How does a speedo sensor work?

[Bitza]

Hi, can anybody explain to me what triggers the speedo sensor on say an early electronic speedo model like a 2004 Monster 1000ds? Bitza.

[Nickj]

They use hall sensors

Technically they are "transducers that vary their output voltage in response to a magnetic fields."
Essentially it's a magnetic switch fixed in place with a single magnet that rotates with the wheel. They usually fitted on the rear wheel using the caliper mount as the sensor stays in the same relative to the disc nuts. One of the disc nuts has a magnet rare earth (strong) embedded in it.
The wheel spins and the sensor switches high to low as the magnet passes. Count the pulses and you know how many turns the wheel has made (distance), count the number of pulses over time and the speedo electronics works out the speed.
You get a small variation with different tyres as the rolling diameters can be different but nothing worth worrying about.

[Capo]

There are no magnets on the disc, however the sensor looks at either the disc bolts or studs in the disc these have to be ferrous for it to work.

[Bitza]

Thanks for that, so I'll need one magnetised bolt/screw to attach the disc (along with the other five non-magnetic ones) to get a sensor to work. Bitza

[slob]

depends how many pulses your clocks are expecting to see per rotation I think

[Capo]

Thanks for that, so I'll need one magnetised bolt/screw to attach the disc (along with the other five non-magnetic ones) to get a sensor to work. Bitza

Repeat there are no magnets involved.

[Darkness]

Repeat there are no magnets involved.

Noted, but how many ferrous fixings (Which aren't magnets) does the sensor need to "see" to measure the correct speed?

[slob]

if you’re using stock clocks, 6 on an 04 1000ie

[Capo]

I have a Nemesis ECU, it has programing provision for the number of pulses (each stud/bolt causes a pulse) per revolution and the rolling circumference of the wheel.

[Bitza]

Well Capo thanks for that, what you say is backed up by the fact that the parts catelogue only lists one part number for all six screws, when you say ferrous does that include stainless steel? Bitza.

[Capo]

Well Capo thanks for that, what you say is backed up by the fact that the parts catelogue only lists one part number for all six screws, when you say ferrous does that include stainless steel? Bitza.

Stainless steel is essentially non magnetic and in this application would not trigger the sensor.

This picture of my fully floating rear disc, shows the 4 ferrous pins used for the speedo.

https://s26.postimg.org/gflbzthpl/SP1020958.jpg