0.0083
250
50
0.010
240
1
MΩ
4.0
30.0
60
0.0083
250
50
0.010
240
10
MΩ to
100
MΩ
4.0
5.0
1
60
0.0083
250
Range
Internal
DMM comm
(ms)
SLO
settling
time (ms)
SLO
measurement
time (ms)
Internal
DMM comm
1 kΩ to
10
kΩ
0.06
0.5
min
max
0.06
0.0083
250
0.010
240
100
kΩ
0.06
1.0
0.0083
250
0.06
0.010
240
1
MΩ
0.06
1.0
0.0083
250
0.06
0.010
240
