Ben_Copeland
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| posted on 1/1/09 at 07:40 PM |
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Magnetic Sensor Problems
I've got a 4 magnetic pickup running off the prop. It's all connected to a Telemetrix Speedo. I'm having major problems
calibrating the speedo.
According to the instructions the calibration number is tyre rev/unit distance x differential ratio x 4. Now, according to the technical line its
worked out by taking number of inches in a mile (63360) divided by tyre circumference (i think its 70inch) times by diff ratio (3.9 escort) times by
4. But however i do it, the number i get gives incorrect speedo calibration and its either miles too fast or hardly reads at all.
Is there anyway of checking the magnets are all being seen by the sensor and has anyone else had similar problems? Any solutions.
Thanks
In Addition the Haynes Book of Lies says my diff ratio is 3.9 is this correct? The axle doesnt have any markings on it anymore to find out.
[Edited on 1/1/09 by Ben_Copeland]
Ben
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Howlor
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| posted on 1/1/09 at 08:06 PM |
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Here goes my thinking. I think the math is correct up to the divide by 4 bit. If you had just 1 magnet on the prop then you would miss out the 4 bit,
if you then have 4 magnets it will read that the prop is going 4 times as fast as it is. Therefore I think you should divide by the number of magnets
on the prop.
I think!
Steve
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Howlor
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| posted on 1/1/09 at 08:07 PM |
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Giving a figure of 882.5.
Steve
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Ben_Copeland
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| posted on 1/1/09 at 08:22 PM |
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Hmmm thats interesting !!
I will give that try and see if it comes up with anything in the table on the instructions
Cheers
Ben
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Ben_Copeland
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| posted on 1/1/09 at 08:27 PM |
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Na cant be that because the numbers too small to be on the chart... must be from 2500 to 135625.
There are a few websites with the instructions and they all say to times it.
Theres too many numbers and possible settings to guess 
[Edited on 1/1/09 by Ben_Copeland]
Ben
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Howlor
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| posted on 1/1/09 at 08:46 PM |
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Does it have a setting on the speedo for how many magnets you are using?
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omega0684
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| posted on 1/1/09 at 08:56 PM |
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i just worked out the figures and got the following results
63360 / 70 = 905.14 (2.d.p) (905 revolutions of the tyre per mile)
905.14 x 3.9 = 3530.05 (number of prop revolutions per mile)
if you have 4 bolts on your prop each giving off a signal then,
3530.05 x 4 = 14118 impluses/mile.
do my calculations add up?
make sure that your speedo is set up for calibration as well.
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Ben_Copeland
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| posted on 1/1/09 at 09:09 PM |
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Yeah, thats one of the calculations i've tried 69 , 70 and 71 inch tyres and none of the figures work out. The speedo has switches inside which
correspond to 0 and 1's on the table that match up to the pulses/mile.
So theres no setting up just switch the switches and try it again
The only thing i can think of is either the diff ratio is wrong or its not picking up all the magnets 
quote:
Originally posted by omega0684
i just worked out the figures and got the following results
63360 / 70 = 905.14 (2.d.p) (905 revolutions of the tyre per mile)
905.14 x 3.9 = 3530.05 (number of prop revolutions per mile)
if you have 4 bolts on your prop each giving off a signal then,
3530.05 x 4 = 14118 impluses/mile.
do my calculations add up?
make sure that your speedo is set up for calibration as well.
Ben
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Ben_Copeland
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| posted on 1/1/09 at 09:11 PM |
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quote:
Originally posted by Howlor
Does it have a setting on the speedo for how many magnets you are using?
No, just in the calculation of pulses/mile
Ben
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omega0684
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| posted on 1/1/09 at 09:28 PM |
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my speedo pick up sensor has a small light on it that flashes when it picks up a signal from each of the prop bolts.
its just hit me! i had a similar problem when i was setting mine up, you need to make sure that the sensor is positioned at the side of the bolt so
that it only triggers the sensor once (and therefore 4 times at equal intervals), if you place the sensor, so that the bolt crosses its path in the
centre it actually triggers the sensor 8 times at irregular intervals,
pulses would be like this
even l....l....l....l....l....l....l (sensor is place on the edge of the bolt so that it only triggers once) this will make your speedo read
correctly
odd l.l....l.l....l.l....l.l (sensor placed across the centre of the bolt) this will make your speedo not read correctly- each pulse (l) is for either
side of the head of the bolt, it crosses the first side and sends a signal, then crosses the opposite side after passing over the centre of the bolt
head.
[Edited on 1/1/09 by omega0684]
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Ben_Copeland
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| posted on 1/1/09 at 09:33 PM |
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Na, mines a sensor with magnets stuck onto the prop flange.
No light, no bolts magnets pass underneath the sensor.
Ben
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omega0684
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| posted on 1/1/09 at 09:36 PM |
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got any pictures? is it like this
[Edited on 1/1/09 by omega0684]
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prawnabie
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| posted on 1/1/09 at 09:41 PM |
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I think what he is trying to say is that most sensors can read the magnet in two places along the sensor, you may have the sensor fitted so that each
magnet is being read twice as it passes the sensor.
HTH
Shaun
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Ben_Copeland
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| posted on 1/1/09 at 09:46 PM |
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Taken from the instructions
The sensor can then be positioned as close as possible to the magnets, using a suitable bracket for the particular installation.
N.B. It is vitally important that the sensor is mounted directly opposite the magnets as they pass its probe, any offset will result in an
unsatisfactory signal. A gap of up to 1/2 inch (1.25 centimetres), between the probe and the magnet can be tolerated by the sensor, but the smaller
the gap the better the signal.
Ben
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Ben_Copeland
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| posted on 1/1/09 at 09:50 PM |
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quote:
Originally posted by omega0684
got any pictures? is it like this
[Edited on 1/1/09 by omega0684]
Yeah thats it 
Ben
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Ben_Copeland
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| posted on 1/1/09 at 09:53 PM |
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clicky linky
Thats the kit i've got, except my magnets are different. round and thicker???!?!?!?!
Ben
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omega0684
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| posted on 1/1/09 at 09:56 PM |
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how far is your sensor mounted from the magnet? 1/2" is a massive gap! i would say ideally you want it about 1-2mm at most, mine is about
1mm.also r u using a shielded wire to run the signal up to the speedo?
just clicked the link you put up as well and it says
"WORKS WITH ISSPRO ELECTRICAL SPEEDOMETER. SOLD SINGULARLY."
maybe it only works with that speedo? i found that with my speedo, i paid £100 for a brand new CAI speedo and then ended up paying £35 for the
sensor kit
just throwing ideas at you now fella
[Edited on 1/1/09 by omega0684]
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Ben_Copeland
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| posted on 1/1/09 at 10:01 PM |
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Its about 1 to 2mm i think.
No shielded cable... but the cables that come out the sensor aint shielded either.
I'm starting to think i'm going to have to buy a new sensor, maybe a different type... but it's another £40 odd quid that i dont
need to be spending
Ben
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omega0684
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| posted on 1/1/09 at 10:09 PM |
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could you not return the one you've got and say that its not compatible with your speedo and therefore its not fit for purpose, they should give
you your money back.
or
buy the speedo that goes with it,
Speedo linky
mind you they are £194 and £110
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Kev99
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| posted on 1/1/09 at 10:14 PM |
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Cant u guess a setting then adjust from there. If u know what way u need to go up or down on the number's that's what I did. I had a
satnav with me as it gives a mph reading so I knew what speed I was doing.
Kev.......
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Ben_Copeland
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| posted on 1/1/09 at 10:14 PM |
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Think i'll have to get a caerbont speedo sensor.
i prefer my speedo ta  link
The sensor came with the speedo (2nd hand, but never used) all i have to say at this point is BALLS
Ben
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omega0684
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| posted on 1/1/09 at 10:21 PM |
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very nice speedo, i was actually looking at that one myself.
have you tried connecting a low voltage LED or light to the end of the wires and seeing if it lights up or even connecting the wires up to an avo so
that you can see the needle move when the magnet passes the sensor
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Ben_Copeland
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| posted on 1/1/09 at 10:36 PM |
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I've tried it on a meter, watched the ohms drop out as the magnet passes. and they all appear to work.
I think i'm going to have to get this one
At least its the correct one for the job and if that dont work there is something else wrong !! SVA papers are in so i'm in a hurry to get it
all finished so i dont get a shock when the date comes back !
Ben
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NeilP
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| posted on 1/1/09 at 10:46 PM |
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Ben,
I have the same speedo - Could only make it work with the inductive sensor not the magnetic reed switch...
Linky
Still not great above 80mph - Going to try shielding the cable next and then ensuring a clean 12v supply to the gauge.
HTH, Neil.
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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Ben_Copeland
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| posted on 1/1/09 at 10:49 PM |
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Thats crazy... why do they do the kit and include it in the instructions if it doesnt work 
and its going to cost £60 for that sensor
[Edited on 1/1/09 by Ben_Copeland]
Ben
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