Page 220 - Dynamics and Control of Nuclear Reactors
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16.2 Sensor characteristics 219
FIG. 16.7
A fast response RTD.
16.2.2.2 Thermocouples
Thermocouples have two dissimilar wires that are joined to form the thermocouple
junction. Reactor thermocouples are contained inside a stainless-steel sheath. Insu-
lator (magnesium oxide) fills the space between the thermocouple and the inner wall
of the sheath. See Fig. 16.8.
A thermocouple creates a voltage that depends on the temperature difference
between the junction and open end of the wires. So, a thermocouple voltage is a func-
tion of the temperature difference between the open end and the junction. The junc-
tion temperature is obtained as follows:
– Instrumentation measures the thermocouple voltage.
FIG. 16.8
A sheathed thermocouple.
