AM16/32A Relay Analog Multiplexer
6.6 Thermocouple Measurement
The datalogger manuals contain thorough discussions of
thermocouple measurement and error analysis. These topics will not
be covered here.
6.6.1 Measurement Considerations
Reference Junction - As shown in Figure 17 and 18, two reference
junction configurations are possible: 1) reference located at the
datalogger or 2) reference at the AM16/32A.
Datalogger Reference - The CR1000, CR800, CR850, CR3000,
CR23X, 21X and the CR7 723-T Analog Input card with RTD have
built-in temperature references. The CR10XTCR Thermocouple
Reference (not standard with CR10X purchase), is installed on the
wiring panel between the two analog input terminal strips.
When the reference junction is located at the datalogger, the signal
wires between th
a-logger and the AM16/32A must be of the
larity" of the
thermocouple wires must be maintained on each side of the
multiplexer (e.g. if constantan wire is input to an L terminal, then a
tween the multiplexer's COM ODD L
easurement terminal). Figures 17 and
mocouple
th respect to the datalogger
res between datalogger and AM16/32A are
e
e dat
same wire type as the thermocouple (Figure 17). The "po
constantan wire should run be
terminal and the datalogger m
18 depict type T thermocouple applications, but other ther
types (e.g. E, J, and K) may also be measured and linearized by the
dataloggers.
If thermocouples are measured wi
reference (i.e. the signal wi
made of thermocouple wire), then it is not recommended that one
make measurements of any other sensor type through the AM16/32A.
Two problems would arise due to the properties of thermocouple
wire:
An extraneous thermocouple voltage would be added to the non-
thermocouple signal at the junction of dissimilar metals (e.g. the
multiplexer COM terminals). The magnitude of this signal would
vary with the temperature difference between the datalogger and th
AM16/32A.
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.
28
Summary of Contents for AM16
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