Instrumentation interview questions and answers

1.What is an Indicator?

An indicator is a human readable device that displays information about the process.

What is a Transducer?

A transducer is device that translates a mechanical signal into an electrical signal.

What is a Transmitter?

A transmitter is a device that converts a reading from a sensor or transducer into a standard signal and transmit that signal to a monitor or controller.

What Are The Primary Elements Usedfor Flow Measurement?

Answer :

The primary elements used for flow measurement are:

1. Orifice Plate.
2. Venturi tube.
3. Pitot tube.
4. Annubars.
5. Flow Nozzle.
6. Weir & Flumes.
7. What Are The Different Types Of Orifice Plates And State Their Uses?
8. Answer :
   The different types of orifice plates are:
   1. Concentric.
   2. Segmental.
   3. Eccentric.
   CONCENTRIC: The concentric orifice plate is used for ideal liquid as well as gases and steam service. This orifice as a hole in concentric and hence known as concentric orifice.
   Eccentric & Segmental: The eccentric orifice plate has a hole eccentric. The use this is made in viscous and sherry flow measurement.
   The segmental orifice place has the hole in the form segment of a circle. This is used for colloidal and sherry flow measurement.

9. What Is The Seal Liquid Used For Filling Impulse Lines On Crude And Viscous Liquid?

   Answer :
   Glycol.

10. How Do You Carry Out Piping For A Different Pressure Flow Transmitter On Liquids, Gas And Steam Services? Why?

    Answer :
    Liquid lines: On liquid lines the transmitter is mounted below the orifice plate. Since liquids have a property of self draining.
    Gas Service: On gas service the transmitter is mounted above the orifice plate because Gases have a property of self venting and secondly condenlate formation.
    Steam Service: On steam service the transmitter is mounted below the orifice plate with condenlate pots. The pots should be at the same level.

11.  An Operator Tells You That Flow Indication Is More? How Would You Start Checking?

    Answer :
    1. First flushing the transmitter. Flush both the impulse lines. Adjust the zero by equalizing if necessary. If still the indication is more then.
    2. Check L.P. side for choke. If that is clean then.
    3. Check the leaks on L.P. side. If not.
    4. Calibrate the transmitter.

    5. How Do You Do A Zero Check On A D.p. Transmitter?

       Answer :
       Close one of the valve either H.P. or L.P. open the equalizing valve. The O/P should read zero.
    6. What is solenoid valve? Where it is used?
       A solenoid is electrically operated valve. It consists of solenoid coil in which magnetic plunger moves. This plunger is connected to the plug and tends to open or close the valve. There are two types of solenoid valves:
       
       1. Normally Open
       2. Normally closed
       
       Use: It is used for safety purpose in different electric work
    7. Name different types of bourdon tubes?
       Types of bourdon tubes:
       1. C type
       2. Spiral
       3. Helix
    8. What are primary elements of measuring pressure? Which type of pressure can be measured by these elements?
       Primary elements of measuring pressure are:
       a. Bourdon Tube
       b. Diaphragm
       c. Capsule
       d. Bellows
       e. Pressure springs
       These elements are known as elastic deformation pressure elements.
    9. What is the use of valve positioner?
       Valve positioner can be used for following reasons:
       a. Quick action
       b. Valve hysterisis
       c. Viscous liquids
       d. Split range.
       e. Line pressure changes on valve
       f. Bench set not standard
       g. Reverse valve operations
    10.  Name different parts of a pressure gauge? Explain the use of hair spring in the pressure gauge?
        Pressure gauge includes following components:
        a. ‘C' type bourdon tube.
        b. Connecting link
        c. Sector gear
        d. Pinion Gear
        e. Hair spring
        f. Pointer
        g. Dial
        
        Use of hair spring: Hair spring is responsible for controlling torque. It is also used to eliminate any play into linkages.
    11. What is the function of 3-way manifold valve?
        excessive pressure to your differential pressure transmitter, you could damage your instrument. This is known as over-ranging the transmitter. 
        
        A three-way manifold valve is a device that prevents the instrument from being over-ranged. It also allows the isolation of the transmitter from the process loop (an option which could be used generaly for maintenance or re-calibration or fitting new equipment).