Initial settings for PID controllers

Time to start the process? Here are some beginning PID values learned in the trenches that should get you off and running.

01/15/2013


Let’s say you’re the lead configuration engineer on the automation portion of a green-field plant installation project, and you need to give your start-up guys a head start with a set of default PID tuning constants. You want to hand it over in a way that the board operators can place some of their basic controls in auto mode with the expectation that the loops will control fairly close to their setpoints without significant oscillation.

The following table offers some time-tested default values for gain, integral time, and derivative time that will work in most common situations as a starting point during initial unit start-up. If your control system uses other tuning constant units (e.g., reset for the integral action, then you’ll have to do the conversion – I’m sure you can handle it).

The following table offers some time-tested default values for gain, integral time, and derivative time that will work in most common situations as a starting point during initial unit start-up.


The values for flow control loops and level control loops will almost always work. In a few cases, a gain of 0.8 for a flow control loop may be too aggressive and should be reduced for nervous valves or loops that tend to oscillate.

The gains for pressure and temperature loops may need to be increased, depending upon the engineering units range of the controller. If the controller has a wide range (e.g., a pressure controller with a 0-500 psig range) and tight control is required around the setpoint (let’s say in this case, SP = 400 psig), then a larger gain may be required to keep the PV close to setpoint. This is because gain works on error as a percent of the engineering units range. So, a 1.0 psig deviation from setpoint is only 0.2% of range – a gain of 2.0 would result in a valve movement of only 0.4% - not much action. In this case, a gain of 5.0 or even 10.0 might be more appropriate.

Temperature is the only variable where derivative action should be applied with confidence in the default case. In general, derivative is reserved for loops with measurement lag. Flows, levels, and pressures do not normally suffer from this destabilizing characteristic. On the other hand, process temperatures are often measured indirectly by devices in thermowells, thereby introducing measurement lag due to the inherent thermal lag. Derivative action in this case can help, since its purpose is to “reverse” the control action as the PV “reverses” its trajectory and starts heading back toward setpoint after a deviation away from setpoint. A small amount of derivative in this case is recommended.

Derivative action is totally inappropriate for “noisy” process variables, as can often be the case for flow and level (and sometimes, pressure) measurements. Derivative action acting on a noisy deviation can produce wild valve swings, depending upon the values of the gain and derivative. In the case of a noisy measurement, a solution that is often suggested is to heavily filter the PV. However, this can often introduce artificial measurement lag, further degrading control loop performance.

The recommended integral time for temperature may need to be increased (less aggressive integral action) for loops with significant process dead time and lag – for example, for controlling a distillation column temperature with reflux flow or reboiler heat.

As is always the case, you’ll need to use your experience and good engineering judgment on these types of projects, but this should give you a good starting point for configuration of these very important PID control algorithm parameters.

This post was written by Dr. Jim Ford, PE. Jim is a process control consultant at MAVERICK Technologies, a leading system integrator providing industrial automation, operational support and control systems engineering services in the manufacturing and process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, and business process optimization. The company provides a full range of automation and controls services – ranging from PID controller tuning and HMI programming to serving as a main automation contractor. Additionally MAVERICK offers industrial and technical staffing services, placing on-site automation, instrumentation and controls engineers.



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
Prescriptive maintenance; Hannover Messe 2017 recap; Reduce welding errors
Safety standards and electrical test instruments; Product of the Year winners; Easy and safe electrical design
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Diagnostic functions for system safety; Specifying industrial enclosures; Effective decision support for a crisis
Transformers; Electrical system design; Selecting and sizing transformers; Grounded and ungrounded system design, Paralleling generator systems
Natural gas for tomorrow's fleets; Colleges and universities moving to CHP; Power and steam and frozen foods

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me