Operation
15
Controlling the Hot Water Circulator (HWC)
The heater is controlled by a PID controller in the software. Click ‘Hot Water
Circulator’ to start the circulator pump then click ‘Control’ to open the controller
window.
The PID controller initially defaults to Off with the heater turned off. The Mode of
Operation must be changed to Manual or Automatic as required to turn on the heater.
In Manual operation the required Manual Output (heater power) is adjusted by the
operator as necessary to obtain the required hot water temperature T2. In Automatic
operation the PID controller varies the heater power continuously to correct for any
error.
The hot water temperature T2 is chosen as the default process variable to provide a
stable temperature T1 inside the reactor. Control of T1 directly would be difficult
because of the lag in the process and significant overshoots in batch or low flow
conditions. As a consequence Reactor temperature T1 will always be stable but
slightly lower than T2. If it is required to maintain Reactor Temperature T1 at a
particular temperature then an appropriate offset can be applied to the setpoint of the
controller so that T2 is elevated slightly to compensate.
If required temperatures T1 or T3 (type K thermocouple sensor not supplied) can be
selected as the alternative process variable but appropriate P, I, D and CT settings
will need to be entered for the system to operate.
