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MMD > Archives > January 1999 > 1999.01.30 > 19Prev  Next

Optical Airflow Sensor for Pneumatic Reader
By Wayne Stahnke

Further Discussion of the Pneumatic-Electric Interface

I have located the working model of the pneumatic-electric interface
that I described in MMDigest 990128, and I would be happy to loan it to
anyone who has the ability to photograph it and place the image in the
MMD archives (or on the web in some other place).

I also located the original drawings that I prepared for the machinist
to use when making the model; they are dated August 7, 1981.  These
drawings give the following specifications for the glass tube:

  Material:                Pyrex
  Inside Diameter (i.d.):  0.1355/0.1345 inch
  Outside Diameter (o.d.): 0.196/0.195 inch
  Length:                  1.253/1.247 inch
  Chamfer i.d. and o.d. 0.010 x 45 degrees

The cylinder is made of Delrin AF, which is Teflon-filled Delrin, and
its natural color is dark brown.  This is in contrast with ordinary
Delrin, whose natural color is white.  The specifications for the
cylinder are:

  Material: Delrin AF
  Diameter: 0.1325/0.1315 inch
  Length: 0.251/0.249 inch

The keepers, one in each end of the glass tube, are identical.  They
protrude into the tube nominally 0.475 inches.  These keepers have a
flange on each end to provide a "stop" when they are inserted into the
tube.  They are secured in place with watchmaker's cement (this is the
material that watchmakers use to bond the watch crystal to the metal
case).  The specifications are as follows:

  Material:         6063-T6 Aluminum
  Inside Diameter:  0.100 inch (nominal)
  Outside Diameter: 0.132 inch (nominal)
  Length:           0.525 inch (nominal)
  Flange diameter:  0.188 inch (nominal)
  Flange length:    0.050 inch (nominal)

The nominal throw of the cylinder is 0.050 inches (1.25 mm).  My memory
failed me here; I previously noted in the MMD that the throw was 1 mm
or less, which was in error.  My memory also failed me regarding the
optical switch; it is in fact an HEI OS-561A-200.  I used a current-
limiting resistor of 330 ohms to power the LED from a 5-volt power
supply, with a nominal LED current is 11 milliamperes.  The pull-up
resistor for the photo-transistor output has a value of 10 kilohms.

I would be pleased to provide whatever support I can to anyone who
wants to build a working pneumatic reader using this approach.  With
best regards,

Wayne Stahnke

(Message sent Sat 30 Jan 1999, 20:15:18 GMT, from time zone GMT-0800.)

Key Words in Subject:  Airflow, Optical, Pneumatic, Reader, Sensor

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