Need a high-temp gear tooth(hall) sensor

[faust9]

Aloha,

Well, I'm working on a traction control system; however, the space constraints are very tight (trying to get brakes and speed sensor to fit inside of a 10" rim) thus the tone ring for the speed sensor was integrated with the rear disks. The problem now is excessive heat generation under heavy breaking is causing the speeds sensors to flake out. I know Honeywell makes these great little 3/8" long hall sensors that can withstand 400 degrees, but cost is a concern and at $200+ for a single sensor, the cost may out weigh the benefits of traction control.

So with that all in mind, does anyone know of a small hall speed sensor which doesn't require an external magnet that can withstand temps of 200C or greater in a cost effective package? Ideally, the axial length needs to be less than 1.25".

Thanks for any input in advance.

 

[MikeHalloran]

Make lemonade.

When the tone wheel gets hot enough to screw up the Hall sensor, it's got to be plenty hot enough to be visible to any old IR sensor.

So use an analog IR sensor, e.g. photodiode, to keep track of the tone wheel temperature, and when it gets above some threshold, derive the tone wheel signal from the IR sensor instead of the Hall sensor.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[rcl41244]

Try Digi-Key as a source for hall detectors. I strongly disagree with the use of opto devices; they are notoriously temp sensitive.
Robert

 

[SolderingGunslinger]

Have you considered putting the Hall Effect devices and the chopper inside the differential housing on the axel side of the gearing? Less heat and a handy location for signal cables to exit with less road vibration and a shorter excursion than at the hub end...assuming independent suspension.

I remain,

The Old Soldering Gunslinger

 

[MikeHalloran]

Uh, yes, opto devices _are_ notoriously temp sensitive; in this case the source we wish to detect is teeth on a brake rotor that are just shy of being visibly red hot to a person. Which is roughly when they become invisible to the Hall sensor, because it's temperature sensitive, too. To in IR sensor, they are plenty bright, and would surely interfere with efforts to detect a regular IR source on the other side of the teeth. If you can't see the IR source for the hot teeth going by, throw away the source and look at the teeth.

What I'm proposing is not an optical chopper, but just the detector half, which by the way should be aimed to look at something relatively cool when there's no tooth in its field of view.

Of course, putting the tone ring _anywhere_ else would be better than building it into the brake rotor, but the design was already screwed up when we got here. ;-)





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[rcl41244]

Firstly, I never assumed the use of an IR source. Secondly, at the temperatures you suggest, no semiconductor device is likely to operate in close proximity to the toothed wheel.
I can offer a suggestion; the toothed wheel operating as a photo interupter with the use of a glass fibre light pipe to transmit the tooth signal to a remote located optosensor/source.
regards, Robert

 

[Ron07663]

Back-biased Hall IC gear tooth sensors are rated for 150C. Much higher temperature than that will affect reliability for the chip, circuitry and encapsulation. For extreme temperature, VRS (variable reluctance sensors) may be a better solution. They are basicly a coil of wire and a magnet. The output is AC with a frequency proportional to wheel speed.

Ron

 

[faust9]

Thanks for the replies. The tone ring was moved to the diff so the sensor cooling problem has been solved.

VRS sensors were researched but most of the units that met the requirements of small axial length and high temp operation ended up costing a little too much.

Again, thanks for the ideas and input.