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wireless in automation  |   Article

Going wireless

Users have expressed their key requirements for plant-wide wireless networks that are to be used for applications in the process industries

Wireless data communications has been described as a disruptive technology. After the introduction of any new but applicable disruptive technology into an established market, usually a paradigm shift is expected in the products sold into that market, and a reordering of the supplier leadership.

I n process control, each disruptive technology change has taken 15-20 years for its impact to dominate or replace older technologies for new system configurations and major plant re-vamps, and longer for general device replacement. In general, each of the previous disruptive technologies has not materially expanded the market, but has replaced the core instrumentation necessary for control of continuous and batch processes.

Wireless instrumentation has been different! It’s first applications have been to extend process monitoring into applications such as process and personnel safety that have previously been too expensive to install, generally due to the necessity to design, install, and maintain a copper wire network. As wireless standards applying to industrial automation are completed, and products conforming to these standards appear, wireless is also expected to follow the time schedule for replacement of instrumentation experienced by previous disruptive technologies, but at a higher degree of market penetration stimulated by its lower installed cost as well as its use for previously uninstrumented applications. Users in various industries have supplied their current and potential applications as the basis of the design for industrial wireless networks. CMC Associates participated in a research through magazine surveys, a few independent research reports, participation in the work of ISA standards committee SP100, and by direct interview of trusted end-users with appropriate experience. The opinion of users participating has been embodied into a user requirements document that draws a set of useful conclusions. A look…

Planned use of wireless networks

Many users have begun the installation of wireless instrumentation. Some are planning new wireless installations, while others have stated their interest, but have not planned installation. Many are waiting for wireless standards to be the basis of the products they will purchase. Most of the same users reported wired instrument installations varying from 10 to more than 25,000 points.

The physical size of the plants studied varied from less than 4000 sq mt to more than 60,000 acres (a county area for a utility.) The average plant size was 52,000 sq mt evenly distributed between 4,000 and 60,000 sq mt, but with nearly 40 per cent of the plants between 80,000 and 100,000 sq mt.A significantly high percentage (almost 50 per cent) of the users favour application of wireless networks to some large plant areas such as storage tank farms, remote transfer stations, and even to well-head monitoring for gas/oil-field use and water/waste pumping stations. Many of the users interviewed have already installed some of the existing proprietary wireless networks, usually with great success. The ‘sweet-spot’ in the wireless market is currently for data acquisition for new measurements never before economical due to the cost of wiring. Many of these are in safety alerting applications such as safety shower usage and safety relief valves. The potential market for wireless instrumentation seems to be about 2,500 – 5,000 instruments for the average plant size of 52,000 sq mt of which we assume 12,000 sq mt (less than 25 per cent) is used for processing. Small plants may have as few as 100-250 instruments spread out across 10,000 sq mt to large plants with 50,000-100,000 instruments spread out over 2,000 hectares. This includes only plant-wide process applications and does not include SCADA applications that tend to be spread over very large areas with small local concentrations of pumping, storage, and processing. Another way to classify wireless instrumentation is by the speed of the intended application. Applications varied from simple alerting and slow data acquisition, 77 per cent, to high speed data acquisition, open-loop, and closed-loop control, 33 per cent. When asked how these applications were being done now, most answered that the application was done manually, with wired instruments, or not at all. A few indicated the current use of wireless including Wi-Fi and other ad-hoc methods. Direct interviews with end-users have confirmed their reluctance to use wireless networks for closed loop control until they gain more confidence in the technology with their early installations. In fact, the current demand for wireless instrumentation all concentrates on relatively low performance data acquisition in monitoring and alerting functions. Most users are not currently thinking at all about control needs for wireless networks, but are concentrating on their difficult data acquisition and monitoring (alerting) needs. In describing a monitoring application, several end-users have stated that they expect to access the data about once every 1-5 minutes, but they also expect immediate (1 second or less) response when the condition being monitored changes state or value. This is now called alerting or alarming and reveals that users expect some form of response faster than slow polling of values or states during abnormal conditions. They expect the field device to originate abnormal states or alarms, and for the network to transport this information without delay.

Integration with plant systems

On being asked about integration of the wireless network with the plant control system, several respondents selected more than one point of integration. The most preferred point of integration was the DCS or PLC (50 per cent). Some indicated integration at the 4-20 mA loop level. An equal number indicated integration at the fieldbus level. These combined make up about 25 per cent of the integration preferences. The rest indicated integration with the plant business (IT) network, which may be interpreted as a need to integrate plant data with asset management systems and/or enterprise resource planning (ERP) tools such as SAP.

Factors influencing the user of wireless

Users were questioned about the most important factors influencing their use of wireless technology. About 51 per cent of the responses were concerned with reliability and security and 30 per cent were concerned with the availability of a single standard, and not multiple standards. Only 15 per cent were concerned with battery life as a primary issue. Other concerns were related to cost, co-existence with other networks, distance, mobility, and speed. In confirming with the given results during personal interviews, it was found that the existence of a wireless standard was expected to resolve their concerns for security and reliability. With these issues removed, the primary factors, according to these users is the use of a single wireless standard for process control field applications, followed by concerns for battery life. The following sections discuss each of these factors.Security and reliabilityUsers just expect the wireless network to be ‘as secure and reliable as an equivalent wired network.’ Most users are very concerned about putting process data on a wireless network. There is a natural privacy with wired networks, except for the connection to the corporate IT network and the internet. While users want this same level of privacy with wireless networks, they express two concerns, increased product cost to provide the capability for encryption/decryption, and increased complexity to use secure networks. They do expect that the network will provide the capability to exclude all devices not configured to join the network, and that messages originating from unauthorised devices will be ignored.Single network standardUsers always expressed a strong desire for a single wireless network standard for all of their applications. They do not want to be ‘locked’ to a specific supplier for their instruments and control actuators that are the result of using a proprietary network. However, whatever is necessary to achieve such a standard is of little interest to the user, as long as it does not excessively impact cost, performance, ease of use, or battery life. Likewise, they expect any industrial wireless network to work in the presence of other networks in the same frequency band. Users expect that the network itself will adapt to any interference as it occurs, and no configuration will be required. While the use of the license-free ISM band makes startup of the network less intrusive to the user (no license application), they are mostly interested in keeping network commissioning simple, low cost, and the same worldwide.

All for the users

Users have long experienced a diversity of wired networks, each optimised for efficiency about the movement of different types of data for one general application. Each has been seen with particular advantages, but are very different from each other. Now, with the shift to wireless, users would like to see this diversity eliminated by design to allow the wireless exchange of data of any type without changes in architecture. Users want a single network using a single standard to do all data exchange.

Users have seen the opportunity for a single universal standard (ISA100) developed by a worldwide standards committee (ISA SP100) under the accepted international rules for standardisation (ANSI and IEC) as the best way to avoid network diversity. The nature of wireless requires such cooperation, and the users want this to be the model for achieving single universal network architecture for all industrial applications, even future applications not yet conceived. True international standards have a unique lineage to trace their work to a single international source.

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