model 2704 controller installation and operation handbook - Soliton

Input Operators
2704 Controller
11.3. THERMOCOUPLE/PYROMETER SWITCHING
This facility is commonly used in wide range temperature applications where it is necessary
to control accurately over the range. A thermocouple may be used to control at lower
temperatures and a pyrometer then controls at very high temperatures. Alternatively two
thermocouples of different types may be used.
Figure 11-3 shows a process heating over time with boundaries which define the switching
points between the two devices. The higher boundary (2 to 3) is normally set towards the top
end of the thermocouple range and the lower boundary (1 to 2) set towards the lower end of
the pyrometer (or second thermocouple) range. The controller calculates a smooth transition
between the two devices.
Input 2
High temperature
thermocouple or
pyrometer
Input 1
Low temperature
thermocouple
2704
Temperature
controller
S
Temperature
Boundary 2/3
Boundary 1/2
S
Controller operates entirely
on the higher temperature
device
RController operates on a
combination of both devices
Controller operates entirely
on the lower temperature
device
U
Time T
Figure 11-3: Thermocouple to Pyrometer Switching
11-8 Installation and Operation Handbook. Part No HA026502 Issue 1.0 Apr-00