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'Sensor questions (maybe [OT])'
1998\04\07@224814 by Clyde Smith-Stubbs

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I need some suggestions on a couple of sensors;

1) I need to measure water level (and thus contents) in a concrete tank.
The tank is about 2m deep, so a float is probably not practical. My
thoughts are either an ultrasonic setup to detect the water surface,
or a pressure sensor. The ultrasonic setup will be complicated, the pressure
sensor would either have to be at the bottom of the tank, or above it with
a hose to the bottom. The hose idea would rely critically on having no air leaks
in the hose, difficult to guarantee for a long time. Submerging the pressure
sensor would leave it liable to getting blocked by stuff on the bottom of the
tank.

2) I need a "light beam" sensor to detect vehicles or people moving down
a driveway - much like a door minder used in shops, but to operate outdoors
spanning a distance of about 20m. It should preferably use infra-red so as not
to be visible (this is not critical, but if it uses visible light it should not
be too bright). The electronics side of this is reasonably straightforward - I'd
modulate the beam at some frequency, recover the modulation and differentiate it
to detect sudden interruptions. This should make it immune to external lighting,
fog etc. The hard part is what kind of light source, detector and lenses to use,
especially for infrared.

All suggestions from this esteemed collection of minds will be gratefully
received.

Clyde

--
Clyde Smith-Stubbs               |            HI-TECH Software
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1998\04\07@233737 by Bob Fehrenbach

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Clyde Smith-Stubbs <clydespamKILLspamHTSOFT.COM> wrote:
>I need some suggestions on a couple of sensors;
>
>1) I need to measure water level (and thus contents) in a concrete tank.
>The tank is about 2m deep, so a float is probably not practical.

   Far out idea #1.
   If the chemical content of the water is constant, you may
   consider the possibility of measuring the conductivity
   between two vertical metal rods.

   Far out idea #2.
   Measure the capacitance between two *insulated*, closely
   spaced vertical plates.

>2) I need a "light beam" sensor to detect vehicles or people moving down
>a driveway - much like a door minder used in shops, but to operate outdoors
>spanning a distance of about 20m.

   I have tested two different brands of 'universal' TV remotes. Both
   performed well at distances of over 20m.  The receiver was able to
   properly decode one of them at a distance of 30m.  To be fair, this
   was indoors but since it appears that you are only looking for
   presence or absence of the beam, it would seem that this should be
   worth a look.


--
Bob Fehrenbach    Wauwatosa, WI     .....bfehrenbKILLspamspam.....execpc.com

1998\04\08@002621 by Clyde Smith-Stubbs

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On Tue, Apr 07, 1998 at 10:00:26PM -0500, Bob Fehrenbach wrote:

>     Far out idea #1.
>     If the chemical content of the water is constant, you may
>     consider the possibility of measuring the conductivity
>     between two vertical metal rods.

Hmm, it's rainwater, so it's probably both not constant, and very low.

>     Measure the capacitance between two *insulated*, closely
>     spaced vertical plates.

That idea has some merit, although the mechanical aspect is a bit
challenging (remember the water level can vary by up to 2 meters).

>     I have tested two different brands of 'universal' TV remotes. Both

Good idea - at least the IR diode is. Also, the distance to be covered is
20m, but the emitter and detector will have to be at the same side with a
reflector on the other (well, maybe not, but the alternative is running
more cable). I had forgotten about IR diodes :-) Derated incandescent lamps
are a good source of IR, but don't modulate well.

--
Clyde Smith-Stubbs               |            HI-TECH Software
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1998\04\08@002627 by D. F. Welch

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At 10:00 PM 4/7/98 -0500, you wrote:
>Clyde Smith-Stubbs <@spam@clydeKILLspamspamHTSOFT.COM> wrote:
>>I need some suggestions on a couple of sensors;
>>
>>1) I need to measure water level (and thus contents) in a concrete tank.
>>The tank is about 2m deep, so a float is probably not practical.

Clyde,
  Look at the National Semiconductor LM1830.  It should work
quite well.  I believe they have a couple of other level detector chips as
well.  The LM1830 is about $5.00 U.S. in single quantity

-Dan

>

1998\04\08@024553 by wft

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Subject:
         Sensor questions (maybe [OT])
   Date:
         Wed, 8 Apr 1998 12:47:47 +1000
  From:
         Clyde Smith-Stubbs <KILLspamclydeKILLspamspamHTSOFT.COM>



I need some suggestions on a couple of sensors;

1) I need to measure water level (and thus contents) in a concrete tank.

The tank is about 2m deep, so a float is probably not practical. My
thoughts are either an ultrasonic setup to detect the water surface,
or a pressure sensor. The ultrasonic setup will be complicated, the
pressure
sensor would either have to be at the bottom of the tank, or above it
with
a hose to the bottom. The hose idea would rely critically on having no
air leaks
in the hose, difficult to guarantee for a long time. Submerging the
pressure
sensor would leave it liable to getting blocked by stuff on the bottom
of the
tank.

>>Ultrasonic can be fairly simple  ( I think it would work...how about
the Polaroid >> setup from WIRZ electronics.   A pressure sensor
connected to copper or other metal pipe should hold correct reading for
a long time.

2) I need a "light beam" sensor to detect vehicles or people moving down

a driveway - much like a door minder used in shops, but to operate
outdoors
spanning a distance of about 20m. It should preferably use infra-red so
as not
to be visible (this is not critical, but if it uses visible light it
should not
be too bright). The electronics side of this is reasonably
straightforward - I'd
modulate the beam at some frequency, recover the modulation and
differentiate it
to detect sudden interruptions. This should make it immune to external
lighting,
fog etc. The hard part is what kind of light source, detector and lenses
to use,
especially for infrared.

>>  Buy a cheapie laser pointer (maybe $30), point it at a visible light
receiver, use a
>>  filter to cut any undesired intensity, adjust receiver.  Have
receiver located in end of
>> long tube to block non-desired light.
>>
>>  Or could use matched pair xmtr/rcvr with modulation included in
pair.  (See DigiKey)
>>  These are shorter distance however.

All suggestions from this esteemed collection of minds will be
gratefully
received.

Clyde
--
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1998\04\08@032331 by Richard Nowak

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At 02:00 PM 4/8/98 +1000, you wrote:
>On Tue, Apr 07, 1998 at 10:00:26PM -0500, Bob Fehrenbach wrote:
>
>>     Far out idea #1.
>>     If the chemical content of the water is constant, you may
>>     consider the possibility of measuring the conductivity
>>     between two vertical metal rods.
>
>Hmm, it's rainwater, so it's probably both not constant, and very low.

Add another very short sensor rod attached to the end of an insulated rod to
get it near the bottom of the pool equidistant from the long conductive
rods.  Set this up in a bridge configuration and drive it with a current
source.  Amplifiy the bridge output with an instrument amp and A/D the
output of the amp.  Haven't tried this - just an idea.

The third probe is used to calibrate out the variation of the rainwater
conductivity.

Rich

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1998\04\08@060730 by Clyde Smith-Stubbs

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On Wed, Apr 08, 1998 at 12:21:44AM -0700, Richard Nowak wrote:

> Add another very short sensor rod attached to the end of an insulated rod to
...
> The third probe is used to calibrate out the variation of the rainwater
> conductivity.

Now that is a great idea! Here's another; use a length of coax cable,
with the outer jacket removed, so the braid forms the long rod, and the
inner conductor, exposed only at the bottom, forms the reference electrode.
Just have to make sure the inner conductor is sealed well where it enters the
insulation. A weight attached to the end will hold it vertical.

I think we're getting somewhere here.

The suggestion someone else had about a laser pointer for a beam is
worth considering, except I can't see how to make it invisible - the receiver
could be in a tube, but in the presence of fog the beam would be very visible.
That may not be a big problem, though.

--
Clyde Smith-Stubbs               |            HI-TECH Software
Email: clydeEraseMEspam.....htsoft.com          |          Phone            Fax
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1998\04\08@111052 by Nicholas Irias

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For what its worth, float switches can be fit into small places.
A compact float switch involves two weights on a cable, hung
over a pulley (actually in contact with the pulley for 450 degtrees
so it doesnt slip).  One of the weights is buoyant and will rise
with the water level, thus turning the shaft.  The shaft is then
connected to a potentiometer for an analog output, or a shaft
encoder for digital.

But the practical way to do this is with a common pressure
sensor.  In the water industry, most tanks are monitored via
pressure sensor.  And each tank has an overflow level float switch
as a backup.  Pressure sensors dont fail often, but avoiding
accidental overflows is a high priority.



----------
{Quote hidden}

pressure
> sensor would either have to be at the bottom of the tank, or above it
with
> a hose to the bottom. The hose idea would rely critically on having no
air leaks
> in the hose, difficult to guarantee for a long time. Submerging the
pressure
> sensor would leave it liable to getting blocked by stuff on the bottom of
the
>  tank.
>
> 2) I need a "light beam" sensor to detect vehicles or people moving down
> a driveway - much like a door minder used in shops, but to operate
outdoors
> spanning a distance of about 20m. It should preferably use infra-red so
as not
> to be visible (this is not critical, but if it uses visible light it
should not
> be too bright). The electronics side of this is reasonably
straightforward - I'd
> modulate the beam at some frequency, recover the modulation and
differentiate it
> to detect sudden interruptions. This should make it immune to external
lighting,
> fog etc. The hard part is what kind of light source, detector and lenses
to use,
{Quote hidden}

---------------------------------------------------------------------------
> HI-TECH C: compiling the real world.

1998\04\08@120236 by Richard Nowak

picon face
>Here's another; use a length of coax cable,
>with the outer jacket removed, so the braid forms the long rod, and the
>inner conductor, exposed only at the bottom, forms the reference electrode.
>Just have to make sure the inner conductor is sealed well where it enters the
>insulation. A weight attached to the end will hold it vertical.

Continuing the refinement of the probe assembly:

Suspend a small diameter tube (to feed the wire for the third sensor) inside
a larger diameter tube. These tubes are kept separate from each other by a
non-conducting mesh similar to the tube mesh used for bundling cable wires.
You should use as open a mesh as possible.  The third sensor is attached at
the bottom of the inner tube but is electrically isolated from either of the
tubular sensor tubes.  The top end of the probe assembly must be vented to
allow the water to rise inside.

Now you have a small diameter compact probe assembly.

The close distance between the sensors afforded in this design lowers the
overall resistivity between the sensors.

I believe you could find such tubes in a hobby shop.  I've seen them in
places that specialize in R/C airplanes.  The length may be a problem though.

Rich

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1998\04\08@121859 by Todd Kanning

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Why not use an infra-red spectrum laser.  If you have a home video
camera which uses a CCD element you could use it to properly adjust the
beam. (since CCDs are sensitive to IR)  As far as I know this would
provide an acurate and invisible beam.  I would think you could also
easily use a reflector configuration to conserve cable.  If I remember
correctly, the IR spectrum lasers are generally less expensive than the
visible spectrum units.

1998\04\08@122114 by Mike Keitz

picon face
On Wed, 8 Apr 1998 00:33:18 -0600 Gus Calabrese <RemoveMEwftKILLspamspamMAIL.FRII.COM>
writes:

>I need some suggestions on a couple of sensors;
>
>1) I need to measure water level (and thus contents) in a concrete
>tank.

>   A pressure sensor
>connected to copper or other metal pipe should hold correct reading
>for
>a long time.

The method using pressure of air trapped in a pipe to the bottom of the
tank is used to control the filling of a clothes washer.  It works rather
well, though the air only has to stay trapped for a few minutes during
the filling process.  Even if the pipe were perfectly airtight, there
would still be a long-term problem of air being lost by dissolving in the
water, which would cause the water level in the pipe to rise and the
indicated level to fall.

It should be possible to use a small air pump to clear all water and
debris out of the pipe and also offset any small leaks.  Once air starts
to bubble (slowly) out of the bottom of the pipe, the pressure inside is
a correct representation of the water depth.  The air pump would only
need to run for a short time before taking a reading.  The pipe should
end an inch or so above the bottom to allow room for debris.

A vertical float in the form of a long tube could be used.  It wouldn't
have to move far; attach it to some sort of force sensor at the top.  The
higher the water rises, the greater the upward force from it.  Of course
at some level the force would become downward due to the weight of the
float.

If it's really important to detect overflow or underflow, back up the
continuous sensor with a float switch.  The types used to control sump
pumps appear to be widely available and duarable.

>2) I need a "light beam" sensor to detect vehicles or people moving
>down
>
>a driveway - much like a door minder used in shops, but to operate
>outdoors
>spanning a distance of about 20m.

Radio Shack used to sell such a unit, maybe they still do.  Infrared LEDs
and photodiodes should work but likely would need lenses.  The Radio
Shack unit has two lenses on it.  One unit functions as transmitter and
receiver and only a simple plastic reflector of the type used on bicycles
is needed at the other end.

> The electronics side of this is reasonably
>straightforward - I'd
>modulate the beam at some frequency, recover the modulation and
>differentiate it
>to detect sudden interruptions. This should make it immune to external
>lighting,
>fog etc.

I've had good results using the 567 tone decoder IC in a closed circuit
like this.  The oscillator signal modulates the source.  The input to the
chip comes from the detector (somewhere, there needs to be a 180 degree
phase inversion from OSC R to IN).  The phase detect output is shorted to
Vcc to force the oscillator frequency to stay constant.  Since the same
oscillator is used for transmitting and receiving, it doesn't matter if
the oscillator frequency drifts.  The 567 includes the oscillator,
synchronous detector, and level gate functions all in one chip.  It uses
more power than some other possible implementations but in this case
quite a bit of power is needed for the IR LED anyway.

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1998\04\08@150429 by Martin R. Green

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Just a quick note.  If you live in Canada, Radio Shack has a very
cheap little IR sensitive card that allows you to "see" the output of
IR lasers and remote controls.  It is credit card sized, and you just
expose it to flourescent (if I remember correctly) light for 1 minute,
then it is highly sensitive to IR light for several minutes.  It works
by reflecting the IR back in the visible spectrum.  A LOT cheaper than
a video camera if you don't already have one.

CIAO - Martin,

On Wed, 8 Apr 1998 10:41:43 -0500, Todd Kanning
<ra7677STOPspamspamspam_OUTEMAIL.SPS.MOT.COM> wrote:

>Why not use an infra-red spectrum laser.  If you have a home video
>camera which uses a CCD element you could use it to properly adjust the
>beam. (since CCDs are sensitive to IR)  As far as I know this would
>provide an acurate and invisible beam.  I would think you could also
>easily use a reflector configuration to conserve cable.  If I remember
>correctly, the IR spectrum lasers are generally less expensive than the
>visible spectrum units.

Martin R. Green
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1998\04\08@152729 by Kalle Pihlajasaari

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hi Clyde,

> > Add another very short sensor rod attached to the end of an insulated rod to
> ...
> > The third probe is used to calibrate out the variation of the rainwater
> > conductivity.
>
> Now that is a great idea! Here's another; use a length of coax cable,
> with the outer jacket removed, so the braid forms the long rod, and the
> inner conductor, exposed only at the bottom, forms the reference electrode.
> Just have to make sure the inner conductor is sealed well where it enters the
> insulation. A weight attached to the end will hold it vertical.

This little horse has had a few beatings already.  Use of a small fishtank
air pump is popular to keep the pipe clear for a pressure sensor type
system.

There is a company Miltronics in Texas and Canada that has released
(Ron in Canada tells me it is not ready until he has his marketing literature)
a Radar level sensor using the elusive MIR technology.  This has not
been confirmed but I can give you a number to call in the US (they wont talk
to me there) that you can check.  Obviously this may turn out to be
a rather expensive method but it rather interesting.

(817) 277-3543     (Texas for USA)
+1 (705) 745-2431  (Canada for international)

Ask about TDR - Radar - MIR level gage

From their web page
 http://www.milltronics.com/invest2.htm
 "Other technology inroads included our expansion into
  Micro Impulse Radar (MIR), a fourth quarter acquisition
  from Titan Pacific Resources Ltd."

From the LLNL web page
 lasers.llnl.gov/lasers/idp/mir/files/MIR_govt_info.html
 "4A. Fluid level sensor (electronic dipstick Version 1.0)"

> I think we're getting somewhere here.
>
> The suggestion someone else had about a laser pointer for a beam is
> worth considering, except I can't see how to make it invisible - the receiver
> could be in a tube, but in the presence of fog the beam would be very visible.
> That may not be a big problem, though.

You could go to the electric gate shop and buy a driveway beam break unit
if you want to avoid the pain.  There is also a device made by SHARP
that does what you want over a short distance but might be scaleable
with an ecternal transistor and more IR-LEDs (I gave up the scaling
excercise after 10 minutes but had other things on my mind at the
time).  The devices were/are available from RS components UK
(NOT Radio Shack) with stock number  564-396  and Sharp part number
of IS471F.  This has modulation, filtering and detector all built in
and is intended for a beam break system.  Ideal for ambient light systems
as it uses a SYNCHRONOUS detection system to cancel out sun and lights.
It is about 5 x 5 x 2.5 mm with 4 pins.

You might be able to drive a IR LASER diode (module or home built)
with the Sharp device to achieve LONG range (>1 km) but a bunch of
5mm IR LEDS in series should do the 20M even with a reflector.

A laser diode module and a 556 or PIC12C508 modulating a signal and
a Sharp (or other) remote control receiver module (IS1U60 works for me)
will allow you to do much the same but you need to send a 500 Hz
signal with a 38kHz carrier and then use another PIC12C508 to do
missing pulse detection.  The IR receivers (all that I have heard
of) are prone to falsing and ambient and carrier desensing so you
do need to use the 500 Hz squarewave modulation.
If you colocate the receiver and transmitter you will often have
problems with crosstalk hence the First Sharp device I mentioned.

Cheers
--
Kalle Pihlajasaari   KILLspamkallespamBeGonespamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer

1998\04\08@153153 by Shahid Sheikh

picon face
I have never tried to make any level measuring systems but here are a
couple of ideas. I dont know how practical they are.

The first one, depending on the resolution of the level measurement, you
can maybe have n parallel pairs of small conduction plates along one of the
walls of the tank and then check and see which pair of plates have a lower
resistance. Maybe have an array of simple BJT's that get turned on if their
corresponding plate is submerged. Then all the transistors can be connected
in a voltage adder format and you can get an analog level measurement. Or
you can use the output of each transistor individually to get a digital
readout.

The other idea is if the water collected is alway going to be very clean,
then maybe a focused beam of light can be injected into the water at an
angle and sensed by a sensor at the bed of the tank. The focused beam
source can be mounted on a stepper so that the incident angle can be
changed. Then you can find a relation between the incident angle of the
light beam and the level so that the light always shines on the sensor. The
stepper would need to track the light beam until the sensor picks up the
light beam. This maybe be too much trouble to do and may be too expensive
to implement and may have a high failure rate. Anyway, it was just a
thought.

Shahid

----------
From:   Clyde Smith-Stubbs[SMTP:EraseMEclydespamEraseMEHTSOFT.COM]
Reply To:       pic microcontroller discussion list
Sent:   Wednesday, April 08, 1998 12:00 AM
To:     @spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU
Subject:        Re: Sensor questions (maybe [OT])

On Tue, Apr 07, 1998 at 10:00:26PM -0500, Bob Fehrenbach wrote:

>     Far out idea #1.
>     If the chemical content of the water is constant, you may
>     consider the possibility of measuring the conductivity
>     between two vertical metal rods.

Hmm, it's rainwater, so it's probably both not constant, and very low.

>     Measure the capacitance between two *insulated*, closely
>     spaced vertical plates.

That idea has some merit, although the mechanical aspect is a bit
challenging (remember the water level can vary by up to 2 meters).

>     I have tested two different brands of 'universal' TV remotes. Both

Good idea - at least the IR diode is. Also, the distance to be covered is
20m, but the emitter and detector will have to be at the same side with a
reflector on the other (well, maybe not, but the alternative is running
more cable). I had forgotten about IR diodes :-) Derated incandescent lamps
are a good source of IR, but don't modulate well.

--
Clyde Smith-Stubbs               |            HI-TECH Software
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1998\04\08@164505 by Clyde Smith-Stubbs

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On Wed, Apr 08, 1998 at 10:41:43AM -0500, Todd Kanning wrote:
> Why not use an infra-red spectrum laser.  If you have a home video

Ok, any suggestions for a source?

> camera which uses a CCD element you could use it to properly adjust the

Well, actually I don't own a video camera - but I do have a Quickcam which
should do the job, although it's not quite as convenient.

> easily use a reflector configuration to conserve cable.  If I remember

Anybody know if the common plastic reflectors are good for IR?


--
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1998\04\08@190726 by Sean Breheny

face picon face
At 06:43 AM 4/9/98 +1000, you wrote:
>

<SNIP>

>Anybody know if the common plastic reflectors are good for IR?

AFAIK, anything which reflects red light well, will also reflect near IR
well. For instance, regular newtonian reflector telescopes will work
reasonably well at IR.

Sean


>
>
>--
>Clyde Smith-Stubbs               |            HI-TECH Software
>Email: .....clydespamRemoveMEhtsoft.com          |          Phone            Fax
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>---------------------------------------------------------------------------
>HI-TECH C: compiling the real world.
>
+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
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1998\04\08@192439 by TONY NIXON 54964

flavicon
picon face
As a simple set up, you may like to try a string pot connected to a
float in the tank. The pot value will change with level variations
and you could read to pot value with an A2D converter in a simple PIC.
At 2M depth an 8 bit A2D would have an approx. resolution of 8mm.

Tony


PicNPoke Multimedia 16F84 Beginners PIC Tools.

**PLUS** - PicNPlay - PicNPlan - PicNPrep - PicNPost
PicNPort - DT Type Saver - *new* PicNQuiz.
Recent addition - DogBoneZ Component.

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1998\04\08@231753 by RICHARD SKINNER

flavicon
face
I understand the concept of air being dissolved into the water, "but",  We
run that setup on locations
everywhere, with ss tubing ran to a "Wc Sensor,  We have no ill effects what
so ever.  Now granted, we
are not reading with great precision, but the sensor is used to trigger high
and low alarms and relays on
a pump.  I would say we are reading well within an inch of level in the tank.

An air pump "Would" be fool proof, "IF"  the location had electricity.

Richard Skinner
TakeThisOuTrwskinnerspamspamworldnet.att.net
http://home.att.net/~rwskinner

----------
{Quote hidden}

1998\04\09@000629 by wft

face
flavicon
face
Subject:
Sensor questions (maybe [OT])
   Date:
         Wed, 8 Apr 1998 12:47:47 +1000
  From:
         Clyde Smith-Stubbs <EraseMEclydespam@spam@HTSOFT.COM>



I need some suggestions on a couple of sensors;

1) I need to measure water level (and thus contents) in a concrete tank.

The tank is about 2m deep, so a float is probably not practical. My
thoughts are either an ultrasonic setup to detect the water surface,
or a pressure sensor. The ultrasonic setup will be complicated, the
pressure
sensor would either have to be at the bottom of the tank, or above it
with
a hose to the bottom. The hose idea would rely critically on having no
air leaks
in the hose, difficult to guarantee for a long time. Submerging the
pressure
sensor would leave it liable to getting blocked by stuff on the bottom
of the
tank.

>>Ultrasonic can be fairly simple  ( I think it would work...how about
the Polaroid >> setup from WIRZ electronics.   A pressure sensor
connected to copper or other metal pipe should hold correct reading for
a long time.

2) I need a "light beam" sensor to detect vehicles or people moving down

a driveway - much like a door minder used in shops, but to operate
outdoors
spanning a distance of about 20m. It should preferably use infra-red so
as not
to be visible (this is not critical, but if it uses visible light it
should not
be too bright). The electronics side of this is reasonably
straightforward - I'd
modulate the beam at some frequency, recover the modulation and
differentiate it
to detect sudden interruptions. This should make it immune to external
lighting,
fog etc. The hard part is what kind of light source, detector and lenses

to use,
especially for infrared.

>>  Buy a cheapie laser pointer (maybe $30), point it at a visible light

receiver, use a
>>  filter to cut any undesired intensity, adjust receiver.  Have
receiver located in end of
>> long tube to block non-desired light.
>>
>>  Or could use matched pair xmtr/rcvr with modulation included in
pair.  (See DigiKey)
>>  These are shorter distance however.

All suggestions from this esteemed collection of minds will be
gratefully
received.

Clyde
--
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4337 Raleigh Street      Denver, CO 80212
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1998\04\09@013515 by Andrew John Thoms

flavicon
picon face
It is possible to get laser diodes that only radiate in the IR part of the
spectrum. I don't know where or how much though.


Andrew

     |
     |         "For God so loved the  world that
 ----+----      he  gave his only son,  that who
     |          so ever believes in him will not
     |          perish but have eternal life"
     |                                 John 3:16
     |
     |

1998\04\09@020234 by bam-mon

flavicon
face
Clyde Smith-Stubbs wrote:
>
> I need some suggestions on a couple of sensors;
>
> 1) I need to measure water level (and thus contents) in a concrete tank.
> The tank is about 2m deep, so a float is probably not practical. My
> thoughts are either an ultrasonic setup to detect the water surface,
> or a pressure sensor. The ultrasonic setup will be complicated, the pressure
> sensor would either have to be at the bottom of the tank, or above it with
> a hose to the bottom. The hose idea would rely critically on having no air
leaks
> in the hose, difficult to guarantee for a long time. Submerging the pressure
> sensor would leave it liable to getting blocked by stuff on the bottom of the
>  tank.
>
> 2) I need a "light beam" sensor to detect vehicles or people moving down
> a driveway - much like a door minder used in shops, but to operate outdoors
> spanning a distance of about 20m. It should preferably use infra-red so as not
> to be visible (this is not critical, but if it uses visible light it should
not
> be too bright). The electronics side of this is reasonably straightforward -
I'd
> modulate the beam at some frequency, recover the modulation and differentiate
it
> to detect sudden interruptions. This should make it immune to external
lighting,
> fog etc. The hard part is what kind of light source, detector and lenses to
use,
> especially for infrared.
>
> All suggestions from this esteemed collection of minds will be gratefully
>  received.
>
> Clyde

To 1)
Have a look at the Magazin ELRAD (from Germany), 2/98 and 3/98, they've
got a
project doing exactly what you want (measuring the waterlevel in a tank
using ultrasonic and controlling various pumps and so on)
Hope I could help a bit,

greetings ,
            Reelf

--
        BAMBERG & MONSEES GbR
 Systeme f|r Wissenschaft und Technik
   Am Postmoor 36 * D-28719 Bremen
Fon +49-421-646775 * Fax +49-421-646785

1998\04\09@031448 by Clyde Smith-Stubbs

flavicon
face
On Wed, Apr 08, 1998 at 09:35:31PM -0500, RICHARD SKINNER wrote:
> I understand the concept of air being dissolved into the water, "but",  We
> run that setup on locations
> everywhere, with ss tubing ran to a "Wc Sensor,  We have no ill effects what
> so ever.  Now granted, we

How often is the bottom of the tube uncovered? This approach is certainly one of
the most convenient from the mechanical point of view, particularly as the tube
could
be run some distance back to a more convenient location for the electronics.
Which
would also make it more feasible to hook in an air pump (the common fish tank
pumps require mains supply since they're just mains frequency vibrators).

Incidentally, the excellent response to this question probably justifies more of
an explanation of the application. I recently moved to a new house which has no
town water and relies on rainwater for household use (so did my old house, but
its single tank had a readily accessible manhole to inspect the contents).

There are two tanks, each about 7000 gallons (imperial); the main tank is filled
from the house roof, and water is drawn from it with a pressure pump. The other
tank
is filled from the garage roof, and also overflow from the main tank, which is
about
2m higher. I just had a pump fitted to allow water to be transferred from the
lower tank to the main one. The level sensing is mainly to know when the top
tank is getting low, so the pump can be turned on refill it. It's also handy to
know when you're about to run out of water (in the middle of a shower is not
a great time) - in dry times it may be necessary to get water trucked in.

Once the level sensing is working ok, I will probably rig it to turn the
transfer
pump off once the tanks reach certain levels, but will probably leave the pump
activation as a manual operation.

Of course this could probably be done just by calling a professional, but then
I wouldn't learn anything :-)

Cheers, Clyde

--
Clyde Smith-Stubbs               |            HI-TECH Software
Email: .....clyde@spam@spamEraseMEhtsoft.com          |          Phone            Fax
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---------------------------------------------------------------------------
HI-TECH C: compiling the real world.

1998\04\09@100025 by Tom Handley

picon face
re: Water level

  Clyde, The common methods of level measurement are floats, ultrasonic,
and RF capacitive sensors. It would help to know a little more about the
application. What kind of resolution do you need? Is the water agitated?
It sounds like you are just collecting rain water in a concrete tank.

  If you just need to know when the tank is full or empty (half-full, etc),
the LM1830 Fluid Level Detector IC is a good choice. It's low cost and very
easy to use. It's designed to detect the presence or absence of a liquid
using conductivity between two metal probes. It excites the probes with AC
which is important with any probe-based techniques to prevent plating.

  Another possibility is a float sensor. You can easily fabricate one
using PVC pipe and fittings for the float. You install magnets in the float
and use reed switches in the pipe. You only need one for a single level. For
additonal levels, you connect them in a series that changes the tap on a
voltage divider.

  For continuous measurements, I'd recommend an ultrasonic sensor. There
have been several projects using the Polaroid module and someone around here
did a low cost PIC-based sensor. Actually, you might just want to buy one of
those cheap distance measuring units from Radio Shack or hardware stores.
That would be easy to `hack'. They cost around $20-$30 and are good out to
40ft or so.

  For capacitive measurement, it would be nice if you had a metal tank...
Given a concrete tank, the most accurate solution is a coaxial probe. The
outer tube is exposed and provides the ground. The inner probe is insulated.
Of course you need to allow for water flow between the two. You could also
use two parallel rods separated by plastic spacers. Again, one rod has to be
insulated. Both versions are fairly immune to contaminates and will provide
a proportional change in capacitance. This capacitance varies the frequency
of an RF oscillator.

  Omega has a good reference in their "The Flow and Level Handbook".

     http://www.omega.com

re: Light Beam sensor

  `Way back when' I was designing IR limit switches for use in saw mills
and Hanna car washes, where the environment included steam, sunlight,
blowing dust, etc. We used a single IR LED and a 1" lens. In testing, we
were able to go several hundred feet with bright sunlight comming into the
receiver. We used a simple 555 timer to pulse the LED and a high-pass filter
on the receiver that fed into another 555 timer configured as a
`missing pulse' detector. We also added an IR filter to the receiver. You
use standard optical design methods for the lens, adjusting for the IR
wavelength. Now days there are lot's of ways to do this.

  Back to your design, you wanted to use a reflector to cut down on the
cable length between the transmitter and receiver. One problem that comes to
mind is that the object (ie: a vehicle) could reflect the signal back to the
receiver and not interrupt the beam. You can reduce this problem with
optical shielding such as a tube but I still think you will get false
readings. A remote receiver eliminates this problem. Another consideration
is the kind of `traffic' you expect in this area. You would want to keep the
beam above dogs, etc. If you have deer or livestock in the area, you have a
new set of problems ;-)

  - Tom

At 12:47 PM 4/8/98 +1000, Clyde Smith-Stubbs wrote:
>I need some suggestions on a couple of sensors;
>
>1) I need to measure water level (and thus contents) in a concrete tank.
>The tank is about 2m deep, so a float is probably not practical. My
>thoughts are either an ultrasonic setup to detect the water surface,
>or a pressure sensor. The ultrasonic setup will be complicated, the pressure
>sensor would either have to be at the bottom of the tank, or above it with
>a hose to the bottom. The hose idea would rely critically on having no air
leaks
>in the hose, difficult to guarantee for a long time. Submerging the pressure
>sensor would leave it liable to getting blocked by stuff on the bottom of the
> tank.
>
>2) I need a "light beam" sensor to detect vehicles or people moving down
>a driveway - much like a door minder used in shops, but to operate outdoors
>spanning a distance of about 20m. It should preferably use infra-red so as not
>to be visible (this is not critical, but if it uses visible light it should not
>be too bright). The electronics side of this is reasonably straightforward
- I'd
>modulate the beam at some frequency, recover the modulation and
differentiate it
>to detect sudden interruptions. This should make it immune to external
lighting,
>fog etc. The hard part is what kind of light source, detector and lenses to
use,
{Quote hidden}

1998\04\09@105315 by WIL REEDER

flavicon
face
I have a rainwater system at my get away in the Gulf Islands and have the
same questions. There is enough carbonic and sulfuric acid in the rain to
use ss rods but if you want to obtain a sort of gas gauge here's the
ticket: a plastic tube containing reed switches connected to a resistor
ladder then to a pin on your pic. the tube is sealed on both ends with the
wires out of one end. then a large cork fitted with a magnet is drilled and
fitted captive on the tube. epoxy coat the float and this set-up will last
for years.

Good Luck

Wil Reeder
Vancouver, Canada

----------
> From: Clyde Smith-Stubbs <RemoveMEclydespamspamBeGoneHTSOFT.COM>
> To: spamBeGonePICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject: Re: Sensor questions (maybe [OT])
> Date: Wednesday, April 08, 1998 11:59 PM
>
> On Wed, Apr 08, 1998 at 09:35:31PM -0500, RICHARD SKINNER wrote:
> > I understand the concept of air being dissolved into the water, "but",
We
> > run that setup on locations
> > everywhere, with ss tubing ran to a "Wc Sensor,  We have no ill effects
what
> > so ever.  Now granted, we
>
> How often is the bottom of the tube uncovered? This approach is certainly
one of
> the most convenient from the mechanical point of view, particularly as
the tube
>  could
> be run some distance back to a more convenient location for the
electronics.
>  Which
> would also make it more feasible to hook in an air pump (the common fish
tank
> pumps require mains supply since they're just mains frequency vibrators).
>
> Incidentally, the excellent response to this question probably justifies
more of
> an explanation of the application. I recently moved to a new house which
has no
> town water and relies on rainwater for household use (so did my old
house, but
> its single tank had a readily accessible manhole to inspect the
contents).
>
> There are two tanks, each about 7000 gallons (imperial); the main tank is
filled
> from the house roof, and water is drawn from it with a pressure pump. The
other
>  tank
> is filled from the garage roof, and also overflow from the main tank,
which is
>  about
> 2m higher. I just had a pump fitted to allow water to be transferred from
the
> lower tank to the main one. The level sensing is mainly to know when the
top
> tank is getting low, so the pump can be turned on refill it. It's also
handy to
> know when you're about to run out of water (in the middle of a shower is
not
> a great time) - in dry times it may be necessary to get water trucked in.
>
> Once the level sensing is working ok, I will probably rig it to turn the
>  transfer
> pump off once the tanks reach certain levels, but will probably leave the
pump
> activation as a manual operation.
>
> Of course this could probably be done just by calling a professional, but
then
> I wouldn't learn anything :-)
>
> Cheers, Clyde
>
> --
> Clyde Smith-Stubbs               |            HI-TECH Software
> Email: clydespam_OUTspam@spam@htsoft.com          |          Phone            Fax
> WWW:   http://www.htsoft.com/    | USA: (408) 490 2885  (408) 490 2885
> PGP:   finger spamBeGoneclyde@spam@spamhtsoft.com   | AUS: +61 7 3354 2411 +61 7 3354 2422
>
---------------------------------------------------------------------------
> HI-TECH C: compiling the real world.

1998\04\09@115507 by John Halleck

flavicon
face
On Tue, 7 Apr 1998, Bob Fehrenbach wrote:

> >1) I need to measure water level (and thus contents) in a concrete tank.
> >The tank is about 2m deep, so a float is probably not practical.
>
>     Far out idea #1.
>     If the chemical content of the water is constant, you may
>     consider the possibility of measuring the conductivity
>     between two vertical metal rods.
>
>     Far out idea #2.
>     Measure the capacitance between two *insulated*, closely
>     spaced vertical plates.

     Far out idea #3.
     Strain guage to measure flex of the bottom of the tank,
     and use it to derive weight and therefore volume.
     (I guess it is non-linear, but you could use a calibration
     table.)

1998\04\09@130232 by wft

face
flavicon
face
There are PSDs  (position sensitive diodes).   You shine a beam at a
reflector (at a slight angle) and depending on the distance, the beam is
deflected.  A PSD develops a voltage proportiional to the postion along
it's length that the beam strikes.

Gus


--
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4337 Raleigh Street      Denver, CO 80212
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1998\04\09@130855 by Frank Mckenney

flavicon
face
On Wed, 8 Apr 1998 14:00:01 +1000, Clyde Smith-Stubbs responded with:
>On Tue, Apr 07, 1998 at 10:00:26PM -0500, Bob Fehrenbach wrote:
--snip--
>>     Measure the capacitance between two *insulated*, closely
>>     spaced vertical plates.
>
>That idea has some merit, although the mechanical aspect is a bit
>challenging (remember the water level can vary by up to 2 meters).

Clyde,

PMFJI, but what I picture is two metal strips, plastic-coated, with
non-conducting spacers bolted between them at intervals to ensure uniform
separation . Is the problem with mounting them?  Getting them insulated in
the first place?  Or something else I'm just overlooking?

Actually, you could just hang the "sensor" inside a piece of PVC pipe and
dangle it into the tank for testing (;-).

What precision do you need?  To a tenth of an inch?  An inch?  Or 1/4 or
1/10th of a full tank, like an automobile gas gauge?

Heck, if you don't need to be all that accurate, you could float a foam
plastic cylinder inside a PVC pipe which has LED/photosensor pairs mounted
at intervals.  The rising cylinder blocks one or more sensors as it rises,
giving you a position within 1/2 sensor distance.


Frank McKenney            / OS/2 Advisor (OS2BBS)
McKenney Associates       / Richmond, Virginia / (804) 320-4887
Internet: EraseMErrs0059RemoveMEspamSTOPspamibm.net / TalkLink: WZ01123

1998\04\09@213621 by Clyde Smith-Stubbs

flavicon
face
On Wed, Apr 08, 1998 at 09:10:40AM -0600, John Halleck wrote:
>       Far out idea #3.
>       Strain guage to measure flex of the bottom of the tank,

Ah, not practical for this application; the tank is concrete, cast on
site, and buried in the ground.

--
Clyde Smith-Stubbs               |            HI-TECH Software
Email: RemoveMEclydeKILLspamspamTakeThisOuThtsoft.com          |          Phone            Fax
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1998\04\09@234029 by Clyde Smith-Stubbs

flavicon
face
On Thu, Apr 09, 1998 at 07:47:50PM -0700, WIL REEDER wrote:
> use ss rods but if you want to obtain a sort of gas gauge here's the
> ticket: a plastic tube containing reed switches connected to a resistor

You'd need a lot of reed switches - given that you want to have at least one on
at any time, and the water level can vary by 2 meters.

Right now the most attractive proposition looks like a weighted plastic tube
running back to a fish-tank air pump and pressure transducer. One pump can
be used for more than one tube, with one-way valves. The really big advantage of
this is that you can run the tubing a long distance from the tank to a
convenient
place for the electronics with no complicated mechanical bits to construct.

1998\04\10@024612 by Michael Ghormley

flavicon
face
Clyde,

For my two cents, ultrasonic measurement looks like the best solution to
your fluid level problem.  Submersing anything electronic just has to
fail eventually.  There are commercial units available or you could "roll
your own."

If you can do a little German --> English translating, I have tracked
down that ELRAD magazine that Reelf suggested, and found their back isues
page at:

       http://www.elrad.de/hefte.html

Although you probably already know this, I'll also pass along these two
links:
       Paul's Cheap Sonar
       http://www.hamjudo.com/sonar/

       Serial Sonar Unit (SSU)
       http://www.pacificnet.net/notesguy/

Your project is a comparatively simple sonar application compared to a
mobile robot.  You have no movement of the transducers or wind (i.e. no
harmonics from vibrations).  You have a controlled environment where you
won't be getting multiple reflections from people walking by, etc.  You
have a very short distance to measure.

We had had a discussion much earlier on this list in which someone
suggested that rather than counting the time for an individual pulse to
go out and return, you could set a counter to zero and begin sending
pulses for a given amount of time.  Every time a ping was received the
counter was incremented and another ping was sent.  After a set amount of
time (maybe timer 1 timing out), the number of pings were counted and
this would give you a very good idea of how far the fluid level was from
the sensor.  It would even average out some ripple in the tank.  It only
works in controlled environments where multiple feedback paths (such as
from more than one object in the path of the ping) are absent.  Your
fluid tank sounds like a strong candidate for this method.

I am no sonar guru, but if I can be of any further help just drop me a
line via personal E-mail.  I even have the schematics (somewhere) that my
students drew up a few years back.  The code was 8051 FORTH,
unfortunately.

Just my ideas, your mileage may vary.

Michael

REMOVE THE .NS (NO SPAM) FROM MY ADDRESS TO REPLY
*****************************************
The strong do what they have to do and
the weak accept what they have to accept.
                            --Thucydides

1998\04\10@082301 by paulb

flavicon
face
Hello Clyde et. al.

 Thoughts various:
1) Tank.

 * Absolute pressure sensor sealed in dry nitrogen (with dessicant)
into silicone bag containing lead weight.  Sealed onto end of cable,
sits on bottom of tank.

 * I like the one about the long bottom-weighted float hanging from a
force transducer above the tank.

 * I really wouldn't be using copper braid as an electrode.

 * For capacitive sensing, use ready-made assembly such as "ladder"-
line for antenna feed (ribbon may work just fine too).  Must be well-
sealed at bottom end to prevent water ingress, where sinker is attached.

 * Pressure pipe to bottom of tank is OK, needs pump, fish-tank pumps
are *not* usually rated to 2m head of water however.

 * If you only want "digital" sensing, (i.e., single level per device)
use a standard float switch, bought or made.  This consists of a mercury
switch in a float on the end of a short loose flexible cable tethered to
the tank wall and which either points up or down, which the mercury
switch senses.  Terribly easy!

2) Driveway.

 * I-R lasers are cheap (kits new, or recycled from printers and CD
mechanisms), bright, work with very small lenses, easily adjusted with
either a SniperScope or a (B/W) video camera.  If the receiver is about
2" away and you use hoods on source and receiver with a red "corner"
reflector, spurious reflection from intermediate objects should be
negligible.

> The hard part is what kind of light source, detector and lenses to
> use, especially for infrared.

 Source: Laser.  Modulation: Few hundred Hz, synchronous detection.
Lens comes with laser usually.  Detector: IR filtered photodiode in
black tube, no lens.  No need with laser but beware of spiders.
Reflector: red or white 1" bicycle reflector.

 Cheers,
       Paul B.

1998\04\10@204847 by Andy Kunz

flavicon
face
ANother option would be to use a ventable sealed tube connected to a
controlled air source.

Assuming the tank of water is not sealed, here's how it works:

       Remove all air pressure from the tube (simple valve).

       Add a known VOLUME of air.

       Measure the pressure.

       High pressure --> higher water level.

       Use the gas laws (or a simple look-up table) to calculate the height.

       If you do this within a short period of time, T can be considered
constant.  Also, there will be essential 0 air dissolved into the slightly
pressurized water, so that can be discounted.

Your best source of air would be from above the water, as it would probably
have the same ambient temperature.

I have used a similar concept to measure when chemical bottles are full.
The liquid is allowed to continue to rise until there is a sudden change in
pressure in a tube set so it's end is at the full point.  If you have foam,
you can sense that too, as the pressure is rising but not nearly as quickly.

Andy

==================================================================
                    Andy Kunz - Montana Design
         Go fast, turn right, and keep the wet side down!
==================================================================

1998\04\10@220121 by Chuck Rice

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You might try getting a length of muscle wire a little longer than the
depth of the water. Attach one end to the bottom of the tank. The other,
attach thru a spring and a switch to the top of the tank.  Heat the wire
and determine now long it takes to pull the switch. The time required to
heat the wire will differ depending on how much of the wire is in the water
(heatsink). When the tank is full of water, the response will be slower.
When empty it will be faster. You will need to set the spring and switch
such that the entire muscle wire has contracted before it trips the switch,
otherwise, the  contraction of the part in the air at the top of the tank
will always trip it. -Chuck-

__________________________________________________________________________
Chuck Rice                                     <RemoveMEChuckspam_OUTspamWildRice.com>

1998\04\11@130025 by Reginald Neale

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>You might try getting a length of muscle wire a little longer than the
>depth of the water. Attach one end to the bottom of the tank. The other,
>attach thru a spring and a switch to the top of the tank.  Heat the wire
>and determine now long it takes to pull the switch. The time required to
>heat the wire will differ depending on how much of the wire is in the water
>(heatsink). When the tank is full of water, the response will be slower.
>When empty it will be faster. You will need to set the spring and switch
>such that the entire muscle wire has contracted before it trips the switch,
>otherwise, the  contraction of the part in the air at the top of the tank
>will always trip it. -Chuck-
>

That's a very innovative idea. Wouldn't it be even better to open a NC
switch and time the relaxation response, which is slower and more
environment-dependent?

Reg Neale

1998\04\11@132802 by William Cornutt

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While I have not been keeping up with this string and am not sure of what susgestions have been made, here are mine, hope they are not repeats.

First method,
take all your wife's perals, string them together so the string reaches >from the top to the bottom of the tank.  The weight of the string will change with the depth of water.

Second method,
the inverse of the first,  Tie your kids wooden blocks to a string so that is twice as long as the tank is deep.  Only tie the blocks to one half of the string.  put the string through a eylet at the bottom of the tank and weigh the pull on it at the top of the tank.  As the water deepens, more blocks will be held under water and the pull will increase.  This has the added benifit of letting you visually measure the depth by counting the blocks floating in the tank.

Third method,
tie the blocks instead of string pearls and use the first method.

Forth method,
kinda of off the wall a little.  It uses a effect that I became aware of while bathing as a kid.  Run a tube down to the bottom of the tank.  pump packets of air into it and listen for the bubble to burst at the top.

Hope this helps,

Bill C.   wcornuttspamspamslip.net

1998\04\12@010439 by Alan King

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William Cornutt wrote:
>
> While I have not been keeping up with this string and am not sure of what
susgestions have been made, here are mine, hope they are not repeats.
>
> First method,
> take all your wife's perals, string them together so the string reaches from
the top to the bottom of the tank.  The weight of the string will change with
the depth of water.

 Likewise I haven't been keeping up too well but thought of something
kind of similar..

 Put a spool and line on a stepper motor.  On the end of the line have
a fishing weight and ping-pong ball, coating the weight in epoxy or
don't use lead if it's drinking water.  Pay out the line and it will
magically become lighter when it hits the water.  You could even put the
shaft in a bearing on a strain gague.  Know what the max weight is out
of water and min is with float supporting weight.  Have the motor wind
up and down to keep the strain about halfway in between and you have a
continuous readout.  Could maybe get by without the strain gague.
Microswitch on top and bottom and spring pulling up on shaft instead.
Weight out of water = switch on bottom closed.  Float all in supporting
weight = spring pulling up closes up switch.  Somewhere in between both
switches off and the float/weight will be riding water level.

 Then throw in a big serial eeprom and thermistor to log level and
temp.  Big drop = water use, big gain = pump, little gain = rain (maybe
not so little), little drop with rate following temp = evaporation rate.

 Yeah it's mechanical, but steppers don't fail too often.  And maybe
put a switch at top to pull float up and index occaisionally.  Or
homemade disk/opto simple encoder on shaft or dots on line.  Seal it all
up in a box with only hole out for line and power and you're set.  Get a
motor with right detent torque and only check level and move every 10
secs or minute and power off in between and it should last forever..

 Wow, perfect cheapie strain gague!  Find a worn out RC heli gyro.
Open gyro case and use magnet / hall effect bridge as the scale.
Sensitive enough with relatively light weight and float and low power
stepper motor.

Alan

1998\04\12@221032 by paulb

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Andy Kunz wrote:

> I have used a similar concept to measure when chemical bottles are
> full.  The liquid is allowed to continue to rise until there is a
> sudden change in pressure in a tube set so it's end is at the full
> point.

 Sounds like another application for - an electret microphone!

 Cheers,
       Paul B.

1998\04\13@011529 by wft

face
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Alan

I am not sure about the legality of revealing a measurement system that
is copyrighted by the US government.  Are you sure you want to run the
risk of being put in prison or worse (being forced to use the spool
method of tank level mesurement)

Gus





Put a spool and line on a stepper motor.  On the end of the line have
a fishing weight and ping-pong ball, coating the weight in epoxy or
don't use lead if it's drinking water.  Pay out the line and it will
magically become lighter when it hits the water.  You could even put the

shaft in a bearing on a strain gague.  Know what the max weight is out
of water and min is with float supporting weight.  Have the motor wind
up and down to keep the strain about halfway in between and you have a
continuous readout.  Could maybe get by without the strain gague.
Microswitch on top and bottom and spring pulling up on shaft instead.
Weight out of water = switch on bottom closed.  Float all in supporting
weight = spring pulling up closes up switch.  Somewhere in between both
switches off and the float/weight will be riding water level.


--
Gus Calabrese    Lola Montes      WFT Electronics
4337 Raleigh Street      Denver, CO 80212
303 964-9670......voicemail      spam_OUTwftspam_OUTspamspam_OUTfrii.com   http://www.frii.com/~wft

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1998\04\13@093456 by Timo Rossi

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On Wed, Apr 08, 1998 at 12:47:47PM +1000, Clyde Smith-Stubbs wrote:
> 2) I need a "light beam" sensor to detect vehicles or people moving down
> a driveway - much like a door minder used in shops, but to operate outdoors
> spanning a distance of about 20m. It should preferably use infra-red so
> as not to be visible (this is not critical, but if it uses visible light
> it should not be too bright). The electronics side of this is reasonably
> straightforward - I'd  modulate the beam at some frequency, recover
> the modulation and differentiate it to detect sudden interruptions.

There are ready-made commercial sensors (which use modulated IR beams)
for applications like this. But the distance you require is quite long,
I'm not sure if the typical sensors can handle it. You definitely
need the type with separate IR transmitters and receivers, the ones
using a mirror on the other side have much shorter distance limits.

(I have successfully used Omron sensors for detecting vehicles,
the distance was approx. 10 meters, which was the speficied
maximum distance for the sensors I used)

--
// Timo Rossi <KILLspamtrossispam.....iki.fi> //

1998\04\13@122438 by John Halleck

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On Sun, 12 Apr 1998, Gus Calabrese wrote:

> From: Gus Calabrese <spam_OUTwftspamKILLspamMAIL.FRII.COM>
> Reply-To: RemoveMEwftRemoveMEspamEraseMEfrii.com
>
> Alan
>
>  I am not sure about the legality of revealing a measurement system that
> is copyrighted by the US government.  Are you sure you want to run the

 More horseshit.

 Measurement systems are not "copyrighted" by anybody.

 1) As I keep pointing out US Copyright law (Title 17, US Code) has a section
 on what it can apply to... this aint it.

 2) US government publications (except for a few statutory exceptions)
 are not subject to copyright. Once again, See title 17 of the US code.

 3) I don't see any evidence that anything being discussed in the message
 has anything whatsoever to do with the US government.

{Quote hidden}

1998\04\13@142243 by Mike Keitz

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On Sun, 12 Apr 1998 23:04:35 -0600 Gus Calabrese <@spam@wftSTOPspamspam@spam@MAIL.FRII.COM>
writes:
>Alan
>
> I am not sure about the legality of revealing a measurement system
>that
>is copyrighted by the US government.

Of course, the US government can't copyright or patent anything.  All it
can do is try to keep it secret.  Most of the technologies used by the
government were developed by private companies, so there may be problems
there.

But a dropping float river level gauge is a very old idea.  Some early
ones were maintained by the phone company and accessed by telephone.  I
think they worked something like this:  When a call came in, the
mechanism would move the float down until it touched the water.  Then a
motor would slowly wind it back up.  The winding mechanism had a cam
linked to a bell.  Every 6 inches or so wound up, the bell would toll,
which would couple to a nearby telephone microphone.  The caller (a
person) would count rings of the bell and look at a chart for the
corresponding river level.  When the float reached the top home position
again, the motor would stop and the phone line would hang up.

With stepper motors and PIC chips, a much more high-tech implementation
of this technique is possible.  Although some moving parts are required,
all the operations are "digital".  No precise analog sensors or
processing is required.

Ideally, the spool at the top would be designed to wind the cable in one
layer, so the number of turns directly corresponds to a distance.  Using
a couple of turns on a drum with a counterweight on the other end of the
cable could make the winding more reliable but then the other cable with
weight attached has to be kept free of the float cable.  The weight and
some of the cable would be underwater all the time in between
measurements.

The tension in a cable is readily measured by passing it through a
zig-zag arrangement of eyelets.  The top and bottom eyelets are in a line
and held stationary.  The center eyelet is out of line and connected to a
micro switch.  Tension on the cable tries to pull the center eyelet in
line.  The switch is adjusted so the weight of the float will close it
but the weight of just the cable (when the float is floating on the
water) won't.  Another switch may be needed to detect when the float is
in the starting position, all the way up.  It would also be possible to
just operate the motor "up" for many steps to be sure that the float is
all the way up (then the motor will stall, and further steps are
ignored).  But then it isn't possible to double-check each measurement by
verifying that the number of steps "down" are roughly the same as the
number of steps "up".

It would also be possible to detect when the float reaches the water by
fitting electrodes on it, either two on the float or one on the float and
a "ground" somewhere else.  This seems almost as complicated as measuring
the tension, and also prone to fouling.  Another variation would be to
use a sinker, and detect electrically when it touches the surface and
mechanically when it touches the bottom.  This arrangement would be
self-calibrating for the height the mechanism is mounted above the
bottom.



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1998\04\13@143845 by Alan King

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John Halleck wrote:

>   Measurement systems are not "copyrighted" by anybody.
>
 Actually, I assumed he was kidding after comparing this method to
being put in prison..  And even to me, it does seem kinda cheesy doing
something simple/mechanical vs strain gague or ultrasonics.  But not
after I think about how many strain and ultrasonic sensors I've seen
that failed and how every stepper motor I've ever pulled from even the
most ancient workhorse printer etc worked fine.  Only stepper or two
I've ever seen failed something electronic went first and burned a
winding..

1998\04\13@160513 by n M. Ranguelov

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Gus Calabrese wrote:
>
> Subject:
>  Sensor questions (maybe [OT])
>     Date:
>           Wed, 8 Apr 1998 12:47:47 +1000
>    From:
>           Clyde Smith-Stubbs <clydespamBeGonespamspamBeGoneHTSOFT.COM>
>
> I need some suggestions on a couple of sensors;
>
> 1) I need to measure water level (and thus contents) in a concrete tank.
>
> The tank is about 2m deep, so a float is probably not practical. My
> thoughts are either an ultrasonic setup to detect the water surface,
> or a pressure sensor.


What resolution is needet ???

Do I am missing somwhat ? Here is my idea: sonds a little bit dumb but
very simple and cheap.

Why dont detect the presnce of whater between 2 probes ?
To prevent any chemical processes in the liquid or on the probes
only AC should be used. There are special chips for this as mentioned
befor.

I have done this with simple CMOS logic gates ( invertors with
schmidt-trigger
inputs) of the 74HCT14. One Gate is used as an multivibritor and is
coupled to one probe trough an Cap and the rest can detect the signal.
(no whater between the probes, no signal).

You can increase the resolution by increasing the number of probes.
For more then 4-5 probes you even can use a PIC at the sensor !

Use some wires with stripped ends as probes. The longest wire ends
at the bottom of the tank and is used as input. Make the striped
ends of the other wires ends in a fixed distans, say every 10 or 20 cm.
So you have 20 or 10 steps for the 2 m tank. Hook this wires trough
caps to PIC pins. For every elektrode generate some pulses on the
pin and look if there is a signal on the sensing elektrode. The PIC
can serial transmit the level value to a controller/display station.


I suppose this method should be immune to dirt in the water.
For clean water maybe silver pleated or carbon electrodes should
be used.


just my 2 cents on the long thread.

St.

wi

1998\04\14@095411 by Tom Handley

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  Timo, you can easily use standard IR LEDs and a lens for the distance
that Clyde requires. We did this in the early 70's... Our products were
required to operate in harsh environments with steam, direct sunlight, etc.
Now days you could easily do this for around $10 in parts not counting
packaging. The main problem I have with the use of reflectors in Clyde's
application, is that IR is going to reflect off of other surfaces such as
vehicles. He really needs a separate transmitter and receiver to ensure the
beam is blocked.

  As far as the rain water tank level, this has turned into a `Rube Goldberg'
contest... After Clyde posted his actual requirement, that of measuring when
the upper tank is getting low, a simple float switch could be used. Heck, you
could use a toilet float and a mecury switch... In anycase, no power would be
required for the sensor, no maintenance, the electronics (even a simple relay)
could be located at a good distance from the tanks, and it would last longer
than the human occupants...

  - Tom

At 04:33 PM 4/13/98 +0300, Timo Rossi wrote:
{Quote hidden}

1998\04\14@101942 by Keith Howell

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Tom Handley wrote:
> this has turned into a `Rube Goldberg' contest...

I agree. BTW, in the UK our equivalent of Rube Goldberg was
a chap called Heath Robinson. I wonder which of them had the
original idea for cartoons of ridiculously complicated
contraptions? Nowadays I guess they'd simply draw a computer.

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