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PRoximity sensor for Tachometer

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Alexanderfitu

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Hi all

Following on from :

https://www.electro-tech-online.com...th-a-proximity-sensor-and-a-rpm-gauge.121705/

I have picked up the following gauge from ebay:

**broken link removed**

Now, this gauge appears to be driven directly by a magnetic pick-up.

as per page 2 of this link:

https://www.electro-tech-online.com/custompdfs/2011/10/Diesel_Magnetic_Tachometer.pdf

I have been playing around with it, and wiring it al up as you would expect, and using a drill with a piece of metal taped on, I can only get it to measure up to 500rpm, any ideas?
 
oddly enough, I have noticed it is mean to be normally open.

Now measuring the output when no metal objects are near shows 12v, move object close and it drops to 0, this sounds like normally closed to me, am I right?
 
I read this:
This is a Magnetic Pickup tach and tests out at 30 teeth.

That tach is designed for use with a 30 tooth gear pitch. So 30 pulses would equal 1 revolution. Therefore 30 PPS (Pulses Per Second) would equal 60 RPM. If you use a single point on a rotating shaft you will only get one pulse per revolution. The tach will read 1/30th of the actual RPM. Have you taken that into consideration? Page 2 of the link for another tach also shows a switch (3 position) for the pitch (teeth).

If you have a function generator that will output high enough amplitude pulses you can try driving the tach with it.

Ron
 
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Yeah I thought about that one, I have a flywheel that has 30 indivudual fan blades that can be picked up individually by the proximity sensor so thats not such a big problem.

The fact I cant get any reading has me more stumped, if I can get the gauge to respond correctly in the test environment, then any problems I am going to have with the flywheel etc will be trivial :)

Any ideas?
 
My take based on the first post was it worked but only was reading 500 RPM with a drill. While for the tach you have they do mention:

Gauge was tested using our gauge tester and works as it should.

They do not mention the pulse or signal amplitude they used. If you had a function generator or even a good audio oscillator it would be easy to run a few signals in and see what it does. Two wire magnetic tach pick ups are pretty common. Unfortunately they don't all output the same amplitudes. Also, the gap between the gear and the pick up figure into things. You may want to give the seller a call and ask how they test the things?

When you posted:

I have been playing around with it, and wiring it al up as you would expect, and using a drill with a piece of metal taped on, I can only get it to measure up to 500rpm, any ideas?

I assumed it worked but read incorrectly. :(

Ron
 
Last edited:
My take based on the first post was it worked but only was reading 500 RPM with a drill. While for the tach you have they do mention:



They do not mention the pulse or signal amplitude they used. If you had a function generator or even a good audio oscillator it would be easy to run a few signals in and see what it does. Two wire magnetic tach pick ups are pretty common. Unfortunately they don't all output the same amplitudes. Also, the gap between the gear and the pick up figure into things. You may want to give the seller a call and ask how they test the things?

Ron

Hmm sounds like a good idea, I was looking into using a 2 wire abs sensor as they are very cheap and I believe should be what I need!
 
I may be wrong but ABS sensors have a pretty low output voltage? This may not be enough to trigger the tach properly. A peak to peak of 5 volts or less from an ABS sensor would not surprise me.

Ron
 
That is true, I would need to double check that.

I have sent the seller an email asking what type of signal the gauge was tested with, and we will see what I can get from there. Thanks for your help!
 
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