Magnetic pick up sensors
Discussion
Hello all,
On a magnetic pick up sensor (for a tacho/speed etc signal), why do some cables going from the sensor (which "sees" the magnet(s) as it passes) contain three wires, and some contain two?
On an existing set up which utilised a cable containg three wires, could you add another cable containg two wires to utilise the original sensor and magnet set up for a seperate application (thus doing away with the need for a second sensor and associated magnets)? If so, which of the three wires would you need to connect to?
I hope that makes sense but I can attempt to clarify if needed?
Many thanks in advance
On a magnetic pick up sensor (for a tacho/speed etc signal), why do some cables going from the sensor (which "sees" the magnet(s) as it passes) contain three wires, and some contain two?
On an existing set up which utilised a cable containg three wires, could you add another cable containg two wires to utilise the original sensor and magnet set up for a seperate application (thus doing away with the need for a second sensor and associated magnets)? If so, which of the three wires would you need to connect to?
I hope that makes sense but I can attempt to clarify if needed?
Many thanks in advance
Edited by Toilet Duck on Tuesday 26th March 16:59
stevieturbo said:
http://en.wikipedia.org/wiki/Hall_effect_sensor
http://en.wikipedia.org/wiki/Variable_reluctance_s...
Cheers for the links, much appreciated http://en.wikipedia.org/wiki/Variable_reluctance_s...
However, as much as I've tried to understand all that was in them, I still can't understand why some set ups use two seperate wires and some use three?
Does it mean a set up using three wires is using a Hall effect sensor, and a set up using two wires is using a variable reluctance sensor?
If thats the case, if you have a set up using two wires, can you splice into an existing set up that uses three wires (just use two of the three). Or am I talking poo?
Sorry for being thick
Two other facts are important when discussing VR verses HALL sensors:
1) The VR sensor has a broadly sinusoidal output waveform with an amplitude proportional to the differential speed between the target wheel and the sensor. Hence, at low speed a VR sensor will be only putting out millivolts, but at high speed they can put out >50V! The system that decodes this signal into a variable frequency pulse train must accomodate that huge varriation in voltage amplitude.
2) The hall sensor out out is generally the same (or very slightly lower) that the driving voltage applied to it (typically ~8Vdc). Because of this active drive, the hall sensor can provide a strong digital signal down to effectively zero speed.
In all cases it is advantageous to use a "twisted" pair cable architecture in the loom to the sensor to maximise inductive coupling between the 2 signal wires, and minimise both radiated and absorbed RF interference.
1) The VR sensor has a broadly sinusoidal output waveform with an amplitude proportional to the differential speed between the target wheel and the sensor. Hence, at low speed a VR sensor will be only putting out millivolts, but at high speed they can put out >50V! The system that decodes this signal into a variable frequency pulse train must accomodate that huge varriation in voltage amplitude.
2) The hall sensor out out is generally the same (or very slightly lower) that the driving voltage applied to it (typically ~8Vdc). Because of this active drive, the hall sensor can provide a strong digital signal down to effectively zero speed.
In all cases it is advantageous to use a "twisted" pair cable architecture in the loom to the sensor to maximise inductive coupling between the 2 signal wires, and minimise both radiated and absorbed RF interference.
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