Active and Passive timing systems

The active transponder is not a new technology. Since AMB started in 1982, systems have evolved so much… until today. Do you know how an active timing system work?

The difference between an active and a passive system is that an active system transponder carries its own power supply, such as a battery, while a passive system tag needs the reader’s signal to be activated. The active system tag is incorrectly called a transponder and not a passive one. Technically, both are transponders.

How do active systems work? 

There are currently two different types of active timing systems on sports timing: phase-based timing systems, for example, MyLaps system, and intensity-based systems (RSSI), i.e. all the others.

Phase based system: MyLaps

Mylaps has developed a system in which the reader throws signals that are constantly “calling” in case a transponder passes by. If a tag passes over the reader’s antenna, the tag is “awakened” by the signal received from the reader and emits an electromagnetic signal, which is then received by the reader’s antenna. Up to this point, it is easy.

How the signal is sent from the transponder to the reader and collected by the loop antenna is the real magic of this system. What’s coming next is not easy to understand.

An electromagnetic signal is composed of its intensity and its phase. They are always alternating signals that have these shapes:

  • Intensity and power are directly related: the greater the signal intensity, the greater the power.
  • The phase is related to the moment the signal is found. As you can see in the graph, the signal can be at a maximum up, at a minimum down or at any point in between, including the point where the signal is equal to zero. 

The reader’s antenna that detects and receives the signal is a loop antenna placed on the ground and it has a rectangular shape, normally. You can see it in the following picture:

These antennas radiate in this way:

As you know when distance increases the power decreases. A tag or transponder that approaches from the left side will emit a signal that will be received with greater intensity by the left side of the loop. The tag will continue its path until it passes over the left part of the loop and will continue to move to the right until there is a point where it begins to be closer to the right part of the loop. At that exactly moment, the electromagnetic strength exerted by the chip on the loop changes from one side to the other, changing the direction. 

An example, imagine you have a hose full of water. First you blow on one side and then you blow on the other: the water changes its path. This explained in electromagnetic terms behaves similarly to the following picture:

Another example: imagine that you are standing on a wooden board and the wood is on an edge. All your weight will be on one side only, if you slowly move your weight to the opposite side there will come a moment when the board will move to the contrary side even if the existing weight change is minimal.

This is called a phase change. And this phase change is very easy to detect electronically and, most importantly, it is very accurate. That’s why Formula 1 is timed with MyLaps technology. 

Intensity based systems: the others

The other active timing systems usually work by incoming power or RSSI (Received Signal Strength Indicator).

The theory says that the stronger the signal received by your active transponder, the closer the tag will be to the centre of the antenna. But in practice, this is not so easy.

If we use our Pixelcom colleagues kart timing system as an example, we will see that they use a 1D antenna because they know in advance how the transponder is gonna be placed in the go-kart, so they only need one dimension. In other words, they have a single RSSI or received power value. They will keep the highest value of received power to obtain the crossing time.

When timing a triathlon, and you must know that there is nothing better than an active system for timing a triathlon, we do not know in advance what orientation the active transponder will have when it crosses a timing point: the athlete can arrive by bike, running or swimming. In the first two cases and caused by the movement of the athlete, the tag placed on the ankle can change its orientation from the ground and the antenna therefore has to change its axis.

This is the reason why it is more interesting to use 3D antennas. A 3D antenna indicates the power received on each Cartesian axis. So, instead of working with one dimension and one RSSI value, it is necessary to work with three dimensions and that complicates the calculation. 

It can occur that a maximum on a rear axle can be greater than that on a front axle, and so an endless number of combinations. It is essential to refine the calculation: is easy to obtain an accuracy of around 0.2 or 0.3 seconds. But obtaining a precision below, for example, 10 times less, is extremely complicated.In fact, at timingsense we think that certain manufacturers do not tell the truth about the accuracy of their systems and overestimate it: because it is very difficult to reach an accuracy of 0.02 seconds.

In this post, we’ll tell you how we’ve achieved greater real-world accuracy on timingsense and why our active system is better than anything else on the market right now. We give you a clue: it allows you to time a timing point with just one mobile phone, amongst others.