Temperature Controller using PLC and SCADA

Temperature Control System can be as simple as comprising of only heating element and sensing element where as there’s no limit on the complexity level. Depending upon where it is to be used, complexity involved as well as system components varies largely. We present an Industrial Grade implementation of Temperature Controller using PLC and SCADA.

Block Diagram- Temperature controller using PLC and Scada.

Temperature controller using PLC and SCADA
Temperature controller using PLC and SCADA

Components: Temperature Controller

Figure 1 shows the system block diagram which comprises of –

  • RTD(Temperature Sensor)
  • Resistance to Current Converter
  • PLC
  • Power Supply
  • Coil(Heating Element)


  • It is a resistive type temperature transducer which converts variation in temperature to variation in resistance and this variation is linear in nature.
  • At 0 Degree Celsius, its resistance is 100 Ohms and it increases linearly with increase in temperature.

Resistance to Current Converter

  • It converts variation in resistance to variation in current(4 – 20mA). It can be operated in 3 different modes depending upon accuracy and applications.

Power Supply

  • System comprises of 2 power supply – 12V DC for PLC & Converter and 230V,50Hz for Heating Element.

  Programmable Logic Controller

  • PLC is the heart of system which accepts Analog current equivalent to temperature via converter to determine actual temperature (14 bit ADC).
  • Depending upon the set point, PLC will vary its analog output (15 bit DAC) to stabilize the system i.e. to achieve desired temperature.
  • Analog Output controls triggering of thyristorized circuit for controlling temperature.

System Code/ Ladder Diagram Flow graph.

Temperature controller Flow graph
Temperature controller Flow graph

The flow graph is somewhat self explanatory. We check the switch positions before making any further process. The temperature from the sensor is sensed by the PID controller and sent to the output of the heater coil. Check out the below image which shows output in GUI.


Temperature Controller Output
Temperature Controller Output


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