motor rpm photo tach sensor

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Joined: Wed Sep 27, 2006 9:51 am

motor rpm photo tach sensor

Post by NathanUnger »

I have a Pico 4444.
I would like to use it for checking starter motor and alternator RPM's so I can plot current against it.
Is there any kind of probe available, like a photo-tach sensor with milli-volt output, or something?

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Joined: Fri Aug 31, 2012 8:14 am

Re: motor rpm photo tach sensor

Post by Rfmotors1 »

Hi NathanUnger,
Instead of advice about probe, here is how I would approach this:
Basically, I need to get accurate RPM from device that rotates in direct ratio to engine RPM. Then it is so easy to get the accurate RPM waveform for anything directly geared to engine, belt or gear, as long as there is not any slip.
So my solution would be to create math channel from the crankshaft sensor, lets say the starter motor has 12 teeth and flywheel 138, then the formula would be crank speed x (138/12=11.5).
In math channel the formula looks like this: crank(A,60)*11.5
In case of belt driven device, you need to measure the diameter of pulleys and calculate the ratio.

This is my workaround and it works well for me

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