When Safety Matters: Using Active RFID Down the MinesFebruary 1, 2004 By: Sven Haagensen Ph.D.
RFID technology can help businesses in many ways. But the greatest promise may lie in enhanced security, access control, and safety for workers in dangerous environments. The RFID system Watcher-ATS has proven particularly useful in mining and offshore oil platform applications.
It's been said that if you think safety is expensive, try an accident. Growing demand for safety in workplaces around the world has resulted in tighter regulations. Keeping track of people and equipment for safety and security can be a personnel-intensive, time-consuming undertaking that diverts attention from an organization's primary business activities. Attempts to automate these basic, but not directly profit-generating, tasks are reflected in a wide range of products. Bar-code and card-based systems dominate the marketplace. However, RFID enjoys several advantages over bar-code systems that make it a better choice for many security and safety situations.
RFID comes in two flavors: passive and active (see "Basics of RFID Technology"). Passive RFID has a reading range of ~1 ft. and is widely used in supply chain and logistics systems. The main advantage is that the tags need not be visible from the reader's position (e.g., to avoid the loss of expensive tools, you can embed tags in the metal).
In an active RFID system the tags have their own power source and transmitter. An active tag can be read up to 300 ft. away, thus broadening the applicability of an RFID system.
Current Security and Safety Systems
An RFID system using active tags is a versatile tool in situations involving restriction of access, movement monitoring, communication between operators and a control system, and locating colleagues in an emergency. You can also tag hazardous equipment, such as gas flasks. In an active RFID system, access control is an inherent feature. Safety and security is the new dimension that opens up.
Let's consider a typical scenario encountered where bar codes or cards are used. A group of people approaches a controlled door. One person will pull out an access card, swipe it, and then courteously hold the door for others?including people the cardholder may not know. If an accident happens, you know who passed the main gate but you do not know where any people in need of rescue are within the facility.
Picture a mine with several tunnel zones. Management is required to know which tunnel each worker is in at all times. Neither workers nor management would accept a system that required all personnel to leave their vehicles so they could pull their ID cards when transiting the zones. Such a system is cumbersome to use and results in greatly reduced efficiency?the frequency could be a stop at every half mile of tunnel! Typical road tolling systems cannot address the problem: If they read the worker's tags in a passing bus at all, few if any systems can read all the tags in a short time frame.
In contrast, a system such as Watcher-ATS can accurately read the tags of an entire busload of workers passing at 40 km/h (25 mph). (See "Watcher-ATS in Action" for a scenario with active RFID.) To achieve this, care has to be taken when tuning the equipment and Watcher software to the application.
Watcher is a software application that is at the heart of the Watcher-ATS system. It is installed on a server. You define PC clients that connect to the server and configure the RFID equipment in the software. You can also integrate additional systems, such as video surveillance and fire alarms.
A tag sends its unique ID to the RFID interrogator (reader). Watcher receives this info, updates tag position in real time, and notes the time of the previous reading. All data, reports, and statistics are handled in the Watcher database. The communication interface is open, so units can exchange data using TCP/IP, RS-232, RS-422, UHF, and VHF.
Watcher-ATS allows you to define and adjust zones while the system is operating. Zones may be overlapping, but field strength measurement still locates the tag (see Figure 1).
Figure 1. Two zones (A and B) each have one antenna. A tag (the red dot) is located between the zones. The tag "belongs" to zone B until the field strength registered by zone A's antenna is greater. Each antenna's signal strength received from the tag is indicated beneath the antenna. Zone B's antenna has a field strength reading of ?15 dB, compared to ?22 dB for zone A's antenna, so the tag is closer to zone B than zone A. The history of the tag (previous readings, indicated by the tinted red dots) indicates that the tag belongs to zone B, because this was the last zone it was in. This history information is especially useful in cases where the field strength measurements are equal or where sudden jumps in the field strengths occur.
The number of zones that can be defined is virtually limitless. Reading ranges can be set between 3 and 300 ft., and the frequency of tag identification can be set to comply with the realistic traffic of tags in the zone (higher frequency in a heavily used entryway and lower frequency in a less-used portion of a tunnel, for instance). The more complex the facility, the more of these options need to be used.
The designer of an active RFID system faces many pitfalls. In order to locate tags, you have to define a geographical zone and locate a minimum of one antenna in the zone. Using several antennas enables more accurate tag positioning using signal strength measurement. There are reflections from walls and equipment to take into account, and in buildings or process industry facilities involving multiple vertical levels, you want to locate the tags on the correct level. In addition, software algorithms must work together with the right equipment to avoid several antennas simultaneously reading a tag or, for a tag within range of several antennas, allocating the tag to one zone.
The Watcher-ATS system has been successfully installed in the ore mines of Swedish giant LKAB. An oil rig installation is being designed, with yet more challenges: reflections from buildings and equipment, multiple levels, and the fact that the placement and tuning of antennas is influenced by the liquid contents of tanks. Water-based liquids absorb frequencies differently; high frequencies allow higher tag identification rates and give a longer range, but the signals are also more easily stopped by walls and other obstructions.
In the case of an oil rig, RFID equipment must comply with the ATEX standard, meaning that it is intrinsically safe (IS) in an "Eex" environment (where explosive gases are likely to be present). In addition, it must withstand shock, dust, and water according to ingress protection classes (in Europe, the IP rating system).
A concrete oil rig platform base clearly illustrates the challenges involved. The space is vast in all dimensions and there is a lot of equipment and changing liquid levels. In an emergency, you need to know where your colleague is, not just that he or she is down on the base (see Figure 3). An access control system typically has registration gates between major structural parts, such as living quarters, production facilities, the oil platform base, and the lifeboat stations. In the mine scenario sidebar, the Carrier is mentioned. This is a handheld searching and communication device supplied by 24-7 Safety Systems. This miniaturized PC with a PDA-like user interface can be used to locate persons wearing tags. Using its own antenna, it acts as a direction finder?helpful to rescue personnel dealing with poor visibility. In noisy environments or locations with poor radio contact, the Carrier's onscreen info may be crucial to rescue personnel. Such an item may come in handy for everyday use as well. An operator can find other colleagues or communicate wirelessly through the system (using a wireless local area network, or WLAN). If you're an automation maintenance worker, you can read a valve positioner without having to bother the control room personnel (during the day, 40%?70% of their time may be devoted to helping maintenance workers). The Carrier may act as the operator's main field-logging and reporting tool, being plugged into a normal screen and keyboard when back in the office.
Making Active RFID Work
Active RFID systems have been improving considerably, and they present a versatile tool for safety, access control, and security. However, to make such a system your extended arm, it must be set up well and have a simple user and maintenance interface. The option of connecting an RFID system to the administrative and process control network multiplies the possibilities and potential payback of such an investment.
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