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Differences and similarities between Temperature Controllers and Process Controllers

Instrumentation & Control Electronics

Process and temperature controllers are similar in many respects, and there are a lot of differences in terms of structure, operation and applications in process control instrumentation. We will analyze these two prominent process control equipments in this article.

Process is a method to change or refine raw materials to craft a finished product. The raw materials may be in the form of solid, liquid, gas or slurry. When a product is being made, the process variables are to be controlled to a definite and preset pattern to get a quality product. In other words, process controllers will measure and control the process variables like temperature, pressure, volume, flow, displacements, chemical & physical properties of materials to produce the end product. Let's look at a simple process. Say, in a process, two ingredients are to be mixed at a certain proportion and at a certain temperature. The end product will be a powder made out of these two ingredients at a fixed pressure. Let's find out the measurements and processes involved in it. Measurements involved are weight or volume, temperature and pressure. We have to control the proportions, temperature and pressure. This process will require three controllers, namely proportion, temperature and pressure controller. All these three controllers may be combined into one process controllers. We may conclude that temperature controller is also a process controller, or the term process controller is a broader aspect in a process control system.

Similarities between Temperature Controllers and Process Controllers:

1. Basic principle of both is alike. A controller will have a reference control parameter. This reference parameter is continuously compared with measured parameter by a sensor, and an error signal is generated. The controller has to generate a system input for the process. The function of the controller is to keep the error signal zero orclose to the accepted accuracy of the controller.

2. The control mechanism of both temperature and pressure controllers are alike. The types of controls for both are on-off, proportional, PID or fuzzy logic control. In both cases, the operator involvement has to be minimized. The electronic control circuitry and algorithm are similar. The set point adjustment techniques are alike. The output signal to the system actuator is also same.

Differences between Temperature Controllers and Process Controllers:

1. Temperature controller controls only the parameter temperature in a process. Whereas, process controller is involved in the control of multiple parameters like flow, volume, pressure, weight, viscosity, proportions etc.

2. Temperature controller sensors are limited to measurement of temperature only. These are thermocouples, RTD etc. Sensors like strain gauges, LVDT, Orifice, chemical sensors and many more are used in process controllers.

3. Process controllers are manufactured with some relevant logic control systems. Temperature controllers are normally built with ordinary logic control mechanism. In process controllers, we can have programmable logic control (PLC), distributed control system and SCADA system. Process controller is built to for batch or continuous control systems. Process controllers are able to implement statistical process control through chart control.
Contributed by: Coulton Fuji Electric Instrumentation & Control
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