It could be argued that the voltage errors and CJC errors are uncorrelated so the
two errors should be combined using a root-sum-square calculations. However,
for simplicity, in our calculations we have just added the two components. The
Seebeck coefficients for various types of thermocouples at various temperatures
can be found in the standard tables for thermocouples, such as
NIST Mono-
graph 175
.
12.3
Operation
Using the 2565 Precision Thermocouple Module with the 1560
Black Stack
is
very simple. The following sections explain the steps for setting up and using
the 2565 to measure with thermocouples. For instructions for installing the
2565 Precision Thermocouple Module onto the 1560 see Section 4.1.
12.3.1
Connecting a Thermocouple
The 2565 Precision Thermocouple Module accepts both bare wires and sub-
miniature size thermocouple plugs. If a plug is used it must match the thermo-
couple type for the internal CJC to be accurate. For example, if you are using a
type K thermocouple you must also use a type K plug.
Each receptacle has a cam lever next to it that opens and closes the receptacle
as shown in Figure 18. Flipping the lever out opens the receptacle. While the
receptacle is open insert the wires or plug. The positive terminal is to the left
and the negative terminal is to the right. Push the lever back in to clamp the
wires or plug. After attaching a thermocouple to the 2565 wait two minutes be-
fore measuring for best results. Some shift in the measurement may occur as
temperature gradients settle .
The input channels are numbered from left to right as explained in Section
4.5.1 and Figure 7.
12.3.2
Selecting the Thermocouple Type
To display temperature accurately each channel of the 2565 must be pro-
grammed for the correct thermocouple type. This is done using the
EDIT
PROBE
soft-key in the
PROBE
menu (see Section 5.2.1). For example, if you
are using a type K thermocouple on Input 1 select the
EDIT PROBE
function
in the
PROBE
menu, select input channel 1, and set the CONVERSION type
to TC-K. The 1560 converts voltage to temperature according to the standard
formulas given in
NIST Monograph 175
(see Section 5.2.1.10).
When calibrating thermocouples, or the 2565 module itself, it is often useful to
display voltage instead of temperature. Voltage is displayed by setting the
CONVERSION type to V (see Section 5.2.1.9).
12.3.3
Selecting the CJC Type
The 1560 and 2565 can operate with either internal or external cold-junction
compensation (CJC). CJC is necessary because a thermocouple can only mea-
149
12 2565 Precision Thermocouple Module
Operation
