http://www.controlguru.com/ Proven Methods and Best Practices for PID Process Control en-us Sun, 04 May 2008 00:00:01 EST doug.cooper@controlguru.com doug.cooper@controlguru.com http://www.controlguru.com/2008/050408.html A feed forward controller receives a measured disturbance signal, uses it to predict an impact on the process variable, and then computes preemptive control actions that counteract the predicted impact as the disturbance arrives to maintain the process variable at set point (PV = SP) throughout the disturbance event. Sun, 04 May 2008 00:00:01 EST http://www.controlguru.com/2008/041308.html Here we explore the addition of a second select override element to create a cross-limiting architecture that prevents the air/fuel ratio fed to the burner from becoming overly rich (too much fuel) or lean (too much air) as operating conditions change. Variations on this cross-limiting architecture are widely employed within the air/fuel ratio logic of a broad range of industrial combustion control systems. Sun, 13 Apr 2008 00:00:01 EST http://www.controlguru.com/2008/030908.html A select element enables decision-making logic to be included in a control strategy, which in turn provides a means for increasing strategy sophistication. A popular application explored in this article is to use a select override in a ratio control architecture. In particular, we explore how a select override can be included in an air/fuel ratio combustion control strategy to enhance safety, limit emissions and maximize useful energy from fuel. Sun, 09 Mar 2008 00:00:01 EST http://www.controlguru.com/2008/021008.html A valve cannot open more than all the way. A pump cannot go slower than stopped. Yet an improperly programmed control algorithm can issue such commands. Herein lies the problem of integral windup (also referred to as reset windup or integral saturation). It is a problem that has been around for decades and was solved long ago. We discuss why it occurs and how to prevent it to help those who choose to write their own control algorithm. Sun, 10 Feb 2008 00:00:01 EST http://www.controlguru.com/2008/012708.html A ratio control strategy can play a fundamental role in the safe and profitable operation of fired heaters, boilers, furnaces and similar fuel burning processes. This is because the air-to-fuel ratio in the combustion zone of these processes directly impacts fuel combustion efficiency and environmental emissions. A requirement for ratio control implementation is that both the fuel feed rate and combustion air feed rate are measured and available as process variable signals. Sun, 27 Jan 2008 00:00:01 EST http://www.controlguru.com/2007/120207.html The ratio control architecture is used to maintain the flow rate of one stream in a process at a defined or specified proportion relative to that of another. A common application for ratio control is to combine or blend two feed streams to produce a mixed flow with a desired composition or physical property. Sun, 02 Dec 2007 00:00:01 EST http://www.controlguru.com/2007/110407.html Like most control room displays, the Controlguru.com e-book presents PV values in engineering units. These are used directly in tuning correlations to compute controller gains, Kc. As a result, the Kc values also carry engineering units. The benefit of this approach is that Kc maintains the intuitive familiarity that engineering units provide. The difficulty is that commercial controllers are normally configured to use a dimensionless values. This article explores how to convert a Kc with engineering units into the standard dimensionless (%/%) form. Sun, 04 Nov 2007 00:00:01 EST http://www.controlguru.com/2007/090207.html When improved disturbance rejection is our goal, one benefit of cascade control over a feed forward strategy is that implementing a cascade builds upon our existing skills. A cascade has two controllers, and the proecedure is a familiar task because it essentially is to employ our controller design and tuning recipe twice in sequence. Sun, 2 Sep 2007 00:00:01 EST http://www.controlguru.com/2007/070607.html Cascade control is an architecture capable of reducing the impact of disturbances on our measured process variable (PV). To construct a cascade architecture, we literally nest a secondary control loop inside a primary loop as shown in the block diagram. Fri, 6 Jul 2007 00:00:01 EST http://www.controlguru.com/2007/042507.html The control objective for the pumped tank process is to maintain liquid level at set point by adjusting the discharge flow rate out of the bottom of the tank. This process displays the distinctive integrating (or non-self regulating) behavior, and as such, presents an interesting control challenge. Wed, 25 Apr 2007 00:00:01 EST