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Documentation Number TCDA0997 Manual 3
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
Chapter 2: Thermocouple Overview
To understand the operation of the TCDA it is necessary to
understand the basic construction of the thermocouple. A
thermocouple consists of two solid wires, composed of dissimilar
metals, joined at one end. The joining of dissimilar metals generates
a small DC voltage based on the temperature of this junction. The
TCDA amplifies this small voltage to a usable level for A/D
converters.
The output of a thermocouple does not have a linear relationship
with temperature. A close approximation for a K-type thermocouple
is 40.6
µV/°C. This approximation is used with the TCDA. Figure 2.1
contains a plot of thermocouple output voltage over a temperature
range.
Figure 2.1: Thermocouple Non-linearity
Actual thermocouple output
0
0
Temperature
O
( C )
Ideal line (40.6uV/C)
O
u
t
p
u
t
V
o
l
t
a
g
e
(
V
)
This plot is not to scale, and the
nonlinearity has been exagerated.
0.0406
Note:
1000