Transponder timing

Transponder timing (also called chip timing or RFID timing) is a technique for measuring performance in sport events. A transponder working on a radio-frequency identification (RFID) basis is attached to the athlete and emits a unique code that is detected by radio receivers located at the strategic points in an event.

Prior to the use of this technology, races were either timed by hand (with operators pressing a stopwatch) or using video camera systems.

Generically, there are two types of transponder timing systems; active and passive. An active transponder consists of a battery-powered transceiver, connected to the athlete, that emits its unique code when it is interrogated.

A passive transponder does not contain a power source inside the transponder. Instead, the transponder captures electromagnetic energy produced by a nearby exciter and utilizes that energy to emit a unique code.

In both systems, an antenna is placed at the start, finish, and in some cases, intermediate time points and is connected to a decoder. This decoder identifies the unique transponder code and calculates the exact time when the transponder passes a timing point. Some implementations of timing systems require the use of a mat on the ground at the timing points while other systems implement the timing points with vertically oriented portals.

RFID was first used in the late 1980s primarily for motor racing and became more widely adopted in athletic events in the mid-1990s on release of low cost 134 kHz transponders and readers from Texas Instruments. This technology formed the basis of electronic sports timing for the world's largest running events as well as for cycling, triathlon and skiing. Some manufacturers made improvements to the technology to handle larger numbers of transponders in the read field or improve the tolerance of their systems to low frequency noise. These low frequency systems are still used a lot today. Other manufacturers developed their own proprietary RFID systems usually as an offshoot to more industrial applications. These latter systems attempted to get around the problem of reading large numbers of transponders in a read field by using the High Frequency 13.56 MHz RFID methodology that allowed transponders to use anti-collision algorithms to avoid tags interfering with each other's signal during the down-link between transponder and reader. Active transponder systems continued to mature and despite their much higher cost they retained market share in the high speed sports like motor racing, cycling and ice skating. Active systems are also used at high-profile events such as the Olympics due to their very high read rates and time-stamping precision.

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