Using Signal Filters In Our PID Loop
ABSTRACT: In our study of the derivative mode of a PID controller, we explored how noise or random error in the measured process variable (PV) can degrade controller performance. As discussed in that article, derivative action can cause the noise in the PV measurement to be reflected and amplified in the controller output (CO) signal, producing "chatter" in the final control element (FCE). This extreme control action will increase the wear on a mechanical FCE (e.g., a valve) and lead to increased maintenance needs.
PID with Controller Output (CO) Filter
ABSTRACT: The derivative action of a PID controller can cause noise in the measured process variable (PV) to be amplified and reflected as "chatter" in the controller output (CO) signal. Signal filters, implemented as either analog hardware or digital software, offer a popular solution to this problem. If noise is impacting controller performance, our first attempts should be to locate and correct the underlying fault. Filters are poor cures for a bad design or failing equipment. If we decide to employ a filter in our loop, an algorithm designed to smooth the controller output signal holds some allure.
PID with CO Filter Control of the Heat Exchanger
ABSTRACT: The same tuning recipe we successfully demonstrated for PI control and PID control design and tuning can be used when a controller output (CO) filter is added to the heat exchanger process control loop. Here we explore PID with CO Filter control using the unified (controller with internal filter) form. We showed in this previous article that the unified form is identical to a PID with external first-order CO filter implementation. Hence, the methods we use and observations we make apply equally to both internal and external filter architectures.
PID with CO Filter Disturbance Rejection in the Jacketed Stirred Reactor
ABSTRACT: The control objective for the jacketed stirred reactor process is to minimize the impact on reactor operation when the temperature of the liquid entering the cooling jacket changes. We have previously established the performance capabilities of a PI controller in rejecting the impact of this disturbance. Here we explore the performance of a PID with controller output (CO) filter algorithm in meeting this same disturbance rejection objective. We use the unified PID with CO filter controller in this study. As detailed in a prior article, the unified form is identical to a PID with external first-order CO filter implementation. Thus, the methods and observations from this investigation apply equally to both controller architectures.