INSTRUMENTATION AND CONTROL ENGINEERING

Admittance (Y) :- An admittance of a linear constant-parameter system is the ratio of the phasor equivalent of the steady-state sine-wave current or current-like quantity (response) to the phasor equivalent of the corresponding voltage or voltage-like quantity (driving force). Capacitance (C) :- Capacitance is that property of a system of conductors and dielectrics which permits the storage of electrically separated charges when potential differences exist between the conductors. Its value is expressed as the ratio of an electric charge to a potential difference. Coupling Coefficient (k) :- Coefficient of coupling (used only in the case of resistive, capacitive, and inductive coupling) is the ratio of the mutual impedance of the coupling to the square root of the product of the self-impedance of similar elements in the two circuit loops considered. Conductance (G):- 1. The conductance of an element, device, branch, network, or system is the factor by which the mean-square volt...

Foundation Fieldbus is an all-digital, serial, two-way communications system that serves as a Local Area Network (LAN) for factory/plant instrumentation and control devices. The Fieldbus environment is the base level group of the digital networks in the hierarchy of plant networks. Foundation Fieldbus is used in both process and manufacturing automation applications and has a built-in capability to distribute the control application across the network. Unlike proprietary network protocols, Foundation Fieldbus is neither owned by any individual company, nor regulated by a single nation or standards body. The Foundation Fieldbus, a not-for-profit organization consisting of more than 100 of the world's leading controls and instrumentation suppliers and end users, controls the technology. While Foundation Fieldbus retains many of the desirable features of the 4-20 mA analogue system, such as a standardized physical interface to the wire, bus-powered devices on a single wire, and intr...

HART stands for 'Highway Addressable Remote Transducer' and is a standard originally developed as a communications protocol for control field devices operating on a 4-20 mA control signal. The HART protocol uses 1200 baud Frequency Shift Keying (FSK) based on the Bell 202 standard to superimpose digital information on the conventional 4-20 mA analogue signal. Maintained by an independent organisation, the HART Communication Foundation, the HART protocol is an industry standard developed to define the communications protocol between intelligent field devices and a control system. HART is probably the most widely used digital communication protocol in the process industries, and: Is supported by all of the major suppliers of process field instruments. Preserves existing control strategies by allowing 4-20 mA signals to co-exist with digital communication on existing 2-wire loops. Is compatible with analogue devices. Provides important information for installation and mainte...

Q. What is a control system? A. A control system consists of subsystems and processes (or plants) assembled for the purpose of obtaining a desired output with desired performance, given a specified input. Q. When is a control system said to be robust? A. control system is said to be robust when 1. It has low sensitivities 2. It is stable over a wide range of parameter variations; and 3. The performance stays within prescribed (but practical) limit bounds in presence of changes in the parameters of the controlled system and disturbance input. Q. What is the main difference between open loop and closed loop systems? A. Open-loop systems, do not correct for disturbances and are simply commanded by the input. The closed-loop system compensates for disturbances by measuring the output response, feeding that measurement back through a feedback path, and comparing that response to the input at the summing junction. If there is any difference between the two responses, the system driv...

■ TRIP : The term trip refers to an action that is initiated by the control system and which forces a device or devices to a pre-determined state. Example of Trip Signals: Close Valve, Open Valve, Stop motor, etc. The Safety Instrument System (SIS) or a Hardwired systems normally initiate trips, however the PLCs or DCS may also initiate trips provided the necessary independence and SIL ratings are met.Once a device or devices have been forced to a pre-determined state by the action of a Trip they will remain in that state until the Trip is manually reset by a conscious operator action. For example: High level in a vessel initiates a trip system which stops the pump feeding that vessel, the pump will remain stopped even if the level in the vessel falls to a safe level. The Trip must be ‘reset’ by the operator before the pump can be re-started. The Trip can only be ‘reset’ if the level in the tank has fallen to a safe level. Resetting the Trip will no...

1.What are different types of orifice plates? State their uses. Different orifice plates are: 1. Concentric 2. Segmental 3. Eccentric – These plates are used for ideal liquid as well as gases and steam service. Concentric holes are present in these plates, thats why it is known as concentric orifice. Concentric: – This plate has hole in the form of segment of the circle. This plate is used for colloidal and sherry flow measurement. Segmental: – This plate has the eccentric holes. This plate is used in viscous and sherry flow measurement. Eccentric: Field instruments interview questions and answers 2.How do you identify an orifice in the pipeline? An orifice tab is welded on the orifice plate which extends out of the line giving an indication of the orifice plate. 3.Why is the orifice tab provided? Following reasons justify for providing orifice tab: 1. Indication of orifice plate in a line 2. The orifice diameter is marked on it. 3. The material of the ...