Model 2701 User’s Manual
Basic DMM Operation
3-35
Internal reference junction
“Internal” implies that a temperature transducer(s) is used to measure the cold junction
(CJC). For the Model 7700 switching module, the cold junction is the screw terminals
with voltage temperature sensors strategically placed to measure the temperature of the
cold junction.
The Model 2701 measures the temperature of the cold junction (screw terminals),
measures the input voltage, and then calculates the temperature reading at the
thermocouple.
External reference junction
For switching modules that do not have built-in sensors to measure temperature, each
module can use a thermistor or 4-wire RTD to acquire the reference temperature. Connect
a thermistor to channel 1 or connect a 4-wire RTD to channel 1 and its paired channel.
Position the temperature transducer near the terminals for the channel(s) being used to
measure temperature. Be sure to electrically insulate the transducer leads to keep them
from making contact with other conductors.
When you close channel 1 to measure the cold junction temperature, that temperature
reading will be used to calculate the temperature when you close a thermocouple channel.
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 could cause an erroneous on-scale reading.
The Model 2701 has an open thermocouple detection circuit. When enabled, a 10µA pulse
of current is applied to the thermocouple before the start of each temperature
measurement. If >12k
Ω
is detected (open thermocouple), the OVRFLW message will be
displayed. If <12k
Ω
is detected, the current is turned off and a normal thermocouple
temperature measurement is performed.
NOTE
Channel average cannot be used with thermocouple temperature measurements
if open thermocouple detection is enabled.
2701-900-01.book Page 35 Wednesday, August 3, 2011 9:43 AM
Summary of Contents for 2701
Page 344: ...12 CommonCommands 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 366: ...15 SCPIReferenceTables 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 393: ...A Specifications 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 399: ...B Model7700ConnectionGuide 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 410: ...C StatusandErrorMessages 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 417: ...D SignalProcessing SequenceandDataFlow 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 430: ...E MeasurementConsiderations 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 450: ...G KE2700InstrumentDriver Examples 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...