Modulating control

valve

Automatic modulating valve Automatic modulating valve

Pneumatic

Actuator

Diaphragm

Pneumatic Actuator

Positioner

Positioner

Air filter

regulator

gauge =

AIRSET

BALL

VALVE GLOBE TYPE

CONTROL

VALVE

Principle of modulating control

Pressure application Temperature application

Level application Flow application

Principle of modulating control

Pressure transmitter Temperature transmitter Level transmitter Flow transmitter

Modulating controller PLC

Programmable Logic Controller

DCS

Distributed Control System

Principle of modulating control

Pressure application Temperature application

Level application Flow application

Why do we need positioner ?

At factory, the control valve is set without any fluid flowing through the control

valve, we call this bench setting. The co-relationship between air supply

pressure & the % of valve opening is represented with “BLUE” line in the above

chart

When the fluid is introduced into the control valve, a normally closed control

valve’s co-relationship between air supply pressure & the % of valve opening

will be shifted as shown in the above chart with “RED” line

Why do we need positioner ?

At factory, the control valve is set without any fluid flowing through the control

valve, we call this bench setting. The co-relationship between air supply

pressure & the % of valve opening is represented with “BLUE” line in the

above chart

When the fluid is introduced into the control valve, a normally open control

valve’s co-relationship between air supply pressure & the % of valve opening

will be shifted as shown in the above chart with “RED” line

Why do we need positioner ?

For many applications, the 0.2 to 1 bar pressure in the diaphragm chamber may not be

enough to cope with friction and high differential pressures. A higher control pressure

and stronger springs could be used, but the practical solution is to use a Positioner.

Positioner is an additional item (see Figure 6.6.11), which is usually fitted to the yoke or

pillars of the actuator, and it is linked to the spindle of the actuator by a feedback arm in

order to monitor the valve position. It requires its own higher-pressure air supply, which it

uses to position the valve.

A valve positioner relates the input signal and the valve position, and will provide any

output pressure to the actuator to satisfy this relationship, according to the requirements

of the valve, and within the limitations of the maximum supply pressure.

A positioner translates the input signal received from a

controller to a required valve’s position & supplies the

valve’s actuator with the required air pressure to move

the valve into the correct position

A positioner ensures that there is a linear relationship

between the signal input pressure from the control

system and the position of the control valve. This

means, that for a given input signal, the valve will

always attempt to maintain the same position

regardless of changes in valve differential pressure,

stem friction, diaphragm hysteresis and so on.

A valve positioner relates the input signal and the valve

position, and will provide any output pressure to the

actuator to satisfy this relationship, according to the

requirements of the valve, and within the limitations of

the maximum supply pressure

Why do we need positioner ?

Smart valve positioner

The output signals from most control systems are

low power 4-20 mA analogue signals but there

is a growing use of digital systems such as

“HART®”, ‘Foundation Fieldbus®' ‘DeviceNet®‘

or 'Profibus®'.

• An analogue system provides a continuous but

modulating signal

• Whereas a digital system provides a stream of

binary numeric values represented by a change

between two specific voltage levels or

frequencies.

Output signal

Noise & Grounding

In transmitting 4-20 mA analog signals across a process plant or factory floor, one of the most critical

requirements is the protection of data integrity. However, when a data acquisition system is

transmitting low level analog signals over wires, some signal degradation is unavoidable and will

occur due to noise and electrical interference.

Noise and signal degradation are two basic problems in analog signal transmission.

Noise is defined as any unwanted electrical or magnetic phenomena that corrupt a message signal.

Noise can be categorized into two broad categories based on the source-internal noise and external

noise. While internal noise is generated by components associated with the signal itself, external

noise results when natural or man-made electrical or magnetic phenomena influence the signal as it

is being transmitted. Noise limits the ability to correctly identify the sent message and therefore limits

information transfer.

Some of the sources of internal and external noise include:

Electromagnetic interference (EMI);

Radio-frequency interference (RFI);

Leakage paths at the input terminals;

Turbulent signals from other instruments;

Electrical charge pickup from power sources;

Switching of high-current loads in nearby wiring;

Self-heating due to resistance changes;

Arcs;

Lightning bolts;

Electrical motors;

High-frequency transients and pulses passing into the equipment;

Improper wiring and installation;

Signal conversion error; and

Uncontrollable process disturbances etc.

Problem with analog signal

Imagine two people, person A and person B, each on

opposite hilltops and each with a flag and a flag-pole. The

aim is for person A to communicate to person B by

raising his flag to a certain height. Person A raises his

flag half way up his pole. Person B sees this and also

raises his flag halfway. As person A moves his flag up or

down so does person B to match. This would be similar

to an analogue system.

Analog signal

Now assume that person A does not have a pole but instead has two boards, one

with the figure '0' and the other with the figure '1', and again wants person B to

raise his flag half way, that is to a height of 50% of his flag-pole. The binary

number for 50 is 110010, so he displays his boards, two at a time, in the

corresponding order. Person B reads these boards, translates them to mean 50

and raises his flag exactly half way. This would be similar to a digital system.

It can be seen that the digital system is more precise as the information is either a

'1' or a '0' and the position can be accurately defined. The analogue example is not

so precise because person B cannot determine if person A's flag is at exactly

50%. It could be at 49% or 51%. It is for this reason, together with higher

integration of microprocessor circuitry that digital signals are becoming more

widely used.

Digital signal

Binary

Explanation of Binary code

Binary

HART® is probably the most widely used digital communication protocol in the

process industries, and is supported by all of the major suppliers of process field

instruments.

• Preserves existing control strategies by allowing 4-20 mA signals to co-exist with

digital communication on existing 2-wire loops.

• It Is compatible with analogue devices.

• Easy to set (can be set by a slave – handheld communicator)

• Provides important information for installation and maintenance, such as Tag-

IDs, measured values, range and span data, product information and

diagnostics.

• Can support cabling savings through use of multidrop networks (maximum 15

devices)

• Reduces operating costs via improved management and utilisation of smart

instrument networks.

HART

Profibus • PROFIBUS® is an open fieldbus standard for a wide range of applications in manufacturing

and process automation independent of manufacturers. Manufacture independence and

transparency are ensured by the international standards EN 50170, EN 50254 and IEC 61158.

It allows communication between devices of different manufacturers without any special

interface adjustment.

• PROFIBUS® can be used for both high-speed time critical applications and complex

communication tasks. PROFIBUS® offers functionally graduated communication protocols

DP and FMS. Depending on the application, the transmission technologies RS-485, IEC 1158-

2 or fibre optics can be used.

• It defines the technical characteristics of a serial Fieldbus® system with which distributed

digital programmable controllers can be networked, from field level to cell level. PROFIBUS®

is a multi-master system and thus allows the joint operation of several automation,

engineering or visualization systems with their distributed peripherals on one bus.

At sensor/actuator level, signals of the binary sensors and actuators are transmitted via a

sensor/actuator bus. Data are transmitted purely cyclically.

• At field level, the distributed peripherals, such as I/O tutorials, measuring transducers, drive

units, valves and operator terminals communicate with the automation systems via an

efficient, real-time communication system. As with data, alarms, parameters and diagnostic

data can also be transmitted cyclically if necessary.

• At cell level, programmable controllers such as PLC and IPC can communicate with each

other. The information flow requires large data packets and a large number of powerful

communication functions, such as smooth integration into company-wide communication

systems, such as Intranet and Internet via TCP/IP and Ethernet

Foundation Fieldbus (FF)

Foundation™ Fieldbus is an all-digital, serial, two-way communications system

that serves as a Local Area Network (LAN) for factory/plant instrumentation and

control devices. The Fieldbus® environment is the base level group of the digital

networks in the hierarchy of plant networks. Foundation™ Fieldbus is used in

both process and manufacturing automation applications and has a built-in

capability to distribute the control application across the network.

Unlike proprietary network protocols, Foundation™ Fieldbus is neither owned by

any individual company, nor regulated by a single nation or standards body. The

Foundation™ Fieldbus, a not-for-profit organization consisting of more than 100

of the world's leading controls and instrumentation suppliers and end users,

controls the technology.

While Foundation™ Fieldbus retains many of the desirable features of the 4-20

mA analogue system, such as a standardized physical interface to the wire, bus-

powered devices on a single wire, and intrinsic safety options, it also offers many

other benefits.

PLC

(programmable logic

controller)

• A programmable logic controller (PLC), or programmable controller is an

industrial digital computer which has been ruggedized and adapted for

the control of manufacturing processes, such as assembly lines, or

robotic devices, or any activity that requires high reliability control and

ease of programming and processing

• PLCs are robust and can survive harsh conditions including severe heat,

cold, dust, and extreme moisture.

• Their programming language is easily understood, so they can be

programmed without much difficulty.

P L C

Boolean Algebra

PLCs are modular so they can be plugged into various setups.

Conventional relays switching under load can cause undesired arcing between

contacts. Arcing generates high temperatures that weld contacts shut and

cause degradation of the contacts in the relays, resulting in device failure.

Replacing relays with PLCs helps prevent overheating of contacts.

P L C

PLCs work with inputs, outputs, a power supply, and

external programming devices

P L C

• A timer is controlling the timing for a batch production

• The 1st move is for the water to fill in the tank There is a level switch to control the opening &

closing of the water solenoid valve

• The 2nd move is the steam coming into the heating coil to heat the water inside the tank, to

become hot water with a certain temperature setting There is a temperature switch to control

the opening & closing of the steam solenoid valve

• The 3rd move is the draining of the hot water When the timer is OFF, the drain solenoid valve will

open to drain the hot water from the tank it is the end of the batch production

Conventional simple control system

Conventional simple control system

• We have to install the timer &

relays inside a simple control

box

• We have to connect/wire the

input level switch & temperature

switch to the timer & relays

inside the control box

• We have to connect/wire the

output solenoid valves to the

relays inside the control box

• It takes time to do the above

sequences

INPUT

OUTPUT

P L C

• PLC has already the relays &

timer integral inside it

• We Just connect/wire the level

switch & temperature switch to

the INPUT terminal of the PLC

• We just connect/wire the

solenoid valves to the OUTPUT

terminal of the PLC

• Then we can program the control

sequence

• It saves a lot of times in doing it

compare with the conventional

system !

PLC

P L C

HMI

(human machine

interface)

HMI Human Machine Interface also known as an HMI is a software application that

presents information to an operator or user about the state of a process, and to accept

and implement the operators control instructions.

• Equipment HMI is a software interface between the machine or plant with the

operator and bystanders. Usually bigger HMI consists of a computer centre and a

few separate computers and is used to monitor and control the machine. Features

used by HMI are a plant information, presentation methods and equipment.

Whereas the components used are media communications, computer hardware

and software HMI.

• Typically information is displayed in a graphic format (Graphical User Interface or

GUI).

HMI

The main HMI terminal is typically a desktop PC complete with a

Microsoft® Windows® operating system and a standard HMI graphics application

package.

Example of the software platform are as follows:

• WonderWare®

• Cimplicity

• FactoryTalk® View

HMI

HMI

Advantages include many advanced features now available through Microsoft

Windows such as networking, data sharing between applications and

multitasking. The system flexibility allows the terminal to be applied as any of

the following:

• Primary Operator Interface

• Historian

• Engineering Workstation

HMI • A Human Machine Interface (HMI) is exactly what the name implies; a graphical

interface that allows humans and machines to interact. Human machine interfaces

vary widely, from control panels for nuclear power plants, to the screen on an

iPhone.

• However, for this discussion we are referring to an HMI control panel for

manufacturing-type processes.

• An HMI is the centralized control unit for manufacturing lines, equipped with Data

Recipes, event logging, video feed, and event triggering, so that one may access the

system at any moment for any purpose.

• For a manufacturing line to be integrated with an HMI, it must first be working with

a Programmable Logic Controller (PLC). It is the PLC that takes the information from

the sensors, and transforms it to Boolean algebra, so the HMI can decipher and

make decisions

HMI There are three basic types of HMIs:

• The pushbutton replacer

• The data handler

• The overseer.

Before the HMI came into existence, a control might consist of hundreds of

pushbuttons and LEDs performing different operations.

The pushbutton replacer HMI has streamlined manufacturing processes, centralizing

all the functions of each button into one location.

The data handler is perfect for applications requiring constant feedback from the

system, or printouts of the production reports. With the data handler, you must ensure

the HMI screen is big enough for such things as graphs, visual representations and

production summaries. The data handler includes such functions as recipes, data

trending, data logging and alarm handling/logging.

Finally, anytime an application involves SCADA or MES, an overseer HMI is extremely

beneficial. The overseer HMI will most likely need to run Windows, and have several

Ethernet ports.

HMI

RTU

(remote terminal units)

RTU • RTU is connected into sensors at site/process and it will converting the sensor

signal into digital data to be sent to the supervisory system such as Scada

• An RTU is sophisticated and intelligent enough to control multiple processes

without requiring user intervention or input from a more intelligent controller or

master controller.

• Because of this capability, the purpose of the RTU is to interface with distributed

control systems (DCS) and supervisory control and data acquisition (SCADA)

systems by sending telemetry data to these systems.

• But in most cases, even intelligent RTUs are connected to a more sophisticated

control system such as an actual computer, which makes their reprogramming,

monitoring and control of the entire system easier for a user.

RTU

• An RTU can monitor a field's analog and digital parameters through sensors and

data received from connected devices and systems it then sends these data

to the central monitoring station, as is the case in many industrial facilities like

power, oil and water distribution facilities.

• An RTU includes a setup software that connects input and data output streams;

the software can define protocols and even troubleshoot installation problems.

RTU

RTU • Depending on the manufacturer, purpose and model, an RTU may be

expandable and custom fitted with different circuit cards including communication

interfaces, additional storage, backup power and various analog and digital I/O

interfaces for different systems.

• Because of their widely varying applications, RTUs come in vastly different

hardware and software configurations and may not even be remotely compatible

with each other.

• For example, RTUs used in telecommunication automation may not be usable at

all for oil and gas applications as the processes and hardware systems used

would be completely different.

RTU

SCADA (Supervisory control and data acquisition) systems help to

maintain efficiency, process data for smarter decisions, and communicate

system issues to help mitigate downtime.

The basic SCADA architecture begins with programmable logic controllers

(PLCs) or remote terminal units (RTUs) which are microcomputers that

communicate with an array of objects such as factory machines, HMIs,

sensors, and end devices, and then route the information from those

objects to computers with SCADA software.

SCADA

Supervisory control and data acquisition (SCADA) is a system of software

and hardware elements that allows industrial organizations to:

• Monitor, gather, and process real-time data

• Directly interact with devices such as sensors, valves, pumps, motors,

and more through human-machine interface (HMI) software

• Record events into a log file

• Control industrial processes locally or at remote locations

SCADA

SCADA

SCADA systems are crucial for industrial organizations since they help to

maintain efficiency, process data for smarter decisions, and communicate

system issues to help mitigate downtime.

• The basic SCADA architecture begins with programmable logic controllers

(PLCs) or remote terminal units (RTUs). PLCs and RTUs are

microcomputers that communicate with an array of objects such as factory

machines, HMIs, sensors, and end devices, and then route the information

from those objects to computers with SCADA software. The SCADA

software processes, distributes, and displays the data, helping operators

and other employees analyse the data and make important decisions.

• For example, the SCADA system quickly notifies an operator that a batch

of product is showing a high incidence of errors. The operator pauses the

operation and views the SCADA system data via an HMI to determine the

cause of the issue. The operator reviews the data and discovers that

Machine 4 was malfunctioning. The SCADA system’s ability to notify the

operator of an issue helps him to resolve it and prevent further loss of

product.

SCADA

SCADA

SCADA

• Data acquisition begins at the RTU or PLC level and includes meter readings and

equipment status reports that are communicated to SCADA as required.

• Data is then compiled and formatted in such a way that a control room operator

using the HMI can make supervisory decisions to adjust or override normal RTU

(PLC) controls.

• Data may also be fed to a Historian, often built on a commodity Database

Management System, to allow trending and other analytical auditing.

SCADA systems typically implement a distributed database, commonly referred to as

a tag database, which contains data elements called tags or points.

A point represents a single input or output value monitored or controlled by the

system. Points can be either "hard" or "soft". A hard point represents an actual input

or output within the system, while a soft point results from logic and math operations

applied to other points. (Most implementations conceptually remove the distinction by

making every property a "soft" point expression, which may, in the simplest case,

equal a single hard point.) Points are normally stored as value-timestamp pairs: a

value, and the time-stamp when it was recorded or calculated.

A series of value-timestamp pairs gives the history of that point. It's also common to

store additional metadata with tags, such as the path to a field device or PLC register,

design time comments, and alarm information.

DCS

Distributed control system

D C S

• PLC- Programming Logic Controller is used for controlling and monitoring

high speed process parameters in a factory automation structure but they

cannot use complex structures because of the restriction of the number of

input devices. But then Distributed Control System (DCS) is mostly

suitable for complex systems where more than one input devices is used

for example batch process control.

• Hence DCS is recommended for complicated management programs with

more variety of I/O’s with devoted remotes. These are used in production

procedures where developing of several products are in several

procedures such as group procedure management.

D C S As the name suggests distributed control system is a control system in which

the control is distributed throughout the system.

Instead of having a central control mechanism by using a central controllers:

• A DCS divides the controlling tasks among multiple distributed system.

This provides the system to have more redundancy then a centrally

controlled system (such as PLC).

• In case any single part of the system fails, the plant still keeps on

operating.

More so a DCS is very similar to SCADA with difference only lying in DCS is

more process oriented then SCADA.

D C S

D C S • The lowest level is process control and measurement on the plant floor.

At this level, microprocessor- based controllers such as programmable

controllers execute loop control, perform logic functions, collect and

analyse process data, and communicate with other devices and to

other levels in the system.

• The process data collected at level 1 is transferred to level 2. At this

level, process operators and engineers use operator consoles that

have a keyboard, mouse, and video display to view and adjust the

various processes being controlled and monitored by the system.

• Also, at level 3, process and control engineers implement advanced

control functions and strategies, and members of the operations

management team perform advanced data collection and analysis on

process information. The various plant management systems—such as

inventory management and control, billing and invoicing, and statistical

quality control—exist at level 3.

• The highest level (level 4) is used in large industrial plants to provide

corporate management with extensive process and operations

information

D C S DCSs are by definition hierarchical systems, although not all systems share an

identical hierarchy.

The image below shows a typical DCS. Individual controllers, supervised by master

controllers, make up the lowest "field" or "plant" level of the hierarchy. The master

controllers connect to individual computers and servers, which are further connected

to video output devices and a human machine interface (HMI), which is the actual

point of user control. DCSs are usually networked using standard protocols such as

PROFIBUS and Ethernet, the latter of which is used in this particular system.