Keithley 3730 User Manual

Series 3700
System Switch/Multimeter User's Manual Section 5:
Basic Digital Multimeter (DMM) Operation
Document Number: 3700S
-900-01 Rev. A / August 2007 5-
37
Open thermocouple detection
Long lengths of thermocouple wire can have a large amount of capacitance that is seen at the
input of the DMM. If an intermittent open occurs in the thermocouple circuit, the capacitance can
cause an erroneous on-scale reading. The Series 3700 has an open thermocouple detection
circuit. When enabled, a 100A pulse of current is applied to the thermocouple before the start
of each temperature measurement.
NOTE Default condition is dmm.opendetector = dmm.ON.
The Series 3700 open thermocouple detection works in similar fashion to the open lead
detection. Refer to Effects of open inputs on ohms readings (see "Open lead detection" on page
5-30). The open thermocouple detection performs as follows:
 VMEAS open voltage: If Input HI V
MEAS
is outside 120mV, the A/D will abort in <100sec
and return an overflow reading.
 A calculated measurement, outside of the ranges contained in the following table, will
cause the "Overflow" message to be displayed.
Type
Range
J
-200°C to +760°C
K
-200°C to +1372°C
N
-200°C to +1300°C
T
-200°C to +400°C
E
-150°C to +1000°C
R
0°C to +1768°C
S
0°C to +1786°C
B
+350°C to +1820°C
 If during a measurement cycle, with dmm.opendetector = dmm.ON, the ohm's function
100A I
SOUR
is pulsed on and off before the start of each measurement. The A/D will
monitor V
MEAS
for 0.8msec. During the I
ONPHASE
, if the resistance >1.15k is detected, or the
input voltage is greater than 120mV, the A/D will abort in <100sec and return an
overflow reading. If <1.15k is detected and the input voltage is in the range of 120mV,
the open lead detection current is turned off and a normal thermocouple temperature
measurement is performed (see Thermocouple connections (on page 5-39)).
 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 7.1V, the A/D will abort in <100sec
and return an overflow reading. The following table notes timing with dmm.opendetector
= dmm.ON.

Keithley 3730 Specifications

General

Brand	Keithley
Model	3730
Category	Multimeter
Language	English