Lap timing systems

Lap timing systems can be broken into 2 groups. The difference is in how they work:

1. Infrared beacon - most car and bike systems use an infrared beacon positioned on the pit wall to be used as a lap marker


2. Magnetic or inductive loop buried in the track. This is used by official lap scoring systems and most kart systems

Infrared is a light beam, at a higher frequency than humans can see. By putting an infrared beacon on the pit wall we have a light beam shining across the track waiting for your vehicle to come past and detect it. Imagine setting a normal battery powered torch on the pit wall pointing over the track - the only difference between the torch and infrared is you can see the torch, but not the infrared.

Magnetic - this is a loop buried into the track. This type can be further split into two types: A kart utilises the magnetic field given off by a loop to trigger a lap position. The lap timing systems used by race organisers use a transponder that constantly transmits a unique serial number that is picked up by the loop when the vehicle runs over it.

Infrared

There are 2 components to an infrared system: a beacon transmitter on the pit wall and a receiver mounted in the car. As this is a light-based system there must be a clear line of sight between the two components.

There are a range of frequencies in the infrared light spectrum, giving the opportunity to have many transmitter/receiver combinations on the pit wall so every team can use their own frequency if desired. While this looks appealing initially, it does have some drawbacks.

AiM have only 2 frequencies. All white beacons are on the same frequency and red split beacons are on another frequency

Pi - the most common Pi beacon is the 10 channel unit – with 10 user selectable channels. Higher end systems have more available frequencies. Pi have gone to the trouble of mounting a monster beacon on Pi Channel 0 in most UK circuit pit walls. This beacon is used by some non-Pi systems but can be unreliable as organisers often turn it off (particularly for track days).

MoTeC have up to 999 different frequencies that users can select from. Other manufacturers run on their own frequencies.

Magnetic loops

Magnetic loops are installed at all kart tracks and most have one or more split loops. There are now magnetic loops installed at all UK car tracks with the exception of Silverstone.

Karts are well suited to this kind of system as they are very low to the ground. As the distance from the buried loop to the receiver increases, these systems become less effective.

The organisers' lap timing equipment is generally manufactured by AMB. This is a very effective system for the organisers to have a reliable lap timing system but is not available for in-vehicle lap displays/data logging.

AiM systems

All use the same beacon. There are 2 types of receiver where the only difference is the length of the cable from the receiver. Car systems are approximately 2.5m and bike systems are about 0.4m

Exceptions: There were a limited number of TG lap timers made that are tuned to run off the circuit beacon 0. These are clearly marked with "UK circuit beacon" on the display body and receiver and on the screen when it is first turned on.

MoTeC

MoTeC make the very expensive BTX transmitter and currently use the BR2 receiver. Earlier BR1 receivers are still in common use. It is possible to configure a MoTeC to use other receivers such as Pi and AiM.

Others

Some low cost lap timers will work off a wide range frequency – even television remote infrared. These units trip off the first infrared beacon transmitter they see, regardless of manufacturer.