Transcript MEP201 S R Kale Mechanical Engineering Drawing Control Diagrams

MEP201
Mechanical Engineering Drawing
1st 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, …)
Output
• Wiring of control cables
• Governing logic for control software development
Interdisciplinary: Chem, EE, Aero, BioMed, ..
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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
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Sequence Control Drawings /
Block Interlock Diagram /
Interlock Diagrams
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Sequence Control Drawings
(Block) Interlock Diagram
Schematic
Control philosophy
Incorporate instruments in schematic to generate P &
I drawing
Interlock diagram
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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
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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 backups don’t work.
• Safe start-up and shut-down of system.
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Interlock diagram - Elements
CONDITION
PS1
L.O. SUPPY PR.
LOGIC
L
ACTION
L1
ON
LAMP
I.D.
I.D.
Parameter
Device
Value
Action
Connect with lines
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Logic Gates
AND
&
OR
OR
NOT
TIME DELAY
On delay/Off delay Period ‘T”
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Bearing Lube Oil Schematic
BEARING
LUBE OIL
TANK
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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
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Bearing Lube Oil I & C Diagram
BEARING
SG
PI1
TI1
LUBE OIL
TANK
L4
L3
L
LS1
LI1
H
TS1
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L1
L2
RLY1
L
PS1
LL
PS2
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Interlock: Bearing L.O. system
CONDITION
LOGIC
PS1
L.O. SUPPY PR.
L
PS2
L.O. SUPPY PR.
LL
ACTION
L1
L.O. PR. L -LAMP
ON
RLY1 FRANCIS TURBINE TRIP
L2
L.O. PR. LL -LAMP
ON
TS1
L.O. SUPPLY TEMP.
H
L3
L.O. TEMP. H -LAMP ON
LS1
L.O. TANK LEVEL
L
L4
L.O. T. LVL L -LAMP ON
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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.
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Domestic Booster Schematic
H
LS4
GROUND
LEVEL
TANK
L
LS3
OVERHEAD
TANK
H
LS1
GROUND
LEVEL
GROUND
TANK
L
LS2
LEVEL
TANK
4 Signals –
One motor.
BOOSTER PUMP
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RELAYS
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Interlock: Domestic water system
CONDITION
LS1
G/L TANK LEVEL
LOGIC
H
LS3
O/H TANK LEVEL
L
LS2
G/L TANK LEVEL
L
LS4
O/H TANK LEVEL
ACTION
SW1
BOOSTER PUMP
ON
SW1
BOOSTER PUMP
OFF
H
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Domestic water system - Alternate
Domestic water system
LS1
GROUND TANK LEVEL LOW
L
&
LS2
GROUND TANK LEVEL HIGH
H
LS3
OVERHEAD TANK LEVEL LOW
L
START PUMP
STOP PUMP
LS4
OVERHEAD TANK LEVEL HIGH
H
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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.
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Air conditioner (window/split)
After power switch is turned ON
Wait 2 minutes then start compressor (TIME DELAY)
Switch-off running compressor if
o
Cool space temperature falls to •
C
Switch-on compressor if
o
Cool space temperature rises to •
C AND
2 minutes have elapsed since compressor was shut-off
(TIME DELAY)
SET POINT OFFSET for cut out/cut in
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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
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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)
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Set point values
Geyser thermostat
* switch is in the power line itself.
o
Set-point is say 55 C
 At water temp. 55 oC, power is switched off.
 At what temp. is it switched on?
o
If at 55 C 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
o
o
HIGH set at 55 C + T, and LOW set at 55 C - T.
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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
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Sequence Control – Haywire
• Equipment damage
• Equipment/device does not start or shut-off
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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
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Modulating Control
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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.
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Automatic controls- Example
• Control loop #1 (CCPP steam system) :Flow control
• Control loop #2 (CCPP steam system) : Pressure &
temperature control
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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.
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Automatic controls
More in course MEL312 Control Theory & Applications
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