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MMD > Archives > January 1999 > 1999.01.30 > 20Prev  Next

Bubble Pressure Sensor for Pneumatic Reader
By Craig Brougher

Re: Reading Music Rolls Using Pneumatic Switches

I don't foresee that vapor or weight would be the main problems in a
liquid sensor system Robbie, but I could be wrong.  I was speculating
on a very thin "silicone oil" medium (using as an example kerosene).
Silicones have very little if any vapor pressure, and if the depth of
the liquid in the tube is only as high as the sensor is thick, that
couldn't weigh nearly as much as a pouch, tube stabilizer, and its
friction.  Not to mention the possible necessity of more weight or a
spring return on the mechanical operated switch to speed the fall.

In the case of a heavier liquid "impedance" factor slowing it down,
well, that speed is adjustable with either the vacuum used, or the size
of the bleed.  That's the same principle used with a pouch-operated
switch, too.  Except with the pouch operated system, the return speed
isn't helped, since the pouch doesn't get "sucked" back down, again.
But with a liquid sensor, air stream appears for as long as the TB is
uncovered, and then it immediately stops.  It doesn't need gravity and
weight to return.

That was really the basis of my comment.  Since the Achilles' Heel of
all roll readers is most importantly its ability to cut off exactly
with the end of the perforation, evenly across the trackerbar, I decid-
ed that some reader might get an idea that turbulence in a tiny vial is
pretty much instantaneous.

I propose the idea as a possibility to those who are not machinists
and who don't have access to $50,000 worth of testing electronics and
supplies, and who knows -- it might work just as well, for the accuracy
required.  Like anything else, it would have to be developed, but it's

It would be so sensitive, however, that a trackerbar hole would be 'way
too large until it was bled down, anyway.  So the builder could make
his own wooden bar, using bleed hole sized ports.  He could even drill
two ports, one above the other, for sensing chain bridging and letting
the combinations 0/1 and 1/0 determine whether to punch at the advance,
or pass.  That would maintain bridging, and give the copy about the
same appearance as the master, say = or - 1/3 hole diameter, or about
one perforator advance, if you space them right.  This way, you
shouldn't have to use too much "logic." It would just be an arming
circuit, basically.

Now what do you think?

Craig Brougher

 [ I like the basic idea, Craig.  It's quite different, and needs
 [ investigation, to be sure.  I hope one of our readers will
 [ pursue it.  As anyone working with optical sensors will attest,
 [ a pneumatic reader isn't affected by the opacity of the paper
 [ (or Scotch tape repairs); it detects only holes.  That's a
 [ _big_ difference!  :-)  -- Robbie

(Message sent Sat 30 Jan 1999, 20:43:29 GMT, from time zone GMT-0600.)

Key Words in Subject:  Bubble, Pneumatic, Pressure, Reader, Sensor

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