In a control system, the process variable is to be maintained in a fixed range, a manipulated variable is adjusted to maintain the process variable.
Here in temperature control process the process variable is the temperature and manipulated variable is flow.
A steam-heated “jacket” envelops the reactor vessel, transferring heat from the steam into the chemical solution inside.
Team-heated “jacket” envelops the reactor vessel, transferring heat from the steam into the chemical solution inside.
The process variable temperature is measured using temperature sensors and the measured value is transmitted in digital bits using temperature transmitter represented in the figure as TT. The transmitter output is directly given to the temperature controller to produce a control action.
The controller is represented as TIC (temperature indicating controller) in the figure. Transmitter output is directly connected to a controller.
The controller compares measured temperature value with a setpoint and produces a control action. The control signal also will be in 4-20ma.
The 4-20mA is converted into a pneumatic signal in a range of 3-15 psi, using a transducer TY which actuates the valves. The pneumatic signal is given to the valve diaphragm. Which controls the valve actuator. So steam flow is controlled, which controls the steam flow to the steam jacket.
If the temperature is higher in the reactor the valve closes to control the temperature, and if the temperature is very low then valves open full to increase the flow of steam through steam jacket.