Sensing RPM from a Spark Plug Wire

Big John T

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Join Date
Nov 2006
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Poplar Bluff
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Is there any sensor out there that will sense the spark pulse and input it into a high speed counter input of a plc? Now we are using red lion sensor that senses the magenet in the flywheel but it is difficult to get positioned correctly for reliable results. This has to be non contact and nothing attached to the engine as this is on an assembly line.

Thanks
John
 
Big John T,

If this engine has a battery charging circuit that uses the same magnet on the flywheel. You might be able to use a diode to prevent voltage coming back from the battery and a resistance voltage dividing bridge (if needed) along with another diode to insure dc voltage to the hsc.

Just a thought.
 
Thanks for the reply.

These are all magneto and has to be done on the fly so to speak so nothing can be attached to the motor. I'm hoping to come up with something like is used in pocket voltage ticks. Where you can just put it near the wire and count the pulses with the plc.

Thanks
John
 
WireGuy1950 thanks for the reply, That type of device has a clip around which could not be used in this application. Also it has no output that could be used by the plc. I need something like a prox that I can move close to the spark plug wire with a pneumatic slide and have the output go to a highspeed counter input on my plc. I'm not really that interested in the RPM but the time to come to a complete stop in this application but the applications next to this one are RPM...

Thanks
John
 
If the flywheel has a magnet, you could use a magnetic pickup attached to your test stand, and use something like an Altronics 1201 tach to get 4-20ma out. That's a fairly cheap solution.

I've seen the mag pickups backed out as far as 1/2" and still generating a signal. The 1201 tach can also use a magneto input, you could clip it on the cylinder 1 coil wire.

DSG-1201, under SPEED/HOURS/TIMING
 
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What it sound like you need is a clamp on ("on the fly"?) like a timing light, with the light signal chopped and squared before being sent to the HSC.

I wish I knew enough about electronics to rattle off a list of parts, but surely someone on here will try.

If you need to sense the crank trigger magnet, and can do that on the fly then I agree with the hall effect sensor. We used to have some pumps that had those connected to a tach interface card. Very simple and reliable.

Good Luck!
 
Big John T said:
WireGuy1950 thanks for the reply, That type of device has a clip around which could not be used in this application. Also it has no output that could be used by the plc. I need something like a prox that I can move close to the spark plug wire with a pneumatic slide and have the output go to a highspeed counter input on my plc. I'm not really that interested in the RPM but the time to come to a complete stop in this application but the applications next to this one are RPM...

Thanks
John
Click to expand...

John

IF I understand correctly
1. You want to measure the time from when you hit the stop button to when the engine stops rolling.
2. You do not want to attach anything to the engine.
3. Later on you may want to measure RPM

How about using sound level meter
measure sound before starting the engine (backgroun)
measure sound while engine running
kill engine
read stopwatch
when sound level returns to background engine stopped stop the stopwatch. You got your time.

What gets me is
IF this is in a factory or on a test stand and you have to attach fuel lines, throttle, kill switch, etc etc then why not a tach or whatever to indicate engine is running or not running??

Dan Bentler

Interesting -- I edited to eliminate word a m b i e n t so that it did not appear as ******t. why is that?? I thought it was a perfectly decent word and not indecent.
 
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leitmotif:

The fuel is fed at the previous station and nothing ever gets attached to the engines in the run tunnel. The engine is running off the fuel in the carb bowl. This happens very fast... Don't think sound would be viable as the other engines running in the same run tunnel. So far I'm going to move a magnet sensor to the position near the location of the magnet on the flywheel. Tests so far are good.

Trying to clamp on a transducer to the spark plug wire would be impossible as they are not in the same place all the time.

So far the red lion LMPCC logic magnetic pickup we got today is working if placed near enough to the magnet. We can read the inputs on our shop plc so that is good. We will have to put the pickup on a pneumatic slide to position it correctly...

Thanks
John
 

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