Remote profibus saves time and money

Control systems and plant control within the water treatment industry are changing. Paul Searby discusses the advantages of a new profibus system, which boosts reliability, cuts downtime and can be accessed remotely.

Earth Tech Engineering says it is moving the control and automation of treatment works into the 21st century using cutting-edge technology.

The company has been specifying and installing profibus systems in water treatment plants for the past five years and, says Paul Searby, the firm's software technical specialist, more companies could benefit from the technology.

Profibus control systems were developed in 1989 and use a complex computer network to give users real time control. Twenty million systems have been installed all over the world - including in Australia, Denmark, Sweden and Russia - and are most commonly used in car manufacturing, heating and air conditioning systems and by textile industries.

The vast majority of water treatment works are controlled by a programmable logic controller (PLC) system. This is a digital computer designed for multiple input and output arrangements, for example; 24v DC and 4-20mA.

In most cases, there are many incoming signals and indicator lamps to control the plant and indicate plant status. Most water companies use systems with controls located in the motor control centre (MCC).

In contrast, the intelligent based systems now being used within the water industry for plant control use the most up-to-date technology and are much more flexible than older-generation systems. The latest technology distributes aspects of the control system, in most cases, via profibus.

Profibus-based control
systems use advanced technological instrumentation that can provide a fail-safe
architecture. And, primarily, the system can be used by water utility companies to help provide cost and operational savings.

The profibus system gives increased plant diagnostics and monitoring, meaning that vital decisions can be made quickly and acted upon so problems can be avoided. For example, valves or dosing systems can be monitored in real time, and measured decisions can be made to maximise the plant's performance, if needed.

Using an intelligent approach over profibus, the system can send the engineer a text message to alert them of any problems. And the programme can be tailored to make them aware of specific information relevant to their plant.

Traditional hardware systems will alert engineers to any problems but are not sophisticated enough to pinpoint the problem. This means that they always have to call someone out to locate the problem.

For example, if an engineer was made aware of a problem at 2am, with the hardware system, someone would have to physically inspect the plant and this could be costly. Even then, the problem could be minor and not time-sensitive.

With profibus, the engineer knows exactly where the problem is located. If the drive has gone into overload and needs re-setting, this can be solved online rather than an engineer having to go on site.

Over a year, according to Earth Tech, the savings in highly skilled call out charges can be considerable. When using a profibus system, the need for large motor control centres to house large numbers of individual components is eliminated.

Plant downtime
Traditional systems use hardwired connections to all the instrumentation within the plant, with attachments for indicator lamps and switches, and interconnection for all the processing instrumentation needed to run the plant.

The new profibus system does away with all the messy discrete interconnections, by siting controls local to the plant itself, processing communication on a network, rather than wires. All the relevant signals and indicators on plant status are presented on dynamic displays, rather than separate and costly indicator lights.

By reducing interconnections, reliability improves, which makes it easier to use and means a reduction in maintenance and potential plant downtime.

One of the main benefits of the system for the water industry is the fact that the system can be accessed remotely off site and in real time. The operator has access to the network via a laptop.

They are connected to the network and not connected by discrete signals so they have access to all information about the plant. The operator can get information about what is happening even at individual sensors. With other systems, the operator has access to limited information - usually just high-level status and alarms at the plant.

This means that, should something go wrong at the plant, more data is available for the operators to analyse and make an informed decision, without affecting the performance of the plant. For example, level and flow information are all available on individual systems and therefore engineers are made aware of any failures with any components on the plant immediately.

According to Siemens, adopting a totally integrated control philosophy via profibus can save companies up to about 11% on their capital expenditure compared with traditional MCCs and plant instrumentation control.

Obviously the saving is difficult to quantify as it varies depending on the particular project. The savings begin with a reduction of the components needed (such as PLC hardware and cables). This also means that the footprint of the plant can be reduced, saving civil constriction costs by specifying smaller buildings.

Less components also mean fewer cables are needed, and as a result, cabling costs are reduced. Should instruments need to be changed, then the advanced software means that parameters can be downloaded to reduce expensive commissioning activities.

Cabling costs can be very high: up to 30-40% of systems costs and therefore a networked approach can provide substantial savings in this area. All of the above means the system takes less time to complete than a traditional system, hence significant savings when installing and commissioning a plant.

Energy efficiency
In terms of operational savings, less equipment means that less power is needed. And smaller panels are used to house components, with a reduced cost to house the panels.

It also follows that less components result in less maintenance, and combined with the diagnostics capability of the system, the plant is more reliable.

This means that there is less risk of the system breaking down and installing it is quicker. Siemens estimates that operational costs will be reduced by 16% when using a totally integrated approach.

In terms of energy efficiency, the profibus system means that the water companies have improved information and reporting abilities providing savings in energy consumption.

Earth Tech, has developed the system using Siemens' Totally Integrated Automation (TIA) technology, and has been installing the system in sites all over Northern Ireland, including sites in Mourne and Fofanny, Carran Hill and Clay Lake.

A total of seven sites have had this system implemented in the Northern Ireland Water region since 2000. The system has been refined over the past seven years, and is currently being implemented on a further four water treatment works for Dalriada Water, again on behalf of Northern Ireland Water.

Even though software engineers at Earth Tech have applied Siemens technology for more than five years, the system is constantly evolving. And, as a result, it has more benefits and is easier to install at plants than ever before.

Profibus-based systems can save water companies space, time and operational costs. Overall, less cabling is needed and therefore fewer trenches need to be dug and smaller support systems are implemented.

The system is easier to maintain and the ability to have remote access can benefit all water companies and ultimately reduce the amount of time needed to be spent on site.

Paul Searby is software technical specialist at Earth Tech. T: 01226 224466

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