Loop checking procedure of Instruments

This article is about the loop checking procedure of all  instruments like flow transmitter, valves, vibration, DCS loop, switchgear loop and ramaining pressure and level types instruments.

Loop checking procedure of Instruments

LIST OF TOOLS AND EQUIPMENT IN LOOP CHECKING

Tools and equipment needed should be in good condition and must be checked by Instrument Supervisor prior to use. Calibration equipment shall comply with the Saudi Aramco Standards requirements and provided with calibration certificate to support the readings of the calibrating equipment these includes but not
limited to:

  1. HART Communicator
  2. Dead Weight Tester
  3. Air Compressor
  4. MC5 FF Multifunction Calibrator
  5. Test Gauges with Ranges per Specification
  6. Absolute Pressure Gauge
  7. Portable 120Vac, 60Hz Gasoline Powered Generator
  8. Pulse/Frequency Generator
  9. DC Power Supply Regulated 24Vdc Variable
  10. Nitrogen Tank w/ High Pressure Regulator
  11.  Thermo Bath
  12. Hydrostatic Test Pump
  13. Set of Precision Weights
  14. Digital Thermometer
  15. Glass Thermometer
  16. Potentiometer
  17.  Portable Pressure Calibrator (DRUCK)
  18.  Process Calibrator
  19.    Advanced Temperature Calibrator
  20.   RTD Conversion Chart
  21.   Circuit Tester
  22.   Decade Resistance Box
  23.   Digital Manometer (Mercury or Water Manometer)
  24.   Mercury and Water Manometer
  25.    Hand Pump
  26.    Hygrometer (Humidity Tester)
  27.   Air Regulator
  28.   Pneumatic Comparator
  29.   Vacuum Pump
  30.   Oscilloscope
  31.   Radio Communication Equipment (intrinsically safe as per approved)
  32.    Multi meter
  33.    Test Bench with clean, dry and oil free instrument air
  34.    Set of Tools, Hose & Fittings
  35. Stop Watch
  36. Millivolt/Temperature conversion chart
  37. TK-3 (for checking of vibration element)
  38. Spirit Level
  39. BEAMEX MC5 Calibrator
  40. Others,if any

All tools utilized in a classified area should be intrinsically safe and suitable for hazardous areas.

LOOP CHECKING PROCEDURE OF FF and Conventional Transmitter (Flow/Level/Pressure)

  1. For FF device commission FF segment prior to loop testing by measuring resistance and DC voltage of segment conductor if all devices are connected otherwise only resistance will be recorded and voltage will be measured after all devices are connected and compare the result with FF segment checkout forms.
  2. Check and verify the DCS configuration for applicable points.  Reference drawings will be P&ID and ISS.
  3. Apply the pressure for all (Analog / Digital) smart transmitters by using test equipment (Hand Pump) for 0%, 25%, 50%, 75% and 100% simulation to check the transmitter response at DCS.  This method shall be used for all smart
    transmitters.
  4. Verify the corresponding reading in the DCS / Integral indicator and at remote indicator if applicable.
  5. For non-smart transmitters case Hand Pump shall be used for simulation or when required (4-20mA) ma source to be used for simulation purpose instead of hand pump.
  6. Alarms function (in DCS) shall be checked by simulating / verifying the required signal using communicator or hand pump using latest P&ID.
  7. For displacement type LT Hydraulic pump will be used with hosepipe and transparent tube with liquid (water).
  8. Normally Transmitter loop test should be performed after completion of the impulse line works including pressure test.  In some case loop test can be executed without impulse tubing being connected if piping is not completed.
  9. In case of impulse line not installed and tested then this exception item to be mentioned in the loop test exception log sheet prior to signing the loop folder.

     

LOOP CHECKING PROCEDURE  FF and Conventional Control Valves Loops

  1. For FF device commission FF segment prior to loop testing by measuring resistance and DC
    voltage of segment conductor if all devices are connected otherwise only resistance will be recorded and voltage will be measured after all devices are connected and compare the results with FF segment checkout form.
  2. Check and verify the DCS configuration for applicable points.  Reference drawings are to be P&ID and
    ISS.
    iii.    If any logic / interlocking are involved in applicable loop. Energize the solenoid valve by forcing the applicable ESD points on functional logic and same procedure to be carried out for DCS logic.
    iv.    If instrument air supply is not available then, dry and clean air or nitrogen shall be used.
    v.    Apply the command from DCS for 0%, 25%, 50%, 75%, 100% and monitor the response of the valve from the field.
  3. Verify the corresponding valve position.
    vii.    Verify the controller action.
    viii.    Verify the control valve action on increase signal.
    ix.    Verify the control valve action on air supply failure.
    x.    Verify the control valve max / min travel stopper setting if applicable.
    xi.    Check the hand wheel manual operation / function if applicable. Auto/ manual calibration is applicable.
    xii.    Normally control valve loop test should be performed after completion of the external air supply piping works.  In some cases when required, loop test can be executed without the internal air supply piping.
    xiii.    In case of air piping is not installed and tested then this exception item to be mentioned in the loop test exception log sheet prior to signing the loop folder.
    xiv.    Loop will be installed only and signed after the clearance of the punch list.

       LOOP CHECKING PROCEDURE  On / Off Valves Loops

  1. Valve response time shall be recorded in loop record sheet.
    ii.    Check and verify the DCS / ESD configuration for applicable points.
    iii.    If any ESD logic / interlocking are involved in applicable loop to energized solenoid valve, should be prepared ESD points on functional logic and same procedure to be carried out for DCS logic.
    iv.    If instrument air supply is not available then connect nitrogen cylinder.  In big size of valve cases, big volume of
    nitrogen will be required then in that case on/off valves function test will be executed upon air supply availability.
    v.    Apply the command from DCS / field for open and close as applicable.
    vi.    Verifying the corresponding valves position in DCS and field.
    vii.    Verify the partial stroke function test of “ZV”.
    viii.    Verify the valve action on air supply failure.
    ix.    Check the hand wheel / hand jack manual operation / function as applicable.
    x.    Normally On/Off valve loop test should be performed after completion of the external air supply piping works.  In some cases when required, loop test can be executed without air.
    xi.    In case of air piping is not installed and tested then this exception item to be mentioned in the loop test exception log sheet prior to signing the loop folder.
    xii.    Loop will be initiated only and signed after the clearance of the punch list.

LOOP CHECKING PROCEDURE  MOV’s Loop

i.     Check and verify DCS configuration for applicable points.
ii.    Valve response time shall be recorded in the loop record sheet against ISS.

iii.    If any ESD logic / interlocking are involved in applicable loop, then first normal condition should be prepared by forcing           the applicable ESD points on ladder on logic and same procedure to be carried out for DCS logic.

iv.    Check and verify the logic / remote switch function.
v.    Stroke the MOV from DCS and field on applicable commands such as open, close and stop.
vi.    Verify the status of the MOV at DCS and field.
vii.  Check the hand wheel manual operation and function if applicable.

LOOP CHECKING PROCEDURE Switches Loops (Flow, Level, Pressure, Temperature)

i.    Check and verify the DCS / ESD configuration for applicable points.
ii.    Simulate the contact operation (Make / Break) at the switch terminal block and verify the status in the DCS / ESD.                          However, ESD switch case actual pressure simulation to be provided with hand pump.
iii.   ESD hand switches, Start / Stop, Open / Close shall be checked by operating the switch mechanism.

LOOP CHECKING PROCEDURE Hand Switch loops

i. Power up loop, check contact status as expected.
ii.    Check and verify the DCS/SIS configuration for applicable loop.
iii.    Hand switches (Including SIS), Start / Stop, Open/Close shall be checked by operating the switch mechanism for both hardware & software switches.
iv.    Complete QC documentation and sign off after clearance of punch list items.

  

LOOP CHECKING PROCEDURE Gas Detectors / Beacon / Horns

  1. Check and verify the DCS / ESD configuration for applicable points.
    ii.    Proceed the verification of gas detector by introducing the applicable sample gas for H2S and LEL.
    iii.    If no calibration gas available on the time of testing hart communicator or test magnet provided by vendor will be used to perform the linearity check and the exception log will be maintained.
    iv.    Check the beacon status at high alarm condition.
    v.    Check the horn status at high alarm condition.
    vi.    In gas detector process, zero will be confirmed using span gas or zero gas or any other means before applying / tuning the actual zero.

 Please check also:  TEMPERATURE TRANSMITTER EXPLANATION & COMPARISON BETWEEN RTD AND THERMOCOUPLE

LOOP CHECKING PROCEDURE RTD /Temperature Transmitter Loops

  1. Check and verify the DCS / ESD configuration for applicable points.
    ii.    Simulate resistance equivalent to the 0%, 25%, 50%, 75% and 100% of the transmitter /DCS range, by using decade resistance box or any other resistance simulator at the RTD terminal head.
    iii.    Verify the corresponding reading in the DCS / integral indicator of transmitter and remote indicator if applicable.
  2. Alarm functions (in DCS) to be checked by simulating / varying the required signals.
    v.    Normalize all the connections prior to closing the terminal and confirm ambient temperature at integral indicator of temperature transmitter and in DCS.  Special consideration shall be given to electrical connection of the RTD.
    vi.    During loop checking, If the instrument is not accurate re –calibration should be done in calibration shop. Zeroing is not allowed.

LOOP CHECKING PROCEDURE  Thermocouple / Temperature Transmitter Loops

  1. Check and verify the DCS configuration for applicable points.
    ii.    Simulate millivolt equivalent to the 0%, 25%, 50%, 75% and 100% of the transmitter / DCS range, by using “mv” source (simulator) at the thermocouple terminal head.
    iii.    Verify the corresponding reading in the DCS / integral indicator of transmitter and remote indicator if applicable.
    iv.    Alarm functions (in DCS) to be checked by simulating / varying the required signals.
    v.    Normalize all the connections prior to closing the terminal and confirm ambient temperature at integral indicator of temperature transmitter and at remote indicator if applicable to DCS.

Please check also: Basic Concept of Vibration Monitoring System

LOOP CHECKING PROCEDURE  Vibration Loops (with Proximitors)

  1.   Check and verify the VMS / DCS configuration for applicable points.
    ii.    Connect a spare probe to extension cable of applicable proximitors.( If applicable)
    iii.    Insert the probe into the TK-3 wobulator (Bently Nevada) and connect the Multi meter leads at proximitors terminals for check gap voltages.(If applicable).
    iv.    Adjust the probe at approximately (-10Vdc) gap voltages and reset VMS rack.( If pplicable)
    v.    Simulate the signal by wobulator 0%, 50% and 100% of the range and verify the corresponding reading at VMS / DCS.( If applicable)
    vi.    Verify the response of the high and high alarms at VMS / DCS as per P&ID.
    vii.    Normalize the connection of extension cables. (If applicable)
    viii.    Actual probe gap voltage shall be adjusted to -10Vdc and check the point shows normal in VMS / DCS after VMS rack reset.( If applicable)

          Please check also:  What is MCC? How Motor Control Centre Works?

LOOP CHECKING PROCEDURE MCC / SWR Loops

  1. Check the Power Transmitter linearity on each cubicle wherever applicable VSD commands i.e. AO/AI Shall be included, and the Testing requirements if no test position available.
    ii.    Check and verify the DCS configuration for applicable points.
    iii.    If ESD logic / interlocking are involved in applicable loop, by forcing the applicable ESD points on ladder logic, same procedure to be carried out for DCS logic.
    iv.    Remove the control power transformer primary and secondary fuses for applicable MCC/SWR units (check / confirm if MCC/SWR unit is on test position by electrical).
    v.    Apply 120Vac power (external power from building outlet) on the secondary fuses load side to energize the control circuit.
    vi.    Apply the command from DCS / ESD Field for start, stop or trip as applicable.
    vii.    Verify the running / stop or trip status in DCS / Field / Sub Station as applicable.
    viii.    Check and verify the local / remote switch function if applicable.
    ix.    After completion of the applicable loop check, the fuses should be returned on the
    control transformer.
  2. All the above mentioned steps can be carried out with removing the pad lock on the MCC/SWR unit breakers.
    xi.    Removal of the pad lock on the breakers required permission from Electrical Mechanical section.

 

 

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4 Responses

  1. Thanks for posting and sharing this work. With the advent of data centric working and mobile solutions you can make loop instructions very specific but keep text generic. This means the user has clear instructions but the management of instructions is optimised. With data centric working you can pre-validate Test Equipment has current certificates and you can feed forward calibration data, loop sheets, etc.

  2. danish anwar says:

    A

  3. manjunath says:

    Nice it will help new and upcoming instrumentation & control engineers.

  1. August 7, 2018

    […] Please read also:  Loop checking procedure of Instruments […]

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