Your SCADA system is calling

Posted on 12 Jan 2005
Any SCADA system, though, is only as good as the interface through which the results are presented. With fixed line systems you still have to be in the right place to monitor the data. What happens if you need access to information, but you are not at your desk, or you are in transit? What happens if the equipment you want to monitor is not near a phone line, or is mobile?

The latest developments in mobile communications prove that immediate response, from anywhere, is now a real possibility. Whether you’re on the other side of your plant or on the other side of the world, advances in cable-free communication mean that you can acquire data and, vitally, act on your findings within minutes.

Radio-based communication

Powelectrics have been providing data communication solutions for many years and have seen the advances in wireless based telemetry at first hand. In the UK these tend to be UHF systems operating around the 400-500Mhz band using set-aside delicensed frequencies. The utilities have pioneered the conversion to radio after successive privatisation has lead to staffing reductions, which inevitably has left some sites unmanned.

The water boards in particular have many sites which are too remote to use a telephone network effectively so the best solution is to employ radio equipment to monitor process signals and relay values to central controls sites. Increased use has lead to increased confidence and many radio installations now offer real-time control facilities.

Engineers are now starting to embrace the freedom that radio systems can bring. Confidence has grown to the extent that engineers now rely on radio communications to monitor effluent systems on pharmaceutical plants and offshore installations.

Power output

These systems work by converting process values, or serial data, into radio signals. Crucially however, to qualify for de-licensed frequencies the power output of each radio has to remain low, which means that ‘low-power’ radio has an effective range of approximately 20km. For local control systems this method of data acquisition offers many advantages but it is now possible to ‘buy’ your own frequency and transmit over greater distances, but the boundary for process monitoring applications is still fixed at about 60km.

If you need to acquire data and control equipment from further afield a wireless solution is already available. With its link to the GSM network, the mobile telephone is increasingly acquiring the functionality of a PC. This provides access to, and control of, data without the necessity of landline connectivity. With web-browsing capability offered by 3G technology, the mobile will soon emerge as a viable alternative to its desktop predecessor.

Sending messages

A new generation of data acquisition systems is driving the development forward. A device like the IN4MA from Powelectrics uses the GSM network to enable engineers and operators to capture data, respond to critical events and maintain control using their existing mobile phone. Utilising the Short Messaging Service (SMS) and the Data transfer functions within the GSM network, the IN4MA provides two-way communication, responding to requests for information or allowing control of the process. In addition, the IN4MA can pass on a message when a certain condition occurs, so the operator can take immediate and appropriate actions in alarm situations.

The IN4MA doesn’t just send messages to a mobile phone. A personal computer can be used as a ‘call centre’ managing messages and distributing them as appropriate. Data can be viewed in a graphical manner or output to other software suites for further analysis.

Instant response, Internet enabled

If you want to escape from the constraints of cable and you need to respond instantly to plant problems from wherever you may be, the solution is cable-free communications. The advances incorporating GPRS enable devices like the IN4MA to interface directly with web based applications. Your web server can simply ‘ping’ the telemetry device and within an instant you have the information in front of you.

Combining the wireless technologies

On site installation costs can be dramatically reduced by the use of completely wireless solutions. An ‘RF’ (radio frequency) network can be established on site – perhaps acquiring data from all the gas, electricity and water meters on site, or across a sewage treatment works where cabling is particularly tricky. At the centre of this RF network lies a GSM enabled hub, which not only logs the data, but also analyses it and takes the appropriate actions.

Those actions could include sending a text message to the on call engineer, telling the plant operator to come over and sort a problem, making a data call to the ‘call centre’ and uploading the information whilst at the same time highlighting the issue to the control desk.

You can also combine the use of GSM with GPS (the global positioning system). Perhaps you are chemical manufacturer and you supply your clients in bulk, and in order to achieve this you have a fleet of tankers. A level sensor on your clients tank can be linked directly to an IN4MA unit which in turn communicates information back to your head office. When a tank is running near to empty you are alerted and can arrange to send a tanker. Your tankers are fitted with a GPS capable IN4MA so you can find out where it is, where it has been and where it’s heading. You can then instantly find out which is the nearest tanker to your needy customer, work out the fastest route to get the tanker to site, you can see when he arrives, how much product is delivered and when, and check that all is OK. Not only can the system be used to help reduce operating costs and improve customer service, but you can also improve safety.

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