• ## Impulse Piping Installation Precautions

### 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 system’s primary controlled variable, the two variables can be interlocked in an override system. The…

### 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)…

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

### 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 –  the controlled variable, to follow in proportion to a second – the wild variable. The proportionality constant…

### Common Control Loops

Common Control Loop  1.Flow   Liquid flow processes are fast,  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 –  are the main dynamic…

### 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…

### Process Control – Integral Control

Integral (or Reset) Control     Integral control (also called Reset control) can be used when unacceptable amounts of offset occur in a process with proportional control. Integral control is used to return the value of the controlled variable to the set…

### Process Control – Proportional Control

Proportional Control  In some processes, the fluctuations around the set point (called oscillation) may be too severe to achieve the desired results. Many processes require a more stable form of control. Proportional control is one way to achieve that stability  When proportional…

### Instruments Used In Control Loop

Instruments  I hope you have a general understanding what a feedback control loop is, if not please refer the following article – Feedback Control Loop  Sensors You have read  that a sensor monitors and measures what is happening in the process. Examples of…

### Basics of Feedback Control – Elements of Feedback control

Feedback Control Feed-back control is gathering information on the controlled variable and comparing it to the set point; making a decision based on that comparison; and taking action to eliminate any differences between the controlled variable and the and the set point…