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ABS speed sensor


MECCANO
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Okay little bit of back ground.

Im doing an HNC in electrical/electronic engineering as part of a modern apprenticeship. Part of this is a design and make project.

Part of my project idea requires to know exactly what signal would be achieved from the wheel speed sensor from a classis rangie. From what ive found so far it suggests i would see a Sine wave where the frequnecy is representative of the wheel speed. However my lecturer wont believe this is the case, and says its mroe likely to be a pulse.

Does any one know, where i could find specific data on their function with out obviosuly getting hold of unit and testing it.

Any help is greatly appreciated. As if i cant prove it i will ahve to do a Plan B boring non landrover related idea :angry:

Although i guess an alternative would be to make my own basic system of measuring the speed.

Chars Muchly

Chris

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Depends which model and age of sensor you are looking at.

New sensors are generally hall effect (that is what we supply anyway) and these have square waves. Generally called active sensors.

If you are looking at the old 'passive' sensors then these are sine wave. These sorts of sensors are probably what is on old Rangie, Disco 2, Defender. Generally these are where you simply push the sensor into the hub and it seats itself. New active sensors are bolted to hub and the air gap and tolerancing of the hub needs to be within strict guidelines.

Hope it helps.

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As suggested, but a scope on one, surely not rocket science?

ABS Sensor (passive / VR type) waveform

Cheers guys, great help

The problem is i dont actually have one to play with yet... and i need to find out before next Wed. :blink:

next question

Were hall effect and passive fitted to the same axles types. ie could i fitted either type to a set of 1987 rangie axles, or am i stuck with using passive?

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Well, if you actually want an ABS sensor, not fitted, obviously, i can supply one, basically i had a mishap with my hybrids brakes and ripped the fibre optic wiring in half.

Hence i have the actual hub sensor, with some fibre optic wiring, in two bits, as i had to remove it from the truck at the connector. Its from a 1990 RRC.

Its spare in a box doing nothing.

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Fibre optic? :blink: Are you sure?

Ooh, yes, its a fibre optic, thats why i had to get a new complete sensor off Jules, cos it could not be reconnected.

I was a tad surprised myself, having never damaged that sort of 'wiring' before!!

EDIT to SAY

Thats why its £226 + VAT for the sensor and small length of 'loom', land rover only, guess how i know!!

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They come up on eBay every now and then - I got a couple for about fifteen quid a while back.

At £226, i did not buy it, got 2nd hand, not that silly, just yet anyway!!

Having said that, i have since replaced the ABS with normal servo brakes, as the pump went.

Anyway back to the question from fridge, its fibre optic as far as i know, the wires were not metal and the 'strands' inside were white 'fibres' bit like the texture of nylon string/ cheap carpet backing!

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Don't really think it is fibre optics....

Maybe some sort of synthetic conductor core is used rather than wire (probably to overcome mechanical fatigue & failure resulting from that) but fibre optics have light in and I ain't seen any light coming out of me brakes :unsure:

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Could be fibre, they are usually padded with kevlar strands (the string you describe) to protect them. Most fibre light sources are not in the visible spectrum so you won't see any light, which is why you should never look down the end of a fibre unless you know the other end is dead. I'm puzzled as to why on earth it would be fibre though as the ABS sensors are either hall or VR, doing it optically would be a right PITFA.

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Seems strange it did not work. Certainly the hall sensors just have 2 twisted wires (twisted for interference reasons).

How many pins on the connector as that would indicate if the white wire does anything.

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Seems strange it did not work. Certainly the hall sensors just have 2 twisted wires (twisted for interference reasons).

How many pins on the connector as that would indicate if the white wire does anything.

Well if the signal is converted optically, then it would suggest that the two leads would form the supply to the emitting diode. It might be possible to break into the unit and wire out the optical part of it.

Optics can be repaired, they would have to polish the faces that are broken to near perfect 90 degrees, and the ends spliced ( butted together) with similar accuracy. (Thats what my last project was on :ph34r: )

Mr Corrode, i will take you up on your kind gesture, i will PM you my address later to arrange postage costs.

Cheers

Chris

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If it's just a bulking-out piece it makes sense, they probably make that stuff anyway for bulking out multi-core fibre cables so it's easy to re-use, plus the kevlar strands will resist stretching and quite a lot of abuse, taking strain off the copper.

Obviously a material used to make bullet proof vests and fighter planes is unable to stand up to Paul's driving though :lol:

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Whatever it is, i have now posted it to Mecanno so hopefully he can do what he needs to with it.

All i know is that after reconnecting the wires only, the ABS did not pulse as expected, when the brakes were applied it pulled to the drivers side, and caused the truck to lurch under braking.

As soon as i put a complete unbroken wire back in, it returned to normal.

Not that i gained much cos the bl00dy abs pump packed up a week or so later, so i replaced it with normal disco brake master cylinder etc.

Dont talk to me about brakes, they have given nothing but grief since building the hybrid, hence why they got changed, i was going through brake fluid nearly as fast as petrol at one point due to the hassles and number of times it came apart!

As far as with standing my driving, wrapping a half inch round piece of rebar around the front axle via the front brake flexis, i would have been surprised it it had survived!!

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