What do commercial espresso machines and the world’s largest 460-MW boiler have in common? They both use PID temperature controllers. Maintaining an accurate temperature within a desired range without PIDs is nearly impossible.
PID controllers are critical to processes requiring accurate temperatures, including food and beverage, chemical, medical, and automotive. This guide will explore the basics of PID temperature controllers, their benefits, and how to choose the right one to ensure your processes run smoothly and efficiently.
What are PID Temperature Controllers, and What Do They Do?
PID is a three-term algorithm used in industrial control systems. The acronym stands for Proportional-Integral-Derivative. It’s a temperature control device in a system that adjusts the power to the heating or cooling unit. Sensors in the system provide data in a feedback loop that continuously measures the actual temperature and compares it to the desired temperature.
An example of a PID controller is a furnace controller that regulates fuel volume to maintain a consistent temperature. The same principle can apply to other thermal processes, ensuring the current process temperature stays within its operating range.
In a different industrial setting, a PID controller can precisely regulate the temperature of a chemical reaction to within a fraction of a degree. In a laboratory, it can maintain the temperature of a test tube.
The controller is a simple computer that regulates the process by calculating the temperature change rate and amount, then applies corrective action. The controller determines the rate of change by monitoring the acceleration and deceleration of the temperature, then using the derivative and the integral functions of the PID algorithm.
How Do PID Temperature Controllers Work?
A PID controller is an automatic feedback control system typically used to control equipment such as immersion heaters.
In this case, they work by regulating the temperature of the immersion heater by using a feedback loop. This feedback loop works by taking into account the three-term algorithm of proportional (P), integral (I), and derivative (D). By adjusting these three process variables, the PID controller can optimize the power supplied to the heater’s element to maintain the desired temperature.
The feedback loop sends temperature information to the controller. The controller adjusts the amount of electrical energy to the heating element based on the temperature difference between the liquid (process variable or PV) and the desired temperature (setpoint or SP).
In other words, a PID controller regulates a system by adjusting the output of a controlled process based on the deviation between a set point and the process variable. They control many industrial applications such as chemical processing, food processing, HVAC systems, etc.
See Wikipedia’s article on PID controllers if you are interested in the calculus used to create a PID.
The Benefits of PIDs
Before PIDs became more prevalent in the 1950s, maintaining a constant temperature meant someone had to watch a thermometer or pressure gauge and manually turn a valve or switch to power up a heating unit. If you think it is impractical for a barista to regulate an espresso machine, manually controlling an industrial process or boiler application is even less efficient.
The advantages of PIDs are:
Process consistency – The ability to maintain the same temperature over time is a crucial benefit of PID controllers. The controller will take initial measurements and then use these to determine the rate of change in the temperature of the process. Once the controller has calculated and determined the rate of change, it will calculate the amount of corrective action needed to bring the temperature back to the desired set point and adjust the output of the process.
High accuracy – A PID controller is more accurate than a thermostat because it considers all three variables that affect temperature. It can achieve an accuracy of 0.1% for temperature and 0.01% for flow. This level of accuracy means that the controller does not need recalibration frequently, if at all. A PID controller does not rely on a single reading, as many other controllers do. Instead, it takes many readings to get an average, which results in greater accuracy.
Minimum maintenance – PID controllers will not need to be replaced or fixed as often as other controllers. Regular cleaning and inspection will reduce maintenance costs, making them a better investment.
Why a PID is an Excellent Choice For an Automation Process
PIDs speed up automation processes by maintaining a near-perfect setpoint, whether temperature, speed, or pressure.
A temperature controller PID is preferred if you need to maintain a constant temperature, such as an immersion heater in a vessel. The control loop feedback ensures the temperature remains at the set point. Once you set the controller, it keeps the output constant based on the temperature sensor feedback.
Various processes use PIDs for more than heating or cooling functions. For example, the cruise control in a car uses a PID to send output signals to the throttle to maintain a constant speed. The speed sensor provides the control loop feedback to tell the PID cruise if the car needs to accelerate or decelerate.
A better way to implement PID functionality is to incorporate them into existing PLC systems.
Integrated PID Controllers with PLCs
The simplest temperature PID controllers are binary. They turn on the power when the temperature drops below the setpoint and turns it off when it reaches the higher setpoint. Another option is integrating a PID controller with a PLC (Programmable Logic Controller). Rather than using a separate PID unit, users can program the input and output cards installed in the PLC. The control loop feedback, or process variable, gets wired to the input card and programmed into the PID. The controlled output, in this case, a screw plug immersion heater, gets wired to the output card.
The advantage is that the PID in the PLC manages all the math and automatically makes decisions based on the variables and setpoints. It’s the best way to set up an automated process.
For additional information, read our Thermal loop guide.
What Types of PID Temperature Controls Are Available On The Market Today?
You’ll find three types of PID controllers offered:
- Single-stage PID controllers are the most common and are best for simple processes that do not require precise control. These PID controllers are affordable, simple to use, and have a single set point. Single-stage controllers cannot be adjusted.
- Two-stage PID controllers are the most versatile. They have two set points: one for the process and one for the safety setting. If the process deviates from the set point, the controller will apply a correction to bring it back. If the process continues to drift away from the set point, the controller will switch the process off to avoid an accident or damage.
- Three-stage PID controllers have the same functionality as two-stage PID controllers, with the addition of a manual override. This feature allows users to manually change the set point to suit the process’s needs.
How to Choose The Right Temperature Controller For Your Needs
With different options available on the market, finding the perfect PID controller for your process can be tricky.
Here are three considerations to make the decision easier.
- Application – The application is the first consideration when choosing the suitable PID controller for your needs. What process will it control? What are the environmental conditions? Knowing what it’s for will make it easier to choose the correct controller.
- Budget – After you know its function, the next step is to consider the budget. PID controllers come in a wide range of prices, so choosing the right one within your budget is essential.
- Technology – There are two main types of PID controllers: analog and digital. Analog PID controllers are manual, whereas digital PID controllers are self-contained. You should choose the technology that best suits your needs and budget.
Tips for Installing and Using a PID Temperature Control
Before installing your first PID controller, keep these things in mind.
Choose the right location – Find an area that is open, easy to access, and has sufficient electrical power. A good place keeps the controller away from personnel or other equipment that might damage it.
Label your wires – Before connecting your PID controller to any power source, label all wires to make it easier to troubleshoot any issues. In the event of a failure, labeling helps reduce downtime.
Follow the manufacturer’s instructions – Always follow the manufacturer’s instructions to understand its features, increase safety and avoid problems.
Maintain your equipment – PID controllers are not maintenance-free, so keeping them clean and inspected is critical to long-term use.
Frequently Asked Questions About PID Temperature Controllers
Here are some of the common questions about PIDs.
What Does PID Stand for in Heating?
As mentioned above, PID stands for Proportional Integral Derivative.
“P” represents the difference between the setpoint and the error or current temperature. The proportional control means that the output will be proportionally related to the present error (the variance between the set point and the actual measured temperature). It maintains the temperature within a narrow range.
“I” integrates the past values of the SP (setpoint) − PV (process variable) error. The “I” term attempts to eliminate the residual error by adding a control effect based on the historic cumulative value of the error. The integral part of the PID controller is responsible for stopping the offset in the system by integrating the error over time.
“D” estimates the SP − PV error trends using its current rate of change. Sometimes called “anticipatory control,” it seeks to reduce the effect of the SP − PV error by exerting a control influence generated by the rate of error change. The faster the change, the greater the controlling or damping effect. The derivative part of the PID controller helps to minimize the overshoot in the temperature by taking into account the rate of change of the error.
Are Thermostats PID Controllers?
Yes, technically speaking, thermostats are considered PID controllers. A thermostat measures the temperature with a thermistor and adjusts the temperature by turning the power on or off.
Both PIDs and thermostats work in a closed-loop system. Manufacturers use thermostats to control things like home ovens because they are less accurate and inexpensive. For example, if you set a home oven to 350°F, the thermostat might not turn on the heating element until the temperature drops below 325°F and won’t switch off until it reaches 375°.
When precise temperature maintenance is critical, a PID controller provides fewer temperature swings above and below the setpoint.
A traditional thermostat is an on-off controller. A PID controller continuously measures and responds to the temperature change rate with less oscillation. It precisely calculates the change with a mathematical algorithm.
How Do I Troubleshoot My PID Controller?
To troubleshoot your PID controller, identify the problem. If you believe there is an issue with it, check the connections to ensure that nothing has come loose. If you are confident that all connections are secure, you should check to see if the controller has an error code that you can identify. If there is no error code, you should check the power source to ensure it is connected and receiving power.
How Long Does It Take To Install and Set Up a PID Controller?
It depends on the type of controller you are installing and how complex your application is. If you install a simple two-stage PID controller, the installation process will take less than a day. If you are installing a three-stage PID controller that has a manual override, it will take longer.
Process temperature controllers are generally easy to use and set up. Let’s say you were to set up a heat trace and enter a set point temperature of 200°F (93.3°C). The PID controller signals the power regulator to power up the heat trace. A thermocouple reads the temperature as the control loop feedback, and the controller turns the heat trace on or off to maintain the correct temperature.
What is Temperature Control Hysteresis?
Hysteresis is a range built into the controller above and below the setpoint. If a temperature controller has a range of 0 to 400°C, with a 0.2% hysteresis, that means the range is 0.8°C. If the controller’s setpoint is 100°C, the output will turn off the heater at a process value of 100.8°C and turn it on at 99.2°C.
Similarly, a pressure switch can be designed to exhibit hysteresis, with pressure setpoints substituted for temperature thresholds.
If you can’t find the answer to your question, contact our engineers at Powerblanket.
The Best Choice for Precise Temperature Control
The PID temperature controller is one of the most common and effective electrical devices used today. It is ideal for precise temperature control, making it the best choice for applications such as industrial ovens and furnaces. The PID controller works by measuring the difference between the desired and actual temperature and then adjusting the output to the process accordingly. The algorithm allows it to maintain a constant temperature over long periods.
Efficient PID controllers use only the energy necessary to maintain the desired temperature. They offer a wide range of settings and functions, making it easy to customize them for specific applications. The PID temperature controller is the perfect choice for any process requiring precise temperature control.
If you need help designing a heating system or finding the proper control solution for your process, Powerblanket’s engineers are ready to assist.
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