Control System- Pressure Regulator

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az                        CONTENT PAGE

TITLE PAGE

1.0        INTRODUCTION                                                

2.0        TYPES OF REGULATORS

                                        

        

2.1        SIMPLE PRESSURE CONTORL SYSTEM(SELF OPERATED REGULATOR)

3.0        PILOT OPERATED PRESSURE REGULATOR

                3.1        INSTRUMENT CONTROL

4.0        COMPUTER CONTROL

5.0        CONTROL ELEMENTS

        5.1        BASIC ELEMENTS

5.2        MATHEMATICAL MODELS OF PHYSICAL DEVICES

6.0        PROCESS CONTROL SYSTEM

7.0        ACCURACY AND SENSITIVITY

        7.1        ACCURACY

        7.2        SENSITIVITY

8.0        FEEDBACK

9.0        PRESSURE MEASUREMENT

10.0        CONTROLLERS

11.0        INPUT AND OUPUT

12.0        REFERENCE LIST

       PRESSURE REGULATOR

1.0        INTRODUCTION-

A type or certain group of elements that function together as a unified whole, is a system. This widened description thus gives some meaning to control systems as a whole. By re-establishing the basic principles and functions worked out, a system’s limit can be extended to include little or more characteristics just as long as each singular variable contributes in a way to the particular system activity. This explains that the system does not halt interaction to other systems or peripherals. In the process industry, the term control system is sometimes normally used to specify a process, and the apparatus basically required to run the process. The system is tested with various actions so it will conform to a standard, these include; load, commands and disturbances which cause it to respond in some individual manner. A system is best made so that it will respond positively.
In order for a system to act in the way prescribed is to control the system. The basic concept of comparing the measured and prescribed system performance, and then taking any action to change the process thereby minimizing errors, is called negative feedback. The system can vice-versa be called a closed-loop control system, or a negative feedback control system. To make a system automated it should be mechanized. To create the maintenance of a constant value in a control, is not the major primary objective of control; once the prescribed behavior is achieved, the control function is fulfilled.
Although the use of control measure is in most cases involved with mechanical equipment, they can also be used in fields such as (e.g. in the social, biological or in different other systems). The science of achieving control, by using or not using feedback, is the method of control theory. This is applicable to system control in general. Most control systems have evolved by the practice of trial and error, for the critical design of system controls with the need for extensive analysis of two factors, the control devices and the process.


  1.  TYPES OF REGULATORS-  

                                                                                                                                   

  1. SIMPLE PRESSURE CONTROL SYSTEM (SELF OPERATED REGULATOR):

For a typical uncontrolled system, let us say it is required for it to provide a standard pressure, P, at a given measure and that the discharge, Q2, provides for an external system, which, its need for this fluid varies. At a given time interval, the external system regulates valve No. 2 to comply with the needed specifications. The curves given in Fig  1.0

FIG 1.1

 Shows the way in which it alters the process of the pressure. In earlier results in time, t1, some initial stable condition exists where, Q1

 and   Q 2 are of the same and the process pressure is significantly at the aimed equivalent. A level change occurs at, Q1 when time is at, t1, this reduces the fluid mass between the valves. This is followed mainly by a drop in the process pressure. For a system which is uncontrolled the pressure decline will continue until the drop over valve No.  1 is enough again to build equal flows and a new constant state functioning condition is gained. The procedure can be controlled; i.e. the suitable needed pressure can be managed if the significant rise in Q1 were gotten by increasing the opening of valve No. 1. 

 A typical way of doing this is given in  Fig   1.1. 

                FIG 1.3

                

The response for the process pressure is sent to a spring opposed diaphragm that gives free way for the pressure to manoeuvre the valve. In a working mode, the contraction in the spring will be set so that at some constant state working condition the required process pressure, acting on the diaphragm section, this balances the force that the spring carries. The aimed process pressure is known as a set point. Changes from the set point which is caused by load variation will be controlled because as the process pressure differs, the matching force given back to the diaphragm will regulate the valve position to reduce the pressure variance to a certain range of value around the set point. The careful control of the pressure will rely on how big a flow change the regulator will be able to carry out for a minimal amount of pressure. The regulator flow change to process pressure change is the gain of the regulator and this will rely on the diaphragm area, the valve size, stiffness of the spring, and the general pressure drop over it.

        

The corrective activity done by the regulator is proportional to the change of the process from its set point. Such an element is called the proportional or proportional mode, control. When using the proportional control, the corrective action can only carry on when some different outlines exist. The final pressure change needed to completely stroke the regulator is known as the proportional band and it shows around what limits the regulator can control.

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                FIG   1.4

illustrates where the process measurement supplies the whole valve actuating force, this is known as self-operated regulators.  

                        FIG   1.5

The above demonstrates a self operated regulators made for the control of temperature, flow and level.  The operation method is practically the same with the pressure regulator. They are widely used in various applications of specialty in the industrial field.

  1. PILOT OPERATED PRESSURE REGULATOR:

This regulator uses a little pilot valve assembly to aide in actuating the main valve. ...

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