Wireless networks can save money and speed turnarounds
Wireless networks can be as reliable as wired ones, and can empower workers to handle tasks they otherwise could not.
Today refineries and other process plants have to run as close to 100% of the time as possible in order to maximize their capital assets, and downtime must be minimized. Of course things eventually do wear out, so periodic shutdowns for maintenance and improvements will always be necessary. The challenge is to make them as short and productive as possible. This article will discuss ways to use today’s wireless technology to maximize efficiency, minimize downtime, and leverage existing resources, especially during shutdowns.
One of the biggest burdens during any plant shutdown that involves changes to control equipment is doing loop checks prior to restart. It’s vital to make sure a valve does not open when told to close, and vice versa, which makes this a critical-path item that translates directly into dollars. The process is burdensome because it requires two people: a worker in the field with a portable radio to watch each valve to make sure it responds correctly when commanded, and a control room operator to send signals to the valve and watch the display to see what happens.
Enter the mobile worker
The wireless worker or mobile worker concept has spread into many businesses, in many cases with workers using their own mobile devices, including laptops, smartphones, tablets, and so on. The trend is seen most often among so-called “road warriors,” who want to keep contact with their companies while traveling, or at least try for the ultimate in telecommuting, and use Wi-Fi hotspots, email, or whatever to maintain contact. They can place orders, track their time, and exchange information with clients.
It would be very helpful to allow plant workers to do the same thing so they could, in effect, take the control room into the field. Using a wireless connection, the mobile worker would be able to not only view a control room display but actually assume the role of an operator, using a remote asset management client with access to such maintenance procedures as calibration, configuration, diagnostics, troubleshooting, and device documentation (Fig. 1). The worker would have access to all the records, documentation, and loop narratives for each device.
Having the ability to take the control room out in the field is a tremendous asset in terms of freeing the people in the control room to do other things. Crews working in the plant do not have to tie up everybody’s time with just mindlessly stroking a valve; they can go out and do it and see it at the same time.
Applying the mobile worker concept to a process plant means equipping the field worker with a portable device that connects wirelessly, generally via wireless Ethernet, to the control room and gives that worker direct access to the control system display, but with the reliability and security of a wired connection. The equipment used is provided by the company, not the individual, and can be a tablet or other handheld device, typically a hardened laptop or tablet computer (Fig. 2.). This is a considerable advance over previous remote DCS client methods that used intranet or Internet connections and required the mobile worker to plug into a plant local area network.
The system can also be set up to allow a control room operator to see what the worker in the field sees. This can even extend to video, if the field worker has the equipment to do it. Such a system can also be used for personnel and asset tracking, which is useful for safety, and for safety mustering. If a person doesn’t move within a certain time (perhaps having fallen or been overcome in some way), the system could set off an alarm.
This can pay for itself in the first or second turnaround. And the good news is, many plants already have wireless systems installed, so no new communications infrastructure would be required. And even if such a system is not in place, the investment is moderate compared to a refinery being down for an extra day.
Installing a mobile worker system
Trying to connect a field worker using the same networking techniques that a traveling salesman uses to contact the office is a recipe for failure. If a road warrior loses contact with his or her base, it is an inconvenience but does not stop all work. If a field worker controlling loops in a process plant loses communication, even for a few minutes, everything can grind to a halt. Security is another issue. Wireless security is probably not a top concern for the average road warrior, but it is vital in a process plant.
Most plants have two types of networks: a wireless field network and a wireless plant network (WPN), each with unique technical requirements. They are frequently used together, with the WPN carrying the field network traffic (which has a very small bandwidth requirement) as highest-priority traffic (Fig. 3).
Wireless field networks
A wireless field network is used for process applications such as measurement, sensing, control, and diagnostics. It connects field devices at ISA95 level 0, generally in a self-organizing mesh configuration, using message forwarding and communicating to higher levels via a gateway. Messages are generally short. Such systems are often deployed without an extensive site survey.
The field network most likely to be found in plants considering the use of mobile workers is WirelessHART as defined by IEC 62591, with radios compliant with IEEE 802.15.4. There are other protocols that offer similar capabilities. Components of the field network include wireless field devices, gateways that connect to the host via a high-speed backbone or other existing plant network, and a network manager, which may be integrated into the gateway, host application, or process automation controller.
WirelessHART supports the full range of process monitoring and control applications, including equipment and process monitoring; environmental monitoring, energy management, regulatory compliance; asset management, predictive maintenance, advanced diagnostics, and closed loop control.
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