Artemetra
Sep 08, 2006, 06:30 PM
I'm using the cheapie little Hangar 9 tach, it seems to work well enough. It displays 1/10 of the speed it reads; you must add a zero. For my helicopter it says 188 so I figure headspeed of 1880.
It works for testing motors, too - put a band of tape on the shaft, mark two hashmarks at about 180o apart, and get a reading, usually close to the nameplate rpm. But indoors, you have to turn off the flourescent lights.
My question comes from the flourescent lights - when they are on, and with the tach set to 2-blades, I get a reading of 360 or 3600 - which is 7200, since at 2 blades it divides actual signal in half. (Head turning at 1880 is sending a signal of twice that, 3760.)
So 360 is a convenient multiple of 60 Hz. But what does the 7200 come from? This works in rooms with multiple bulbs - fixtures with twin tubes - as well as fixtures with only a single flourescent tube in them, no other lights on. Anybody have any hunch as to what goes on?
It works for testing motors, too - put a band of tape on the shaft, mark two hashmarks at about 180o apart, and get a reading, usually close to the nameplate rpm. But indoors, you have to turn off the flourescent lights.
My question comes from the flourescent lights - when they are on, and with the tach set to 2-blades, I get a reading of 360 or 3600 - which is 7200, since at 2 blades it divides actual signal in half. (Head turning at 1880 is sending a signal of twice that, 3760.)
So 360 is a convenient multiple of 60 Hz. But what does the 7200 come from? This works in rooms with multiple bulbs - fixtures with twin tubes - as well as fixtures with only a single flourescent tube in them, no other lights on. Anybody have any hunch as to what goes on?