Instrument QC Inspectors Test Question Answers
Mention 4 major functions of a Qc Inspector?
What is a home-run instrument cable?
ANS: A cable typically multi pair / triad extending between the field junction boxes and marshalling cabinets in control room or PIB building.
What is branch or secondary instrument cables·?
ANS: A cable typically multi pair / triad extending between the field junction boxes and field instruments.
What is the grounding systems required for instrumentation?
ANS: Safety ground b) instrumentation circuit ground
What are the 2 types of temperature elements?
ANS: RTD Type b) Thermocouple type
What are the 3 hazardous classification areas?
- Zone O – Zone in which an explosive atmosphere is present continuously for long period
- Zone 1 – Zone in which an explosive atmosphere is likely to occur in normal operation
- Zone 2 – Zone in which an explosive atmosphere is likely to occur in normal operation and if it occurs it will exist for a short time
How many bends are allowed for a conduit system?
ANS: Not more than 360 degree
what is EXd’ OR flameproof protection?
ANS: The potentially incentive components contained within enclosure in to which flammable atmosphere can enter but which contain resultant explosion and prevent its transmission to flammable atmosphere outside the enclosure.
What is IP6?
ANS: Ingress of protection against ingress of dust.
what is the color code of signal pair?
- Positive – Black 2. Negative – White
What is the color code of signal triad?
1)Positive – Black 2)Negative- White 3) Third wire – Red
What tubings extended between the tapping point & instrument manifold Value?
ANS: Impulse line
what is the minimum slope in impulse line?
ANS: 1:12 inches
what pipe is extended between the control valves & instrument main header?
ANS: Instrument sub header and branch header line.
what range using for the calibration of transmitters?
ANS: Set range
what is the output signal range of pressure transmitter?
ANS: 4-20 mA
what type of instrument cables for ana1og signal to be used from field JB to field instruments.?
16 AWG, 300 V, PLTC/ITC, Single Twisted / Shield Pair or triad.
Is it allowed to make splicing for instrument cables?
ANS: No splicing is not permitted for instrument cables.
What is the distance of·sea1 fitting within the instrument Junction box
ANS: 18 inch
HOW ·many wires installed in RTD type temperature elements?
ANS: 3 wires
How many wires installed in thermocouple type temp ·Elements?’
ANS: Two wires
What is the temperature range of RTD type temperature element?
ANS: Upto 800 degree centrigrade
What is the minimum height of stanchion mounted instrument?
ANS: 1.4m above grade or platform
Give 5 examples of in-1ine & on-1ine instruments?
- Flowmeters 2. Valves 3.Orifice Plate 4. Gauge Glasses 5.Displacement Type level transmitter
What is the minimum height of conduit & cable tray above access way?
ANS: 2.1 meter
What is the maximum distance between supports for 1inch instrument airline?
ANS: 3.6 meter
what is the maximum distance between supports of impulse line for vertical & horizontal installation?
ANS: Horizontal line 1.5 meter and ‘Vertical line 3.0 meter
In airline piping ·for 1/2″ pipe, how many users are permitted?
ANS: 1-4 users are permitted
What is the height of audible alarms & flashing beacons from grade?
ANS: 2.4 meters
What is the height of combustible & H2S gas detectors?
ANS: 305-457 mm from grade
What is the maximum length of flexible conduit to be installed between conduit system & field instrument ?
ANS: Not exceed 3 feet
What is the meggering acceptable value of a instrument cables?
ANS: Greater than 1 mega ohm.
What are the basic variables of instrumentation?
- Pressure 2. Temperature 3. Flow 4. Level
How to check the instrument installation?
- Check the identification tag
- Check the elevation if it is above or below the tapping point
- Support shall be rigid
- The instrument shall be accessible
How to test the impulse line?
- The impulse line to be blown by compressed air to ensure no foreign bodies are present
- The hydraulic pump or nitrogen compete tank with test gauge shall be connected to drain or vent port
- The pipe shall be pressurized as per line or tapping point pressure and isolated from the pressure and held for 5 minutes
- The pressure in system shall not be fall
How to test the pneumatic lines?
- Instrument sub and branch header shall be blown by compressed air to remove foreign bodies present inside pipe.
- Instrument air line shall be pressurized and isolated the line from pressure source and check the joint with soap solution. The pressure in system shall not and held for 10 minutes.
- After the completion of test pipe line to be blown and dried using compressed air.
How to test the instrument cables?
- Instrument cables rated 600 volts shall be tested 500 volt megger and if rated 300 volt shall be tested at 250 vdc.
- Check the continuity of each core, individual drain and overall drain.
- Check the insulation resistance between cores and individual coresm screen and armor.
- The result shall be greater than 1 mega ohm.
How to check the installation of instrument Panels?
- The complete assembly shall be checked to ensure alignment and level after tighten the bolts
- The instrument shall be checked against identifying labels & tags are installed as per layout drawings.
- Earthing of panel shall be checked as per layout drawing.
- Installation shall be rigid.
- Panel doors and detachable covers shall be checked to ensure proper enclosure and sealing.
What is the maximum length of impulse tubing in control loops?
ANS: 6 meter or 20 feet
What is the minimum separation of power cables (120 VAC) and analog signals between conduits?
ANS: 150 mm