In a message dated 03/09/2005, gcouger@.......... writes:

Chris,

See:  www.sas.org/E-Bulletin/2001-10-05/labNotes2/labNotes.html

The small  tube is typically a glass tube drawn down to less than 
..01 inch diameter  maybe a lot smaller. The bubble is injected in 
one end an moved to the  center by adding fluid drop by drop.
    The bubble will move by 1/2 the volume of the drop,  but you can get some 
stiction. This may be serious in tubes of 1 mm or  less.

The  miscues formed by the air water interface makes a large dark 
band across a  sensor just try it with a laser pointer and glass 
of water. In fact the  shadow of the air water interface is so 
large it is a problem to get very  much dynamic range over the 
range of a CCD sensor unless you look  at just one edge of the 
water bubble.

Temperature would be  more of problem than pressure on the size 
of the bubble. But if the two  edges of the bubble are both 
tracked the bubble size can be canceled out.  This would take a 
rather complex machine vision project. 
    Try a couple of Si photocells? You can buy them 1"  long x 0.1" wide.

A more  realistic solution may be use a very thin grade of oil and steel 
piston  between a pair of coils on the tube to sense the its movement..... 
    No. You need to eliminate all mechanical  friction. This could be done 
with mercury, sensing the end of the  column either optically or capacitatively. 
    Another way would be to use metal bellows and sense  the position of the 
closed end.
 
    What is "a magnetic guild"?
 
    Regards,
 
    Chris Chapman






In a message dated 03/09/2005, gcouger@.......... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
  size=3D2>Chris,

See:=20
  www.sas.org/E-Bulletin/2001-10-05/labNotes2/labNotes.html

The small=
=20
  tube is typically a glass tube drawn down to less than 
.01 inch diamet=
er=20
  maybe a lot smaller. The bubble is injected in 
one end an moved to the=
=20
  center by adding fluid drop by drop.
    The bubble will move by 1/2 the volume of the d=
rop,=20
but you can get some stiction. This may be serious in tubes of 1 mm or=20
less.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>The=20
  miscues formed by the air water interface makes a large dark 
band acro=
ss a=20
  sensor just try it with a laser pointer and glass 
of water. In fact th=
e=20
  shadow of the air water interface is so 
large it is a problem to get v=
ery=20
  much dynamic range over the 
range of a CCD sensor unless you look=20
  at just one edge of the 
water bubble.

Temperature would be=
=20
  more of problem than pressure on the size 
of the bubble. But if the tw=
o=20
  edges of the bubble are both 
tracked the bubble size can be canceled o=
ut.=20
  This would take a 
rather complex machine vision project.=20

    Try a couple of Si photocells? You can buy them=
 1"=20
long x 0.1" wide.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>A more=20
  realistic solution may be use a very thin grade of oil and steel piston=20
  between a pair of coils on the tube to sense the its movement.....=20

    No. You need to eliminate all mechanical=20
friction. This could be done with mercury, sensing the end of the=20
column either optically or capacitatively. 
    Another way would be to use metal bellows and s=
ense=20
the position of the closed end.
 
    What is "a magnetic guild"?
 
    Regards,
 
    Chris Chapman