Hi Morris:
The GR 631 StroboTac includes a power line driven vibrating reed sticking into the reflector and so it's motion is
stopped by the strobe.
The patent has hand written comments regarding that idea.
http://www.prc68.com/I/GRstrobotac.html#2331317
http://www.prc68.com/I/Images/Strobotac631-01b.jpg
The idea here was to use the power line as a frequency reference.
This would be fine since most of the applications for this strobe were related
to line driven motors.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
-------- Original Message --------
HI all,
Thanks to all those who responded to my post and also for the great pics of
other tuning forks. It's amazing that they were still being used for
electronic purposes as recently as the 1960s. Actually now that I think
about it I have seen little tuning forks used to check the function of
modern police speed radars so they still have some use. Musicians don't use
them any more - guitar players will know the little electronic tuning
devices clipped to the neck of the instrument that displays the frequency
or key of each string. Doctors still use 125 Hz forks to test vibration
sense and higher frequency ones to test for conductive hearing loss.
In answer to some of the questions posted: no there was no documentation
with the unit. The most useful thing was the "12 volts in" label on the
power socket so I knew where to start. The rest of it was necktop analysis.
The fork is maintained by means of a central electromagnet and small leaf
spring contacts on the tines - they also provide the 25 Hz power for the
motor which runs at 12 volts. Of course they would reduce the Q of the fork
a little and affect its resonance but I'm sure that was taken into account
by the designer and the frequency & symmetry can be adjusted with the
weights on the ends. Operating current is about 0.5A at 12 volts when
running and 1A when the fork is not vibrating. There's a switch marked "Neon
Lamp" that controls the AC supply to a pair of clips between the tines of
the fork. They are about 3-4 inches apart and I have no idea what sort of
long thin tubular lamp would fit between them. Just for fun I'm going to
make a simple stroboscope with a 555 timer and some high intensity white
LEDs I have lying around to see if I can use it on the fork.
Cheers,
Morris
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