Pumps & Systems, September 2008
Wireless technology has significantly impacted business worldwide. It enables a greater degree of connectivity among devices for enhanced monitoring and utilization of existing assets. It has also led to the development of new applications that improve productivity, uptime and overall business performance.
However, wireless technology has not substantially impacted one segment of the global economy-industrial automation. Major industries, such as oil and gas, chemical, power and water and wastewater treatment, continue to operate their plants mostly with older, hard-wired control systems. A typical process facility will have more than 1,000 measurement points, none of which currently use wireless technology, and many additional points that go unmeasured because of the cost of running wires to each. This paper discusses the need for standards-compliant, wireless, sensor-based technology in these industries for enhanced plant asset management and the consequent benefits.
How Standards are Changing the Landscape: Wireless Hart and ISA100
The rapid adoption of wireless technology will be driven by new wireless standards such as ISA100 and HART (Highway Addressable Remote Transducer) Wireless. The HART Communication Foundation has developed the WirelessHART standard, which is aims to leverage the information collected by HART devices. WirelessHART is geared specifically to the process industry, with a goal of enabling reliable, robust and secure wireless communication in real-world industrial plant applications.
ISA100, currently under development, will support multiple protocols, including HART, and process and factory automation applications. The two groups are cooperating to ensure continuity and uniformity with wireless standardization.
Today's typical wireless deployment in an industrial setting usually requires the purchase of proprietary wireless instrumentation and systems from a single vendor. The headaches accompanying this strategy include dependence on that vendor, added complexity for plant staff and escalated project and maintenance costs. These standards try to alleviate these problems by allowing vendors to build infrastructure products that work with products from other vendors and with what is already installed in the plant. Based on open standards, wireless retrofit products will work with installed systems and devices and present a lower cost, lower risk path toward broad use of wireless sensing.
The WirelessHART standard will allow vendors to develop adapters capable of connecting directly to installed HART devices-without changing anything on the device. These adapters will extract the intelligent HART data and then wirelessly transmit it directly to plant and enterprise applications, such as plant asset management, energy management or monitoring and control. The data is then used to improve predictive maintenance and avoid major problems such as unplanned plant shutdowns.
It is estimated that each HART device contains 35 to 40 data items that can be used to improve the performance of an industrial plant. It varies by instrument, but this data identifies a device, its properties, calibration settings, measured process variables and diagnostic alerts related to it. Retrofitting makes all of these variables continuously available to plant applications.
Demand is growing in this typically conservative industry due to needs for plant efficiency and competitiveness. With these new standards, end user concerns over security, reliability and interoperability will abate and adoption rates should intensify. In a recent analyst briefing, Venture Development Corp. presented that wireless growth is driven by monitoring and measuring applications and the prospect of seamless integration with existing devices and networks (see Figure 1).
Using Wireless to Retrofit Instrumentation
Overall, the process industries have opted to upgrade plants rather than build new ones. In an environment where new construction is not an economical option, plants and refineries have been retrofitting aging equipment as an alternative upgrade path to newer technology. Wireless sensor networking is emerging as a tool for retrofitting at the field device level to economically upgrade a plant for improved operational productivity. Every plant has a list of measurement points to add to the control scheme when budget and time allow.
Using wireless technology to retrofit existing instruments by connecting directly to installed instruments allows plants to minimize downtime and production interruptions without the expense of an entirely new wireless implementation. Unless new points are added, the wiring for the old instruments is typically already in place, and the ability to take advantage of that cost in ROI calculations makes it difficult to justify the premium for the entirely new wireless device and networking infrastructure.
Plants have been increasingly replacing older 4-20 mA field instrumentation with intelligent HART instrumentation. Intelligent devices collect and maintain valuable digital data about their own performance, commissioning, condition, calibration and production processes.
In older control systems, given the expense of adding HART modems to the systems, the diagnostic and digital capabilities of the HART instruments were never enabled for continuous access (see Figure 2). The HART instruments were essentially used as 4-20 mA analog field instruments.
As discussed above, the emerging wireless standards enable the design of wireless adapters that can be retrofitted onto existing 4-20 mA loops to extract digital performance data and wirelessly transmit this information to plant applications that drive operational improvements, like a PAM (Plant Asset Management) system or process data historian. An adapter can connect anywhere on a 4-20 mA loop to immediately retrofit existing HART devices for wireless transmission of intelligent data to critical plant and enterprise applications. By retrofitting the infrastructure onto existing HART devices, intelligent data can bypass legacy control systems (Figure 3).
[[{"type":"media","view_mode":"media_original","fid":"698","attributes":{"alt":"enhancing-plant-fig.3.jpg","class":"media-image","id":"2","style":"float: left; margin: 3px;","typeof":"foaf:Image"}}]]Beyond PAM, wireless retrofits of intelligent instruments can be valuable to control room operations. For example, digital process values provide an alternative to analog 4-20 mA signals, especially when the analog signal has problems. These wireless retrofits can also provide completely new measurement points-if there is field power available, any 4-20 mA wired instrument in combination with a wireless adapter can readily add a new measurement valuable for making advanced control decisions.
As many as an estimated 85 percent of the 25 million HART devices in use today cannot directly connect their digital data to systems that manage, monitor and control industrial plants. The problem is clear: valuable digital data that can improve plant efficiency and uptime
