Fieldbus Operations Benefits.pdf

7/18/2019 Fieldbus Operations Benefits.pdf

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1 Freedom to Choose. Power to Integrate.1 Freedom to Choose. Power to Integrate.

Freedom to

Choose. Power to

Integrate.

Operation

Benefits

Andrew Sia,

Rockwell Automation




Operation Benefits Topics

Why FF? Higher performance control

Early process warning from device alerts

Increased availability

High fidelity




- Why Digital Fieldbus?

Operation & Maintenance – Better accuracy

• No precision lost in D/A & A/D

– High signal integrity• Distortions can be detected

– More powerful diagnostics• More current for devices

– Engineering unit• Measure to sensor limits

• No range mismatch

– Stave off obsolescence

• Firmware download

– Easier device troubleshooting• Remote Diagnostics

– Validity display and loop shuts

down

– Predictive maintenance• Diagnostics Alerts

– Fewer Connections




Easier:Fewer Connections Fewer signal wires to disconnect and connect

when replacing devices – Electric actuator (MOV)

• Open, stop, close, ESD, overload...

– Valve positioner

• Setpoint, feedback, limit switches... – On/Off actuator

• Setpoint, limit switches...

– Mass flow transmitter• Mass, volume, density, temperature...

Faster, fewer mistakes Conventional:

Multiple pairs

Per device

Bus:

Single pair

Many devices

Two wires,

non evenpolarity




Easier and Safer:High Signal Integrity

Digital signal does not get "limited" – If 18 mA becomes 16 mA you won't know• Increase in resistance due to terminal corrosion

– If 16 mA becomes 18 mA you won't know• Ground loop due to inadvertent ground connection

Digital signal distortion does not go undetected – It is not possible to tell difference between analog

signal noise and process fluctuations

Electrical noise or actual process? Any distortionof a digital

process

variable is

alerted

mA

t




6

0

2

4

6

8

10

12

14

16

18

20

%

I n s

t r u m e n t a t i o n

V a l v e s

H e a t E x c h a n g e r s

V e s s e l s

P u m p s

C o m p r e s s o r s

D r i v e s

E l e c t r i c a l s

F u r n a

c e s / B o i l e r s

P i p i n g

P a i n t s / C o a t i n g s

M i x

e r s / A g i t a t o r s

I n s u l a t i o n

M a t e r i

a l s H a n d l i n g

T o o l s

O t h e r

Major Components of Maintenance Costs

Highest Maintenance Spend ing o n Field Devices


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63%“Unneeded” Trips To The Field- Avo ided Through Remo te Diagno st ics

35%

28%

20%

6% 6%4%

0%

10%

20%

30%

40%

50%

RoutineCheck

NoProblem

FailedInstrument

PluggedLines

ZeroOff

CalibrationShift

Source: Dow Chemical Company

Avoid “Unneeded” Trips To The Field



Freedom to

Choose. Power to

Integrate.

High Performance

Digital Closed Loop Control



Some “Digital Control Systems”Aren’t

If it’s not fieldbus, it’snot a digital control system

Hardwired Fieldbus

Process Discrete Process Discrete

Real-time

control

Analog

(4-20 mA)

Binary

(on/off)

Digital

(FF)

Digital

(FF)

Device

management

Digital

(HART and

proprietary)

None Digital

(FF)

Digital

(FF)

Digital Digital Digital Analog Analog

Digital Digital DigitalDigital Digital

Hardwired:

Fieldbus:



End-to-End, Fieldbus Control is Faster

Analog Control – AI scan, controller, and

AO scan asynchronous• A 250 ms controller

cycle does not mean

250 ms control responseperiod

Fieldbus Control – AI scan, controller, and

AO scan asynchronous

AI

Controller Controller

AO AO AI PID AO

250 ms 250 ms 250 ms

> 2 x Controller Cycle Macro Cycle



Freedom to

Choose. Power to

Integrate.

Early Warning

Act before process is affected



Smart Diagnostics- Integrated Device Diagnostics

Normal operation... Device failure...

Faceplate...

Diagnostics

– No deviceconfiguration by

operator

Detailed

diagnostics in twoclicks

Help on the third



On/Off Valves Fieldbus does discrete too

One pair of wires for multipleon/off valves

One pair of wires for solenoid

and limit switches

Diagnostics

HART not applicable



Freedom to

Choose. Power to

Integrate.

Real-time Status

If its not the process, don’t trip

unnecessarily



Digital All the Way- Digital Closed Loop Control

Speed

30 times faster than

hybrids of analog/digital

250 ms loops possible

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.

Only fieldbus

eliminates the analog

signal

Validity:

Good/Bad/Uncertain

Initiate Fault-State

Command

Limited: High/LowBumpless Transfer

Windup Protection

Fault-state Status

Designed for

process control



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 betweena 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 deviceproblem



Valve and Positioner Actual position transmitter feedback

transmission on the same two wires – Further reduced wiring

– No AI card

– More than just value: status

Software limit switches

– No DI cards – No extra wiring

Easy to add feedback as an afterthought

Bumpless transfer on local hand operation – Smoother operation

Bumpless firmware download – Upgrade while process is running, without

replacing circuit board

Continuous, real-

time, actual

position feedback

for every control

valve



Easy Operation- Status in Historian Status logged and shown next to value and color

codes trend



Freedom to

Choose. Power to

Integrate.

Fidelity



Digital Fidelity- Better AccuracyHardwired

Accuracy lost in signalconversations: – Digital to analog

– Analog to digital

Accuracy lost incurrent calibration

differences

Fieldbus

Measurements are notdistorted

Particularly important: – Tank gauging

– Batching

Transmitter

FF

BUS

FF

CTRL

CPU

CPU

Digital

Digital

Digital

AI

A/D

D/A4-20 mA




Easier and Safer:High Signal IntegrityHardwired

Analog gets distorted – Increased resistance

limits current

– Ground loop offsets

current ‘On-scale” distortion

cannot be detected

Fieldbus

Digital signal does notget "limited"

Any distortion of a

digital process

variable is alerted

AI

Marshalling

Field Junction Box

4-20 mA

Resistance = Voltage

Drop = Limited Current

Leakage = Ground Loop =More Current




Fieldbus Operational Benefits Summary

Higher performance control – Faster than analog

Early process warning from device alerts – Diagnostics in operator console

– Diagnostics from discrete devices

Increased availability – Real-time status

High fidelity – High accuracy

– No range mismatch



2323

Freedom to

Choose. Power to

Integrate.

Thank you !

Fieldbus Operations Benefits.pdf

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