I have noticed the GPS is slow to react to the change in speed of my vehicle. Maybe a couple of seconds. I have always supposed that this is the time it takes to get the signal from the satellite to the lorry. Is that right?
ChrisArbon:
I have noticed the GPS is slow to react to the change in speed of my vehicle. Maybe a couple of seconds. I have always supposed that this is the time it takes to get the signal from the satellite to the lorry. Is that right?
They update about once a second and calculate how far you have travelled in that second. So if you were doing 50 then 1 second later you had slowed to 40 then it would be showing 45 as that would have been the average speed over that second. (In fact I suspect they are damped further than that to take account for inaccuracies so you probably need to be going at the same speed in a straight line for 2 or 3 seconds to get a true reading)
The gradient would make a difference if it was steep enough, but it would have to be stupidly steep. Even on a 1:4 it would only make 1.7mph difference at 56 (now there’s a thought on the limiter on a 1 in 4)
I think the M90 heading towards Perth is 1:20 and that would only make 0.07mph change at 56mph to a GPS reading
I think Sonflower/Sunflower in Wales will correct us (me) if we make any errors, but dont GPS units work by comparing time signals from Satellites? Your in cab unit takes a time signal from multiple (4) satellites. The time signal sent out by these satellites is VERY accurately synchronised. Your in cab unit will receive 4 separate signals all saying 10hr00 but they will be received at slightly different times: the signal from the nearest sat will arrive first of course. By calculations inside the unit, taking the different times of receiving said signals, the unit can work out how far it is from these sats. By comparing two or more positions over a known time period your speed follows. Different units with different hardware and software may be more or less accurate. The software may update the speed at different intervals, and also update the display at different intervals, thats down to the unit. A unit that updates displays 10 times a second wont be usable after all ! If between taking position readings you swerved off the road, did a circuit of field, and rejoined the road, the speed would be way out, but in the real world that aint gonna happen.
I`m no expert so await corrections.
GPS 100% without any fear of being incorrect
raymundo:
GPS 100% without any fear of being incorrect
If a Tacho is set -up with a setting for tyres of diameter “x”, is fitted with tyres of “x plus delta-x”, and the tyres wear down to less than “x” at one point it will show the speed perfectly. It will be a bit like a stopped clock being correct twice a day, perfectly correct for an instant, but not necessarily useful!
Outside of Pure Mathematics, surely nothing is 100% correct? Or more accurately, if it is, how can one choose the !00% accurate result?
Cue a split into
a- philosophical treatise about the nature of accuracy
b- philosophical treatise about the concept of truth
c- philosophical treatise about whether Scannies are 100% better than Ivecos
d- choosing who`s got 100% real ■■■■ on page 3
mrcreosote90:
Would fitting different circumference tyres affect the speedo ?
even dozy couldnt come out with that question…or is this the new standard of steering wheel attendant ?
dieseldog999:
mrcreosote90:
Would fitting different circumference tyres affect the speedo ?
even dozy couldnt come out with that question…or is this the new standard of steering wheel attendant ?
Come on DD ! He`s asking about the circumference of the tyre not the diameter !
, and it has nothing to do with the elevation lmao, so what they saying the closer the gps is to the sky to more accurate it will be 
