Maximizing Your Process Heating Performance With a PID Controller

Imagine being the engineer of a locomotive in the 1930s and 40s. Back then, locomotive engineers were kings, respected, and admired for their technical prowess. They had to undergo rigorous training and physicals before running a train. Engineers had to know when to adjust the many levers and valves to control 600 tons of steel, fire, and steam, which generated up to 8,000 horsepower. By visually monitoring pressure gauges and using that information to adjust heat and pressure, the locomotive engineers essentially did the job that PID controllers do today. 

If you’re in the manufacturing industry that requires heat, you know how vital temperature control is to operations. Applying controlled heat is crucial for melting metals, baking bread, curing epoxy, and everything in between. One significant challenge has always been maintaining consistent and accurate temperatures throughout the heating process. That’s where a PID controller comes in. Using the correct PID controller optimizes your process heating for maximum performance. 

This article will explore the basics of a PID controller, how it works, why it’s essential for industrial applications, and how to choose the right one for your needs. 

What Is A PID Controller, And How Does It Work?

PID is an acronym for Proportional-Integral-Derivative. Like an engineer controlling a locomotive, a PID controller calculates input signals and then adjusts a specific output to bring a process value to the desired set point. In our case, we’re discussing process heat, so the controller automatically adjusts the amount of heat in a process to maintain a consistent temperature. 

PID controllers use a feedback loop to continuously monitor the process temperature, known as the process value. It adjusts the heat source based on the difference between the actual temperature and the desired temperature. 

It continuously measures the system’s output and compares it to a desired set point. The controller then adjusts the input (increasing or decreasing the heat) to the system to bring the output closer to the set point. The PID controller uses three components, Proportional, Integral, and Derivative, to calculate the input adjustment: 

1. The Proportional calculates the difference between the set point and the current output and multiplies it by a gain factor. The gain is the ratio of the output response to the error signal. Proportional represents the input value. 
2. The Integral calculates the sum of the error over time and multiplies it by another gain factor. Each time the controller makes the PID calculation (perhaps every 100 ms), it adds the newly calculated integral value to the integral total. The controller adds the integral value to the proportional value to smooth out the system’s response. 
3. The Derivative calculates the rate of change of the error and multiplies it by another gain factor. This value is subtracted from the Proportional term to prevent overshoot and oscillation. The derivative’s purpose is to predict where the process is going and prevent the controller from over-shooting the set point.

Overall, the PID controller works by continuously measuring, calculating, and adjusting the input to keep the output as close as possible to the desired set point. It is essential in the heat treatment of metals, baking, curing rubber, drying, and any industrial process requiring set temperatures. To learn more, see our article, How Temperature Controllers Work.

PIDs function beyond heating applications. They automate other tasks, such as robotics and automation to regulate pressure, speed, and other variables.

A Simple PID Example

Here is a basic but actual example of a PID controller in action:

In this example of a commercial oven, the variables are:

• Process value = temperature
• Set point = desired or optimal temperature
• Output = electrical heating element or gas burner

A commercial bakery requires an oven to maintain 350°F for optimal baking.

Each time the door opens to add product, it loses heat, and the temperature drops to 320°F.

If the set point is 350°F and 320°F is the actual temperature, then the error value is 30°F. 

The PID controller calculates the new error value and determines how much to control the output, to bring the oven back to the desired set point.

The controllers will continue calculating the Error Value, adding heat until the oven’s temperature returns to the 350°F set point. At  350°F, the error becomes zero, and the controller shuts off the heat until a new Error occurs.

PID Algorithm and Error Signal

As mentioned above, the PID algorithm consists of three components: proportional, integral, and derivative. 

The error signal is the difference between the set point and the measured process variable.
The PID algorithm continuously monitors the signal. For example, an oven thermostat adjusts the heat control to minimize the difference between the actual and set temperatures.

The error signal plays a critical role in the PID algorithm by providing the feedback necessary to make control adjustments. Without this signal, the algorithm would not know if the process variable was moving closer to or further away from the set point and would be unable to make the necessary adjustments.

The algorithm’s ability to calculate and use the error signal to make real-time control adjustments is critical to maintaining optimal process performance. 

Applications of PID controllers In Temperature Control And Beyond

Besides temperature control, PID controllers are essential for various applications such as robotics, industrial automation, and motion control. Here are four examples:

1. In robotics, PIDs control the position and movement of robotic arms and grippers. 
2. In industrial automation, they control the speed and torque of electric motors. 
3. In motion control, they control the position and speed of linear and rotary actuators.
4. In flow control, PIDs control pumps for fluid in pipelines or levels of liquid in tanks.

One of the advantages of PID controllers is their versatility. They suit different applications in both open-loop and closed-loop systems. 

In open-loop systems, the controller output does not feed back to the input. Some examples of open-loop systems are automatic traffic lights, automatic washing machines, and immersion heaters.

In closed-loop systems, the output does provide feedback to the input, making them more accurate and stable than open-loop systems. Closed-loop systems are ideal for applications that require precise control. An example of a closed-loop is an oven thermostat. The input from a temperature sensor detects whether the temperature is below or at the set point. The controller turns the heat on or off accordingly, continuously monitoring the temperature.

Another advantage of PID controllers is their ability to handle disturbances and variations in the process. The derivative term of the controller responds to changes in the process, while the proportional and integral terms respond to steady-state errors. By combining these three terms, PID controllers can quickly and accurately respond to changes in the process, maintaining a stable output.

As technology advances, PID controllers will likely become even more critical in controlling complex processes.

Benefits of Using PID Controllers for Process Heating Applications

Using the right PID controller for a process heating application has four primary benefits.

1. A PID controller provides accurate and precise control over the process variable, leading to consistent and high-quality output. The controller continuously measures and adjusts the temperature to ensure it stays within the desired range, reducing the risk of variations that can compromise the end product. 
2. PIDs are highly versatile for various process heating applications. It can be customized to suit the application’s specific requirements, such as the type of material to be heated, the desired temperature range, and the heating rate. 
3. A PID controller can help to reduce energy consumption, a key consideration in any process heating application. By maintaining a consistent temperature and avoiding unnecessary temperature overshoots, the controller can help to optimize the heating process and reduce energy waste.
4. Using PIDs reduces or eliminates the need for manual adjustments to the heat source, freeing up people for other tasks. It can also reduce the risk of human error, leading to costly mistakes or safety hazards.

Factors To Consider When Choosing a PID Controller

The first consideration is the type of heat source. Electrical and gas heat sources may require different PID controller settings or configurations to maintain a consistent temperature.

The process’s size and complexity is also a factor. Larger or more complex processes may require more sophisticated PID controllers and additional sensors to maintain a consistent temperature.

The accuracy and reliability of the temperature sensor are other crucial factors. An inaccurate sensor can lead to incorrect temperature readings, resulting in improper adjustments to the heat source. Some questions to ask when selecting a PID are:

• Will a 41°F (5°C) to 50°F (10°C) On/Off controller work, or do you require an accuracy of 35°F (2°C) to 39°F (4°C)? 
• How many loops per device will you need – 1, 2, 4, 16?
• What is the system voltage – 240V, 480V, 600V, or 690V?
• Where will the PID mount – DIN panel, Rail, or In-Line controller?

Finally, it’s essential to consider the specific features and capabilities of the PID controller itself. Different PID controllers may offer additional features, such as programmable setpoints or alarms, beneficial for particular applications.

How Can PID Controllers Improve Process Heating Performance In Your Plant or Business?

Precise temperature control is critical to fulfilling diverse industrial tasks. Here are some examples:

• In conserving blood cells for blood banks or research, the cellular temperature must remain within a narrow range of ±1°F for the extended bioactive cell life. A failure in temperature control will shorten the lifespan or do fatal damage to blood cells.
• When milling pharmaceutical powders, maintaining a set temperature is vital. The surface ratio and surface energy are extremely temperature sensitive. 
• Precise temperature control systems play a crucial role in various industrial facilities operating safely and efficiently. Examples include experimental space science instruments, vehicle manufacturing, painting, batch reactors, refuge chambers, and medicine capsule machines.

PID controllers can improve process heating performance by maintaining a consistent temperature, reducing energy consumption, and minimizing product defects. The controllers use feedback loops to continuously monitor the process variables, such as temperature, and adjust the control output accordingly. The PID’s feedback loop eliminates deviations from the target temperature, ensuring the process runs smoothly and efficiently.

PID controllers also help reduce energy consumption by adjusting the output based on the error signal, meaning it only supplies the necessary energy to the process. They can improve process heating performance by preventing overshoot and oscillation and providing a more stable operation. This reduction in wasted energy translates into cost savings for the business.

Another benefit of PID controllers is they minimize product defects. Fluctuations in temperature can cause product defects, resulting in waste and revenue loss. PID controllers eliminate these fluctuations, ensuring the process consistently produces high-quality products.

Finally, PID controllers can help optimize the performance of your process heating equipment. You can extend equipment lifespan and reduce repairs or replacements.

How to Properly Configure and Use a PID Controller To Get The Most Out Of It

First, confirm that the sensor used to measure the temperature of the process is accurate and reliable. Calibration of the sensor may be necessary to ensure accurate readings.

Next, it’s important to properly configure the PID controller based on the specific needs of your process. Proper configuration may involve adjusting the proportional, integral, and derivative settings to achieve the desired temperature control through tuning.

Once configured correctly, it’s important to monitor its performance regularly. Check the temperature readings, review the controller’s output, and make any necessary adjustments.

Eliminate unnecessary downtime by cleaning and calibrating the sensor regularly. Replacing worn or damaged components immediately.

PID Controller Tuning for Optimal Performance

The controller ensures the process remains as close to the desired setpoint value as possible, regardless of the disruptions. 

Most PIDs come with factory-set values. However, tuning them for a specific process before entering service is advisable. Controller tuning involves correctly setting the Proportional-Integral-Derivative values for particular process requirements. 

Several manual controller tuning methods involve observing the process response after causing controller setpoint changes.

The Trial and Error tuning method involves increasing the setpoint change and repeating the procedure until the process enters a steady oscillation state. While this method produces adequate results, it’s impractical for applications such as forcing a fluid level in a tank to reach a constant state oscillation. 

The Process Reaction Curve Technique measures variables in a working system. Engineers obtain data by allowing the system to maintain a steady state, then introducing a disturbance such as changing the setpoint or a process variable. For example, if a thermostat can only change by 10 degrees increments, then raising the temperature by one degree would be a 10% disturbance to the system.

The Process Reaction Curve method works in open-loop systems and produces a response to a step function change. Measured parameters include transportation lag or dead time, the time for the reaction to change, and the ultimate value that the response reaches the steady state.

For tuning PIDs in Closed-loop systems, use the Zeigler-Nichols method. It starts by setting the integral and derivative gains to zero and then increasing the proportional gain from zero until it reaches the ultimate gain. The output of the control loop is stable with consistent oscillations at a constant amplitude.

Most modern controllers have auto-tuning capabilities. The PID “learns” how the process responds to a change in setpoint and suggested PID settings. A seasoned professional should tune it to get the desired response, whether manual or autotuned.

Monitoring and Maintenance of PID Controllers

Regular monitoring and maintenance of PID controllers are necessary to ensure their continued performance. 

Monitoring means checking the temperature readings, reviewing the controller’s output, and making necessary adjustments. Maintaining PIDs means regularly cleaning and calibrating the temperature sensor that measures the process temperature. Regular cleaning ensures accurate readings and prevents errors in temperature control.

Always replace any worn or damaged components and upgrade to a more advanced PID controller whenever feasible.

Upgrading to a Better PID Controller

As technology evolves, newer and more advanced PID controllers become available. Upgrading to a more advanced PID controller can offer additional features and capabilities. More recent models usually provide improved accuracy, reliability, and better performance.

When considering an upgrade, evaluate the specific needs of your process and choose a PID controller offering the features and capabilities most important to you. Working with a knowledgeable supplier or manufacturer can help you select a suitable controller for your process.

Frequently Asked Questions About PID Controller

Although we may have answered some of these earlier, finding your answer to common PID questions may be easier here.

How Does a PID Control a Thermal Loop?

A thermal loop comprises a sensor, controller, relay, and thermal source. Temperature control or thermal loops maintain a set temperature. Equipment like PID controllers sets the temperatures and activates heating mechanisms when the temperature drops beneath a specific threshold.

You can read all about the thermal loop here.

What Are The Benefits of Using a PID Controller?

PID controllers offer several benefits. 

• They provide precise control over process variables.
• Help to improve product quality and reduce waste. 
• Offer fast response times, which is critical in specific applications. 
• Easily integrated into existing control systems.

 PIDs are a versatile solution for a wide range of industrial processes.

How Do I Choose The Right PID Controller for My Application?

Choosing the suitable PID controller depends on several factors, such as the process type, the required accuracy, and the operating environment.

Some controllers are designed for specific applications, such as temperature control, while others are more general-purpose. Carefully consider your requirements before choosing a PID controller.

What’s The Difference Between On/Off Controller and PID Controller

When it comes to maintaining precise temperature control in industrial processes, two popular options are the On/Off Controller and the PID Controller. While both have benefits and drawbacks, the PID Controller is more versatile and practical.

An On/Off Controller turns the heating, air conditioning, or cooling system on or off when the temperature crosses a certain threshold. One example is a fan that cools an electrical transformer. The controller turns on the fan as the transformer’s heat rises above the set value. When the temperature drops below the threshold, it turns off.

While this can effectively maintain a consistent temperature within a specific range, On/Off controllers can lead to frequent fluctuations and overshoots. Inaccuracy can be particularly problematic in sensitive processes where even minor temperature variations can significantly impact the outcome.

A PID Controller, on the other hand, uses a sequence of proportional, integral, and derivative control to maintain a much more precise temperature range. By continuously monitoring the temperature and adjusting the heating or cooling system accordingly, the PID Controller can quickly respond to changes and prevent overshoots. The accuracy of PIDs makes them a particularly effective option for processes requiring high precision and consistency.

Of course, there are also some disadvantages to using a PID Controller. Implementing it can be more complex and expensive, requiring careful tuning to ensure optimal performance. In some cases, an On/Off Controller may be sufficient for maintaining temperature control, particularly in less sensitive processes where small fluctuations are less of a concern.

Ultimately, the choice between an On/Off Controller and a PID Controller will depend on the specific needs of your temperature control system. A PID Controller is the best option if precision and consistency are top priorities. However, if cost and simplicity are more important, an On/Off Controller is the way to go.

How Do I Tune a PID Controller?

Tuning a PID controller involves adjusting the controller’s settings to achieve the desired control performance. Tuning a PID controller can be complex, and several methods exist. You can review the information earlier in this article.

When tuning a PID, change only one parameter at a time, making minor adjustments. Use a data-logging instrument to view and compare results. After each test, compare the effects of each change. Use the same method for adjusting the tuning as when operating the furnace or other heating element.

If ramping up to a setpoint, tuning tests should employ the same ramps and rates. Longer ramps will introduce more accumulated error which affects the I (integral). If not monitored, large overshoots can occur.

Check control systems regularly for integrity and linearity to optimize response during tuning. The systems to review in heating systems include:

• Control valve
• Regulators
• Combustion air blowers
• Burners
• Silicon Controlled Rectifier (SCR)
• Heating elements
• Thermocouples

For example, to tune a PID that controls a valve, you first set the control-loop output to 0%. Check that the valve is in the closed position. Next, set the control loop to 100% to confirm it is fully open. Continue verifying the open positions at 25%, 50%, and 75% output. The valve should not close before 0% or fully open before 100%.

There are software tools available that can help simplify the tuning process. Most newer PIDs come with an autotune function.

For a visual explanation, watch How to Tune a PID Controller.

What Are Some Of The PID Controller Examples?

In temperature control applications, PID controllers are often used to regulate the temperature of a system, such as a furnace or an oven. The controller takes feedback from temperature sensors and adjusts the heating or cooling elements to maintain a desired temperature. 

PIDs control the speed and position of machines, such as a conveyor belt system. It can monitor and adjust the belt’s speed to maintain a consistent flow of materials. 

PIDs are essential components in robotics to precisely control the movement and position of robotic arms. In this application, the controller takes input from sensors that detect the arm’s location and adjusts the motors to maintain the desired position. 

Automotive cruise control systems incorporate PIDs to maintain a constant speed while driving.

What is The Difference Between a PID Controller and PLC?

PID controller and Programmable Logic Controller (PLC) are two control systems used in industrial automation. Both systems control various processes but differ in functionality, design, and applications. 

A PID controller is a closed-loop control system that provides proportional, integral, and derivative control actions to maintain the desired output. It compares the measured process variable with the desired setpoint and calculates the error signal. It then adjusts the control output to minimize the error signal and maintain the setpoint.

On the other hand, a PLC is a digital computer that controls entire industrial processes. The hardware has a programmable memory for storing instructions and input/output modules connecting to the sensors and actuators. PLCs are programmed using ladder logic or other programming languages and can be used to control various processes such as production lines, machine tools, and traffic lights.

The main difference between a PID controller and a PLC is that a PID controller is a single-loop control system that controls a single variable. A PLC is a multi-loop control system that can manage multiple variables simultaneously. 

PID controllers are best for applications such as temperature, level, and flow control, where precise regulation of a single variable is required. PLCs control multiple variables simultaneously and are the best choice for complex motion, process, and machine automation applications.

How Do You Prevent PID Controller From Overshooting

PID controller overshooting can lead to instability, oscillations, and other undesirable effects that can affect the quality and efficiency of the process. However, there are three ways to prevent it from overshooting and maintain stable and accurate control.

The most effective way to prevent overshooting is to adjust the PID parameters – the proportional, integral, and derivative gains. These gains determine the controller’s response to the error signal, the difference between the setpoint and the actual value. You can adjust the controller’s speed, stability, and damping by tuning these gains and achieving the desired response. Start with small gains and gradually increase them until you get the desired performance. But don’t make them too high, as this can lead to overshooting and oscillations.

Another way to prevent overshooting is to use a low-pass filter, a moving average, or a first-order lag function to smooth the signal and reduce the overshoot. This can help eliminate the high-frequency components of the error signal that can cause overshooting and improve the controller’s stability. Be advised that these filters can introduce some delay and phase shifts in the system, affecting the response time and accuracy.

A third overshoot prevention method is to use a feedforward control strategy. Feedforward anticipates the changes in the system and adjusts the controller output accordingly. It eliminates lag and delays while improving response time and accuracy. For example, if a sudden change in the setpoint causes the system to overshoot, you can use a feedforward signal to compensate for this change and reduce the overshoot. Adding feedforward requires knowledge of the system dynamics. You’ll also need modeling and simulation tools to design and implement the feedforward strategy.

Preventing PID controllers from overshooting requires a combination of tuning, filtering, and feedforward strategies, knowledge of the system dynamics, and modeling. By following these guidelines and testing the system carefully, you can achieve stable, accurate, and efficient control of your process.

How To Choose The PID Controller Sampling Rate?

The sampling rate refers to the frequency with which the PID controller measures the system parameters and adjusts the control output accordingly. The sampling rate is typically measured in seconds or milliseconds, depending on the application.

Choosing the correct sampling rate for a PID controller can be challenging. The ideal sampling rate varies depending on the system, the type of sensor used, and the desired control response time. A higher sampling rate generally leads to more accurate control but requires more processing power and can lead to higher system noise.

One important consideration is the frequency response of the system. A high sampling rate is critical to ensure accurate control if the system has a high-frequency response. On the other hand, if the system has a low-frequency response, a lower sampling rate may be sufficient.

Another critical factor is the type of sensor measuring the system parameters. Some sensors, such as thermocouples, have a slow response time, while others, such as pressure transducers, have a much faster response time. Choosing a sampling rate appropriate for the sensor used ensures accurate control.

Choosing the right sampling rate for a PID controller requires careful consideration of the system’s frequency response, the type of sensor, and the desired control response time. 

Is a PID Controller Necessary?

A PID controller is critical in maintaining consistent product quality and production rates for plant or business operations. It can automatically adjust the input variable in response to system output variable changes. In addition, it can regulate temperature, pressure, level, and flow, helping prevent equipment damage and reduce maintenance costs. 

However, the need for a PID controller ultimately depends on the specific process and the level of control required. Some applications require minimal manual control, while others require more sophisticated control mechanisms. Process complexity, product quality requirements, and the cost of implementation should decide whether a PID controller is necessary.

PID Controllers Enhance Industry Heating Process Efficiency

PID controllers have revolutionized the way industries approach their heating processes. With the ability to continuously monitor and adjust temperature levels, these controllers have become indispensable for ensuring optimal efficiency and output. 

By utilizing a temperature sensor, PID controllers can make real-time adjustments to the amount of generated heat, allowing for precise and accurate control over the heating process. This ensures that the desired temperature is reached quickly, minimizes energy waste, and reduces the risk of overheating or underheating. With the ability to fine-tune the heating process, PID controllers have become an essential component of modern industrial operations, helping businesses to optimize their output while minimizing their environmental impact.

Powerblanket’s industrial control solutions allow you to automate, remotely control, and monitor your valuable materials and equipment. Explore Powerblanket’s Controllers.