Campbell Scientific AM16/32B Relay Multiplexer - Manual (Page 40)

AM16/32B Relay Analog Multiplexer
6.6 Thermocouple M
The data
measure
r analysis. These topics will not be covered here.
6.6.1 Measurement Con
Referenc
reference
datalogg
ce at the AM16/32B.
23X,
in
temperat
standard
two anal
When th
between
the therm
must be
wire is in
multiple
terminal
applications, but other thermocouple types (for example, E, J, and K) may also
be measu
It is not
the AM1
reference
M16/32B are made of
thermocou he properties of
thermocouple wire:
An extraneous thermocouple voltage would be added to the non-thermocouple
signal at the junction of dissimilar metals (for example, the multiplexer COM
terminals). The magnitude of this signal would vary with the temperature
difference between the datalogger and the AM16/32B.
Some thermocouple wires have a greater resistance than copper, which adds
resistance to the non-thermocouple sensor circuit. For example, constantan is
approximately 26 times more resistive than copper.
easurement
logger manuals contain thorough discussions of thermocouple
ment and erro
siderations
e Junction — As shown in FIGURE 6-8 and FIGURE 6-9, two
junction configurations are possible: 1) reference located at the
er or 2) referen
Datalogger Reference — The CR1000, CR800, CR850, CR3000, CR
21X, and the CR7 723-T Analog Input card with RTD have built-
ure references. The CR10XTCR Thermocouple Reference (not
with CR10X purchase) is installed on the wiring panel between the
og input terminal strips.
e reference junction is located at the datalogger, the signal wires
the datalogger and the AM16/32B must be of the same wire type as
ocouple (FIGURE 6-8). The “polarity” of the thermocouple wires
maintained on each side of the multiplexer (for example, if constantan
put to an L terminal, then a constantan wire should run between the
xer’s COM ODD L terminal and the datalogger measurement
). FIGURE 6-8 and FIGURE 6-9 depict type T thermocouple
red and linearized by the dataloggers.
recommended to make measurements of any other sensor type through
6/32B if thermocouples are measured with respect to the datalogger
(the signal wires between the datalogger and A
ple wire). Two problems would arise due to t
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