PID Control and Derivative on Measurement
ABSTRACT: Like the PI controller, the Proportional-Integral-Derivative (PID) controller computes a controller output (CO) signal for the final control element every sample time T. The PID controller is a "three mode" controller. That is, its activity and performance is based on the values chosen for three tuning parameters, one each nominally associated with the proportional, integral and derivative terms. As we had discussed previously, the PI controller is a reasonably straightforward equation with two adjustable tuning parameters. The number of different ways that commercial vendors can implement the PI form is fairly limited, and they all provide the same performance if properly tuned. With the addition of a third adjustable tuning parameter, the number of algorithm permutations increases markedly. And there are even different forms of the PID equation itself. This creates added challenges for controller design and tuning.
The Chaos of Commercial PID Control
ABSTRACT: The design and tuning of a three mode PID controller follows the proven recipe we have used with success for P-Only control (e.g., here and here) and PI Control (e.g., here, here and here). The decisions and procedures we established for steps 1-3 of the design and tuning recipe in these previous studies remain unchanged as we move on to the PID algorithm. Step 4 of the recipe remains the same as well. But it is essential in this step that we match the rules and correlations of step 4 with the particular controller algorithm form we are using. The challenge arises because the number of PID algorithm forms available from hardware vendors increases markedly when derivative action is included. And unfortunately, these PID algorithms are implemented in many different forms across the commercial market.
PID Control of the Heat Exchanger
ABSTRACT: In recent articles, we investigated P-Only control and then PI control of a heat exchanger. Here we explore the benefits and challenges of derivative action with a PID control study of this process. Our focus is on basic design, implementation and performance issues. We follow the same four-step design and tuning recipe we use for all control implementations. A benefit of the recipe, beyond the fact that it is easy to use, widely applicable, and reliable in industrial applications, is that steps 1-3 of the recipe remain the same regardless of the control algorithm being employed.
Measurement Noise Degrades Derivative Action
ABSTRACT: At the start of a recent Practical Process Control workshop, I asked the attendees what the "D" in PID stood for. One fellow immediately shouted from the back of the room, "Disaster?" Another piped in, "How about Danger?" When the laughter died down, another emphatically stated, "D is for Do not use." This one got a good laugh out of me. I had not heard it before and thought it was perfect. And here's why…
PID Disturbance Rejection Of The Gravity Drained Tanks
ABSTRACT: We have explored disturbance rejection in the gravity drained tanks process using P-Only and then PI control. In the PI study, we confirmed the observations we had made in the PI control of the heat exchanger investigation. Here we investigate the benefits and challenges of derivative action and PID control when disturbance rejection remains our control objective.