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AM16/32B Relay Multiplexer 29
When the reference junction is located at the data logger, the signal wires between the data
logger and the AM16/32B must be of the same wire type as the thermocouple (
). The
“polarity” of the thermocouple wires must be maintained on each side of the multiplexer (for
example, if constantan wire is input to an L terminal, then a constantan wire should run between
the multiplexer COM ODD L terminal and the data logger measurement terminal).
and
depict type T thermocouple applications, but other thermocouple types (for
example, E, J, and K) may also be measured and linearized by the data loggers.
It is not recommended to make measurements of any other sensor type through the AM16/32B if
thermocouples are measured with respect to the data logger reference (the signal wires between
the data logger and AM16/32B are made of thermocouple wire). Two problems would arise due
to the properties of thermocouple wire.
First, 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 data logger and the AM16/32B.
Second, 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.
FIGURE C-1. Differential thermocouple measurement with reference junction at the data logger
FIGURE C-2. Differential thermocouple measurement with reference junction at the AM16/32B
(using 107-L thermistor)
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