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Author Topic: Wheel speed sensors  (Read 4735 times)
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SPARKY
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« Reply #15 on: June 26, 2017, 01:06:41 PM »

Thanks Jim
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WhizzbangK.C.
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« Reply #16 on: June 26, 2017, 02:46:17 PM »

Here is the spec for the 3 wire I am using it is a hall effect with a power, ground and signal output. The 2 wire type is just an on/off switch activated by a magnet.

Slight correction, the 2 wire type has a winding around a magnet in the sensor, and the tone ring is a toothed wheel. The teeth passing through the magnetic field generate a voltage that is read as speed.
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« Reply #17 on: June 26, 2017, 11:34:33 PM »

so what about the ones that pass over a magnet? That is just generating a frequency that is being logged and converted to rpm or such am I understanding this correctly?
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Miss LIBERTY,  changing TKI  to noise, dust and RUST!!!

The # 1 issue is: TO KEEP THE REPUBLIC      
   Center for Self Governance            tncsg.org     mrspowell.org

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller
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« Reply #18 on: June 27, 2017, 01:11:17 AM »

often a reed switch if a magnet is involved
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WhizzbangK.C.
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« Reply #19 on: June 27, 2017, 09:15:18 AM »

often a reed switch if a magnet is involved

Oh yeah, sorry, I forgot about that style since nothing I deal with uses them.   cheesy Tunnel vision on my part I guess.
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« Reply #20 on: July 10, 2017, 01:37:49 PM »

Two wire sensors are generally Variable Reluctance (VR) and three wire are Hall Effect or "logic sensor" (logic being in a state of either on or off).  There is always a magnet involved in some way.  Most VR sensors have the magnet inside of them and when a ferrous target passes them, they generate their own AC voltage that looks like a sine wave.  MSD changed it up and made the magnet the moving target and put the ferrous core inside the sensor.  Same exact concept, just a different way of doing it. 

Hall Sensors are "powered" by either 5v or 12v depending on the sensor.  Hall sensors work on a principle similar to VR sensors and also use a magnetic field.  Many/most Hall sensor are "open collector" which is just a fancy way to say that they output a ground signal when triggered on.  What the receiving electronics want to see is a square wave (usually at 5v or 12v amplitude).  Well since a ground signal alone has no amplitude, there is a pull up resistor in the signal circuit that "pulls up" the signal's voltage to something like 5v or 12v in order to get the signal to transition from high to low as the sensor turns on and off.  Some sensors have a pull up resistor already in them and output a square wave by default but this comes down to the specific sensor - check the sensor's spec sheet.

Won't be long and we'll be talking about noise cancellation techniques...
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« Reply #21 on: July 10, 2017, 02:04:58 PM »

Thanks Nathan, looking forward to when you share your thoughts on "The Noise"
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Miss LIBERTY,  changing TKI  to noise, dust and RUST!!!

The # 1 issue is: TO KEEP THE REPUBLIC      
   Center for Self Governance            tncsg.org     mrspowell.org

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller
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