PID controllers for temperature

 Since a vast number of applications in industry required temperature monitoring and control it is not strange to find a temperature dedicated controller. Therefore, some major comments are needed for this piece of equipment.

Image showing two dedicated temperature PID controllers. Model XMTA-808 only admits temperature sensors while model ESM-9930 may work with most industry available sensors for temperature, pressure, flow or others.

 CONTENTS

 Some things you can do with a PID temperature controller

 Other things to do with a PID temperature controller

 ** A temperature ramp

 ** Programming an alarm

 ** Recording data

 ** Setting a switch

 Measuring temperature

Some things you can do with a PID temperature controller

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There are two most important things,

• control of cooling
• control of heating

It would seem obvious but from the point of view of operating/using/programming this device this is a fact you need to know a priori. In cooling mode the controller works to keep the temperature at a set-point approaching from a high temperature, and vice versa for heating mode.

While heating or cooling users not always pay attention to the way in which temperature is kept at its set-point it is of interest to know this so that you can get more profit from your controller.

Other things to do with a PID temperature controller

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Once, heating or cooling operation have been devised further details need to be carefully specified. For example,

• programming a temperature ramp,
• programming an alarm,
• recording data,
• setting a switch.

Of course, not all PID controller models offer these options but you better consider what you will need before buying one of these or setting-up an experiment. Here are some details on these options.

A temperature ramp

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A temperaure ramp refers to increment or decrement of temperature with time at certain pace. For example: you may need to increase the temperature from 25$^\circ C$ to 85$^\circ C$ slowly in about 1 hour. Without a controller it would be hard since this operations should be done manually and with little precision. On the other hand, you may program the controller to increase 1$^\circ C$ per minute and after that keep the fluid/material at that temperature.

Schematicsof a temperature ramp

This could be important for several applications in which the fluid sample or material can not withstand sudden temperature changes without degradation.

Programming an alarm

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First, you should know that there are three common types of alarms. For example,

• sound,
• visual and
• message alarms.

Sound alarms may be produced by buzzers, for example, so that the user is notified by means a noise that something occurs (as when set temperature has been achieved). Visual alarms may be produced by pilot lights of different colors which may also blink. The typical pilot light color for alarms is: yellow. Message alarms are modern versions of alarms in the form of a message in your cell pnone or blinking text in a screen control panel. The main advantage of this kind of alarm is that it conveys more details on the nature of the cause of the alarm.

Recording data

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Depending on the nature of the experiment, support information obtained from it and required further analysis, temperature data recording may be key. This is, you may need to register temperature data every second during while the experiments are performed.

Therefore, you may wish this data in a excel file format or other and the possibility of plugging your laptop some how to something to obtain the file with the valuable information.

This is a kind of controller feature not always available at low cost but again, you should forsee what you will need from the PID controller.

Setting a switch

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What happen if you can not stay present during temperature measurements by the controller and unexpected increment/decrement of temperature occurs? Perhaps, you would wish to turn off, or on, a heating/cooling element. In that case, a switch would be needed.

Most PID controllers allow the user to set a switch for such cases, for example. Many different other applications could benefit from a switch.

Measuring temperature

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Temperature measurements require suitable sensors. In this case, the user should choose among some commercially available options such as,

• thermocouples, from which diffferent types are to be considered: L,J, K, R, S, T, B, E, N, C
• RTD's, from which the Pt-100 is widely used.

Not all controllers admit the same type of sensors. This means that: you should check first what are your sensor specifications before buying a controller or checking your controller's specifications before buying a sensor.

You are advised to read the post: Thermocuples vs RTD's

Depending on the model and manufacturer you could choose among options such as: number of digits after the decimal point and units, for example. 

Check your knowledge on PID controller for temperature applications

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Please, follow the link below to find a quizz on this topic and test what you have learned,

What you know about temperature PID controllers

This is the end. I hop you find useful the information of this post.

Any question? Write in the comments and I shall try to help.

Other stuff of interest

• LE01 - AC and DC voltage measurement and continuity test
• The pros and cons of bulb thermometers
• The pros and cons of bimetallic thermometers
• Some examples of temperature instruments
• Minor losses  - Formulas
• What is a process variable?
• What are the most important process variables?
• Time dependence of process variables
• A list of process variables
• Valves - Gate design

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Ildebrando.