Temperature Sensor:

• Measures the temperature of the system. Several types exist, including Resistance Temperature Detectors (RTDs), Thermistors, and filled-tube thermometers. The sensor provides a signal representing the measured value (MV) of the temperature.

Transmitter:

• The transmitter receives the signal from the temperature sensor. Its primary function is to amplify and condition this signal, making it suitable for comparison and processing by the controller. It converts the sensor's output into a standardized signal (e.g., 4-20 mA).

Comparator:

• The comparator compares the measured value (MV) signal from the transmitter with the set value (SV) or desired temperature. The difference between the MV and SV is the error signal. This signal reflects how far the actual temperature deviates from the desired temperature.

Temperature Controller:

• This is the brain of the system. It receives the error signal from the comparator and uses a control algorithm (often a PID – Proportional, Integral, Derivative – controller) to determine the appropriate corrective action. The PID algorithm adjusts the output signal to minimize the error.

Signal Converter:

• This component takes the output signal from the controller and converts it into a form suitable to operate the actuator. For example, it might convert an electrical signal into a pneumatic signal (compressed air pressure) or a hydraulic signal.

Actuator (or 3-way Valve):

• The actuator is the final control element. It receives the converted signal and makes adjustments to the system to correct the temperature. Examples include pneumatic diaphragm control valves, which control the flow of a heating or cooling medium. A higher signal might open the valve to allow more heat, while a lower signal would reduce the flow.