Posts Tagged ‘automation’

Automation industry battles through global economy issues.

Wednesday, October 7th, 2009

By Gregory Hale
With the ebb and flow of the world’s volatile economic environment, it comes as no surprise the economy was on people’s minds at ISA EXPO on Tuesday.

While no one has a crystal ball, it is clear the real winners are those companies and people that saw the economic disaster coming and made plans early so they did not have to react in a hasty manner.

Guillaume Coffinier from Dallas, Tex.-based Texas Instruments has felt the aftermath of the downturn.

“It has affected my company, but not my job. There were some layoffs that were big for some plants, but I don’t think it will affect me. It’s over—hopefully. I’m doing business development for semiconductors, selling to the automation market.”

It is easy to dwell on the negatives these days, but how about looking at the silver lining.

“With the economy slowing down, one of the good things is we are spending time teaching (users) how to use their technology,” said Rich Chmielewski, marketing manager Chemical and Biofuels Process Automation at Siemens.

“Before they would get it and put it in and operate right away. Now they have time.”

Even in a tight market, there are some companies that said they are doing well.

“We are up 10% for the year, but we are a small company around $20 million over last year,” said Kevin Finnan, vice president of marketing at Semaphore.

One of the advantages Finnan said his company enjoys is they are diversified. “No one vertical market is 25% of our company. We are working on emerging markets like solar, and it seems to be sticking.”

Finnan sees anything related to energy as a growth market for the future.

“People are wasting so much energy. It is all about getting organized. In the past year, people are seeing a pay back. People can save up to 25% with the right energy management plan. Green energy initiatives are not going away.”

But it all comes down to whether it is a profit or a loss. “Nobody is going to do much unless it affects the bottom line,” Finnan said.

“We haven’t seen the impact other companies have seen,” said Chris Martin, senior director of product management at security provider Industrial Defender. “At the end of the day, if companies have an incident that affects them, it is not an option.”

Martin said he has found if you can show you can generate a real return on investment that will always go in your favor. “Seven years ago when we started this, it was all evangelizing, but now it is a lot better as people have a lot more information available,” he said.

Even those companies that started the year off slow are starting to see some type of rebound.

“Up until the last three weeks, business has been down on a par with the other companies out there,” said Arun Sinha, director of business development at Opto 22, a networking and I/O provider. “In the last three weeks, though, business has been up to normal levels.” Sinha said earlier in the year business was down between 20% and 30%.

The same is true with Ron Seredian, vice president of marketing at Falcon Electric, a UPS provider.

“It has really slowed down, but we are just now starting to see more business pick up. We are actually starting to see business come in from university labs.”

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Automation runs on energy, not on politics

Wednesday, October 7th, 2009

By Ellen Fussell Policastro

John Hofmeister came to ISA EXPO to present a problem he does not believe anyone can solve with all the intelligence and know-how that we as individuals and companies have with respect to automation.

But it is a problem we can solve as U.S. citizens and voters. “Imagine the future 10-12 years from now without sustainable supplies of electrons. Imagine what will happen in the factories, labs, and processing that needs to be done automatically if the supply of electrons is short, unstable, and insufficient,” he said during his keynote address Tuesday morning at the Reliant Center.

The basic problem, as Hofmeister sees it, is by 2018-2020 the U.S. will enter a period of energy instability of liquid fuels. “The problem we all face in this country is 300 million people will be short on electricity and liquid fuel at the rate we’re going. It will take another decade to work our way out of what we’ve spent a decade working toward,” he said. And that is energy independence.

Hofmeister’s solution is a Federal energy reserve board, “which will only happen by a grassroots movement of Americans saying, ‘We’ve had enough,’ ” he said. Hofmeister is the founder and chief executive of Citizens for Affordable Energy and former president of Shell Oil Co.

He formed Citizens for Affordable Energy not to lobby, but to put the facts out there—to help people better understand what is at stake, what is required, what is possible, and how we have a 21st Century of national security to protect affordability and to save our lifestyle.

He wants to create a new independent regulatory agency called a federal energy resources board to take energy policy away from Congress, which has had 46 years, “and we’re worse off than we’ve ever been because every politically correct endeavor came for naught,” he said. “Our economy is suffering; our lifestyles are hurting; we need an independent regulatory agency.”

Energy problem

Hofmeister reminded ISA EXPO attendees that automation devices do not run on political aspirations, they run on electrons. “You need coal, uranium, gas molecules; you have to have reliable electrons. It affects you directly—your company and your personal well-being. We can’t let political talk determine what the future looks like,” he said.

In the last five years, this country has shelved or delayed or stopped the plans for 100 electricity pulverized coal generating facilities—to begin to replace an aging generation of 600 coal plants where the age is 35 years, Hofmeister said.

Seeing as how 93% of today’s energy comes from hydrocarbon and nuclear (50% from coal, 20% from nuclear, 17% from natural gas, and the rest from oil), it is amazing “we’re not investing in any one of those areas except natural gas,” Hofmeister said. He wondered why we cannot understand this 93% is so critical to our national security, lifestyles, and economy.

Partisan paralysis

The problem lies in the dichotomy between creating energy policy in political time. “We need to create energy policy in energy time,” he said. “Political time is defined as every two years because of who’s in office and who’s not. People are getting ready for an election—to be reinstated by voters. That’s what they focus on. Along comes an energy crisis or high-price crisis … then suddenly we have to do something about that.”

Problems can only be solved by citizens at the voting booth, Hofmeister said. To do that, we need to elect a government that looks at energy security in a pragmatic, coherent, short-, medium-, and long-term manner. “Companies are successful because they have a strategy and a plan to implement it. That plan positions resources, people, and technology to accomplish what this company is setting out to do. You set milestones and measure and fund progress. And you reap the results. What we do with our political system is, every two years, we throw it up in the air and say, ‘Try again.’ ”

In political time, we have evolved into a system of partisan paralysis endlessly going from one extreme to the other—right to left, “which produces a policy that doubles the amount of imports we require while we’re fighting for energy independence,” he said.

Hofmeister’s goal is to build a social network. “We’re not trying to promote individuals to take action themselves, but a network makes an impact,” he said. “We can control our future energy resources, infrastructure, what will be built, and when. I don’t expect the political system to activate. We need citizen involvement. We have the web site set up to build that social network (www.citizensforaffordableenergy.org). In the mean time, we’ll be educating and informing.”

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Allen Bradley SLC 500 Sale.

Friday, May 22nd, 2009

Just wanted to let everyone know that the PLC Superstore is having a Spring Allen Bradley sale. Thru the end of June we are offering a 10% discount from our already low prices on reconditioned Allen Bradley PLCs.

Visit our web site at: www.tek-supply.com for great deals on Allen Bradley automation products.

Also visit www.plcsuperstore.com and www.allenbradleyplc.net for more savings on Allen Bradley controls and plcs.

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Automation IT – MES ownership up in air

Thursday, January 15th, 2009

IT or engineering? Users need both

FAST FORWARD

  • IT has strong knowledge of information technologies.
  • Production knowledge is a strong characteristic with engineers.
  • Combining strengths is easier said than done.
By Bianca Scholten

MES typically is an IT layer, and it ought to be an IT responsibility,” one user said. Conversely, another said, “Our IT colleagues do not have any process knowledge. It is essential that you understand the processes about which MES reports, well. If not, you are reporting rubbish.”

Everybody agrees, more or less, the manufacturing execution system (MES) is the responsibility of users, mostly production. But where can production go when they want to select and implement a new MES? Where can they go with their questions about changes and maintenance of the system?

A small and informal survey made it clear that not only are there different opinions, but also, in reality, there are different ways in which industrial companies handle these issues. Traditionally, there are two parties that take care of automation: IT and engineering. What can they learn from each other? How can they combine the best of both worlds in order to develop, select, implement, and maintain better MES solutions, and last but not least, to use these solutions?

A production manager said she wanted to purchase an MES solution. She contacted the engineers for help, but they sent her to the IT department. When she went to the IT department, they sent here back to engineering.

IT departments traditionally handle ERP and other systems used in the office. The functionality in these systems, like order processing, administrative material management, and cost accounting, belongs largely to ISA95 level 4. These IT people “speak” Java, .Net, and other programming languages. Engineers are working in a completely different world, namely the world of instrumentation, PLC, SCADA, and DCS with programming languages like ladder diagram, SFC, and function blocks. They are active on ISA95 level 2, 1 and 0.

But who takes care of the automation of activities at ISA95 level 3, often called the MES layer? This is about activities like finite production scheduling, recipe management, data collection, tracking, and tracing. Traditional level 2 process control system vendors have offered more level 3 functionality over time, with historians, standard production reporting, and recipe management. These systems closely integrate with the systems on level 2, so it is essential to have thorough knowledge of the process and its automation. This suggests engineers are the ones to support MES and execute MES projects.

On the other hand, there are reasons to think MES should be supported by IT. MES software vendors have based their historians, reporting functionality and recipe management on the operating systems, programming languages and network protocols characteristic for IT environments. Moreover, the term Manufacturing IT is becoming more predominant today.

Quick snapshot

In an effort to gain more insight into who really owns MES, I decided to conduct an informal, non scientific survey among a series of users to get a snapshot of what they were thinking about the issue.

“It can not be a coincidence that we keep addressing the same subjects,” was the reaction of one MES project leader. “I’ve just become a member of a European working group to investigate this very same subject. It appears that in our plants in Europe, we think differently about it. The purpose of the working group is to develop a recommendation for a boundary between the different disciplines and the related organization. The final goal is to develop a common approach.” Others responded enthusiastically. It appears to be a hot topic that needs clarification.

The survey went out to 18 end users; 15 responded before the deadline. The respondents all work for international companies with headquarters in Europe and in the U.S. Every one of them has a good understanding of the ISA95 standard, so I am relatively sure we all have the same basic idea of what is meant by level 4, 3, 2, 1, 0, and MES.

Most of the respondents work in pharmaceutical and chemical industries, but some work in food, tobacco, energy, and biotechnology. Almost a quarter of them is active within level 4 IT, almost half of the group is active within level 3 IT, almost a quarter is active within engineering, and one works for production.

Except for one, all of these companies have implemented one or more MES systems. The other is using SAP on level 3, for electronic batch records. In 33% of these cases, support of MES projects and maintenance are the responsibility of IT. In 20% of cases, it is the responsibility of engineering, 40% have shared responsibilities, and 7% have not decided.

When asked how closely IT and engineering are working together in their companies, 20% said there is no collaboration at all, 43% said they work together in case of projects, and 23% said they work together closely on a daily basis. The remaining 13% could not give a single answer because there are too many differences between divisions.

“In my opinion, IT and engineering do not collaborate in our company,” an engineer said. “Even worse, they are opposed to one another. Although the technical gap between IT and engineering is getting smaller, the chasm between the departments still is huge. I think this heavily impacts the success of MES implementations.”

One respondent said within MES projects, their IT and engineering departments work together closely, but for the support of MES systems, the collaboration could improve.

In case of daily collaboration, IT and engineering usually report to the same entity. Several respondents said the relationship between IT and engineering strongly improved from the moment they had to work on an integrated architecture. This led to more clarity about roles and responsibilities, and they started to trust each other more. Establishing a level 3 IT department also seems to positively impact collaboration. Nevertheless, people keep competing, and IT people seem to stay convinced the ERP system can do anything.

Some of the survey participants emphasized the level of cooperation between IT and engineering strongly differs per division. “Generally speaking, there is not enough cooperation,” one of them said. “Nevertheless, it is becoming clearer that there is a need for a separate manufacturing IT entity. Neither engineering nor IT can offer enough for effective MES functionality. We need a bridge, and we can build that bridge by establishing a dedicated manufacturing IT group that combines IT skills with automation skills,” she said.

Can’t we get along?

Survey respondents mention strong points and weak points of IT as well as engineering, concerning the question, “Which party would better support MES projects and maintain MES systems?” Not surprisingly, strong points of IT are weak points of engineering, and vice versa.

IT strengths

One of IT’s strong points is its knowledge of information technologies, like Ethernet, the IT infrastructure, networks, protocols, topologies, databases, MES data, data management, security and software development technologies, tools, and methods. “An MES is an application that is oriented toward interfaces and databases. Databases are not part of a technical engineering environment,” one respondent said.

Another respondent said, “Engineering in most companies has been stripped to the bone and fragmented to provide support for manufacturing systems and equipment in diverse sites. This severely limits the talent pool at any single site.”

Several respondents said IT tends to be more professional when it comes to system maintenance. IT is better at systems monitoring, making back ups and developing system documentation. Engineering, on the contrary, does support “on the side.” It is not their core task and they handle it less professionally. Furthermore, IT can work with several disciplines.

Another advantage for the support of MES is its central place within the company. From there, IT has an overview over the complete site, or even over the company. So IT is familiar with the infrastructure MES uses and are already responsible for the desktops MES uses. Furthermore IT knows the other business processes and systems MES has to exchange information with.

From this central position, IT has a better basis for harmonization and standardization and to avoid double functionality. IT would be capable of developing a corporate MES strategy and integrate this with the corporate IT strategy. This would lead to synergy between plants. A company could reuse the implementation knowledge over all plants.

Engineers do not have this overview. Historically, they focus on local projects, with a scope that does not reach beyond a production machine or a production line. One of the respondents said their engineering department had once implemented OEE functionality for a production line that was not interesting from a business perspective at all because it had too much capacity. That could mean unnecessary sub-optimizations could result when investments do not undergo an assessment from a higher level.

It is about savings

IT’s central position can lead to cost efficiency. It can limit implementation and maintenance costs. Moreover, IT has professional negotiation power.

IT has knowledge of level 4 systems and their interfacing possibilities. If a company wants to realize all the possible advantages of the MES system, then it will have to integrate MES and ERP.

In short, the 15 respondents mentioned advantages where IT is responsible for the support of MES projects and the maintenance of MES systems. This suggests IT ought to be responsible. But let’s see if there are any significant advantages if engineering is responsible.

Engineering strengths

Almost every respondent acknowledges production knowledge and affinity are strong characteristics of engineering.

“Even if process automation will be more and more influenced by information technologies, detailed knowledge will always be required about the production process, product specifications, and the limitations of the process and the equipment. I hope that engineering will always be available to deliver this knowledge,” one respondent said.

“When the production process is a mixture of manual steps (supported by MES) and automated steps (supported by the level 2 system), then MES will have to be in close harmony with the level 2 systems, and this is something that engineering can take care of,” another respondent said.

One of the companies deliberately put MES projects and support under the responsibility of engineering. “MES systems contain process information that process people need. Management information is only a summary of this process information. That is why we think it should be supported by engineering.”

IT is not known for its knowledge of the process. They are physically, as well as in their experience, far away from the processes MES deals with. One respondent said, “it is not feasible to train IT-people to be able to deal with this.” Another said, “the biggest challenge for an IT person is to think like a production person. For example: Reliability between the four walls of a production plant is much more important than corporate efficiency, being able to work at a distance. You cannot decide just like that on a Friday night to shut down the system for a few hours of maintenance. The engineers within our company are realizing that much more than the IT people. They are much closer to the reality of the production process.”

Local support works

For production departments, it is better to have one party that can solve their problems and handle their wishes in the field of automation,” said one respondent. “Engineers usually report directly to production departments, and they are part of what companies call ‘production’ or ‘supply chain.’ ”

“Engineering people are familiar with the requirements of production and willing to develop solutions meeting these requirements. Engineering does not start after a functional specification is ready, but helps to get a user requirements specification and develops the functional specification on its own,” said someone who works for an engineering department. Many respondents mention engineering can provide 24/7 support, whereas that is not the way IT tends to work. “IT is not trained to help blue collar personnel and give support for a 24 hours/seven days environment. To shut down an ERP system during a weekend for maintenance is OK for an office but not in production.”

Knowledge is key

Some of the advantages of engineering supporting MES systems and projects relate to their knowledge of production process systems and methods. “MES will have to be integrated with level 2 systems,” one respondent said. “On level 2, there are many systems, all with their own specific technologies, and they can only be maintained by engineering. For integration, you need knowledge of these systems. The IT people are not familiar with the process automation landscape in which systems, platforms, and technologies are used that are sometimes more than 25 years old, but also very new software is used.”

“A large part of the process data that are needed within MES originate from the PLCs, SCADA, and DCS systems,” said another respondent.

MES projects and maintenance of MES systems have points of concern that have resemblances with the methods used by engineers. “Engineering projects have direct impact on production processes. Often these projects can only be realized by production stops. Those stops have to be as short as possible. This is an aspect that IT people are not familiar with,” said one engineer. “IT people are not known for their understanding of real-time production environments and the impact of system errors on production,” a respondent said.

End users’ perspective

In short: Engineering and IT bring in important knowledge and skills for MES projects and support of MES systems. Companies seem to be in a situation where that has grown organically instead of it being the result of a conscious, strategic decision. The ones that did make a conscious decision did not all make the same decision. There still are many diverse options, and nothing points out that one scenario is better than the other. For example, you could make IT responsible and have them communicate with engineering on a project basis. This is also possible the other way around. Another possibility is to establish a dedicated manufacturing IT department. But such a department will have to communicate with IT as well as with engineering. Yet another possibility is to put IT and engineering under the same responsibility, to merge the departments.

It is not yet clear what the advantages and disadvantages of all these scenarios are.

Finding utopia

Picture the ideal situation: There is this industrial company, taking a conscious, strategic decision about making IT and/or engineering responsible for the support of MES projects and the maintenance of MES systems. They purchase an MES from a solution provider that sells mature MES products, with a very high percentage of standard functionality, but also with enough flexibility to adapt it to the specific characteristics of the plant’s production process. And finally the industrial company hires a system integrator specializing in the MES solution of this specific provider, and that has decided to combine the best of both worlds (IT and engineering) in its MES project approach. By the time this becomes true, that guarantees success, right?

Users have relied upon several parties: IT, engineering, the MES software supplier, and the MES system integrator. Nevertheless, there is one important task for them. If you want an MES project to be successful, it is very important the users prepare themselves for using the system. Already at the start of the MES project, they should start writing documentation, develop procedures and train colleagues in adopting these new habits, involve the communication department in order to send newsletters, and write articles on the intranet about the upcoming changes. There are end users not aware of this necessity. This of course has something to do with the lack of clarity about responsibilities in MES projects, but it is also due to the fact that production people and other users of the system just are not specialists in the aspects of automation and IT projects.

In the end, there are quite a few questions, but no real answers. After more research, the issue may clear up, but until then, we can move forward on an individual basis, finding our own way.

ABOUT THE AUTHOR

This story was taken from a paper presented at WBF 2008 in March in King of Prussia, Pa. Bianca Scholten is a fellow at Ordina ISA95 & MES competence centre in the Netherlands. Her e-mail is bianca.scholten@ordina.nl.

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Wireless sensors

Thursday, December 11th, 2008

Wireless sensors

By Steve Toteda

The information you need to run your industrial plant more safely and efficiently is all around you; the challenge is getting access to it in a reliable, cost-effective way. Today’s new standards-based, ultra low-power wireless sensor systems allow you to do just that, with their ability to measure critical parameters like differential pressure, temperature, level, and flow.

You can put wireless sensors almost anywhere with little or no regard for the existing wired infrastructure. They are easy to install and cost only a fraction of wired installations. Equally important, these sensors are simple for plant technicians to use with most deployments boasting an up-and-running network within hours of installation.

Major corporations are using wireless sensing to ensure environmental conditions are safe, monitor critical process parameters and equipment conditions, and gain easy access to the critical performance metrics contained in the sensors themselves.

Wireless essentials

Wireless sensors, the basic elements of a plant solution, create a redundant, fault-tolerant wireless network of connections among themselves. This mesh network, which carries data to a gateway connected directly to the main monitoring and control system, delivers superior reliability compared to alternative solutions that require direct line-of-sight communication between each device and gateway.

Wireless mesh networking uses the industry standard 802.15.4 radio from IEEE. The 16 channels available for individual communications give wireless sensors the ability to choose a different radio channel for each transmission, thereby avoiding interference. Use of the IEEE standard makes straightforward the issue of coexistence with WiFi, another common wireless standard used in a plant. WiFi is also based on an IEEE standard called 802.11, and the IEEE dealt with the potential for coexistence issues in the development of the standard. Extensive testing of multiple applications within the industry has shown these technologies can and do coexist well, even under difficult circumstances.

Wireless has a notorious reputation in the canyons of steel that make up a typical plant, and much of this is well-founded. Most assume the major stumbling block with wireless deployments will come from interference with some other type of radio, and then spend time and money attempting to profile the overall spectrum they will use. However, the real culprit of poor reception or blocked transmissions often comes from the signal bouncing around the plant, canceling itself out if it bounces in just the wrong way.

By channel hopping and taking advantage of the multiple paths in the mesh network, devices and gateways work together to find paths
and channels that optimize data reliability while minimizing power consumption and eliminating points of failure. This gives the network wire-like reliability while avoiding problems with radio-frequency (RF) interference from other radios and from the electromagnetic noise of motors, lights, and other sources common in plant environments. Most vendors report performance metrics that exceed 99.9% data reliability, with numerous real-world examples of 100% over extended periods of time.

The individual sensors in a wireless mesh network are also equipped to transmit and receive data to and from the gateway in a time-synchronized manner. This means sensors share the same clock, knowing precisely when to talk, listen, and most importantly, when to turn themselves off. Time-synchronized communication is critical for conserving battery life, allowing sensors to operate on the equivalent of two AA-batteries for seven to 10 years or more.

As far as security and reliability goes, all measurement and control traffic between sensors is secured, and all messages are encrypted, authenticated, and checked for integrity. Today’s wireless standards typically use a proven AES 128-bit cipher to provide authentication and encryption. End-to-end security is an altogether different story, and you’ll need to carefully think through selecting equipment that permits a secure wireless link form the filed device all the way to the control room, in most cases passing over unsecured wiring.

Future applications

Companies can realize the potential of process production facilities with the emergence of open standards-based field wireless infrastructure. Typical refineries deal with the harsh environments created by the complex piping of the production facilities through the previously described advanced techniques. Such environments are often quite hostile to RF signals, exacerbating the traditional RF issues of path loss, fading, and multipath.
The low installation cost of wireless makes it tempting for a company to get its feet wet. But plants can realize a bigger cost savings through improved predictive maintenance and better operational performance.

Future advances in wireless sensor technology will further reduce power consumption of the sensors and their wireless networking interface. We are already seeing wireless sensors harnessing the vibration of the machine it is measuring to generate their own power to report on the health of the equipment. This will give more options in where to embed devices.

Here are some tips to consider when selecting wireless sensor products:

  • Make sure to adopt a full mesh networking architecture with channel hopping to ensure wire-like reliability.
  • Choose an automation vendor whose wireless sensors and gateways provide dynamic network optimization to accommodate the inevitable changes in the RF and physical environment of your plant.
  • Choose a solution based on an industry-accepted standard.
  • Insist on security in your wireless solution.
ABOUT THE AUTHOR

Steve Toteda is an executive member of the board of directors of the Wireless Industrial Networking Alliance (WINA) and vice president of product management at Dust Networks in Hayward, Calif. Contact him at stoteda@dustnetworks.com.

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Communicating with SCADA

Thursday, December 11th, 2008

Communicating with SCADA

By Stuart Boyer

Supervisory control and data acquisition (SCADA) enables a user to collect data from one or more distance facilities and to send limited control instruction to those facilities. SCADA includes the operator interface and the manipulation of application-related data. But it is not limited to that. Some manufacturers are building software packages they call SCADA, while these are often well suited to act as parts of a SCADA system, because they lack communications links and other necessary equipment, they are not complete SCADA systems.

Communications is the movement of data or intelligence from one location to another. For communications to happen, several things must be in place. First, a communication path must exist; the data must travel over some selected medium. Second, equipment must exist at the sending end of the communications path to condition the data and to put it into a form that we can send over the communications medium. Third, equipment must exist at the receiving end of the path to extract the message from the medium and understand its meaning.

Given a SCADA system consists of one or more master terminal units (MTUs) sending instructions to and receiving data from one or more remote terminal units (RTUs), it is clear communications plays a vital role in the operation of the system.

Installing SCADA is usually justified because of the remoteness of a site and the difficulty or cost of manning it. In a few cases, it is dangerous, unhealthy, or otherwise unpleasant for a person to be at a site. In most cases , it is simply too expensive to have an operator stay at the site for extended periods of time or even to visit the site on a once-a-shift or once-a-day basis.

As long as you can establish some type of communications path between the remote sites and the central or master site, you can pass data. If you cannot establish a communication link, you cannot develop a SCADA system.

In analog-to-digital conversion, all data that moves between the MTU and the RTUs is binary data. It may have originated that way as a status condition of an on-off switch, or it may have converted to binary form from analog form.

Long distance communication is serial. All data that moves between the MTU and the RTUs is serial. That means a single string of binary characters goes one after another. The alternative to serial is parallel. Parallel buses see use within computers and from computers to printers, but the cost of the extra communications medium (wire) becomes prohibitive for long distance communications paths. To communicate the digital word from the analog-to-digital converter in serial format, you need to define some convention to transmit first the most significant bit, then the next smaller, then the next smaller until you send all bits. Or you need to define some convention to transmit first the least significant bit followed by the next larger, followed by the next larger, and so on. This convention would be part of the communications protocol.

Protocol

A protocol is a set of rules that defines the meaning of a pattern of binary words. The messages you send from the MTU to the RTUs are a series of binary digits. But what will the first bit represent? What about the second or the 247th? Protocol tells us—it supplies the code to create this long series of ones and zeros.

The same code allows the receiving station to decode it. The same code the sender uses, the receiver must also use. This is not to say only one protocol is available; there are dozens. Equipment manufacturers developed them before any standards organizations became interested. Many equipment manufacturers continued to use their proprietary protocols even after the standards organizations had developed open standards. And some even developed new proprietary standards after these open standards were available. Some are better for certain applications than others; some are worse for all applications than others. The important thing to know is you must have the same protocol at the RTU as at the MTU.

Modems

The modem is at the lowest two levels in the ISO/OSI seven-layer model. It checks to determine use of the communications medium and turns the radio transmitter on. It changes the low-power binary signals as they feed to it from the MTU or RTU into a form that will travel to the other end of the medium, and another modem receives them.

Early attempts to send direct-current (DC) signals long distances over wireless demonstrated that resistance reduced the signal. Attempts to send more and more pulses per second down the line demonstrated inductance, and capacitance effects also affected the signals. We reached limits to data rate and distance early because we affected the shape of the pulses.

We can separate a wave form mathematically into a series of sine waves. Sharp-edged pulses contain more high-frequency components than do round-edged pulses. The inductive reactance of a long pair of wires will selectively attenuate the high-frequency components, effectively rounding off the pulse.

The communications modulator varies one of three characteristics of the carrier. It may change the amplitude, the frequency, or the phase. Amplitude modulation (AM) varies the amplitude of the relatively high-frequency carrier by multiplying it by the amplitude of the data. The result is a series of sine waves at the carrier frequency that vary in amplitude at the data rate. Frequency modulation (FM) varies the frequency of the carrier according to the amplitude of the data. Output amplitude is constant. Because most atmospheric noise is amplitude-related, and FM does not receive any intelligence from the signal amplitude, FM signals are not affected by atmospheric noise as much as are AM signals.

ABOUT THE AUTHOR

Stuart Boyer is president of Iliad Development Co

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