Posts Tagged ‘CO’
How to Perform a Step Test
Tuning PID controllers is a multi-step process. While it is important to understand each step in the process, performing the bump test and collecting dynamic data is the most crucial step that generally dictates the outcome. This post delves into one particular type of test – the Step Test – before introducing other tests commonly used in PID controller tuning.
Read MoreCommon Industrial Applications of PID Control
A previous post about the Derivative Term focused on its weaknesses. As noted, the primary challenge associated with the use of Derivative and PID Control is the volatility of the controller’s response when in the presence of noise. Noise is a major stumbling block for Derivative and PID Control as production data is routinely replete with process noise and other sources of variability. The use of PID Control in such an environment can drive frenetic changes in a loop’s Controller Output (CO) and unnecessarily wear out the associated Final Control Element (FCE). In summary: Little to gain; lots to lose.
Read MoreWhat is the Purpose of a PID Controller’s Integral Term? Why is PI Control So Widely Used in Industry?
In the realm of process control it makes complete sense that the primary goal is – you guessed it – to control the process. For decades the PID controller has proven a reliable tool for fulfilling that objective. Even so, there are various forms of the controller that can be used and each has its unique performance attributes. In spite of the added complexity associated with the Integral Term the PI controller is the form most widely used in industry.
Read MoreWhat is On-Off Control?
On-Off Control is not a highly sophisticated control method. Even so, examples of its practical, everyday use can be found all around. Look no further than the appliances in your home. Kitchen appliances such as ovens and refrigerators utilize On-Off Control. Similarly the furnaces, water heaters, and air conditioners found in most basements rely on On-Off Control. Although it’s unsophisticated, On-Off Control plays a significant role in our lives.
Read MoreHow Do I Calculate Dead-Time?
Adults can learn a thing or two from children. That’s especially true when it comes to matters of time. Whereas adults view it as fashionable to show up to a social event 15 or more minutes late, children can’t wait to go and be a part of the action. When at a theme park adults typically their time strolling from place to place while children know that each minute of delay can cost hours longer in line. Simply put: When it comes to time every second matters. That viewpoint seems highly relevant to process control, control loop tuning, and calculating Dead-Time. Dead-Time is generally the model parameter that’s easiest to calculate when tuning a PID controller.
Read MoreHow Do I Detect Valve Issues and Prevent Failures?
It’s generally known that the behavior of final control elements (FCEs) (valves, air handlers, etc.) change over time. Like most things the dynamics of FCEs are different from the time they’re first installed to the time they’re serviced and ultimately replaced. Sometimes the change in dynamic behavior is subtle. Other times the change is dramatic. Unfortunately that’s the nature of things, and that’s the primary reason why monitoring for valve issues is beneficial.
Read MoreWhat is the Process Time Constant? How Do I Calculate the Time Constant of A Process?
Party hosts often cringe when guests arrive early or late. Seemingly subtle shifts in timing can throw off planned details that are of importance to the host and utterly lost on guests. So too the timing of a PID control loop’s response is important. Premature or delayed responses negatively impact the controller’s performance. Previously the calculation of Process Gain – the “how far” variable – was covered. The Process Time Constant is equally important to process modeling and PID controller tuning. As with most things, timing is everything.
Read MoreHow Do I Tune a Level Controller?
Level controllers present challenges that are different from others. Although their presence is significant they lag behind Flow controllers in their overall share of the typical production facility’s process control landscape. Unlike other processes such as Temperature, Pressure and Flow, Level control loops demonstrate different dynamics, they don’t play by the same rules as the non-integrating (also known as self-regulating) types. And although best-practices for modeling and tuning Level loops are similar they involve nuances that can hamper a less experienced practitioner.
Read MoreDoes Tuning a PID Controller Require a Bump Test?
It’s generally accepted that tuning a PID controller requires some form of testing. Whether a step, bump, doublet, or pseudo random binary sequence, the test forces a change to the Controller Output (CO) which drives a response in the Process Variable (PV). The dynamic relationship between the CO and PV provides the basis for modeling a process’ behavior. In turn, the model is converted into tuning parameters corresponding with your controller. All of this is made possible by conducting a simple test. But what if it’s not that simple.
Read MoreHow Do I Perform an Effective Bump Test?
Bumping a process is a standard requirement when tuning a PID controller – whether you tune manually or with the help of software. And, either way, applying industry best-practices will save you significant time and money.
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