What's a PID?
A PID loop is a mathematical formula used to drive a process variable toward a particular value (the setpoint) and keep it very close to that value by controlling an output.
PID loops are often used in process-oriented applications to control temperature, flow, pressure, or velocity.
In temperature control, for example, the PID's formula controls the output to maintain the desired temperature. The loop compares feedback from an input to the desired setpoint, compensates for changes in load, such as an influx of cold air, and adjusts the output accordingly.
- The input is a measurement of process temperature from a temperature sensor (analog input).
- The setpoint is the desired temperature, perhaps from a thermostat (analog input) or an operator HMI.
- The output is a heater control (analog output).
A PID can control just one isolated system or be part of a larger, cascaded system, where one loop controls the setpoints or input variables of others.
PID calculations are complex, and most PIDs require tuning to maximize effectiveness. When you tune a PID loop, you make real-time changes to gain, integral, and derivative values as necessary to stabilize the system and increase efficiency.
How do I do PID loop control?
If you have an Opto 22 SNAP PAC rack-mounted controller or brain, you already have the ability to do PID loop control. Each controller or brain has 96 PID loops built right in. To configure and tune them, you use PAC Control programming software.
- Because PID loop control is built into the distributed I/O unit, PIDs run locally and continue to run even if communication with the controller is interrupted.
- Five algorithms are available; you can choose the one you want for each PID loop.
- For maximum flexibility, any PID input, setpoint, or output can be determined by commands in your PAC Control program.
- The graphical tuner in PAC Control makes tuning a loop much easier.
- You can also put PID graphs into your PAC Display HMI, so authorized technicians can view or even tune a PID loop when needed.
PAC Control and PAC Display are both included in the free download PAC Project Basic. Product Support is also free. So all you need is a SNAP PAC rack-mounted controller or a SNAP PAC brain, and you're ready for PID loop control.
Read about PIDs
Tuning a PID Control Loop Technical Note. Defines the components of a PID control loop and shows you how to tune your real-world PID in our helpful online PID tuner.
SNAP PAC PID Tutorial. The tutorial is designed for a SNAP PAC Learning Center—a package of hardware and software for learning about automation and Opto 22 products—but concept sections are excellent for anyone doing PID loop control.
PAC Control User's Guide (form 1700): Configuring PIDs, Tuning PID Loops
Use our online PID tuner to calculate P, I, and D values for your loop. The tuner calculates values based on data you enter for a specific loop. It also suggests a scan rate.
See the webinar
Learn how to calculate dead loop time, configure and tune a PID graphically, and save parameters to your Opto 22 PAC Control strategy. Recommended for customers with a basic understanding of PAC Control.
Introduction to PID Loops Webinar (archived)
Duration: 45 minutes plus Q&A
You can also run PID loops on remote intelligent I/O used with A-B PLC systems: Using SNAP I/O with Allen-Bradley Controllers: Part 4, PID Loop Control
More information in the OptoForums
Join our OptoCommunity to ask and answer questions about PIDs. Anyone can search the OptoForums for information. Here's a post specifically about PIDs.
To post questions or answers, just get a free My.Opto22 account and post away.