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'[EE][PIC] How to measure level of liquids and sens'
2000\05\28@174123 by Hugo Jorge Mčller

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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

2000\05\30@092333 by M. Adam Davis

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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:
{Quote hidden}

2000\05\31@094056 by Hugo Jorge Mčller

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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 removed}

2000\05\31@101338 by riest

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Maby I'm jumping in the middle of a discussion but ever thought
about using ultrasonic transducer?
The only thing you have to do is doing some calibration.

Ries

2000\05\31@102419 by Alok Dubey

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yeah they are the best soln.. sonar type thngies//
alok

-----Original Message-----
From: Ries van Twisk [spam_OUTriesTakeThisOuTspamFRANKSINTL.NL]
Sent: Wednesday, May 31, 2000 3:01 PM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [EE][PIC] How to measure level of liquids and sense
relativehumidity?


Maby I'm jumping in the middle of a discussion but ever thought
about using ultrasonic transducer?
The only thing you have to do is doing some calibration.

Ries

2000\05\31@103251 by Robert A. LaBudde

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<x-flowed>The normal method of measuring effective humidity in wood, concrete, sand,
etc., is by conductivity.

Use a 1 kHz square-wave from the PIC through two stainless steel probes
spaced a fixed distance apart. For wood and concrete, use needles.

Measure the conductivity as an unknown resistance in a bridge and read it
with an ADC input.

The method is not a priori specific for water, but it can be calibrated on
materials in a specific environment.

The official method for moisture is to weigh the sand, cook for 4 hrs @ 125
C (=270 F), and weigh again. The weight loss is crude moisture.

Conductivity is also used as a surrogate for other measurements, such as pH
in pool water or plant soil.

Tap water usually has a conductivity of 1-200 uS/cm. The water in the sand
would be probably 100x larger than this, up to 20,000 uS/cm. Therefore the
effective resistance of 1 cm apart probes would be expected to be 50 ohm or
more.


================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ralspamKILLspamlcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

</x-flowed>

2000\05\31@114707 by Don Hyde

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Some colleagues here took on a liquid-level sensor based on ultrasonic
ranging, and were suprised at what a major project it turned into.

For starters, cost was an important issue.  It turns out that, like with
many things, there are two kinds of ultrasonic transducers -- cheap ones
that aren't very good and very expensive ones that are still only pretty
good.

After spending a lot of time dealing with analog noise, they got down to
difficult problems with ringing in the transducer, multiple reflections, and
the fact that all the transducer's properties varied a whole lot with
temperature.  Then they got to work compensating for the fact that, while
the speed of sound in air and water vapor is fairly well-behaved, the speed
of sound in diesel fuel vapor is not.  It varies a lot, and in a highly
nonlinear fashion, with temperature (and to a lesser extent, from one batch
of fuel to another).

> {Original Message removed}

2000\05\31@115957 by Dan Michaels

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At 10:42 AM 5/31/00 -0500, you wrote:
>Some colleagues here took on a liquid-level sensor based on ultrasonic
>ranging, and were suprised at what a major project it turned into.
>
>For starters, cost was an important issue.  It turns out that, like with
>many things, there are two kinds of ultrasonic transducers -- cheap ones
>that aren't very good and very expensive ones that are still only pretty
>good.
>
>After spending a lot of time dealing with analog noise, they got down to
>difficult problems with ringing in the transducer, multiple reflections, and
>the fact that all the transducer's properties varied a whole lot with
>temperature.  Then they got to work compensating for the fact that, while
>the speed of sound in air and water vapor is fairly well-behaved, the speed
>of sound in diesel fuel vapor is not.  It varies a lot, and in a highly
>nonlinear fashion, with temperature (and to a lesser extent, from one batch
>of fuel to another).
>

For a slightly different viewpoint, I consulted with a company that
used std Polaroid ultrasonic transducers to determine the level of
ice in an icemaker machine. They had 10s of 1000s of unitsin the
field. This device is quite easy to interface, and fairly cheap,
and used just a couple of chips running off a 6805 uC, which provided
control and took measurements.

However, the transducers always had a heavy coating of water
condensate on them, so I was always amazed they didn't have
horrendous reliability problems. Eventually, they gave them up for
a simpler/cheaper solution involving a thermistor in a tube.

best regards,
- Dan Michaels
==============

2000\05\31@153624 by Mark Willis

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Laser could be aimed at say 30 degrees from vertical onto the waters'
surface, a sensor at 30 degrees the other side of vertical would pick up
specular reflection, BUT:

Water's top surface isn't perfectly flat so you get early "hits",
perhaps want several photodiodes and to think on how to handle the top
surface wave problem there.  If you have a top styrofoam "float" atop
the water, stick a reflective mylar sheet on there and you have specular
reflection again, and reduce the wave problem <G>

There are capacitive sensors used to detect water levels also.

What's wrong with a cheap and easy, hot bead thermistor solution,
though?  Constant current through a thermistor to intentionally
self-heat it to say body temperature or so, when in free air -  then
measure the resulting voltage - when water level rises to where the
thermistor is covered in water, it'll cool the thermistor in a heck of a
hurry, thus voltage change and you know the water's there.  Want the
water to not spray onto the thermistor, of course, placing the
thermistor inside a tube or if needed adding a tank water inlet baffle
will solve that though <G>  Yeah, it's contact sensing, I know.

 Mark

Hugo Jorge M|ller wrote:
{Quote hidden}

<snip>

2000\05\31@155109 by Patrick J

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And how about another even simpler way ?
(which might even prove to work in the real world!)

Just stick a pipe down in the fluid and measure the air pressure that
builds in the pipe when the level rises. There are sensors availfor it.

2000\05\31@160118 by Dan Michaels

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Mark Willis wrote:
.........
>What's wrong with a cheap and easy, hot bead thermistor solution,
>though?  Constant current through a thermistor to intentionally
>self-heat it to say body temperature or so, when in free air -  then
>measure the resulting voltage - when water level rises to where the
>thermistor is covered in water, it'll cool the thermistor in a heck of a
>hurry, thus voltage change and you know the water's there.  Want the
>water to not spray onto the thermistor, of course, placing the
>thermistor inside a tube or if needed adding a tank water inlet baffle
>will solve that though <G>  Yeah, it's contact sensing, I know.
>

Plus, I suspect you could use 2 or more thermistors arranged
vertically within the tube, plus a little math, to actually
determine the level, not just whether above/below one point.

2000\05\31@163637 by Mark Willis

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Dan Michaels wrote:
> Mark Willis wrote:
> .........
> >What's wrong with a cheap and easy, hot bead thermistor solution,
> >though?  Constant current through a thermistor to intentionally
> >self-heat it to say body temperature or so, when in free air -  then
> >measure the resulting voltage - when water level rises to where the
> >thermistor is covered in water, it'll cool the thermistor in a heck of a
> >hurry, thus voltage change and you know the water's there.  Want the
> >water to not spray onto the thermistor, of course, placing the
> >thermistor inside a tube or if needed adding a tank water inlet baffle
> >will solve that though <G>  Yeah, it's contact sensing, I know.
> >
>
> Plus, I suspect you could use 2 or more thermistors arranged
> vertically within the tube, plus a little math, to actually
> determine the level, not just whether above/below one point.

True on multiple height determination - though (despite my being pretty
good in math) I don't see where the math's needed/applicable.  I thought
with 3 hot beads, you'd know one of 4 states, {"Height < A" || "Height
>= A" || "Height >= B" || "Height >= C"}, don't see how you can determine shades of height between say A and B (putting A lowest, C highest here, to clarify.)  Am I missing something?  Has been a "Bad Brain Day" to some degree <G>  (There's not a big difference for thermistor B in temperature, between temperature for water say 1 foot below it and 1 inch below it, barring splashing, is there?  Has been a while since I last hot-beaded <G>)

 Mark

2000\05\31@190953 by Dan Michaels

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Mark  wrote:
....
>>
>> Plus, I suspect you could use 2 or more thermistors arranged
>> vertically within the tube, plus a little math, to actually
>> determine the level, not just whether above/below one point.
>
>True on multiple height determination - though (despite my being pretty
>good in math) I don't see where the math's needed/applicable.  I thought
>with 3 hot beads, you'd know one of 4 states, {"Height < A" || "Height
>>= A" || "Height >= B" || "Height >= C"}, don't see how you can determine
shades of height between say A and B (putting A lowest, C highest here, to
clarify.)  Am I missing something?  Has been a "Bad Brain Day" to some
degree <G>  (There's not a big difference for thermistor B in temperature,
between temperature for water say 1 foot below it and 1 inch below it,
barring splashing, is there?  Has been a while since I last hot-beaded <G>)
>

Not that I've ever tried this, but I figure the temperature variation
would distribute itself along the tube in some manner [to be measured
and calibrated empirically], and the math would be some weighted
averaging routine. Just a thought. The sorta thing you try once, and
immediately get a strong hunch whether it will ever work or not.

- Dan

2000\05\31@194532 by Gennette, Bruce

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Yeah, my washing machine uses this to 'control' the level of water used.
It's not very accurate, but in a washing machine who cares if it's a few
litres out?  But in a concrete plant the amount of water added controls the
workability, setting time and, to a degree, the final strength of the
concrete, so it *MAY* not be accurate enough.

Bye.

       {Original Message removed}

2000\05\31@235651 by John Orhan

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Hi ,
Where can I find sensors to measure the air pressure. I had exactly the same
idea for a water level meter on a boat, but could not source any sensors to
do the pressure measuring. Please advise.John Orhan
Detection Systems / EDM Engineering Department
Ph: 02 96721233 (ext 219)
Fx: 02 9672 4093
Email: .....jorhanKILLspamspam.....edm.com.au


{Original Message removed}


'[EE][PIC] How to measure level of liquids and sens'
2000\06\01@024621 by markwillcox56
picon face
<x-flowed>put carbon granuals, powder, or antistatic foam in a plastic pipe,open at
one end for pressure. connect one wie to each end and you have a pressure
sensitive resistor. or mabey use an old carbon mic from a telephone? just
some thoughts..... Mark


{Quote hidden}

>{Original Message removed}

2000\06\01@025450 by markwillcox56

picon face
<x-flowed>how about a float from a toilet connected to a LVDT or a pot at the fulcrum?


>From: John Orhan <RemoveMEJOrhanTakeThisOuTspamEDM.COM.AU>
>Reply-To: pic microcontroller discussion list <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
>To: TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU
>Subject: Re: [EE][PIC] How to measure level of liquids and sense relat ive
>             humidity?
>Date: Thu, 1 Jun 2000 13:57:01 +1000
>
>Hi ,
>Where can I find sensors to measure the air pressure. I had exactly the
>same
>idea for a water level meter on a boat, but could not source any sensors to
>do the pressure measuring. Please advise.John Orhan
>Detection Systems / EDM Engineering Department
>Ph: 02 96721233 (ext 219)
>Fx: 02 9672 4093
>Email: RemoveMEjorhanspamTakeThisOuTedm.com.au
>
>
>{Original Message removed}

2000\06\04@182854 by Hugo Jorge Mčller

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John:
  search en http://www.motorola.com for MPX sensor line of sensor or search
Databook DL200/D ( Sensor device data/handbook) in the literature section of
web site.

Good luck.

Thanks to all that contribute to my original question " [EE][PIC] How to
measure level of liquids and sense relat ive humidity?"

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

----- Original Message -----
From: John Orhan <JOrhanEraseMEspam.....EDM.COM.AU>
To: <EraseMEPICLISTspammitvma.mit.edu>
Sent: Thursday, June 01, 2000 12:57 AM
Subject: Re: [EE][PIC] How to measure level of liquids and sense relat ive
humidity?


> Hi ,
> Where can I find sensors to measure the air pressure. I had exactly the
same
> idea for a water level meter on a boat, but could not source any sensors
to
> do the pressure measuring. Please advise.John Orhan
> Detection Systems / EDM Engineering Department
> Ph: 02 96721233 (ext 219)
> Fx: 02 9672 4093
> Email: RemoveMEjorhanEraseMEspamEraseMEedm.com.au
>
>
> {Original Message removed}

2000\06\05@074905 by Mike Witherden

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face
The most accurate maturement of liquid level I have dealt with in the Petro
Chemical Industry is the long wire float method, where a float is guided on
one or two vertical wires which run from the top to the bottom of the tank.

The float then either has a flexible wire of some sort  which runs from the
float up to a spool on the top of the tank so the height of the liquid is converted
into a rotational position which can be read using a potentiometer. (some
gearing may be used.) (This can also be done digitally.)

The top of the float may also be used as a reflector and a simple beam of
light or Infra Red or laser etc can be reflected of the top of the float giving a
very accurate reading once the height of the float above the liquid is subtracted.

If the whole thing is put into a 'still tube' the effect of liquid sloshing around is eliminated.

This method enables you to very accurately read liquid levels in tanks tens of
meters high containing just about anything.

MikeW



2000\06\05@121350 by Mike Witherden

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face
The most accurate maturement of liquid level I have dealt with in the Petro
Chemical Industry is the long wire float method, where a float is guided on
one or two vertical wires which run from the top to the bottom of the tank.

The float then either has a flexible wire of some sort  which runs from the
float up to a spool on the top of the tank so the height of the liquid is converted
into a rotational position which can be read using a potentiometer. (some
gearing may be used.) (This can also be done digitally.)

The top of the float may also be used as a reflector and a simple beam of
light or Infra Red or laser etc can be reflected of the top of the float giving a
very accurate reading once the height of the float above the liquid is subtracted.

If the whole thing is put into a 'still tube' the effect of liquid sloshing around is eliminated.

This method enables you to very accurately read liquid levels in tanks tens of
meters high containing just about anything.

MikeW



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