How to measure the accuracy in an active transponder?

An active tag must be accurate, reliable and durable. In our last post we explained why the timingsense active chip was the most durable on the market. Today we are going to explain the other two most important features: accuracy and reliability.

When talking about accuracy, the initial challenge is how to reliably measure it. You need to keep in mind the active chip can produce readings ranging from 100 milliseconds (ms) to 50 ms, 10 ms or even less.

The active transponder receives a low-frequency signal to detect the passing of a chip. The chip has a 3D antenna to detect the signal from whatever direction it comes from. The closer it is to the center of the reader’s loop antenna, the higher the power. The farther it moves away, the lower until it disappears.

chip activo modo broadcast

Being a 3D antenna, it has 3 axes on which the power is distributed. If the chip is fixed on a bicycle, the signal can become predictable. When the chip is on a moving ankle, this is not possible. Therefore, we must define an algorithm that gives us the highest possible accuracy no matter which axis the power comes from. 

Ways of measurement

The first way we thought to measure the accuracy in timingsense was to compare it against a photo finish system with about 1000 frames per second, which gives us an accuracy of 1 ms. The problem with this system is its price but, more importantly, it is expensive to extract the step times at each pass (or athlete step) and compare with the chip step times. Anyone who has seen one of these photo finish systems working will know how un-automated the process of extracting the exact passing time is.

At this speed, if we separate the tags by 20 cm, we should see a separation of about 20 ms between each chip. Also, the order of the chips is perfectly known when placing them on the holder. 

The time separation is something really easy to measure, that’s what the Classic Loop Box does; it delivers a sequence of chips with their passing time among other things. So measuring accuracy becomes a very quick and automatable task.

And so… how accurate is the active timingsense system? After many measurements, modifications of the algorithm, working with the powers, the loop antenna shapes of the Classic Loop Box… The accuracy is 20 milliseconds, i.e. 0.02 seconds. This is real precision, not an inflated one.

We show you some of the many measurements we have made in the last few months. The important thing to see is the line spacing is the same. Not all passes are perfect, but they are close:

Active timing