Difference in Electronic timing and HLT

[SargeZ06]

Is there a way to adjust something to allow for a difference in what an electronic timing system shows and HLT?

Ex: Autox timing system is 0.4s longer than HLT.

Electronic time: 37.347
HLT time : 36.930

Seems to be related to a delay to start HLT when I cross the Start trigger.

Thanks for any ideas.

Sarge

[Harry]

As long as the triggers are set in the same spot like the transponder or other system is located, there is no delay or general gap introduced by LapTimer. The delay you are mentioning is about the signal you are hearing in real time - which is indeed deferred. The gap however is fully compensated in LapTimer's recordings as it can access the original time stamps.

In case you get a regular gap of 0.4s, please check your trigger positions. In case you get different gaps by lap, check your GPS / mounting position. Using LapTimer, you should get timing accuracies better than 0.1 or 0.05s - depending on the sensor equipment used. This is what you get from GPS systems and is directly dependent on the accuracy of the sensor input.

Harry

[SargeZ06]

We have staging area that we start from and cross the start rolling. Would how hard I leave the staging line effect HLT starting when I cross the start line? Does how hard I accelerate from the staging area make a difference?

[Harry]

What time do you want to record? In case it starts once you move, you will accelerate as hard as possible anyway. The faster acceleration or speed start up, the earlier LapTimer will start. However, we are talking about hundreds seconds.

- Harry

[gplracerx]

In my experience, using a standing start trigger fifteen to twenty feet before the timing line adds about one second to the time. Sixty foot times at a drag strip for a car on street tires are usually two seconds or greater. The accuracy is also going to depend on the speed at the line. I can see getting 0.1 second or better accuracy at a race track when you're going 100+MPH across the timing line. It's not going to be as good at 20MPH for the start and probably less than 60MPH at the finish.

[Harry]

Yes, for standard triggers, speed is relevant for accuracy. Higher speeds are better fro accuracy. That's simply a question of distance made good per second.

- Harry

[SargeZ06]

What time do you want to record? In case it starts once you move, you will accelerate as hard as possible anyway. The faster acceleration or speed start up, the earlier LapTimer will start. However, we are talking about hundreds seconds.

- Harry

I want it to start when I cross the starting line. How fast I leave the staging area will depend on wheel spin. Sometimes are faster than others.

[gplracerx]

If you are using the autocross assistant, then you are given the option when you set the starting line to either choose a standing start or a startling line. Don't pick standing start and set the start at the timing line, not the staging line. If you get a Staged button, when you approach the line, you picked the wrong one. If you select the track set in Lap List, you get a list of POI's, just start and finish if you used the AX assistant to create the course. Touch the Start line on the screen and you get the characteristics of that POI. Scroll down to the Trigger area and you will see a Type line that will tell you how the start is set to trigger. You want Go, not Standing Go or Stop/Go. Setting a direction is a good idea too.

[jwmelvin]

I do as gplracerx suggests and I also see a difference between HLT time and the optical system used at autocross. I use an XGPS160. The difference is generally a few tenths.

[gplracerx]

jwmelvin,

Me too. If I get times within 0.1 seconds, I'm pleasantly surprised. Usually it's more like 0.3 sec and usually faster than the timing lights. It's mainly that GPS accuracy is several feet or a couple of meters while the timing lights aren't going to change by more than a fraction of an inch. Not only is there a probability of an error when positioning the timing line by GPS, there's additional error in location when you make a run, including drift from when you set the line to when you make a run. That doesn't make much difference if you were crossing start/finish on a track at 100+mph. But it gets larger as speeds are lower. I suspect most of the error involves the starting line trigger.

Here's a post I did on GPS accuracy comparing a VBOX Sport, an Emprum Ultimate and and XGPS160: http://www.gps-laptimer-forum.de/viewto ... t=accuracy