AM16/32 Relay Analog Multiplexer
28
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 AM16/32.
Datalogger Reference - The CR1000, CR23X, 21X and the CR7 723-
T Analog Input card with RTD have built-in temperature references.
The 10TCRT Thermocouple Reference (not standard with CR10(X)
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 the data-logger and the AM16/32 must be of the same
wire type as the thermocouple (Figure 17). The "polarity" 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
constantan wire should run between the multiplexer's COM ODD L
terminal and the datalogger measurement terminal). Figures 17 and 18
depict type T thermocouple applications, but other thermocouple types
(e.g. E, J, and K) may also be measured and linearized by the
dataloggers.
If thermocouples are measured with respect to the datalogger reference
(i.e. the signal wires between datalogger and AM16/32 are made of
thermocouple wire), then it is not recommended that one make
measurements of any other sensor type through the AM16/32. 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 the
AM16/32.
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.
Summary of Contents for AM16/32
Page 6: ...This is a blank page...
Page 42: ...AM16 32 Relay Analog Multiplexer 36 This is a blank page...
Page 44: ...This is a blank page...
Page 45: ...This is a blank page...
