On-off Vs PID Temperature Controller: Differences You Need To Know

Temperature controllers are used wherever temperature plays a significant role in controlling or completing a process or maintaining a distinct environment. They play a crucial part in process control.
These handy components can be used to control the temperature for heating, cooling or to remain at a set point temperature. In a broad sense, there are two types of temperature controllers: On-off and PID. In this article, we will examine these temperature controllers and tell you the differences you need to know about them. This way, you can choose the right one for your specific needs and applications.

Without further delay, let’s get into it.

What is an on-off temperature controller?

As their name suggests, on-off temperature controllers control temperature through an on-and-off mechanism. In essence, you set the desired temperature you want, and the controller will use this mechanism to remain within this threshold. If the temperature gets too hot, the controller will send an output signal and turn off the heater. If it gets too cold, the controller will turn on the heater. You will likely be familiar with this mechanism in your thermostat. The controller detects temperature courtesy of an electric temperature sensor, which is crucial to how this mechanism works.

What is a PID temperature controller?

PID stands for proportional, integral and derivative. These temperature controllers use these three elements to control the temperature using a formula. Here are what they stand for:

• Proportional stands for the variance between the actual temperature and the set temperature.
• Integral stands for the previous temperature variance from the setpoint temperature.
• Derivative stands for the predicted future variance using the previous two elements.

This way, the controller can maintain a set temperature with accuracy and consistency while adjusting to any sudden temperature changes in the environment. There are various types of PID temperature controllers, which include:

• PID controllers with cascade control loops
• Multi-Zone temperature PID control.

Differences between on-off and PID temperature controllers

Accuracy

Regarding accuracy, PID temperature controllers are the ones you are looking for. On-off controllers are not designed for accuracy and are unsuitable for applications where an error can lead to failure. For example, consider a pot of water being heated with an on-off controller set at a temperature of 100C. The controller will switch off the burner when the water reaches the boiling point. However, this temperature will continue to increase for a bit, which may not be a big deal in this scenario but can be for sensitive applications. On the other hand, a PID temperature controller will lower the current that it provides to the burner as the temperature nears 100C and ensure that it stays at that temperature. In addition, it will even be able to respond to temperature changes.

Cost

On-off temperature controllers are significantly more affordable than their counterparts as they use a simple mechanism. Additionally, they do not control the temperature much, reducing costs due to less current. This can be useful for people who require controllers where accuracy is not the primary concern, resulting in a lower-cost solution. PID controllers are much more complex and use a constant current to control the temperature. This makes them much more expensive than on-off temperature controllers. They are also used in applications like sterilizing medical equipment, where the costs cannot be sacrificed as lives depend on these tools.

Mechanism

On-off temperature controllers work with a simple mechanism for turning the heater on or off. This mechanism depends on whether the current temperature has exceeded the setpoint temperature. Therefore, the only parameter you need to set is the setpoint temperature and switching differential. Due to this simplicity, many people prefer these controllers if they do not require accuracy. It can also be easier to fix if a fault occurs. On the other hand, PID controllers are much more complex in how they work as there are various elements and parameters to consider. An engineer would have to manually set parameters into the controller, including the proportional, integral, differential and level of power values. These values will then determine how the controller will maintain the setpoint temperature.

Applications

The applications for these temperature controllers are very different due to their varying mechanisms and costs. On-off temperature controllers are used in applications where the accuracy is unimportant, and some temperature drops or increases are not much of an issue. You can use them in simple devices like thermostats, temperature alarms or refrigerators. On the other hand, PID temperature controllers are used for applications where precise control is required, regardless of the costs. You may not want a small temperature change from the setpoint temperature in such an application. This makes them ideal for sterilizing medical equipment and manufacturing processes in factories.

To sum up
Process control is essential for various manufacturing and production houses and industries, as it ensures that products manufactured or their intended purpose is fulfilled. This is where temperature controllers are vital devices as they can ensure that the temperature stays at a particular setpoint temperature. There are two main types of temperature controllers that we have looked at in this article: on-off and PID. We have looked at each of them and what they do so that you can understand how each of them works. Additionally, we have looked at significant differences you need to know to choose the ideal one for your needs and applications. These differences mainly deal with the controllers’ accuracy, costs, mechanisms and applications they are suitable for.

We hope this article has been informative and enables you to choose the suitable temperature controller for you. Thank you for reading!