# Control System

## Basics of PID controller (Proportional – Integral – Derivative)

PID (Proportional – Integral – Derivative ) Controller Proportional The proportional term makes the current error signal multiplied with a gain (Kp).The result will be output signal. So output signal = Kp * Error_Signal Integral The integral term makes the current error signal value and duration multiplied by with a gain (Ki). The result will …

## Override Control

Override It is sometimes necessary to limit a variable in order to maintain safe operation or protect process equipment. If this variable is a function of the systemâ€™s primary controlled variable, the two variables can be interlocked in an override system. The primary variable maintains control as long as the second variable does not exceed …

## Feedforward Control System

Feedforward A Feedforward control system measures a disturbance in variable, predicts its effect on the process and applies corrective action. Given an exact model of the process, the feedforward controller will adjust the manipulated variable (m) so that the controlled variable (c) is unaffected by the disturbance. In fact, the controlled variable has no influence …

Cascade In cascade control system two controllers are cascaded Â to each other as shown in the diagram below. Â Primary controllers output is fed to secondary controller as a Set point. Both the controllers has their own sensing elements but only secondary controller gives output to the control valve. Primary controller receives set point from …

## Ratio Control

Ratio Control In Ratio Control, the controlled variable is the ratio of two measured variables. Control is effected by adjusting one of the variables – Â the controlled variable, to follow in proportion to a second – the wild variable. The proportionality constant is the ratio. Ratio relays are nothing more than manually adjustable gain devices …

## Common Control Loops

Â  Common Control LoopÂ  1.Flow   Liquid flow processes are fast, Â typically 0.5 sec response or less. Gas flow is slightly slower because of the compressibility of the gas. Control components – transmitter, valve and transmission lines – Â are the main dynamic elements. Â The most common measuring means is the orifice plate and differential pressure …

## Derivative Or Rate Control

Derivative Control Derivative control (also called rate control) responds to the rate of change of the controlled variable. For example, if the temperature of a process is changing rapidly, the controller must respond quickly to keep the temperature within acceptable limits. In effect, derivative control action uses the rate of change in a process to …

## Two-position control

With two-position control, the final control element may be in only one of two positions. These two positions are sometimes called on/off or open/closed. Consequently, it is often called on-off control. Two-position control is used in many systems, such as heating and air conditioning, water heaters and ovens. In the example, two-position control is the …

## Instruments Used In Control Loop

InstrumentsÂ  I hope you have a general understandingÂ what a feedback control loop is, if not please refer the following article – Feedback Control LoopÂ  Sensors You have readÂ  that a sensor monitors and measures what is happening in the process. Examples of sensors include: thermocouples, floats, limit switches, pressure switches, pressure switches, moisture meters, and …

## Components of Pneumatic Control System

Pneumatic Control SystemÂ  What is pneumatic ? Pneumatic is the technology that makes use of gas or pressurized air. Components of Pneumatic control system 1.Directional control Valves Â  These are functional valves used in logic implementation. Divided according to the number of ports / passages available and number of valve positions 2.Two Way Valves …

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