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MEP201 Mechanical Engineering Drawing 1 st semester 2005-2006

MEP201 Mechanical Engineering Drawing 1 st semester 2005-2006. S R Kale Lecture. Control Diagrams. Control Drawings - Background. Pre-requisites Schematic, P&I drawings Control philosophy About the plant From equipment/package manufacturers Team: All designers (EE, ME, ChE, I&C, …)

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MEP201 Mechanical Engineering Drawing 1 st semester 2005-2006

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  1. MEP201Mechanical Engineering Drawing1st semester 2005-2006 S R Kale Lecture Control Diagrams

  2. Control Drawings - Background Pre-requisites • Schematic, P&I drawings Control philosophy • About the plant • From equipment/package manufacturers Team: All designers (EE, ME, ChE, I&C, …) Output • Wiring of control cables • Governing logic for control software development Interdisciplinary: Chem, EE, Aero, BioMed, .. Controls (2005)

  3. Control Drawings - Types Sequence Control Sequence Control drawings Interlock Drawings Block Interlock Diagrams ON/OFF : If … then … Modulating Control Control Logic Diagram (feedback, modulating type) Sense feedback signal, Set point  Controller (PID)  Output signal  Device  Feedback signal Controls (2005)

  4. Sequence Control Drawings /Block Interlock Diagram /Interlock Diagrams Controls (2005)

  5. Sequence Control Drawings(Block) Interlock Diagram Schematic Control philosophy Incorporate instruments in schematic to generate P & I drawing Interlock diagram Controls (2005)

  6. Sequence Control Diagram – Basics • Logic from process designer & eqpt. manufacturer: What are the safe operating limits? What action to take if safe limits are exceeded? Logic or its execution – not unique • Within the limits, automatic control system operates. • Sequence control supercedes automatic control. • ON-OFF control • Signal processing – via relays and/or software Controls (2005)

  7. Sequence Control Diagram – Objectives • Operate equipment and system within safe limits. • Auto start / stop of equipment WHY? • Avoid damage to equipment (expensive repairs) • Initiate automatic protective action in case of malfunction. • Avoid plant shut down by switching to stand-by device. • Safely shut-down system even if all safety back-ups don’t work. • Safe start-up and shut-down of system. Controls (2005)

  8. CONDITION LOGIC ACTION L1 LAMP ON PS1 L.O. SUPPY PR. L Interlock diagram - Elements I.D. I.D. Parameter Device Value Action Connect with lines Controls (2005)

  9. & OR Logic Gates AND OR NOT TIME DELAY On delay/Off delay Period ‘T” Controls (2005)

  10. Bearing Lube Oil Schematic BEARING LUBE OIL TANK Controls (2005)

  11. Bearing Lube Oil System • Requirements (order by importance): • Oil pressure at inlet • Indication on gauge • Generate alarm if low • Generate signal to trip turbine if low low • Oil temperature at inlet • Indication on gauge • generate alarm if high • Oil flow rate • Measure (?) expensive – not really needed • Visual indication of flow • Oil level in tank • Indication • Alarm if low • Power supply is available for pump • Indication • Voltage and current drawn Controls (2005)

  12. BEARING PI1 TI1 LUBE OIL TANK L2 L1 L3 L4 RLY1 L LL H L PS1 PS2 LS1 TS1 LI1 Bearing Lube Oil I & C Diagram SG Controls (2005)

  13. CONDITION LOGIC ACTION L4 L3 L1 L2 RLY1 FRANCIS TURBINE L.O. TEMP. H -LAMP L.O. PR. L -LAMP L.O. PR. LL -LAMP L.O. T. LVL L -LAMP ON ON TRIP ON ON PS2 TS1 PS1 LS1 L.O. SUPPY PR. L.O. SUPPLY TEMP. L.O. SUPPY PR. L.O. TANK LEVEL H L L LL Interlock: Bearing L.O. system Controls (2005)

  14. Domestic water booster system Booster pump, ground tank, overhead tank Pump to start if Overhead tank is empty AND Ground tank has enough water Pump to stop if Overhead tank is full OR Ground tank is empty Indications to operator (panel lights or PLC display): Overhead tank - Full, Empty. Ground tank – Full, Empty. No power supply. Pump status – Running, Stopped. Controls (2005)

  15. H L L LS4 LS2 LS3 GROUND LEVEL TANK GROUND LEVEL TANK GROUND LEVEL TANK OVERHEAD TANK H LS1 BOOSTER PUMP Domestic Booster Schematic 4 Signals – One motor. RELAYS Controls (2005)

  16. CONDITION LOGIC ACTION SW1 SW1 BOOSTER PUMP BOOSTER PUMP ON OFF LS2 LS4 LS3 LS1 G/L TANK LEVEL O/H TANK LEVEL G/L TANK LEVEL O/H TANK LEVEL L H H L Interlock: Domestic water system Controls (2005)

  17. LS1 GROUND TANK LEVEL LOW L & LS4 LS2 LS3 OVERHEAD TANK LEVEL LOW GROUND TANK LEVEL HIGH OVERHEAD TANK LEVEL HIGH L H H Domestic water system - Alternate Domestic water system START PUMP STOP PUMP Controls (2005)

  18. Diesel engine of DG set/Loco Diesel engine On engine start signal (key) energize starter motor if Water temperature is OK AND Fuel tank is not empty After starting if Lube oil pressure is low after 3 seconds, then SHUT-OFF (TIME DELAY) Engine is running, then SHUT-OFF if Lube oil pressure falls to 3 bar(g) OR Jacket water temperature rises to 105 oC OR Speed increases to 1545 RPM OR Speed decreases to 1425 RPM. Controls (2005)

  19. Air conditioner (window/split) After power switch is turned ON Wait 2 minutes then start compressor (TIME DELAY) Switch-off running compressor if Cool space temperature falls to  oC Switch-on compressor if Cool space temperature rises to  oC AND 2 minutes have elapsed since compressor was shut-off (TIME DELAY) SET POINT OFFSET for cut out/cut in Controls (2005)

  20. Airplanes Airplanes (ref.: aeroPeru603/Air Crash Investigation) Auto-pilot gets engaged if 2 out of 3 readings of altitude/speed are same. (TWO OUT OF THREE LOGIC) IF NOT, fly the plane manually Controls (2005)

  21. Francis turbine Francis Turbine (Badagrah Nala) 2 x 100 % Lube oil pumps, give START signal to stand-by pump if • Turbine is running AND • L.O. level in tank in NOT low AND • Standby pump is available AND • (Other pump has been switched OFF OR • Lube oil header pressure is LOW) Controls (2005)

  22. Set point values Geyser thermostat * switch is in the power line itself. Set-point is say 55 oC • At water temp. 55 oC, power is switched off. • At what temp. is it switched on? If at 55 oC then ??? Confusion! Therefore: one switch for one sensing only, i.e. one TS for HIGH and another TS for LOW. And, offset cut-out and cut-in HIGH set at 55 oC + T, and LOW set at 55 oC - T. Controls (2005)

  23. Sequence Control Diagram – Examples • BFP of CCPP : start and trip permissive • Standby BFP of CCPP : start permissive • Representation on P&I diagram • Typical interlock diagram - CCPP Controls (2005)

  24. Sequence Control – Haywire • Equipment damage • Equipment/device does not start or shut-off Controls (2005)

  25. Sequence control - Summary Outcome: • Details of signal sources • Signal connections • Control logic for programming and hardware • Merge with layouts to generate control cable routing, its length and size (BoM) • Modify piping drawings to accommodate instruments/switches Controls (2005)

  26. Modulating Control Controls (2005)

  27. Automatic Control System Automatic modulating control • Dynamic real-time control • Sense signals (parameters)  Generate control signal  Adjust control device • Feedback control loops • Every machine has its control system P-based, PLC-based, DAS • Expensive, need maintenance, critical. Controls (2005)

  28. Automatic controls- Example • Control loop #1 (CCPP steam system) :Flow control • Control loop #2 (CCPP steam system) : Pressure & temperature control Controls (2005)

  29. Automatic controls - Elements Name and symbol Controller output not taken as input for sensing resulting action, e.g. signal produced for adjusting valve stem. As a result of this action what is the position of the valve stem?  Sense valve stem position with a position sensor. Controls (2005)

  30. Automatic controls More in course MEL312Control Theory & Applications Controls (2005)

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