8686130 Instrument2.Es.en

7/31/2019 8686130 Instrument2.Es.en

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Introduction

How to govern a process automatically?

Basics of Control Fundamentals of Instrumentation


3/149

Manual operation of a process

Observe

Compare

DecideAct


4/149

Operating a process

Process

MeasureAct

Dynamic response

Manual or open loop

Changes Replies

Compare

Decide


5/149

Automatic operation

ProcessMeasuAct

Changes Replies

Regulator

Values

Wish

Closed loop operation


6/149

Automatic Operation

LT LC

Measure

Compare

DecideAct


7/149

Components

Process

Variablesto control

Regulator

Values

Wish

Actuator

TransmitterMeasured values

Variables

to act


8/149

Temperature Control

Measure

Compare

Decide

Act


9/149

Index

Control Systems: Terminology

Control Continuous / Discrete

Transmitters

Definitions and types

Level, Pressure, Flow, Temperature ...

Actuators:

Valves

Pumps and Compressors

System Dynamics


10/149

Terminology

Disturbance

Variable

Manipulated

Variable

Controlled Reference

LT LC


11/149

ProcessRegulator

TransmitterControlled Variable

Variable controled CV

Process Variable PV

Output (the process)

Reference

Motto

Set Point SP

Manipulated variable

Manipulated Variable MV

Output to Process OPInput (the process)

w

MV or

and (Europe)

CV and

x

Disturbances

Deviation Variables DV

Block Diagram


12/149

Continuous Control

The controlled variable, taking values in a continuous range, is

measured and continuously acts on a range of values

Actuator

Variable

Manipulated

Variable

Controlled Reference

LT LC

Disturbance


13/149

Discrete control

Peak detector

and minimum height

Solenoid

ON / OFF

Relay

The only variables

support a set

finite state


14/149

Process diagrams P & I

Instruments

Measurement and control

represented by

circles with

numbers and letters

Processing units

and actuators

represented by

special symbols

Connection lines

LT

102

LC

102


15/149

Tools

Indicators

Transmitters

Recorders

Converters

Drivers Actuators

Transducers

Connected by lines

Transmission:

Pneumatic

Power

Digital


16/149

Tools

LRC

128

PT

014

Field Mount

Process connection

or feeding

Pneumatic signal

Panel Mounting

Electrical signal

The number is the same for all instruments of a

same control loop


17/149

Digital Instruments

LRC

128

PT

014

Not normally accessible

to the operator

Accessible to the operator

Shares several features:

display, control, etc..

Software configurable

Network access

The number is the same for all instruments of a

same control loop

DCS controller,

microprocessor

controller, ...


18/149

Digital Instruments

LRC

128

Computer

Unlike a DCS controller

Several functions: DDC,

logging, alarms, etc..

Network access

Connection

software or digital

network


19/149

Digital Instruments

Or sequential logic

controlOr sequences PLC /

DCS logic of a

Accessible to the operator

Not accessible to the operator


20/149

1st letter: measured variable or related

2nd letter: You can qualify to the firstDifferential D

F ratio

S security

Q integration

3 rd ff: Instrument function

I indicator

A record

C Control

T transmitterValve V

And calculation

High H

L under

A analysisDensity D

Voltage E

Flow F

Current IJ Power

L level

M moisture

Pressure P

Speed S

Temperature T

Viscosity V

W Weight

Z position

1st letter


21/149

Tools

PDT LRC PIC

DTT

DT

FY FFC ST


22/149

Warmer

MV

CV

DV


23/149

Transmitters

Sensor: Parent element sensitive to a

physical property related to the variable

being measured. Transmitter: System sensor attached to

converting, conditioning and normalizes the

signal for transmission at a distance. Indicator: combines a sensor and a

measuring system analog or digital.


24/149

Pressure Transmitter

Electronic circuit

Sensor

Piezoelectric

AmplificationFiltered

Calibrated

Power

Normalization

Pressure

Signal

standard


25/149

Transmitters

Pneumatic signal: 0.2 to 1 kg / cm2

3 to 15 psi

Electrical Signal: 4 to 20 mA1 to 5 V dc, ....

Frequency: pulse / time

Other: RTD, Contacts, ...

Digital signal: HART, Fieldbus, RS-232 ...


26/149

4-20 mA

The current signal is the same in any point of the line

You can differentiate a fault or break in line of range

lower measurement

You can connect a maximum number of loads or instruments

Transmitter

mA

FC


27/149

Pulse / Frequency

Transmitter FCCounter

Pulse

The number of voltage pulses received

per unit time is proportional to

value of the measured quantity


28/149

Feeding

TransmittermA

Transmitter

mA

220 V ac

24 V dc

Consumption

Connectors

Working conditions

Protections

Mounting


29/149

Connection

XT

Protection

and isolation Filtered

Tomas

auxiliaryConditioningXC

SP

CV

MV


30/149

Shielding

Transmitter

mA

FC


31/149

Wiring, Reliability, ...

Control

Room TT

FT

DT

Wiring costs

Noise

Reliability of equipment

Calibration, maintenance, ...

Distance


32/149

Fieldbus

PLC

Computer

Digital Bus 1101 ...

Microprocessor

Module A / D and

Communications

TT FT

DT


33/149

Intelligent Instrumentation

It incorporates a

microprocessor

This gives youcomputing power and

storage of information:

Instrument Data

Dynamic Data

Provides a digital

communications

system which may bebidirectional

Provide new features


34/149

Intelligent Instrumentation

Fully digital fieldbus

Communications

between all elementsconnected to the bus,

instruments and

control systems

Hybrid: combines

analog transmission

and digital HARTprotocol

Communications

between transmitters

and control systems


35/149

Fieldbus

Save wiring

Noise Rejection

New features: Remote setting rank, test, documentation, ....

More elaborate information

Architectures and Protocols

PLC

Computer

Digital Bus

1101 ...


36/149

Fieldbuses

Foundation Fieldbus (H1 and H2 levels)

Profibus DP, PA

WorldFIP

CAN

DeviceNet

.....


37/149

HART

UnitHART RS-232

LT

PT

FT

Superimposed digital communicationto the signal 4-20mA

Allows test, calibration. Etc.

from your computer or handheld module

4-20 mA

1011 ..


38/149


39/149

Serial interface

Analyzer

Point to point RS-232, RS-422

RS-485 Bus

A / DCommunication protocol

11010 ...


40/149

Terminology (SAMA)

Rank

Span

Dynamic error

Accuracy

Sensitivity

Repeatability

Dead zone and hysteresis


41/149

Transmitters

Range: 20 - 80 C

Span: 80-20 = 60 C

20 mA

4 mA

20 C 80 th C

Calibrated:

read = f (actual value)

Zero and Span Adjustme

mA = 0.2667 C - 1.3333


42/149

Transmitters

20 mA

4 mA

20 C 80 th C

Calibrated:

read = f (actual value)

Zero and Span Adjustme

mA = 0.2667 C - 1.3333

Zero

Span


43/149

Transmitters

20 mA

4 mA

20 C 80 th C

Linearity error

Due to the

nonlinearity of theactual calibration curve

% Span

Value indicated

Actual value


44/149

TransmittersDead Zone:

Change in variable

As not alter

reading.

% Of span

20 mA

4 mA

20 C 80 th C

Area

dead


45/149

Transmitters

Repeatability

20 mA

4 mA

20 C 80 th C

Repeatability:

Ability to obtain the same reading to read the same value

of the variable measured in the same direction of change.

% Of span

Hysteresis:

The same but in different directions of change.


46/149

Transmitters

20 mA

4 mA

20 C 80 th C

Actual value

dynamic error

value indicated

Accuracy:

Maximum Limit

possible error

by linearity,hysteresis, etc. ....

% Of span

% Of reading

Direct value ...


47/149

Transmitters

1 unit

20 mA

4 mA

20 C 80 th C

Sensitivity

Sensitivity:

Change in reading

corresponding

to a unit change

in the variable

% Of span


48/149

Temperature Transmitters

Bulb

RTD (Pt100 0 C 100 )

Thermistors (Semiconductors)

Thermocouples E, J, K, RS, T

Pyrometers (high temperature, radiation)


49/149

Pt-100

0 C 100

The electrical

resistance changes

with temperature

Electrical bridge

for conversion to

electric voltage

signal

Range of use: -200 500 C Sensitivity: 0.4 / C

Accuracy: 0.2%


50/149

Bridge

V

R R

RRt

Pt100

When the bridge is balanced, the voltage V

is zero. If you change Rt the voltage V is

changed.


51/149

Three-wire connection

V

R R

RRt

Pt100

The length of the connecting wires is important as the third

line makes the same resistance is added to each branch and

offset imbalance in the bridge


52/149

Thermocouples

T1T2

I

At the juncture of certain

metals is generated emf if

the ends are at different

temperatures. The f.e.m.depends on the

temperature difference

Thermocou

ple

T

M

Measure: Opposes a

known voltage to the

thermocouple to the output

of amp. differential is zero


53/149

Thermocouples

Type Range Accuracy

T -200 250 C 2%

J 0 750 C 0.5%

K 0 1300 C 1%

R / S 0 1600 C 0.5%

W 0 2800 C 1%


54/149

Pressure Transmitters

Absolute pressure

Pressure gauge

Differential pressure

Measures based on:

DisplacementGauges

Piezoelectricity


55/149

Sensor

displacement

Capacity

Induction

Potentiometer


56/149

Pressure


57/149

Piezoelectric sensor

Quartz crystal

Force

Metal plate

+

-


58/149

Gauges / Hall Effect

N

S

Current

Force

Hall Effect

Strain gagesThe

deformation

varies R


59/149

Pressure Transmitter


60/149

Level Transmitters

Displacement

Float

Force: Archimedes Principle


Capacitive

Ultrasound

Radar


61/149

Level: differential pressure

LT

(P0+gh) - p0

Measuring the

pressure difference

between bothbranches

It is assumed

constant density

Condensation in the

tubes


62/149

Capacitive

Between the electrode

and the shell wall is

formed a capacitorwhose capacity depends

on the level of liquid


63/149

Level: Ultrasound

The time between

transmission andreception of high

frequency waves is

proportional to the

level


64/149

Flow Transmitters


Electromagnetic

Turbine

Vortex

Doppler Effect

Mass (Coriolis) .....


65/149

Orifice plates

P1 P2

D

d)PP(g2

4

D

1Cq 21

2

4

2

Based on the

differential pressure

measurement

Dd


66/149

S

Electromagnetic flowmeters

N

S

B

In the conductor

(liquid) flowing at

a rate within thefield B induces an

EMF proportional

to speed, which is

collected at theelectrodesN

-

+


67/149

Actuators

Final control elements. Altering the

manipulated variable of the process

according to the control signal.Valves

Engines

Variable speed pumpsPower amplifiers

....


68/149

Valves

Device for varying the flow rate through a

driving modifying the pressure drop across

it by a variable shutter.

Manual closing

Retention

Security

On / Off

Regulation


69/149

Regulating valves

Structure and function

Types of valves

Calculation Formulas Static characteristics

Cavitation

Installed Features A valve dynamics


70/149

Pneumatic seat

Air

Fluid

Shutter

Seat

Flanges

Membrane

StemSpring

Top

Indicator

Body

ServomotorTire

Electric

3 -15 psi


71/149

Regulating valves

Air Seat or balloon

Double seat

Needle

Saunders

GateButterfly

Camflex II

2 -3 waysSealing

Maximum pressure

Flow capacity

Fluid type

Fluid


72/149

Butterfly

Body


73/149

Air open / close

Air

Air

Air closesOpen

air

Air

close

s

Open

air

/


74/149

I / P

3-15 psi air

IP4 to 20

mA

Low accuracy in

positioning the rod

Air and electric power

P iti


75/149

Positioner

Positioner

Air Supply

Air

Control signal

4 to 20 mA

P D


76/149

Pressure Drop

pa C

qv

1

2 2

2

pressure drop pflow q

a fraction of opening

Coefficient C

density

q

p

to

p1 p2

C l l ti F l


77/149

Calculation Formulas

qaC pv v116.

q aC p p pv v 72 4 1 2.( )q t / hp bars

to both a

q m3 / h

p bars

densityonto both a

Saturated steam

Liquids

q

p

to

p1 p2

Flow coefficient Cv

St ti h t i ti


78/149

Static characteristics

% Of position

rod

% Area of

Seat 100%

% Of peak flow

in cond. nominaltoconstant p

Linear

Isoporcentuales

Quick opening

ButterflyCamflex

0% 100%

0%

St ti h t i ti


79/149

0% 100%

0% Butterfly

Quick

opening

Linear

Equal

percentage

Static characteristics

R bilit


80/149

Rangeability

0% 100%

0%

maximum controllable flo

R = -------------------------------

minimum controllable flow

% Position of the rod

Flow

uncontrollable

R = 50 ... 20

Ca itation


81/149

Cavitation

length

pressure p1

p2

length

pressure p1

p2

Steam pressureSteam pressure

Vapor Pressure:

Pressure at which boiling

liquid at room

work

Cavitation


82/149

Cavitation

qaC pv v116.

Cavitation

incipient

pv

q

Maximum pto regulate flow

Critical flow

p K p pv c v ( )1

Kc Coefficient

incipient cavitation

p C p pp

pM f v

v

c

2

1096 028( . . )

p Maxima caida de presion admisibleM

CF Flow factor

critical

pc pressure

critical point



83/149


qa C C p y y

y

C

p

p

f v

f

v

1

3

1

0148

54 5

16315

( . )

.

..

gas

y

q t / h

p bars

qa C C p y y

qa C C p

f v

f v

1

3

1

0148

837

837

( . )

.

.

vapor saturado

flujo critico

Installed Features


84/149

Installed Features

qaC pv v116.

q

pv

to

p1 p2

h

qp gh

Ka C

L

v

1

116 1

0

2 2

.

p p K q ghv L02

p0

Installed Features


85/149

Installed Features

qp gh

Ka C

L

v

1

116 1

0

2 2

.

% Position of the rod

% Q

Smart Valves


86/149

Smart Valves

Positioner +

Microprocessor

Air

Fieldbus

Characterizatio

n

DiagnosticsAlarms

Control blocks,

etc..

Pumps


87/149

Pumps

Positive Displacement

Centrifuges

Installation

Power and performance

Characteristic curves

Cavitation



88/149


Piston, diaphragm, ...

Centrifuges


89/149

Centrifuges

Engine

AsynchronousImpeller

Electric power Mechanical energy

Centrifugal pumps


90/149

Centrifugal pumps

p aw bqb 2 2

P p q P P

P W

b

36 022. otencia suministrada

W Potencia absorvida

P kw

q m3 / hp bars

Increased energy = energy supplied - losses



91/149


pb

q

1

22 > 1

Operating point


92/149

Operating point

pb

q

q

pv

to h

p p p K q gh

pa C

K q gh p

b v L

b

v

L

0

2

2 2

20

1

( )

p0pb

Variable speed pumps


93/149

Variable speed pumps

M Drive

4 to 20 mA

Compressors


94/149

Compressors

pb

q

1

2 2 > 1

Pumping line (surge)

Electric motors


95/149

Electric motors

N

S

B

F

F

Electric motors AC / DC


96/149

Electric motors AC / DC

MAmplifier

CC

4 to 20 mA

Feeding

M Drive

4 to 20 mA

DC

Motor

ACinduction

motor

THE PROBLEM OF


97/149

CONTROL

ProcessControllerorw and

SP CV

v

MV

DV

Drivers


98/149

Drivers

Generate a control signal to the actuator

normalized according to the measured value

of the variable to be controlled and itsdesired value.

Reference

Controlled variable

4-20 mA

Error

+-

Variable

manipulated

4-20 mACalculation and

normalization

Drivers


99/149

Drivers

Technologies:

Pneumatics

Electronics

Digital

Loop controllers (PID)

PLCs (PLC)

Distributed Control Systems (DCS)

Control Computer (PC)

Controller


100/149

SP 45

45.5 PV

4-20 mA

transmitter

4-20 mA to

actuator

MV

38%

Governor Signs


101/149

g

ProcessRegulator

Transmitter

Actuatorw

The input and output signals to the controller are

normalized signals, usually 4-20 mA

or and

4-20 mA

4-20 mA

THE PID CONTROLLER


102/149

THE PID CONTROLLER

signal based controllerDoes not incorporate

explicit knowledge of the process

3 tuning parameters Kp, Ti, Td

Various modifications

e t w t y t

u t K e tT

e d Tde

dtp

i

d

( ) ( ) ( )

( ) ( ) ( )

1


103/149

Two options

ProcessR

w or

ProcessRw or

Mr.

mAMr.

Mr.

Mr.

mA

Mr. %

%

mAa

n

d

a

n

d

mA

%

+

-

+

-

%

Kp % /%

Kp % / Eng


104/149

Analysis of the regulator

GpR

100/span

Actuator

W

The input and output signals to the controller usually

expressed in% of the span of the transmitter and the actuatorrespectively.

The conversion of the regulator should correspond to

Transmitter Calibration

U

%

%%

+

-

And

100/span

PID parameters


105/149

p

Kp gain / proportional term

% Span control /% controlled variable span

proportional band PB = 100 / Kp Ti Full time / full term

minutes or sg. (By repetition) (reset time)

replicates per min = 1 / Ti Td Derivative time / term derivative

minutes or sg.

Proportional action


106/149

p

u t K e t biasp( ) ( )

and

t

or

t

An error of x% causes a control actionofKp x% of the actuator

bias = manual reset (CV = SD)

Direct / reverse action


107/149

LT

Direct acting controller Kp 0

u (t) = Kp(W-y) if u increases and decreases with Kp

positive

consider the type of

valve

LCLT

LC

Proportional action


108/149

M

Kpw or

Mr.

Ampl.a

n

d 30%

+

-

1500rpm

1500

rpm

u (t) = Kp e (t) + 30You can only reach an

equilibrium with zero error

Integral action (Automatic reset)


109/149

a

n

d

a

n

d

w w

t t

or

t

or

t

A regulator does not eliminate P

stationary error

self-regulating processes

Integral action continues

changing or until the

error is zero

K

Ted

p

i

Integral Action


110/149

M

Kp

w or

Mr.

Ampl.

a

nd

+-

1500

rpm

K

Ted

p

i

1500rpm


111/149

Derivative action


112/149

a

n

d

an

d

w w

t t

or

t

or

t

A P controller with gain

high for rapid response

may cause oscillations

for u too

The derivative action accelerates

or if the moderates and grows and

decreases, preventing oscillations

)td

edTe(K)t(u dp

Derivative action


113/149

u t K Td e

d tp d( )

and

t

and

t

KpTdtoIf e = a t

Td

Kpand

With e varying linearly, the derivative givessame or that the proportional give Td sg. later

Anticipatory action

Not influence the steady state

PD

Derivative action


114/149

u t K Td e

d tp d( )

and

t

and

t

KpTdtoIf e = a t

Td

K Td e

d tK T a K at t Tp d p d p d

Td time taken for the

derivative action in match

proportional action

if e = HV

Kpand

PID tuning methods


115/149

Trial and error methods

Methods based on experiments

Estimate certain dynamic characteristics of the process

with an experiment Calculate the controller parameters using tables or

formulas derived on the basis of the dynamic

characteristics estimated

Analytical methods based on models Minimization of error indices

Phase margins and / or gain


116/149

Dynamic response


117/149

Change

step

variable

manipulated

time

level

Dynamic response


118/149

Process

MV

or

time

CV

and

time

ExperimentationMathematical model

Dynamic response


119/149

Stationary

time

or

and

Transient

Types of processes


120/149

Self-regulated No self-regulated

or Integrators

time

or

and

time

or

and

Types of processes


121/149

Minimum phase Non-minimum phase

or inverse response

time

or

and

time

or

and

Stability


122/149

0 2 4 6 8 10-0.5

0

0.5

1

1.5

2

open loop response

0 2 4 6 8 10-0.5

0

0.5

1

1.5

2

open loop response

Stable Unstable

A limited entry is for a limited output

or

and and

Damping


123/149

0 2 4 6 8 10-0.5

0

0.5

1

1.5

2

open loop response

0 2 4 6 8 10-0.5

0

0.5

1

1.5

2

open loop response

Overdamped Underdampedor

and and

Dynamic response


124/149

time

+5% Of final value

or

and

Retardation

time

settlement

dynamic response


125/149

Overshoot in% = 100 Mp /and

Gain = and /or

or

andand

or

Mp

time

Gain


126/149

Positive gain Negative gain

or conversely

time

or

and

time

or

and

dynamic response


127/149

or

and

time

period

oscillation

Rise time

90%s

10%s

ands final valu

Mathematical model


128/149

Process

or

time

and

time

Model

andm

time

Discrete Event Systems


129/149

Many processes are not continuous

Its variables support only a finite number of

values The values of the variables change

continuously over time, but in certain

moments. Control problems and sequential logic

Discrete states


130/149

Engine:

Running or

stopped

Deposit:

With fluid or

vacuum

Valve:

Open or

closed

Instrumentation


131/149

Closed

circuit

Open

circuit

Minimum level

detector: when

the level drops

the minimumvalue is set / or

off the sensor

signal

Instrumentation


132/149

Process

PS

TS

Thermostat:

When the

temperatureexceeds a limit

on / off sensor

Pressure

Instrumentation


133/149

Presence

detector

Transmi

tter

Receiver

Limit

Instrumentation


134/149

On / off valve

Solenoid

Motor starter

~

Combinational Systems


135/149

Associated alarms or logical operation

The answers depend only on the inputs

through logic functions and, or, not IF (logical conditions)

THEN (action)

Combinational logic


136/149

AND 1 0

1 1 0

0 0 0

OR 1 0

1 1 1

0 1 0

NOT 1 0

0 1AND A.B

A + B ORA NOT

BAB.A

B.A)BA(

MorganLaw

Logic gates


137/149

&A

B

1A

B

A.B

A +

B

1A A

DIN

nomenclature

Logical expressions may be equated to electrical circuits inwhich the conditions are true or false in the presence or

absence of signal and the conclusion is expressed in terms

of the output signal

Logic circuits


138/149

& 1

B

C (C + B).A

1&

A

B

D&

C

A.B + C.D

1A A

Contact diagrams


139/149

Normally open contact Normally closed contact

Logical expressions may be equated to electrical circuitsthat true or false conditions correspond to closed or open

contacts and the conclusion is expressed in terms of current

flows or not


140/149

Contact diagrams


141/149

A

B

C D

+ -

Logical function: (A + B). C.D

Relays


142/149

A device that can implement logical actions and

act on physical elements

~Load

S1

S2

IF (S1 and S2 = closed = closed)THEN load driven

coil

Ladder diagram


143/149

relay coil

S1 S2

X1

Normally open push

NC button

Other items:

timers, counters,buttons, etc..

+ -

Example

X2

S2


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M ~

relay

S1 P1

X1

+ -

S1P1

X1

X1 X2

X2

S2

Sequential Processes


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AB

Discharge

Succession of stages

of operation with

specific actions andtransition conditions

including

1 Wait 2 Load 3

Operation 4Download

M

State transition graphs


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State transition graphs

A BM

1

2

3

4

Start

Full tank

Operation

terminated

Empty

tank

States

Transitions

Waiting

Load

Operation

Discharge

PLCs


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Programmable devices designed to

implement sequential logic functions

and connected to a process

CPU

Communications

I / O

Feeding

Architecture

Modicon TSX Nano


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PC + PLC + Process


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Documents

8686130 Instrument2.Es.en