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]

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

Giving a figure of 882.5.

Steve

Hmmm thats interesting !!

I will give that try and see if it comes up with anything in the table on the instructions

Cheers

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]

Does it have a setting on the speedo for how many magnets you are using?

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.

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:

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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.

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quote:

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Originally posted by Howlor
Does it have a setting on the speedo for how many magnets you are using?

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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]

Na, mines a sensor with magnets stuck onto the prop flange.

No light, no bolts magnets pass underneath the sensor.

got any pictures? is it like this



[Edited on 1/1/09 by omega0684]

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

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.

quote:

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Originally posted by omega0684
got any pictures? is it like this



[Edited on 1/1/09 by omega0684]

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clicky linky

Thats the kit i've got, except my magnets are different. round and thicker???!?!?!?!

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]

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

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

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.......

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

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

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,

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.

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]

I have the same speedo as you and used the small magnet detector (looks like the perception type) from Caerbont/Telemetrics sourced from Europa.
4 magnets on the rear prop flange, 1mm to 2mm gap.
Had major problems at SVA and knocked 2 magnets off and rewired whilst there, passed just.
My solution when i got back home was to rewire with shielded twin core replaced the 2 magnets so now read off 4 and re-calibrated. Problem solved.
I would highly recommend shielded twin core with the shield earthed one end.
Yesterday i calibrated another Telemetrix with wheel revs per mile of 900.63 (205 50 15) on a 3.62 diff with 2 magnets this gave a calibration number of 6520 and a dip switch position of 0111111100 thats - 1 x Off. 7 x On. and 2 x Off.

The recent speedo calibrated is using a push bike speedo magnet sensor, cheap but i don't know how durable.

[Edited on 2/1/09 by snapper]

[Edited on 2/1/09 by snapper]

Think i'll try knocking off 2 magnets and going from there...

How did you wire yours up?

My one has one cable to the red/blue on the back of the speedo and the other cable is connected to earth.

quote:

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Originally posted by snapper
I have the same speedo as you and used the small magnet detector (looks like the perception type) from Caerbont/Telemetrics sourced from Europa.
4 magnets on the rear prop flange, 1mm to 2mm gap.
Had major problems at SVA and knocked 2 magnets off and rewired whilst there, passed just.
My solution when i got back home was to rewire with shielded twin core replaced the 2 magnets so now read off 4 and re-calibrated. Problem solved.
I would highly recommend shielded twin core with the shield earthed one end.
Yesterday i calibrated another Telemetrix with wheel revs per mile of 900.63 (205 50 15) on a 3.62 diff with 2 magnets this gave a calibration number of 6520 and a dip switch position of 0111111100 thats - 1 x Off. 7 x On. and 2 x Off.

The recent speedo calibrated is using a push bike speedo magnet sensor, cheap but i don't know how durable.

[Edited on 2/1/09 by snapper]

[Edited on 2/1/09 by snapper]

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After a day of messing about fitting a screened cable, its getting better. Got it down to either 10mph too fast or 10mph too slow

Got the correct sensor from caerbont today so will try fitting that tomorrow. My Previous sensor from isspro didnt need a 12v supply, but this one does so hopefully it'll make some difference.

Using the speedo's calibration table there are 4 sets of numbers to work with first one makes the speedo run 10mph too slow, 2nd one is ridiculously miles out, the 3rd set again too fast but better than 2nd, and the 4th is 10mph too fast... Work that one out. Will have to try less magnets or maybe more magnets????

Ben- where did you get to with this? Sorry about reviving an old thread, but I'm currently wiring the same speedo up using a 3 wire inductive probe, and I'd quite like to only do it once!

I was being dim and had been reading to flip switches wrong. Works fine with or without screened cable