benefits of foundation in the operational phase
DESCRIPTION
John Rezabek Presentation from our North American SeminarsTRANSCRIPT
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation1
Field-based Control : Freedom to Choose the Ultimate DCS
John Rezabek
Process Control Specialist
Ashland, Inc.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation2
What is Fieldbus Again?
• Fieldbus is a communication protocol, right?
• The “OSI Model”: Seven Layers for “Open Systems Interconnection”
• Foundation fieldbus uniquely adds the “User Layer” – why?
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
USER LAYER
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation3
Why Have a “User Layer”?
• Analog In, Analog Out, Digital In, Digital Out• Do some scaling, linearization, filtering, configure fault
states & propagation, etc. outside the host / DCS• Devices are “peers” with the host’s interface
• ARTHM, ISEL, SGCR, INT• Relieve the HOST DCS of some compensation,
characterization, totalizers, etc.
• PID, CSEL, SPLTR• Configure CONTROL IN FIELD DEVICES, using the
world’s only vendor-independent totally distributed digital control system
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation4
Why “Distributed” Control?
• 1980’s costs for CPU and memory meant many loops-per-controller for reasonable “cost per loop”
• Users of the day wanted “single loop integrity” = one fault > loose no more than one loop
• Controller, I/O, and Network Redundancy• Commercial model became “functionally”
distributed
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation5
The Need For Reliability
ARC Insight
10th June 2010
The global process industry loses $20billion, or five percent of annual production, due
to unscheduled downtime and poor quality.
ARC estimates that almost 80 percent of these losses are preventable, with 40 percent largely
due to operator error.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation6
Fieldbus = Truly Distributed Control
• Foundation Fieldbus allows return to true single-loop integrity
• Robust control independent of DCS, needs only power, devices, and schedule (“LAS”)
• Intelligence of devices is exploited, employing signal status, diagnostics
• But – is it truly more reliable?
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation7
Fewer Components = Longer MTBF
PSU
PSU
AND Foundation fieldbus also communicates signal status with every scan, which enables smart mode shedding, bumpless transfer and initialization.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation8
Digital All the Way- Digital Closed Loop Control
Fieldbus eliminates the analog signal
Validity:Good/Bad/Uncertain
Initiate Fault-State Command
Limited: High/LowBumpless TransferWindup ProtectionFault-state Status
Designed for process control
Default behavior on Bad or Uncertain PV is shed mode to MAN and hold last output – the same macrocycle the fault is detected.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation9
Process Variable Validity
Hardwired Device drives current <4
mA or >20 mA on device failure
– Looks like process problem PID counteracts thus
tripping the loop Operator cannot tell the
difference between a process alarm and a device alarm
Fieldbus Device health indicated by
associated status Controller holds last
position on device failure– Shutdown is optional
Operator can easily distinguish process problem from a device problem
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation10
FF – A Standard for High Availability
Distributed Control, Speed, & Determinism Real-time value and status Status Propagation (CIF & CIC) Validated information
Quality and limits Windup protection Bumpless transfer for valves Fault-state for valves etc.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation11
SIL - Putting a Number on Reliability
• Ed Marszal, ISA 84.001 and IEC 61508 expert, author and president of Kenexis consultants
• Entered reliability numbers into reliability models for safety system calculations
• “ FF is significantly better – MTTF (mean time to fail) of 48.2 [years] versus MTTF of 15.9 [years]”
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation12
Reliability
Analogue
With CIF
15.9y
48.2y
MTTF
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation13
Customer Experience
CIF enabled
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation14
Customer Experience
FOUNDATION FieldbusCIF with inherent backup capability
prevented 2 incorrect plant shutdowns, which would have resulted from communication
interruptions.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation15
But . . . Isn’t Fieldbus “Slow”?
• Early devices had longer function block execution times
• Many early jobs used FF for IO only• Host PID to FF Macrocycle sync is not easily
addressed – oversample?• Variable latencies, overly busy segments• Add commissioning, diagnostics, downloads• = Many bogged down segments
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation16
Control In The Field Study
Control in the Field:
Analysis of Performance Benefits
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation17
Comparison
CIF enabled
No CIF
125
625
105
ms
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation18
Settling Times: Fastest Process
50
54
58
62
Process output (%)
0 4 8 12 16 20Time (seconds)
60%
Setpoint Case 1 - CIFCase 3 - Control in DCS (async)
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation19
Settling Times: Very Fast Process
50
54
58
62
Process output (%)
0 4 8 12 16 20Time (seconds)
Setpoint Case 1 - CIFCase 3 - Control in DCS (async)
55%
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation20
Settling Times: Fast Process
50
54
58
62
Process output (%)
0 4 8 12 16 20Time (seconds)
Setpoint Case 1 - CIFCase 3 - Control in DCS (async)
66%
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation21
Settling Times: Medium Process
50
54
58
62
Process output (%)
0 4 8 12 16 20Time (seconds)
Setpoint Case 1 - CIFCase 3 - Control in DCS (async)
39%
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation22
Presence Of Disturbance: Fastest Process
Process output (%)
40 50 60 70 80 90 100Time (seconds)
Setpoint Case 1 - CIFCase 3 - Control in DCS (async)
56
58
60
66
62
64
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation23
Presence Of Disturbance: Different Processes
Fastest1.811
2.132
0.517
0.82
0.642
1.058
0.231
0.53
65% better
50% better
55% better
35% better
Very Fast
Fast
Medium
Setpoint CIF1.811 control in
DCS (async)
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation24
ISC Study on Control in the Field
“Control in the field: analysis of performance benefits” study from ISC (industrial systems and control)
40-60% faster settling time on setpoint change
30-50% better disturbance rejection
Most significant for fast processes (flow and pressure)
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation25
Impact of Tighter Control Loop
Manual
PneumaticAnalogue
Digital
Control limit
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation26
Recommended For Fast Loop Response
Control in the field usingFOUNDATION fieldbus technology is
recommended by SGSI for simple and cascading loops, not for complex loops.
Major benefits identified by SGSI are reduced process controller loading, reduced network traffic enabling more loops per segment, as
well as very fast loop response.
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation27
Empirical Studies: CIF Fast as 4-20
Host
Host
Host
Host
Study by Daugherty, Coughran, and Ford, “Effects of Macrocycle Time and Sampling Rates on Control Loop Performance”
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation28
8 simple loops, CIC
Study by Daugherty, Coughran, and Ford, “Effects of Macrocycle Time and Sampling Rates on Control Loop Performance”
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation29
Same 8 loops, CIF (valve positioner)
Study by Daugherty, Coughran, and Ford, “Effects of Macrocycle Time and Sampling Rates on Control Loop Performance”
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation32
Blower – Combustion Air to Boiler
• Keeping the Blower out of the surge region means a more stable flow
• More stable flow allows running closer to constraints
• Running closer to constraints means less fuel, CO2
AIR TO BOILER
AIR BLOWERPREHEATER
TO
BU
RN
ER
S
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation33
Inside “peak pressure” line, flow is unstableInside “peak pressure” line, flow is unstable
Peak Pressure
Desired Flow fell here
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation34
Field-based control of blow-off valveField-based control of blow-off valve
• Controls total flow• Allows operation
close to low-flow BMS trip point
• Saves fuel costs and reduces CO2 emissions
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation35
Surge Control SchemeSurge Control Scheme
Blow-off Flow
Flow to Burner
FICInlet
Louvers
Σ FIC(Total Flow)
Blow-off Valve
Discharge Pressure SGCR SP
PT (Discharge)
FT1
FT2
Blow-off Valve Pos.
Inlet Louver Positioner
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation36
Blower Anti-surge schemeBlower Anti-surge schemeFlow to Burner
Total Flow Setpoint
Total Flow Controller
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation38
10,000 HP Turbine / Blower Anti-surge10,000 HP Turbine / Blower Anti-surge• Large critical
un-spared asset
• Typically runs at 5000 to 7000 RPM
• Expensive to repair; lost production even more expensive
2012 End User SeminarFieldbus Foundation
© 1994 – 2012 Fieldbus Foundation44
Summary• FF was specified & designed to deliver
robust control by default – STANDARDIZED across suppliers
• Control in Field Devices is being used in critical process applications with fast cycle time requirements
• Modern devices are executing function blocks faster than ever • (note: like cars, there are Yugos and Porches, so
choose according to your needs)