saigonij
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| posted on 19/7/08 at 04:44 PM |
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Smiths Speedo Calibration - Help Needed
Hi all,
I need help calibrating my Smiths telemetrix speedo...
My tyres are 205x45xR16.
my DIF is 3.62
The tyre travels 71.5 inches in one full revolution.
someone ( zetec ) said that the standard MT75 produces a calibration number of 8000, but im a bit stuck.
the website is not much help. it tells you have to caluclate the revolutions per mile, then seems to skip and goes straight on to calibrating using
magnets on a prop - which mine is not - it seems ti miss out the Hall Effect speed sensor information all together!
help please! do i just stick the 8000 in that the MT75 is meant to produce?
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mad-butcher
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| posted on 19/7/08 at 06:32 PM |
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Hall effect sensor, Number of poles on sensor x cable drive revs per mile or kilometre = calibration number
greengauges.com
far easier to use this option
 
Rescued attachment speedo pickup mount.jpg
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snapper
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| posted on 19/7/08 at 09:14 PM |
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The gearbox means nothing, its only the rotation of the wheels, so all the sensing is done post gearbox.
If you have hall effect the you sense rotation off passing bolt heads, if you have magnets you sense off passing magnets.
You could use the gear ratio calculator and workout what speed the car will be doing at say 20 mph (not to much if you have the car on stands and you
are in first) then compare that with speedo and modify calibration to match
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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saigonij
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| posted on 19/7/08 at 09:25 PM |
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im using the mt75 speed senser, so there are no bolts or cable turns. its running directly from the speed sensor
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snapper
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| posted on 20/7/08 at 06:51 AM |
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If it senses off the back of the gearbox you need to know howmany pulses per revolution.
Wire a bulb in to the sensor. power to bulb wire from bulb to sensor earth other side of sensor, rotate prop 1 revolution count pulses.
My calculation for 4 pulses and your setup comes out at 12831 or 6415 for 2 etc
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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zetec
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| posted on 20/7/08 at 07:59 AM |
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You need to sus out pulses per mile. You can count the number of times your prop turns over a measured distance..For example measure out a set
distance, for example 1/50th of a mile, mark your prop and push the car over the set distance and measure how many times the prop turns. Get the
calculator out and work out revolutions per mile...times this by number of pulses your speed sensor gives per turn of the propshaft and you have the
answer. Try it 3 or 4 times to try and get a more accurate figure. Works well because it takes the amount the tyre squashes into account. Then go for
a drive with a Satnav and see if you are accurate. I didn't have a satnav to check mine but was within 2% accurate and easily passed SVA.
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saigonij
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| posted on 20/7/08 at 08:05 AM |
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i dont know how many pulses my speed snesor gives out.
this is all very confusing!!! :-)
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mark-wiring
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| posted on 20/7/08 at 09:05 AM |
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Stole this off another web site hope they dont mind;
Tyre Revolutions per mile x Diff ratio x Transducer Pulses per revolution/ Speedometer drive Ratio
= Number of pulses per mile
Which in your case i think works out to;
886x3.62x7x4/22=4082
http://www.v10viento.co.uk
Have to recommend
http://www.extraefi.co.uk/
For all Megasquirt needs
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saigonij
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| posted on 20/7/08 at 03:16 PM |
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i think the speed sensor gives out 8 pulses per rev, as when i had it set to 4054 it was showing 60 mph by the top of the road - which i dont think
was my true speed!
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saigonij
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| posted on 21/7/08 at 04:23 PM |
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i called CAI today, and after giving them my details, he called back and said the number is 7824!
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zetec
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| posted on 23/7/08 at 12:38 PM |
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There you go, I said it was about 8000 ish. 
" I only registered to look at the pictures, now I'm stuck with this username for the rest of my life!"
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