How a Temperature Control Loop Works ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

How a Temperature Control Loop Works

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A temperature control loop is designed to measure and control the temperature of a process.  A typical process whose temperature is required to be controlled is an Oven which has a heater. Another very common process in the home is water bath temperature in a water heater whose temperature is controlled by a thermostat.

Basic Elements in a Temperature Control Loop:
As shown above, there are four basic components of
a typical temperature control loop. They are:
(a) The process
(b) The temperature sensor/Transmitter
(c) The Temperature Controller
(d) The final control element

The Process
The process whose temperature is required to be controlled e.g an Oven or Water temperature.

Temperature Sensor/Transmitter
A Temperature sensor which measures the process temperature. In an industrial process, it is typically either an RTD or a Thermocouple. The Temperature Transmitter amplifies, conditions and transmits the signal to a temperature controller. Typically the sensor and transmitter is an integral unit not separated from each other.

Temperature Controller
The temperature controller is the instrument that initiates the temperature control action. It does this by comparing the process temperature we wish to control called the process variable with the desired value of temperature called the set value. The difference between these values is known as the error (Deviation). The Temperature controller uses this error to decide how much heating or cooling is required to bring the process temperature back to the desired value.

Final Control Element
The output signal from the controller is known as the manipulated value and is normally connected to a final control element which is a heater, control valve, fan or some other device which actually adds or removes heat from the process.

Temperature Control Mechanism of an Oven

To  understand how a temperature control loop works in real life, consider the temperature control mechanism of an Oven. As can be seen above, a thermocouple sensor/transmitter measures the temperature of the oven (the process) and sends a signal to the temperature controller. Based on whether the temperature of the Oven is above or below a pre-determined set point, the controller initiates a control action to either put on the heater (final control element) to add more heat or turn off the heater to remove heat.

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