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