Extended-life magnetic heads help achieve the ultimate gate
maintenance goal: cost-reduction and minimal downtime
during peak periods.
Worldwide, magnetic ticket technology has made life easier for millions of travelers. But surviving the harsh environment of a subway, bus, or parking lot is no easy matter for the tiny component that makes magnetic ticket technology possible: the magnetic head.
Not only does this electromechanical device have to "read" and "write" information such as point of origin; date of issue; value of the fare; and in stored value cards, the balance remaining--it must do so in the time it takes a traveler to "swipe" a ticket through a slot: about 21 milliseconds. And the magnetic head must do this thousands of times each day.
Consider, also, that this precision component functions in temperatures that can range from below zero to a hundred degrees plus--where dirt, dust, wind, and spilled sodas are a way of life--not to mention the folks who get their kicks sticking strange objects into ticket slots. Even the tickets themselves are abrasive to the head's surface.
Mass transit operators are turning to extended-life head technologies to reduce maintenance time and achieve scheduled maintenance goals--reducing costs and avoiding downtime during peak travel periods.
Applying the Product to the Real World
Metropolitan
Atlanta Rapid Transit Authority (MARTA) has evaluated three extended-life
heads in ticket encoding machines since 1993. New paper tickets are very
abrasive, especially in their first-pass state. All three heads are still
going strong--one of them has even recorded an incredible 40 million
cycles.
While MARTA's ticket encoding equipment is in a "clean" environment, extended-life heads have a far less friendly home in the New York subway system. Cubic Automatic Revenue Collection Group (CARCG) has installed heads from Brush Industries Inc. throughout the MTA New York City Transit System as part of the new "Metrocard" fare collection system (see Mass Transit Sept/Oct. 1994).
Raymond L. DeKozan, Chairman and CEO of CARCG, calls the New York program "the largest of its type anywhere in the world, and the first to incorporate 'Swipe Read/Write' technology." The heads are installed in electromechanical turnstiles that accept tokens as well as Metrocards.
"In part due to the heads, the reliability of this equipment has dramatically exceeded all contractual requirements," says DeKozan. "The contract calls for 120,000 cycles between failure. Monthly figures have at times exceeded two million cycles." Since the equipment was installed in January 1994, cumulative reliability rates in excess of 660,000 MCBF have been achieved (a cycle equals one swipe of a Metrocard through the slot).
"When we say the turnstile has this reliability rate, there are several components that have failures other than the reader heads," continues DeKozan. "The reader heads certainly contribute to that high rate, and are one of the most reliable features of the system. And preventive maintenance of these heads is simply swiping through a head cleaner card." To the MTA, the high reliability has resulted in half the number of maintenance calls of the existing, older turnstiles. This is especially impressive performance considering that the older turnstiles simply accepted a token and released a tripod to turn. The new turnstiles do this, too but they also have reader heads, an electro-mechanical comparator that rejects slugs, traffic lights allowing the customer to set entry/exit directions for flow, and a communications system giving an LED display of remaining card value. Even with all these features, the new turnstiles require only half as many maintenance calls.
Cubic, which designs and builds integrated fare collection systems worldwide, has also installed extended-life heads in the Washington Metropolitan Area Transit Authority (WMATA) system and in Atlanta, Miami, Hong Kong, Singapore, and London..
Another international manufacturer of automated fare collection systems is Compagnie Generale d'Automatisme (CGA). With equipment in place in the United States, Brazil, Venezuela, Chile, Paris, Korea, Cairo, and other countries, CGA has a huge interest in extending magnetic head life.
"Of course, the cost of long-life heads is higher, [but] in the long term you have a benefit because they will reduce your yearly expense in terms of magnetic heads by a factor of three to five," says Pierre Lereboullet, Director of the Public Transport Department of CGA. "That far exceeds the additional cost [of upgrading] from a regular to a long-life head."
Understanding Technology
The
standard magnetic head is basically designed for such "clean"
applications such as tape recorders and computers. Standard heads usually
perform well in laboratory tests, but have such short life spans in field
use that even the least expensive heads, in terms of initial price,
ultimately prove very costly, as they continually fail in service.
In 1969, the first of a series of proprietary methods of manufacturing metals was perfected. This unique technology resulted in materials that are physically tough, while retaining good magnetic properties. The heads were used in professional videotaping and playback.
Proprietary alloys and designs resulting in longer and longer lifespans continued to be developed. At the same time, applications for magnetic heads moved into the digital realm. As magnetic stripe technology advanced, physical materials were sought after that would keep pace with demands for high traffic installations.
For example, in 1987, Brush Industries introduced Supermium®, a completely new alloy of iron, silicon, and aluminum. Supermium® is used for the core of the head, the place where the magnetic activity occurs. Alone, Supermium® delivered 18 times the lifespan of the "mu metal" cores than considered standard technology. When the surface of the head was coated with ceramic, the heads were able to last more than a hundred times as long as standard heads.
"Failure" may not necessarily mean the head's surface has become worn, but that electrical performance is not being achieved. In Bucknell University's study, heads were eliminated when they became unable to sense the prerecorded signal with sufficient voltage to render the signal useful.
Heads with mu metal cores, even when coated with ceramic material, suffer "gap erosion" and "scalloping" after a relatively brief period of time. The gap across which the magnetic field is created can smear or plug shut. Or it can "scallop," as repeated contact with magnetic stripes wears away the softer mu metal core. Gap edges in ferrite core magnetic heads can become brittle and break, causing failure.
CGA's Lereboullet believes that magnetic ticket technology has a future in mass transit operations. "There will continue to be categories of travelers using single journey tickets that will require magnetic tickets," he says. "Therefore, technological improvements in the magnetic field are important for the mass transit industry. Among other factors, the lower cost of magnetic ticket technology will continue to make it an attractive choice. The industry is talking very much about contactless, but we feel there is a future for the two technologies to live together."
Reprinted from Mass Transit May June/1995
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