1 March 2007
Building the perfect beast
The ISA-100 wireless use-case process reveals unique characteristics of industrial facilities
By Paul Sereiko
What do wind farms spanning hundreds of square miles in the North Sea, robots on a Detroit auto assembly line, West Texas crude oil fields, East Chicago sewage treatment plants, and South Dakota fertilizer-manufacturing facilities all have in common?
First, each has real, defined applications to employ wireless sensors and actuators in their operations. Second, each has taken the time to share their needs with the ISA-SP100 Wireless Systems for Automation committee through the development of a "use-case."
Outreach effort to gather
The ISA-SP100 formed in 2004 with the charter to establish standards, recommended practices, technical reports, and related information for implementing wireless systems in the automation and control environment with a focus on the field level.
Since then ISA-SP100 has grown significantly with 250+ companies represented on the group mailing list, 50-60 attendees working at quarterly meetings held around the globe, and scores of participants in the weekly teleconferences.
It is in these weekly meetings where this all-volunteer army of scientists, developers, engineers, end users, and product managers get the bulk of their work done. Much of this work involves in-depth knowledge of radio technology, interoperability of radio systems, field bus architectures, and other highly technical information.
If the committee only relied on the expertise its active members brought to the process, the resultant standard might be very elegant technically, but could run the risk of limited market applicability. To eliminate this risk, significant input is necessary to understand exactly how end users intend to use wireless technology in their facilities.
Given the wide range of applications for wireless sensing and monitoring, ISA-SP100 realized the importance of soliciting user input from a large audience, and in June, the ISA-SP100 Marketing Work Group began an outreach effort to gather use-case information from a broad base of end users.
Needs through technology
So, what is a use case? It is a description of a process or task an end user feels could take place more effectively and efficiently by leveraging wireless technology.
The challenge of creating a use case lies in gathering information from the user in a language the user understands and then communicating that information to the ISA-SP100 technical committees in terms relevant for wireless system standards design.
To address this challenge, the ISA-SP100 Marketing Work Group and a team of end users created a standard template for gathering information. The three major elements of this template include:
- Site description: The size, environment, construction, and regulatory requirements of a facility all have an impact on wireless communications effectiveness. It is also important to know whether the facility needs to have blanket wireless coverage, or if hot spot wireless is sufficient.
- Wireless application: This section answers the following questions. What is it you want to do with wireless? How does the handling of this application transpire now? Which groups and systems use the information generated from the wireless system? How large is the application, which is to say, how many end points? Are the end points fixed or mobile? Do they require batteries to operate or not?
- Task description: For the wireless standards designer, this section contains some of the most specific information. It includes information on the sensor and actuator types used in the application. How much data do these sensors generate? How frequently must they be read and under what circumstances? Do we need to know exact read-time of the information? Once read, how quickly must the network transport this information to other elements of the plant network? Finally how secure must the system be?
The committee collates this information using phone interviews and e-mail exchanges with willing industrial participants.
Clusters of wireless needs
The use-case process is an ongoing one.
To date, over 80 companies have agreed to supply information to ISA-SP100 from a sampling of the following industries:
- Oil and gas
- Food processing
- Waster water treatment
- Nuclear power generation
- Electric power generation
- Aircraft manufacturing
- Consumer products manufacturing
The process is yielding a wide range of interesting results, some expected and others surprising.
It is not surprising, for instance, that industrial facilities are large. The smallest of the surveyed sites thus far is 10 acres, while the largest, a wind farm, is the size of a small city.
At first glance, this would indicate a requirement for massive deployment of wireless infra-structure. However, in fact, further questioning indicates the actual area of wireless coverage that facilities expect is far smaller than the facility itself.
Thus, hot-spot coverage that can grow through a "tiling" model, as need dictates, seems the most practical solution.
Further, there is an array of applications end users see for wireless. Within the ISA-SP100 database, some companies would like to:
- Transmit tolerance information from robotic assemblers to robotic controllers over a distance of less than 10 feet as the robot inserts thousands of fasteners per shift.
- Monitor the level of chemicals that slowly change over time in a tank farm covering hundreds of acres.
- Gather multiple sensor readings periodically from windmills in the North Sea and transmit that information to control centers hundreds of kilometers distant for improved preventive maintenance procedures.
As disparate as these applications are, the physical variables monitored, and more importantly for wireless system design, the rate at which these variables change cluster nicely around three time intervals-milliseconds, seconds, and multiple minutes.
This data becomes more meaningful when end users report their power requirement needs for their wireless systems.
A significant majority of the ISA-SP100 use cases indicate a need for battery operable field devices.
Thankfully, end-user battery life requirements do not show wide variance, with an expected life of four-five years seemingly sufficient to meet most user needs.
When taken in context of the information presented, wireless standards developers have a powerful set of information from which to work toward standards creation.
- The standard will need to address power management and battery operability characteristics.
- Network design should allow for hot spots, scalability, and integration with existing plant infrastructure.
- The standard should allow for products creation that matches the performance demands of specific classes of user applications.
The information presented in this article represents only a small sample of all that is coalescing in the ISA-SP100 use cases. Security, network management, integration with legacy systems, and packaging/regulatory re-quirements are receiving due scrutiny as well.
ABOUT THE AUTHOR
Paul Sereiko (firstname.lastname@example.org) is co-chair of the ISA-SP100 Marketing Work Group and president of KAPM Strategic Management, a wireless systems consultancy. He founded Sensicast Systems. He has a computer engineering degree and an MBA.
Refinery: Relief valve
Petroleum companies are among the largest worldwide consumers of control and automation products, so it is no surprise they are one of the constituencies that is anxiously awaiting the emergence of wireless standards for industrial automation.
A relief valve in an oil refinery is a purely mechanical device used to protect equipment from overpressure. It protects the refining process when it is out of balance.
A typical refinery covers over 20 acres and can have between seven and 10 different processing areas where hydrocarbon emissions can occur. Each of these areas is roughly 100 square meters and can contain a 200-or-more relief valves.
Gas pressure builds up for various reasons in the refinery setting. When it goes above a predetermined, safe level of pressure the relief valve opens and gas vents to the atmosphere. When the pressure drops to an acceptable level, the relief valve closes.
The government monitors these gas emissions, and if they exceed established thresholds, the refinery must pay a fine. Therefore, there is monetary benefit in controlling these emissions.
The question is how to monitor and measure gas emissions from a purely mechanical device? Well, actually make that over 1,000 mechanical devices spread over a discontinuous square kilometer. Enter wireless.
In this application, there is no power readily available, and the total cost of running a power or control wire to each of these valves is prohibitive.
However, there is one physical variable that we can be sense-it is the hissing sound gas makes as it escapes from the valve. By monitoring the volume and duration of the hissing sound from the valve, estimates of the amount of gas going to the atmosphere are possible. This information then transmits to the process control system's data historian for logging and archiving.
Several automation companies are now working to develop battery operable acoustic sensors and wireless transmitters to capture this information and ensure the refinery remains in compliance.
The next logical step would be to feed the emission information and the location of the emitting valves back into the control system to enhance the efficiency of the process thus further reducing emissions.
Steel plant: Giant furnaces
There are few places more inhospitable to a sensor than a steel plant.
Extreme temperatures and harsh chemical, metallurgical, and mechanical processes make any monitoring a challenge.
At a point in steel making, electrical current often arcs to the sides of the furnace. This super heats the furnace wall, sometimes overloading its temperature control mechanism.
If the cooling system fails, the molten steel could burn through the walls of the furnace in a matter of minutes, allowing molten metal to pour out onto the shop floor, endangering workers' lives and millions of dollars in equipment.
For one major steel manufacturer, it was critical to find an accurate and cost effective way to monitor and record temperature fluctuations within the water jackets of their giant furnaces.
They eventually chose a wireless sensor network.
With 24/7 production, there was almost no downtime to install or replace the sensors. They had to go in place quickly and during a brief cool period in the melting cycle.
Even during these "cool" periods, the temperature at the sensor site measures over 125°F.
The need for a quick installation, the high heat, and difficult positioning made installing wired sensors impossible. Moreover, molten steel splashing around would vaporize any wires it touched.
Simple traditional wireless monitoring techniques were out, too. Strong magnetic and electrical fields, plus the large masses of steel, would interrupt their transmissions, causing communication outages. In an application where a minute's delay can mean disaster, this was not acceptable.
The temperature sensing nodes went between the inner and outer walls of the furnace. They were able to withstand the heat from melting steel, wide temperature swings, powerful magnetic fields, water spray, and vibration.
The wireless technology routes data around any temporary trouble spots that might occur. Frequency hopping lets the smart sensors search out the best channel for clear communication. This insures a constant and accurate flow of information to the plant's maintenance and management teams.
Further, the technology accommodated an OPC system enabling it to deliver data directly to its control system. The company depends on this critical information to handle preventive maintenance and to eliminate unscheduled downtime that can turn a profitable steel plant into a loser.
- Power management and battery operability demand attention in
a wireless standard.
- Unwired network design should allow for hot spots, scalability, and integration.
- Any wireless standard must have room for specific classes of user applications.