Selector Control Functions
In the broadest sense, a “selector” control strategy is where one signal is selected from multiple signals in a system to perform a measurement control function. I will use the…
Limit Controls : High Limit & Low Limit Functions
A common application for select and limit functions is in cascade control strategies, where the output of one controller becomes the setpoint for another. It is entirely possible for the…
Limit, Selector, and Override controls
Another category of control strategies involves the use of signal relays or function blocks with the ability to switch between different signal values, or re-direct signals to new pathways. Such…
What Temperature are Celsius and Fahrenheit Value Same ?
Simple Conversions of Celsius and Fahrenheit Temperature Scales 1. Standard Conversion °F to °C : Deduct 32, then multiply by 5, then divide by 9 °C to °F : Multiply by…
Feedforward Control with Dynamic Compensation
As we have discussed, feedforward control is a way to improve the stability of a feedback control system in the face of changing loads. Rather than rely on feedback to…
Proportioning Feedforward action
Feedforward control works by directly modulating the manipulated variable in a control system according to changes sensed in the load(s). In order for feedforward to function optimally, it must adjust…
Feedforward Control Principle
Let us consider a liquid level control system on an open tank, where three different fluid ingredients (shown in the following P&ID simply as A, B, and C) are mixed…
What is Feedforward Control ?
“Feedforward” is a rather under-used control strategy capable of managing a great many types of process problems. It is based on the principle of preemptive load counter-action: that if all…
Relation Control System
A control strategy similar to ratio control is relation control. This is similar to ratio control in that a “wild” variable determines the setpoint for a captive variable, but with…
What is Ratio Control ?
Most people reading this article have likely had the experience of adjusting water temperature using two hand valves as they took a shower: one valve controlling the flow of hot…
