OT: Biodiesel

ISTR that early puncture warning systems worked by comparing wheel speeds. If one was consistently lower than the others, it was assumed it's radius had reduced due to lower tyre pressure. I'm not sure what the current sensing systems detect.

As for sat nav speeds, my speedo v sat nav reads about 10% low up to

50 the a steady 5mph low until my nerve runs out. The speedo is electronically driven analogue with 100,000 miles on it should that make a difference. The sat nav takes a couple of seconds to catch up when the speed changes. This is especially noticable when my enthusiasm is at work. As for bends however, 2 seconds makes very little difference. If the speed is high, the car cannot rotate through an arc small enough to make any real difference and if I'm driving like that the speedo is the last thing I'm looking at. If the speed is lower, the error due to resolution exceeds that of the speedo and, anyway, who cares how accurate these things are at 10mph. Much more useful are the warnings I get of speed camera locations. Not that I exceed the speed limit of course but they're only placed at accident black spots. Of course there is the theory that most of these accidents are due to drivers braking hard when they see the camera.

John

"AJH" wrote

Mostly above my head I'm afraid. My last foray into Doppler techniques was in the 1980's on radar systems where it can be used to discriminate between moving targets and stationary 'clutter' - different targets also produce a unique Doppler profile ISTR in tests that an Arab on a bicycle was particularly distinctive - though not too likely to be encountered on the battlefield! Anyway, with what little understanding I might have of the subject, I remain impressed with its application to GPS velocity measurement.

Great thread BTW - started off OT and drifted from there!

Nick H

John,

If you obeyed the speed limits you would not worry about the information of where the cameras are :-))

My Sat-Nav and speedo appear to change >

snipped-for-privacy@easynet.co.ukhttp://www.oldengine.org/members/dieselhttp://www.stationary-engine.c...>

ISTR that early puncture warning systems worked by comparing wheel speeds. If one was consistently lower than the others, it was assumed it's radius had reduced due to lower tyre pressure. I'm not sure what the current sensing systems detect.

As for sat nav speeds, my speedo v sat nav reads about 10% low up to

50 the a steady 5mph low until my nerve runs out. The speedo is electronically driven analogue with 100,000 miles on it should that make a difference. The sat nav takes a couple of seconds to catch up when the speed changes. This is especially noticable when my enthusiasm is at work. As for bends however, 2 seconds makes very little difference. If the speed is high, the car cannot rotate through an arc small enough to make any real difference and if I'm driving like that the speedo is the last thing I'm looking at. If the speed is lower, the error due to resolution exceeds that of the speedo and, anyway, who cares how accurate these things are at 10mph. Much more useful are the warnings I get of speed camera locations. Not that I exceed the speed limit of course but they're only placed at accident black spots. Of course there is the theory that most of these accidents are due to drivers braking hard when they see the camera.

John

You know me Martin, I always obey the speed limits. The warnings are to alert me to areas of great danger so I can slow down even more.

I've noticed that my speedo and sat nav change in unison when I'm in a slow van as well.

John

You obviously do not drive the sort of van I drive then :-)) I have yet to see whether technology and a 60's hot hatch go together.

You know me Martin, I always obey the speed limits. The warnings are to alert me to areas of great danger so I can slow down even more.

I've noticed that my speedo and sat nav change in unison when I'm in a slow van as well.

John

There ain't nothin' slow about the new vans....

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

Peter,

What you have to realise about John is that as he gets older its his perception of speed that slows down and as it was slow in his younger years it is now stopped relatively speaking. :-))

Martin P

Well since this is a group for stationary engine enthusiasts, I suppose anything that moves must seem quick :-)

John