Magnetic speed sensor

bennettdan

Hello,
··· I have a VSS (vehicle Speed Sensor) that outputs about AC wave form from a gear that has 40 teeth on it so thats 40 pulses per revolution at .5 volts·at 100RPM to 100 volts at 8000RPM is what the datasheet says. I want to buffer this signal to be a square wave and was wondering if using a opamp as a comparator would be ok for this and would I need some type of isolation from the AC wave going to the op-amp?
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PJAllen

0.5 to 100V?·

That's quite a range.

bennettdan

Yes I know it sounds like alot but the sensor is actually a tachometer generator and the voltage does not matter to me I just want to catch the collapse of the magnetic feilds when the gear tooth is not infront of the sensor. I just care about the pulses per revolution.

stamptrol

bennnettdan,

Your plan should work. You can either use a diode to kill one half of the AC wave and feed that into your op-amp (it will be necessary, of course to clamp the maximum voltage going into the op-amp with a zener diode).

Or, to see every pulse, first go through a precision rectifier then into the comparator. See any microelectronics textbook or google "precision rectifier".

Many of these sensors depend on the change in field as the tooth goes by. Stopping the gearwheel with the gap or the tooth in front of the sensor may not give any signal. Sensors that detect presence/absence many times are not fast enough to generate pulses off a gearwheel.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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bennettdan

Thanks Tom I will try it and see what happens.