Adam:
   How work the laser measurement of liquid (water) level ? Do you know
something that sell this sensores ready to use ?

With respect to wet sand properties, i don't have more information that
you.. sorry  I am in the beggining of my project and
recolecting information, I am not a expert on sand and concret ;-)

TIA.

Hugo

----- Original Message -----
From: M. Adam Davis <adavis@UBASICS.COM>
Sent: Tuesday, May 30, 2000 10:22 AM
Subject: Re: [EE][PIC] How to measure level of liquids and sense
relativehumidity?


> You are putting this into a concrete plant?  You should really use some
sort of
> industrial solution.  A number of companies make non contact and contact
> distance sensors specifically for liquid level measurement.  The one I am
> thinking of now for your application is a non contact laser liquid level
sensor,
> which you simply point down on the liquid.  Many of these can be used in
> corrosive environments (glass, stainless steel, etc) as well.
>
> As far as the water content of sand, the only thing I can think of would
be to
> take a certian volume of the sand, and weigh it.  The same volume will be
> heavier the more damp it is.  I don't think the usual method of electrodes
> spaced so far apart will be very accurate (nevermind having to replace
them
> every month, and recalibrate them daily due to wear) Most
dampness/humidity
> sensors require contact with the substance you are measuring.  Perhaps you
can
> tell us more about the properties of wet sand.  Does it reflect a
lightsource
> differently depending on its dampness?
>
> -Adam
>
> Hugo Jorge M|ller wrote:
> >
> > Hello
> >
> > I am beginning to work in the final project of my career of Electronic
> > Engineering and at the moment, we have decided to make the following
work
> > (with a friend): To automate a plant of Concrete.
> >
> > The idea is to use a PC for the general control of the plant and to arm
a
> > network (Possibly RS485) with terminals that will be slaves working with
> > PICs, to complete different tasks, as the following ones:
> >
> > 1) To control the pneumatic servos and read proximity sensores and
other.
> >
> > 2) To Sense the weight of the materials with cells of loads, indicate
the
> > value measured in a  7 segments display and to send the measures througt
the
> > network when they are requested or periodically. This partly would be
> > resolved, but I accept ideas and suggestions in this respect.
> >
> > 3) To Sense the level of water in the main dosificador tank. The tank
should
> > be filled until certain level and then it is pumped to the truck
concrete
> > mixer. I have think in sense the height of the column of liquid with a
> > sensor of pressure Motorola of the series MPX, I also thought of the
> > ultrasonic solution  but I don't have idea that resolution i can
achieve.
> > The tank in question has 1100 Liters and a height of about 2 meters.
aprox.,
> > it is cylindrical. I need a precision of about 5 liters. (or better).
> > Ideas? Comments? Other viable methods?
> > On the other hand I should dose some aditives, special liquids that
> > unfortunately they are corrosive and at the moment it is filled a small
tank
> > of about 26 liters by means of a key, for graveness, then they closes
this
> > key (superior) and two keys open up, one in the inferior part that
allows
> > the exit of the preservative toward the MIXER and the other one in the
> > superior part that injects compressed air at 10 Kg/cm^2 to impel to the
> > preservative and to pump it without having contact with the same one.
> > The problem is to measure the level or the quantity of this aditive
without
> > touch it and to be able to pump it too to the mixer.
> > I thought of measuring it with sensor MPX, but the problem is when
opening
> > the key of compressed air, the sensor doesn't support 10 Kg/cm^2
(although
> > it could measure in differential form, but I suppose that the transitory
one
> > provoked, it would destroy to the silicon sensor).
> > Here it is where I request them help that mensuration methods advise me?
> >
> > Somebody had worked with sensor MPX with PICs ?  What kind of interface/
ADC
> > use ?
> >
> > 4) Another topic not less difficult of solving it is to be able to
measure
> > the relative humidity that there is in the sand and in the concrete once
> > blended. Here the only method that I am happened (electronic) it is
between
> > two by means of the mensuration of conductivity electrodes of a material
> > that is not oxidized, located inside the material to measure, at a
certain
> > distance. That other methods or variantes suggests me?
> >
> > As for the net RS485, has somebody used them with PICs? That protocols
> > suggest? Some link with information?
> >
> > Good, I won't extend more in the detail, I wait their collaboration with
> > ideas...
> >
> > Sorry if there are errors in the text, but my language is Spanish  :-)
> >
> > Thank you from already.
> >
> > Hugo J. M|ller
> > H.J.M. Hardware & Software Diseqos Electrsnicos
> > San Nicolas 683
> > Tel-Fax : 54-(0)-343-424-5953
> > (3100) Parana (Entre Rmos) Argentina
> > Email : hmuller [ANTISPAM-QUITAR-ESTO] @arnet.com.ar
> > Web Site: http://www.pagina.de/hjm
> > UIN (ICQ) : 38.605.074
>