[Farmall] Tachometer

[Howard R. Weeks]

There are at least two different versions of those counters.  One counts for exactly 1 second, 1 minute,
or ten minutes and resets.  The counting window is switch selectable.

The other counts as long as it is able to detect the trigger pulse.  On those, you normally use a stop watch
and count for a period of 1 minute or several - then do the math to translate the result to RPM.

Most that I have worked with are triggered by a small piece of reflective tape (foil) that is stuck on the 
rotating machinery somewhere.  The sensor (triggered by light) is aimed at the tape.  It picks up the reflected
light from the tape each time it passes and counts or accumulates them.  They can be very accurate as long
as the sensor is reliably triggering on the tape.  That can be helped by shining a light at the tape.

They will measure the RPM of most anything that you can stick the tape to.

Howard