Industrial process automotive systems : design and implementation

B. R. Mehta

Y. J. Reddy

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Industrial Process

Automation Systems

Design and Implementation

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1

CHAPTER

Industrial Process Automation Systems

Copyright © 2015 Elsevier Inc. All rights reserved

INDUSTRIAL AUTOMATION

1.1 INTRODUCTION

Industrial automation of a plant/process is the application of the process control and information sys￾tems. The world of automation has progressed at a rapid pace for the past four decades and the growth

and maturity are driven by the progression in the technology, higher expectations from the users, and

maturity of the industrial processing technologies. Industrial automation is a vast and diverse discipline

that encompasses process, machinery, electronics, software, and information systems working together

toward a common set of goals – increased production, improved quality, lower costs, and maximum

flexibility.

But it’s not easy. Increased productivity can lead to lapses in quality. Keeping costs down can lower

productivity. Improving quality and repeatability often impacts flexibility. It’s the ultimate balance of

these four goals – productivity, quality, cost, and flexibility that allows a company to use automated

manufacturing as a strategic competitive advantage in a global marketplace. This ultimate balance is

difficult to achieve. However, in this case the journey is more important than the destination. Compa￾nies worldwide have achieved billions of dollars in quality and productivity improvements by auto￾mating their manufacturing processes effectively. A myriad of technical advances, faster computers,

more reliable software, better networks, smarter devices, more advanced materials, and new enterprise

solutions all contribute to manufacturing systems that are more powerful and agile than ever before.

In short, automated manufacturing brings a whole host of advantages to the enterprise; some are incre￾mental improvements, while others are necessary for survival. All things considered, it’s not the manu￾facturer who demands automation. Instead, it’s the manufacturer’s customer, and even the customer’s

customer, who have forced most of the changes in how products are currently made. Consumer prefer￾ences for better products, more variety, lower costs, and “when I want it” convenience have driven the

need for today’s industrial automation. Here are some of the typical expectations from the users of the

automation systems.

As discussed earlier, the end users of the systems are one of the major drivers for the maturity of

the automation industry and their needs are managed by the fast-growing technologies in different time

zones. Here are some of the key expectations from major end users of the automation systems. The

automation system has to do the process control and demonstrate the excellence in the regulatory and

discrete control. The system shall provide an extensive communication and scalable architectures. In

addition to the above, the users expect the systems to provide the following:

• Life cycle excellence from the concept to optimization. The typical systems are supplied with

some cost and as a user, it is important to consider the overall cost of the system from the time

the purchase is initiated to the time the system is decommissioned. This includes the cost of the

system; cost of the hardware; and cost of services, parts, and support.

1

2 CHAPTER 1 Industrial Automation

• Single integration architecture needs to be optimum in terms of ease of integration and common

database and open standards for intercommunication.

• Enterprise integration for the systems needs to be available for communication and data exchange

with the management information systems.

• Cyber security protection for the systems due to the nature of the systems and their deployment

in critical infrastructure. Automation systems are no more isolated from the information systems

for various reasons. This ability brings vulnerability in the system and the automation system’s

supplier is expected to provide the systems that are safe from cyber threats.

• Application integration has to be closely coupled, but tightly integrated. The systems capabilities

shall be such that the integration capabilities allow the users to have flexibility to have multiple

systems interconnected and function as a single system: shop floor to top floor integration or

sensor to boardroom integration.

• Productivity and profitability through technology and services in the complete life cycle, in terms

of ease of engineering, multiple locations based engineering, ease of commissioning, ease of

upgrade, and migration to the newer releases.

• Shortening delivery time and reducing time of start-up through the use of tools and technologies.

This ability clearly becomes the differentiator among the competing suppliers.

• SMART service capabilities in terms of better diagnostics, predictive information, remote

management and diagnostics, safe handling of the abnormal situations, and also different models

of business of services such as local inventory and very fast dispatch of the service engineers.

• Value-added services for maximization in profit, means lower product costs, scalable systems,

just-in-time service, lower inventory, and technology-based services.

• Least cost of ownership of the control systems.

• Mean time to repair (MTTR) has to be minimum that can be achieved by service center at plant.

The above led to continuous research and development from the suppliers for the automation sys￾tems to develop a product that are competitive and with latest technologies and can add value to the

customers by solving the main points. The following are some of the results of successful automation:

• Consistency: Consumers want the same experience every time they buy a product, whether it’s

purchased in Arizona, Argentina, Austria, or Australia.

• Reliability: Today’s ultraefficient factories can’t afford a minute of unplanned downtime, with an

idle factory costing thousands of dollars per day in lost revenues.

• Lower costs: Especially in mature markets where product differentiation is limited, minor

variations in cost can cause a customer to switch brands. Making the product as cost-effective as

possible without sacrificing quality is critical to overall profitability and financial health.

• Flexibility: The ability to quickly change a production line on the fly (from one flavor to another,

one size to another, one model to another, and the like) is critical at a time when companies strive

to reduce their finished goods inventories and respond quickly to customer demands.

The earliest “automated” systems consisted of an operator turning a switch on, which would

supply power to an output – typically a motor. At some point, the operator would turn the switch

off, reversing the effect and removing power. These were the light-switch days of automation.

Manufacturers soon advanced to relay panels, which featured a series of switches that could be

activated to bring power to a number of outputs. Relay panels functioned like switches, but allowed

1.1 Introduction 3

for more complex and precise control of operations with multiple outputs. However, banks of relay

panels generated a significant amount of heat, were difficult to wire and upgrade, were prone to

failure, and occupied a lot of space. These deficiencies led to the invention of the programmable

controller – an electronic device that essentially replaced banks of relays – now used in several forms

in millions of today’s automated operations. In parallel, single-loop and analog controllers were

replaced by the distributed control systems (DCSs) used in the majority of contemporary process

control applications.

These new solid-state devices offered greater reliability, required less maintenance, and had a lon￾ger life than their mechanical counterparts. The programming languages that control the behavior of

programmable controls and DCSs could be modified without the need to disconnect or reroute a single

wire. This resulted in considerable cost savings due to reduced commissioning time and wiring ex￾pense, as well as greater flexibility in installation and troubleshooting. At the dawn of programmable

controllers and DCSs, plant-floor production was isolated from the rest of the enterprise operating

autonomously and out of sight from the rest of the company. Those days are almost over as companies

realize that to excel they must tap into, analyze, and exploit information located on the plant floor.

Whether the challenge is faster time-to-market, improved process yield, nonstop operations, or a tighter

supply chain, getting the right data at the right time is essential. To achieve this, many enterprises turn

to contemporary automation controls and networking architectures.

Computer-based controls for manufacturing machinery, material-handling systems, and related

equipment cost-effectively generate a wealth of information about productivity, product design, qual￾ity, and delivery. Today, automation is more important than ever as companies strive to fine tune their

processes and capture revenue and loyalty from consumers. This chapter will break up the major cat￾egories of hardware and software that drive industrial automation; define the various layers of automa￾tion; detail how to plan, implement, integrate, and maintain a system; and look at what technologies

and practices impact manufacturers. Industrial automation is a field of engineering on application of

control systems and information technologies to improve the productivity of the process, to improve

the energy efficiency, to improve the safety of equipment and personnel, and to reduce the variance in

the product quality and hence improve the quality.

The terminology and nomenclature of the industrial automation systems differ based on the indus￾try of the applications. The term for computer-integrated manufacturing (CIM) is used in the manu￾facturing industry context and plant wide control in a process industry context. The essential of both

these terms is to interconnection of information and control systems throughout a plant in order to

fully integrate the coordination and control of operations. The automation engineering spans from

the sensing technologies of the physical plant variables to the networks, computing resources, display

technologies, and database technologies.

Improved human operator productivity will be realized through the implementation of individual

workstations, which proved the tools for decision-making as well as information that is timely, accu￾rate, and comprehensible. Time lines of data will be assured through the interconnection of all worksta￾tions and information processing facilities with a high-speed, plant-wide LAN network and a global

relational database.

The broad goal is to improve the overall process and business operations by obtaining the ben￾efits that will come from a completely integrated plant information system. The continual growth of

the linkage of the process operations data with product line, project, and business systems data will

be supported. The system will make such data readily available, interactively in real time, to any

4 CHAPTER 1 Industrial Automation

employee with a need to know, at workstations scattered throughout the plant and, above all, easy to

use. The resulting comprehensive plant information management system will be the key to long-range

improvements to process control, product line management, plant management, and support of busi￾ness strategies.

One of the major challenges in today’s automation jobs is evaluating the suppliers. This challenge is

more apparent in the recent days because the systems appear same across the suppliers. Here are some

of the guidelines that can be considered in the selection process.

These guidelines helps to set out your organization’s needs, understand how suppliers can meet

them, and identify the right supplier for you. The 10 Cs are Competency, Capacity, Commitment,

Control, Cash, Cost, Consistency, Culture, Clean, and Communication. Used as a checklist, the 10 Cs

model can help to evaluate potential suppliers in several ways. First it helps to analyze different aspects

of a supplier’s business: examining all 10 elements of the checklist will give a broad understanding

of the supplier’s effectiveness and ability to deliver the system on time, on budget with quality while

having a sustained relationship for the rest of the life cycle including engineering, installation, precom￾missioning, commissioning, operation, and services.

1.2 INNOVATORS

The industrial automation cannot be described without remembering the pioneering works of the vari￾ous scientists, whose contributions helped these technologies to mature and become commercially vi￾able over a period of time. Few of the pioneering scientist’s contributions are listed below.

ALESSANDRO VOLTA (1745–1827)

Alessandro Volta, Italian physicist is known for his pioneering work in electricity (Figure 1.1). Volta

was born in Como and educated in public schools there. In 1800, he developed the battery called Upper

Volta, a pioneer of the electric battery, which produces a constant flow of electricity. The electrical unit

known as the volt was named in his honor owing to his work in the field of electricity. A year later, he

improved and popularized the electrophorus, a device that produced static electricity. His promotion of

it was so extensive that he is often credited with its invention, even though a machine operating on the

same principle was described in 1762 by the Swedish experimenter Johan Wilcke.

ANDRE MARIE AMPERE (1775–1836)

Andre Marie Ampere was a French physicist and mathematician who was generally regarded as one of

the main founders of the science of classical electromagnetism, which he referred to as electrodynam￾ics (Figure 1.2). The SI unit of the measurement of electric current, the ampere is named after him.

Ampere showed that two parallel wires carrying electric currents attract or repel each other, depending

on whether the currents flow in the same or opposite directions, respectively – this laid the foundation

of electrodynamics. The most important of these was the principle that came to be known as Ampere’s

law, which states that the mutual action of two lengths of current-carrying wire is proportional to their

lengths and to the intensities of their currents.

1.2 Innovators 5

GEORG SIMON OHM (1789–1854)

Ohm was a German physicist and mathematician who conducted research using the electrochemi￾cal cells (Figure 1.3). Using equipment of his own, Ohm found a directly proportional relationship

between the potential difference (voltage) applied across a conductor and the resultant electric cur￾rent. This relationship is called the Ohm’s law. In his work (1827), the galvanic circuit investigated

mathematically gave complete theory of electricity. In this work, he stated that the electromotive force

acting between the extremities of any part of a circuit is the product of the strength of the current and

the resistance of that part of the circuit.

WERNER VON SIEMENS (1815–1892)

Siemens was a German inventor and industrialist (Figure 1.4). Siemens name has been adopted as the

SI unit of electrical conductance, the Siemens. He was also the founder of the electrical and telecom￾munications company Siemens.

THOMAS ALVA EDISON (1847–1931)

He is an American inventor and businessman (Figure 1.5). He developed many devices that greatly

influenced life around the world, including the phonograph, the motion picture camera, and a long￾lasting, practical electric light bulb. He was one of the first inventors to apply the principles of mass

production and large-scale teamwork to the process of invention, and because of that, he is often cred￾ited with the creation of the first industrial research laboratory.

Edison is the fourth most prolific inventor in history, holding 1093 U.S. patents in his name, as well

as many patents in the United Kingdom, France, and Germany. More significant than the number of

FIGURE 1.1 Alessandro Volta FIGURE 1.2 Andre Marie Ampere

6 CHAPTER 1 Industrial Automation

Edison’s patents are the impacts of his inventions because Edison not only invented things, his inven￾tions established major new industries worldwide, notably, electric light and power utilities, sound

recording, and motion pictures. Edison’s inventions contributed to mass communication and, in par￾ticular, telecommunications.

Edison developed a system of electric power generation and distribution to homes, businesses, and

factories – a crucial development in the modern industrialized world. His first power station was on

Pearl Street in Manhattan, New York.

FIGURE 1.4 Werner Von Siemens

FIGURE 1.5 Thomas Alva Edison

FIGURE 1.3 Georg Simon Ohm

1.2 Innovators 7

MICHAEL FARADAY (1791–1867)

He is an English scientist who contributed to the fields of electromagnetism and electrochemistry

(Figure 1.6). His main discoveries include those of electromagnetic induction, diamagnetism, and elec￾trolysis. He was one of the most influential scientists in history. It was by his research on the magnetic

field around a conductor carrying a direct current that Faraday established the basis for the concept of

the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light

and that there was an underlying relationship between the two phenomena. He similarly discovered the

principle of electromagnetic induction, diamagnetism, and the laws of electrolysis. His inventions of

electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely

due to his efforts that electricity became practical for use in technology.

JOHN BERDEEN (1908–1991)

He is an American physicist and electrical engineer, the only person to have won the Nobel Prize in

Physics twice: first in 1956 with William Shockley and Walter Brattain for the invention of the transis￾tor; and again in 1972 with Leon N. Cooper and John Robert Schrieffer for a fundamental theory of

conventional superconductivity known as the BCS theory (Figure 1.7). The transistor revolutionized

the electronics industry, allowing the Information Age to occur, and made possible the development of

almost every modern electronic device, from telephones to computers to missiles. Bardeen’s develop￾ments in superconductivity, which won him his second Nobel, are used in nuclear magnetic resonance

(NMR) spectroscopy or its medical subtool magnetic resonance imaging (MRI).

WALTER H. BRATTAIN (1902–1987)

He is an American physicist at Bell Labs who along with John Bardeen and William Shockley, in￾vented the transistor (Figure 1.8). They shared the 1956 Nobel Prize in Physics for their invention. He

devoted much of his life to research on surface states. His early work was concerned with thermionic

FIGURE 1.6 Michael Faraday

8 CHAPTER 1 Industrial Automation

emission and adsorbed layers on tungsten. He continued on the field of rectification and photo-effects

at semiconductor surfaces, beginning with a study of rectification at the surface of cuprous oxide. This

was followed by similar studies of silicon.

WILLIAM SHOCKLEY (1910–1989)

He is an American physicist and inventor (Figure 1.9). Along with John Bardeen and Walter Houser

Brattain, Shockley coinvented the transistor, for which all three were awarded the 1956 Nobel Prize in

Physics. Shockley’s attempts to commercialize a new transistor design in the 1950s and 1960s led to

California’s “Silicon Valley” becoming a hotbed of electronics innovation. In his later life, Shockley

was a professor at Stanford and became a staunch advocate of eugenics.

JACK KILBY (1923–2005)

He is an American electrical engineer who took part (along with Robert Noyce) in the realization of the

first integrated circuit while working at Texas Instruments (TI) in 1958 (Figure 1.10). He was awarded the

Nobel Prize in Physics in 2000. He is also the inventor of the handheld calculator and the thermal printer.

ROBERT NOYCE (1927–1990)

Nicknamed “the Mayor of Silicon Valley,” cofounded Fairchild Semiconductor in 1957 and Intel

Corporation in 1968 (Figure 1.11). He is also credited with the invention of the integrated circuit or

microchip, which fueled the personal computer revolution and gave Silicon Valley its name. Noyce’s

leadership in the field of computers and his invention in the field of electronics and physics led to the

computer chip we know today.

FIGURE 1.7 John Berdeen FIGURE 1.8 Walter H. Brattain

1.2 Innovators 9

GORDON E. MOORE (1929–TODAY)

Engineer and entrepreneur Gordon Moore earned degrees in Chemistry and Physics from CalTech, was

hired by William Shockley’s Shockley Semiconductor in 1956, and was one of the “traitorous eight”

engineers who left Shockley in 1957 to form the pioneering electronics firm, Fairchild Semiconductor

FIGURE 1.9 William Shockley

FIGURE 1.10 Jack Kilby

FIGURE 1.11 Robert Noyce

10 CHAPTER 1 Industrial Automation

(Figure 1.12). At Fairchild, he became one of the world’s foremost experts on semiconductive materi￾als, which have much lower resistance to the flow of electrical current in one direction than in the op￾posite direction, and are used to manufacture diodes, photovoltaic cells, and transistors. In 1968, with

Robert Noyce, he cofounded Intel, which has since become the world’s largest maker of semiconductor

chips.

1.3 INDUSTRIAL REVOLUTIONS

Human’s ability to use the machine power as a replacement for the human or animal effort can

be treated as the first revolution of the industry. From the above perspective, steam engine can be

treated so because of its ability to create a large amount of work with minimum human effort. This

lead to a large need to automate these machines because the true value of these machines can be

realized only if they can be controlled as needed. The second industrial revolution can be seen as

electricity and its benefits.

The electrical power and its ability to transport the power from one place to another changed the

industrial landscape and created a large growth and new possibilities for industry. Microelectronics

created another revolution with the ability to miniaturize and use less power to create bigger things.

Subsequent revolution can be seen after the invention of micro controllers. At present, world is experi￾encing the revolution created by the Internet and the way it can impact all the industries and common

people. The wealth of information and ability to connect multiple things together changes the way

industries operate and yield efficiencies.

FIGURE 1.12 Gordon E. Moore

1.5 Evolution of automation from technology perspectives 11

1.4 EVOLUTION OF AUTOMATION FROM NEEDS PERSPECTIVES

Initial automation needs in the industrial process operations were driven by the needs to automate the

existing manual process and hence gain better yield and consistency in the product quality. The tech￾nologies available from the late 1970s fulfilled this need. Subsequently, the automation needs of the

industry are driven by the standards and regulations for keeping up the environmental standards. In the

1990s the safety of the equipment and people became an additional requirement in the automation of

the plant and led to the widespread usage of the safety systems and emergency shutdown and startup

operations being automated. During the subsequent years in the 1990s the pressure on the process

industries for improving the bottom line revenue led to the importance of having better efficiency in

the plant operations. Industrial process automation systems play a bigger role in assisting the process

operations for better efficiency (Figure 1.13).

1.5 EVOLUTION OF AUTOMATION FROM TECHNOLOGY PERSPECTIVES

First-generation automation systems were mostly used in the place where there is a need to replace

human force by machines. The mechanization of the industries leads to automation using mechanical

gears and fixtures. The control signals and mechanisms were mostly hydraulic. The pressure of the

liquid in small volume is used to transmit the signals from one place to another and is subsequently

manipulated for multiplication and division. However, due to the inherent nature of liquid compress￾ibility and the energy required to create the signals, the pneumatic systems come into the place. The

pneumatic signals were used to drive the sensors and valves and also for transporting the signals from

one place to another.

The next generation sees that the electrical signals in the form of voltage were used as the technol￾ogy of choice for the control systems. The fourth generation of the systems used the digital electronics

as the technology of choice in the control systems. In the 1960s, the 4–20 mA analog interface was

established as the de facto standard for instrumentation technology. As a result, the manufacturers of

instrumentation equipment had a standard communication interface on which to base their products.

Users had a choice of instruments and sensors, from a wide range of suppliers, which could be inte￾grated into their control systems.

FIGURE 1.13

Evolution of automation from technology perspective

12 CHAPTER 1 Industrial Automation

With the advent of microprocessors and the development of digital technology, the situation has

changed. Most users appreciate the many advantages of digital instruments. These include more

information being displayed on a single instrument, local and remote display, reliability, economy,

self-tuning, and diagnostic capability. There is a gradual shift from analog to digital technology.

There are a number of intelligent digital sensors, with digital communications and capability for

most traditional applications. These include sensors for measuring temperature, pressure, levels,

flow, mass (weight), density, power system parameters, and analytical sensors such as oxygen O2,

carbon dioxide CO2, pH, dissolved oxygen, UV, IR, and GC. These new intelligent digital sensors

are known as “smart” instrumentation.

The main features that define a “smart” instrument are intelligent, digital sensors, digital data com￾munications capability, and ability to be multidropped with other devices in the system. There is also

an emerging range of intelligent, communicating, digital devices that could be called “smart” actuators.

Examples of these are devices such as variable-speed drives, soft starters, protection relays, and switch￾gear control with digital communication facilities. The microprocessor has had an enormous impact on

instrumentation and control systems.

Historically, an instrument had a single dedicated function. Controllers were localized and, although

commonly computerized, they were designed for a specific purpose. It has become apparent that a

microprocessor, as a general-purpose device, can replace localized and highly site-specific controllers.

Centralized microprocessors, which can analyze and display data as well as calculate and transmit con￾trol signals, are capable of achieving greater efficiency, productivity, and quality gains.

Currently, a microprocessor connected directly to sensors and a controller requires an interface

card. This implements the hardware layer of the protocol stack and in conjunction with appropriate

software, allows the microprocessor to communicate with other devices in the system. There are many

instrumentation and control software and hardware packages; some are designed for particular propri￾etary systems and others are more general purpose. Interface hardware and software now available for

microprocessors cover virtually all the communications requirements for instrumentation and control.

As a microprocessor is relatively cheap, it can be upgraded as newer and faster models become avail￾able, thus improving the performance of the instrumentation and control system.

1.6 CHALLENGES THREE DECADES BACK

Automation systems have seen a large change in the last three decades. Due to limited communica￾tion systems, the communication between the users and the systems was limited. Due to the lack of

real-time information, large inventories were planned. There were many islands of automation. The

information flow from the plant floor to the executives is very limited leading to high energy costs of

operations due to noncoordinated systems. The discrete and process automation is seen as two different

distinct systems and information flow is slow or limited. The information on new products and new

solutions available in the market is very limited. There is limited information on how other peer in￾dustries are performing and their best practices with the automation systems. All the above-mentioned

problems have been resolved now due to technology and differently trained operators. The technology

made more data available at an affordable price and communication revolution made the data available

at any convenient location at a much faster rate. The overall plant operations have changed with the

new technologies.

1.8 Technology trends 13

1.7 CURRENT CHALLENGES

Current challenges in the industry are fewer human resources, same or fewer assets and an increase

in demand for more production, demands for less waste, more efficiency, better quality and improved

tracking. Regulations and compliance aspects are increasing across all the domains of plant opera￾tions, especially at pharmaceuticals and petrochemicals, equipment types as distinct process and dis￾crete is disappearing and is going toward a mix of both analog and digital. The goal to reduce energy

utilization is another challenge to face. The challenges in automation and control are, demand for

reduced development, engineering, and commissioning costs, and multidisciplinary control systems,

namely discrete, motion, process, drives, and safety applications for improving machine uptime and

reduction in machine down times, plant floor to enterprise connectivity, remote diagnostics, and web

access.

1.8 TECHNOLOGY TRENDS

Overall, the industrial automation is undergoing technological changes and the major trends are mov￾ing from hardwired/proprietary systems to bus-based open systems. This is driven by the need of the

users to have the lowest cost of ownership on the capital expenditure and also to have the ability and

flexibility to upgrade and use multivendor products. The communication between the systems within

the same plant operations is becoming an open, object-based, standard-based interface.

The general architecture of the automation systems is moving from a single large monolithic solu￾tion to a scalable and modular system. This approach is driven by the need to have the lowest capital

investment in the beginning of the plant and grow with the operations. This approach also is driven

by the needs such as lowest single point of failures in the system. The information collected from the

automation system is moving from a repository of process information to more qualitative informa￾tion supporting the business decisions. Various custom-built applications deployed on the automation

systems provide valuable insight into the process operations such as inventory, and scheduling. The

information so collected becomes or is becoming real-time archival instead of an archival that occurs

on batches or some scheduled time of a day.

The smart field instruments became a source of information with process diagnostics and prognos￾tics from a dumb process measuring instrument. This led to more information for the process opera￾tions on the maintenance strategies and shut-down planning. Similarly, the communication between

various subsystems is moving toward wireless for the industrial environment from a point-to-point

wired communications (Figure 1.14).

The automation engineers in the last three decades have experienced a wide change in the apparatus

used for various automation applications. The different types of appliance used for different purposes

are indicated below. The local indicators typically used to communicate the process variable to the field

engineer or operator have used different display technologies. Initially all the local indicators used to

be mechanical in nature and directly convert the process variable into some mechanical movement in a

scale or a direct indication of the position of some specific level.

The same indicating instruments today come with LCD displays for the local operator and the display

technologies have long life and the flexible orientation for ease of access. Similarly, the remote indicators

are used to communicate the process variable at some other place than the measurement point and the signal