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 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Leaders Under 40 program features outstanding young people who are making a difference in manufacturing. View the 2013 Leaders here.
The new control room: It's got all the bells and whistles - and alarms, too; Remote maintenance; Specifying VFDs
2014 forecast issue: To serve and to manufacture - Veterans will bring skill and discipline to the plant floor if we can find a way to get them there.
2013 Top Plant: Lincoln Electric Company, Cleveland, Ohio
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.
Electric motor power measurement and analysis: Understand the basics to drive greater efficiency; Selecting the right control chart; Linear position sensors gain acceptance
Protecting standby generators for mission critical facilities; Selecting energy-efficient transformers; Integrating power monitoring systems; Mitigating harmonics in electrical systems

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

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.