piclist 2000\06\02\061235a >
Thread: [PIC]: How to measure level of liquids and sense
www.piclist.com/techref/microchip/devices.htm?key=pic
BY : Peter L. Peres email (remove spam text)

Hi,

the method that uses an air column raised by the liquid is actually VERY
accurate. The output value (air pressure in tube wrt atmosphere above free
surface of liquid) will practically depend only on the liquid density (rho)
and the height. Since 10 meters of water column ~= 1 at you can use a
differential pressure gauge for atmospheric use to read the height in most
usual tanks, and it will be accurate to within the height of the measuring
tube inlet (i.e. the vertical size of the tube opening under the liquid
surface). The readings will be off if the liquid is moving (flowing river =
Bernoulli suction on the tube inlet). Keeping the plumbing clean is a pain
however. Overflowed washing machine anyone ? <g>

Afaik, the humidity of construction materials (such as sand) is indeed taken
by weighing, cooking, and weighing, on a probe taken by a worker. They also
determine the density of the material after cooking. The measuring recipient
is a small round cylindrical pot with a hemispherical bottom which is to be
filled to the upper rim and evened. With a kid's sand tools ;-). They use a
sieve to make the input even and they push it in to remove air pockets. The
vessel I say holds about 2 liters of water (~ 5-7 kg of dry sand). The
density can be very important when working with large quantities (ever run
out of some ingredient with 95% of the concrete poured ? <g>). For materials
that cannot be heated (coffee, tobacco, more) the water is removed by using
vacuum at room temperature (0.3 at will dry it in a few hours). The rest is
the same as above. The recipient is also the same afaik. Another thing they
determine for concrete is the Ph of the input materials. This is done on the
wet material. Having a bad Ph in concrete input materials can really ruin