Interview Questions for Instrument Technician .doc

8/14/2019 Interview Questions for Instrument Technician .doc

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Q.1-What is trim & trim parts in control valves?Includes all the parts that are in flowing contact with the process fluid exceptthe body !"##$% and body flanges and gasets. %he plug seats stemguides bushings and cage are some of the parts included in the term trim.

Q.'-What is bench set & how can we ad(ust it?!ench )et on a *ontrol +alve is basically on a pneumatic control valve it,sthe amount of air reuired to start to move an uncoupled actuator from ero

to full stroe position.

Q./-What are accessories of control valves?0ressure regulators positioner +olume !ooster relay Quic $xhausts relay%rip relay oc up relay limit switch solenoid valve.

Q.2-What are basic configuration parameters of smart positioner?3ns- +alve type 4)liding stem or 5otary6

+alve action 4air to open or air to close6 %ravel sie

7iaphragm sie

3nalog input range low 4lie as 2 ma63nalog input range 8igh 4lie as '9 ma6

Q.:-What is +alve *+?%he *+ is defined as the number of ;) gallons of Water per minute 4atstandard pressure & temperature6 that will flow through a wide open valvewhen there is pressure 1-psi pressure drop across it.

Q.-What is the purpose of positioner? What are disadvantages withoutpositioner?

Q.-*ommon %ypes of control valve pacing?- 0%@$ + 5ing- aminated & @ilament Araphite.

Q.=-If 0rocess variable is hunting what will be your step to identify theproblem@irstly put controller on manual & then chec that problem in transmitter orin control valve if both stable then problem in controller tuning.

Q.19-What is the purpose of booster relay? Where it is mostly used?%o increase the volume of signal in very short time. It is used where uicaction reuire 4lie anti surge valve6

Q.11-What are the control valve plug characteristicsinear *haracteristicQuic opening *haracteristic$ual percentage *haracteristic.


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Q.1'-*ontrol valve leaage classes.)ix different seat leaage classifications%he most common used are *lass I+ + and +I*3)) I+ metal to metal.*3)) +I soft seat

Q.1/-What is pacing follower?3 part that transfer a mechanical load to the pacing from the pacing flangeor nut.

Q.12-3 70 transmitter range is 9 B199 mm 8'9 installed across orifice. Itsconfiguration in suare root mode. WhatCs input pressure values applied tothe transmitter for calibration?9 D - 9 mm':D - :D - :


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0roximitor is "scillator 7emodulator. ;pon energiing oscillator produce 1.:B '.9 E8 radio fre. it deliver to probe. 0robe gives output to demodulatorthat compared it with generated 5@ value & give output to monitor.

Q.''-What is float of a machine.3xial clearance of a machine rotor 4given by vendor6 in which it can runsuccessfully.

Q.'/-@unction of wobulator in %J/It can produce vibration of ' mills to 19 mills pea to pea for checing thevibration probe characteristics.

Q.'2-Aeneral vibration Questions.+ibration proximitor supply -'2 + 7c#ormal linear range of probe sensitivity -' + dc to -1 + 7*+ibration system lengths 40robe to 0roximitor6 : Etr > Etr = Etr)cale factor of proximitor '99mvFEill "5 >.>mvFmicro

meter5ecommended gap voltage -=.: +dc.+ibration measurement unitCs mill micro meter1mmK /=./> mill or 1999 micro meter1millK ': micro meter1millK '99 m+ dc.1 + dcK : mill1 mmK + 7c.

Q.':-What is the resistance of L mm series = mtr long vibration probe?=.> ohm

Q.'


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Q./9-What is the *haracteristics of 3nti )urge +alve.3ir @ail to open Quic "pening is less than 'sec on surge detection4achieved by uic exhaust relay6

Q./1-What is cascade control loop?%he "ut put of master controller is the set point of the )lave controller.

Q./'-)ystems in Aas %urbines.1. @uel gas system'. ube oil system/. +entilation system2. )tarting system:. 0ulse (et system. *ore engine system

. @ire & Aas )ystem=. Water washing system19. )ealing & cooling air system

Q.//-What is magnetic picup & how it wors? 8ow can calibrate the speeddetection system of %urbine?!y applying freuency eual to speed to the monitoring system at speedprobe input point.

Q./2-3t what speed in gas turbine fuel introduce for ignition?#ormally '1 D of normal load speed.

Q./:-What is difference between diode & transistor?7iode and %ransistor both are semiconductor devices 7iode has twoterminals 3node 436 and *athode 4J6 where as transistor has three terminals*ollector 4*6 $mitter 4$6 and !ase 4!6. 7iode has one (unction where astransistor has two (unctions. !oth act lie switch but transistor trigger bybase signal.

Q./-If watchdog timer times out then what will be the status on discreteoutput cards?3ll will go to ero state

Q./-What is the difference between half-duplex and full duplexcommunication?In half duplex only one can communicate at a time whereas in full duplexboth can communicate at the same time.


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Q./=-What is *ommunication 0hysical & soft protocols? Where it is used? %hemaximum allowable range for 5)-'/' communication?

Q.29-$xplain Intrinsically )afe Instrument?%he Instruments those are unable or made unable to release sufficientenergy to cause ignition either by thermal or electrical means.

Q.21-What is meant by IP class?0rotection against ingress of solid foreign ob(ects and ingress of water in anenclosure.

Q.2'-We want to enter a pneumatic tube in (unction box what type of tubingconnector used?!ul head %ubing union connector

Q.2/-3n open tan height is 1999mm & liuid sp.gravity is 9..what is thecalibration range of its 70 type transmitter installed at tan ero bottom

point?9 to 99mm of 8'"

Q.22-3 70 transmitter range is - 999 pa to M999 Jpa. What is calibrationprocedure?@or 2 m3 apply 999pa at low side of the transmitter.@or '9 m3 apply 999pa at 8igh side of the transmitter

Q.2:-What is 835% Its Eodels name? What is its woring principle?835% stand for Highway Addressable Remote Transducer. It is a protocoldeveloped by @isher-5osemount to retrofit 2-'9m3 current loop transducerswith digital data communication.835% *ommunicator Eodels 268, 275, 375, 4750rincipleG %he 835% 0rotocol maes use of the !ell '9' @reuency )hift Jeying 4@)J6standard to superimpose digital communication signals at a low level on top of the 2-'9m3.

%his enables two-way field communication to tae place and maes it possible for additionalinformation beyond (ust the normal process variable to be communicated toFfrom a smartfield instrument. %he 835% 0rotocol communicates at 1'99 bps without interrupting the 2-'9m3 signal and allows a host application 4master6 to get two or more digital updates persecond from a smart field device. 3s the digital @)J signal is phase continuous there is nointerference with the 2-'9m3 signal. 835% technology is a masterFslave protocol

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$ N J 5 ) %

Q.:9-What is the J type thermocouple wires colour coding in 3#)I43merican6 system? What its material?

Mve wire Hellow 4*homimium nicel6-ve wire 5ed 43luminium #icle6

Q.:1-What can be cause for the Easter @uel %rip in !oiler.

1. $xcessive steam pressure or water temperature.'. ow water level./. 8igh or low gas pressure.2. oss of combustion air supply.:. oss of flame.

-8ow much value of resistance in 5%7 0%199 at 199C* temperature1/ "hm

Q.:-What is difference between 5%7 & %hermocouple?

5esistance %emperature 7etectors 45%7s6 are sensors that measuretemperature by correlating the resistance of the 5%7 element withtemperature. 5%7 is more sensitive good stability excellent accuracygood linearity low temperature range.


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3 thermocouple consists of two dissimilar metals (oined together atone end. When the (unction of the two metals is cooled or heated avoltage is produced that can be correlated bac to the temperature.%hermocouple is least stable less accurate non-linear hightemperature range.

Q.:-What type of @ire & Aas 7etector used in "il & Aas industry?I5 @lame 7etector ;+ @lame 7etector

*82Aas 7etector8') Aas 7etector0oint Aas 7etector"pen 0ath Aas 7etector

Q.:=-What is difference between step-up & step-down transformer?)tep-up %ransformer increase voltage and decrease current where as step

down %ransformer decrease voltage and increase current.

Q.

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Interview Questions for Instrument Technician .doc