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'[EE]: Conductive Liquid Sensor'
2001\09\21@005337 by Dave VanEe

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face
Hello,
I'm trying to make a simple fuel level indicator for a fuel tank.  I only
need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
I'm thinking of having two wires (or other electrical contact) actually -in-
the gas, and using the fuel to "close the switch".  I'm pretty sure this
would work for water, but I don't know if the gas will be able to conduct
electricity well enough.  There is also the ignition issue, but at the
voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
for my purposes.

Does anyone have any idea if this would work, or possibly have another
suggestion?

Thanks,
Dave

PS: I will be putting some gas in a container and checking the resistance w/
a multimeter to test it myself, but there might be a better solution.

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2001\09\21@012601 by Sean H. Breheny

face picon face
Hi Dave,

I'm pretty sure that gas does not conduct since conduction in liquids
requires ions in the liquid and gas should have very few ions.

What conditions does this have to work under? Does it have to work even if
the tank is not level? Does it have to deal with "sloshing"? I'm pretty
sure that the general consensus of this list (based on previous similar
threads) is that float sensing is the best and simplest way, although
weighing the tank might also be a workable solution.

Sean

At 09:16 PM 9/20/01 -0700, you wrote:
{Quote hidden}

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2001\09\21@021233 by Dave VanEe

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The tank will be in a racecar travelling at speeds up to 100mph.  There will
be sloshing (some effort will be put in to reduce this).  The float idea
seems to require excess mechanical components.  Weighting the tank is not
really an options since that's extra weight on the car.  If I had the need
for a full range of fuel levels I would use a float for sure, but since I
only need a few values I figure there's a better (easier) method out there.

Dave

PS: I caught the hint to check archives more, will do.


{Quote hidden}

actually -in-
{Quote hidden}

w/
{Quote hidden}

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2001\09\21@021300 by Jinx

face picon face
> sure that the general consensus of this list (based on previous
> similar threads) is that float sensing is the best and simplest way,

And putting the float in a holed vertical tube to baffle the sloshing

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2001\09\21@035800 by Gennette, Bruce

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At the bottom of the tank put a stretchy membrane (urethane resists petrol?)
and place 3 micro switches below/beside it (depends on where the hole is,
bottom/lower side of tank).
Put a little fuel in the tank and clamp #1 micro switch so that it is just
open.  You have a near empty indicator.
Put more fuel in the tank and clamp #2 micro switch so that it is just open.
You have a part full indicator.
7/8 fill tank and clamp #3 micro switch so that it is just open.  You have a
near full indicator.

Debounce the switches with a L O N G G G G delay.

Bye.

{Original Message removed}

2001\09\21@041926 by Alan B. Pearce

face picon face
>I'm trying to make a simple fuel level indicator for a fuel tank.  I only
>need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
>I'm thinking of having two wires (or other electrical contact)
actually -in-
>the gas, and using the fuel to "close the switch".  I'm pretty sure this
>would work for water, but I don't know if the gas will be able to conduct
>electricity well enough.  There is also the ignition issue, but at the
>voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
>for my purposes.

I think I would be wary of travelling in your vehicle/boat whatever. The
nice brand new Mini car has just had a recall because of slight static
discharges around the fuel filler, I do not like the idea of electrics
inside the fuel tank.

Instead try something like this. Use a Perspex rod of suitable length, and
thin it down at suitable points by turning it down in a lathe. It is then
possible to sense liquid level by shining a suitable source of light down
the rod and measuring the reflectivity. Quick ASCII art.

       __________
LED    |          \_________
      |___                 \_______
          |                        \
       ___|                 _______/
Sensor |          __________/
      |_________/

You will probably need a slot between the LED and sensor to minimise the
light spillage between them. It may also be possible to design that end of
the rod so it is a nice interface to the reflective opto sensors available,
but I would just drill a hole in the end so a TO18 type can or plastic
equivalent was a snug fit into the rod. The rod can then be mounted in a
suitable gland to keep the electronics outside the dangerous vapours.

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2001\09\21@041943 by Alan B. Pearce

face picon face
>Debounce the switches with a L O N G G G G delay.

This is where some good DSP coding comes in to average the sloshing effect.
It can actually make quite accurate measurements despite the apparent random
motion. This will also be needed on my light pipe idea if you need
reasonable accuracy.

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2001\09\21@075852 by Olin Lathrop

face picon face
> I'm trying to make a simple fuel level indicator for a fuel tank.  I only
> need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
> I'm thinking of having two wires (or other electrical contact)
actually -in-
> the gas, and using the fuel to "close the switch".  I'm pretty sure this
> would work for water, but I don't know if the gas will be able to conduct
> electricity well enough.  There is also the ignition issue, but at the
> voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
> for my purposes.
>
> Does anyone have any idea if this would work, or possibly have another
> suggestion?

I don't know, but if I needed to I'd stick ohm meter probes into a glass of
gasoline.  I would think that these kinds of hydrocarbons don't conduct
electricity well for lack of ions, but I have no idea what the effect is
after all the additives.  But again, it seems like finding out for yourself
is quicker and more reliable than asking the list.


********************************************************************
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(978) 742-9014, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\09\21@093636 by P.J. McCauley

picon face
Dave,

Will the fuel will act as a di-electric material? If so you might try using
2 coaxially mounted metal tubes (air spaced as much as possible). Make the
spacing between them as small as you can. Make sure they don't touch. Mount
this assembly vertically in the tank, ensuring that the fuel level can  rise
and fall freely between the tubes. This will cause a change in capacitance
between the tubes which is proportional to the level of fuel. I use this
method to measure the level of liquid Nitrogen in a tank. It gives a full
range of levels.

Can anyone comment if it will work for fuel or not?

Joe


{Original Message removed}

2001\09\21@100114 by Ward, David

flavicon
face
Take a look at http://www.qprox.com they have capacitive sensors that will do just
this kind of thing



-----Original Message-----
From: P.J. McCauley [.....pmcculeyKILLspamspam@spam@TCD.IE]
Sent: 21 September 2001 14:34
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: Re: [EE]: Conductive Liquid Sensor


Dave,

Will the fuel will act as a di-electric material? If so you might try using
2 coaxially mounted metal tubes (air spaced as much as possible). Make the
spacing between them as small as you can. Make sure they don't touch. Mount
this assembly vertically in the tank, ensuring that the fuel level can  rise
and fall freely between the tubes. This will cause a change in capacitance
between the tubes which is proportional to the level of fuel. I use this
method to measure the level of liquid Nitrogen in a tank. It gives a full
range of levels.

Can anyone comment if it will work for fuel or not?

Joe


----- Original Message -----
From: "Dave VanEe" <.....dvaneeKILLspamspam.....MECH.UBC.CA>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Friday, September 21, 2001 7:09 AM
Subject: Re: [EE]: Conductive Liquid Sensor


> The tank will be in a racecar travelling at speeds up to 100mph.  There
will
> be sloshing (some effort will be put in to reduce this).  The float idea
> seems to require excess mechanical components.  Weighting the tank is not
> really an options since that's extra weight on the car.  If I had the need
> for a full range of fuel levels I would use a float for sure, but since I
> only need a few values I figure there's a better (easier) method out
there.
{Quote hidden}

if
> >the tank is not level? Does it have to deal with "sloshing"? I'm pretty
> >sure that the general consensus of this list (based on previous similar
> >threads) is that float sensing is the best and simplest way, although
> >weighing the tank might also be a workable solution.
> >
> >Sean
> >
> >At 09:16 PM 9/20/01 -0700, you wrote:
> >>Hello,
> >>I'm trying to make a simple fuel level indicator for a fuel tank.  I
only
> >>need to be able to sense a few levels (i.e. Full, ~1/3 full, Near
Empty).
> >>I'm thinking of having two wires (or other electrical contact)
> actually -in-
> >>the gas, and using the fuel to "close the switch".  I'm pretty sure this
> >>would work for water, but I don't know if the gas will be able to
conduct
> >>electricity well enough.  There is also the ignition issue, but at the
> >>voltages I'd use it shouldn't matter.  I will be using 94 Octane
gasoline
> >>for my purposes.
> >>
> >>Does anyone have any idea if this would work, or possibly have another
> >>suggestion?
> >>
> >>Thanks,
> >>Dave
> >>
> >>PS: I will be putting some gas in a container and checking the
resistance
{Quote hidden}

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2001\09\21@102610 by Roman Black

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face
Hi Dave, I think you're asking the wrong people. :o)
Try an auto mechanic. My Suzuki motorcycle has two
fuel level sensors, they are 2-wire thermistor type
and with 2 sensors this gives 3 total fuel levels
that can be sensed.

These are a self contained metal "blob", with no
moving parts. From what I can see they sense the fuel
level by temperature difference between fuel and air,
and probably by heating themselves a tiny bit they
can easily detect if they are surrounded by air or
fuel.

You may be able to use a simple thermistor, heat it
by setting the PIC pin to output, then switch the
PIC pin back to input and see how long it takes to
change state.

No sane person is going to start running electricity
through fuel?? Please??

Reducing the sloshing is easy, buy some "fuel cell
foam" from a hotrod shop and stuff it in the fuel
tank. Common problem, common solution. :o)
-Roman


Dave VanEe wrote:
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2001\09\21@103233 by David VanHorn

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At 09:16 PM 9/20/01 -0700, Dave VanEe wrote:
>Hello,
>I'm trying to make a simple fuel level indicator for a fuel tank.  I only
>need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
>I'm thinking of having two wires (or other electrical contact) actually -in-
>the gas, and using the fuel to "close the switch".  I'm pretty sure this
>would work for water, but I don't know if the gas will be able to conduct
>electricity well enough.  There is also the ignition issue, but at the
>voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
>for my purposes.

You might meter the outflow instead of measuring what's in the tank.
You're likely to be able to get a very good measurement of consumption
there, but I don't know how reliable your fill level is.

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2001\09\21@104443 by Dale Botkin

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On Fri, 21 Sep 2001, Olin Lathrop wrote:

> > I'm trying to make a simple fuel level indicator for a fuel tank.  I only
> > need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
> > I'm thinking of having two wires (or other electrical contact)
> actually -in-
> > the gas, and using the fuel to "close the switch".  I'm pretty sure this
> > would work for water, but I don't know if the gas will be able to conduct
> > electricity well enough.  There is also the ignition issue, but at the
> > voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
> > for my purposes.
> >
> > Does anyone have any idea if this would work, or possibly have another
> > suggestion?
>
> I don't know, but if I needed to I'd stick ohm meter probes into a glass of
> gasoline.  I would think that these kinds of hydrocarbons don't conduct
> electricity well for lack of ions, but I have no idea what the effect is
> after all the additives.  But again, it seems like finding out for yourself
> is quicker and more reliable than asking the list.

I seem to recall SCCA track oficials using some sort of resistive testing
to check for illegal fuel additives (or higher levels than allowed), so I
think Olin's point is valid.  On the other hand, that would also mean
you'd have to use the exact same fuel formulation every time -- good luck
with that.  8-P

Dale

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2001\09\21@104955 by Lawrence Lile

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face
My old tractor had a very simple gas gauge, which had few moving parts and
no electricity in the fuel tank.  Easy to hack to an electronic sensor.

It had a float which ran up and down two parallel rods.  Friction with the
rods helped dampen sloshing , and it was near the center of the tank, which
might get less sloshing than the extremities (??)

The float had a slot in it, which drives a flat piece of steel that is
twisted into a spiral, maybe 3/4 turn.  The end of the spirally-twisted flat
had a rod welded to it, which sticks through the top of the sensor. The
spirally-wound flat is free to rotate around it's long axis.  The whole
thing was attached to the inside of the tank's fill cap, which made it easy
to remove and clean.

As the float goes up, it drives the spiral right.  As the float goes down,
it drives the spiral left.

The rod coming out of the top ran a little mechanical gauge, but could also
easily run a potentiometer.  I notice most gas gauges respond VERY slowly,
like over minutes' time, to eliminate sloshing problems.

Don't hack electric stuff inside your fuel tank.  This is done by the pros,
with VERY CAREFUL design and testing, limited energy wiring, special
coatings, materials and so on.  Yes, we are all pros, but this is something
to avoid.

--Lawrence Lile

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2001\09\21@110233 by Ian Jordan

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face
Just a note on the "sanity" of running electricity through fuel, and it's
conductivity:

Electric fuel pumps in gas tanks aren't insulated. The wires just run to
bare metal terminals on the top of the fuel pump. So there is a 12V
differential about 1-2" apart in almost all modern fuel tanks.

As long as the connections are tight and there are no sparks, it doesn't
matter if you run electricity in a fuel tank. I will note that all the fuel
pumps I have seen do take great care to make sure the connections are tight
and stay that way.

I would also say that this demonstrates that gasoline is a poor conductor.

--Ian


> No sane person is going to start running electricity
> through fuel?? Please??

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2001\09\21@111720 by Tom Messenger

flavicon
face
I was going to mention this also but Ian beat me to it. One other datum
point: my old 1970 Volkswagen beetle's gas gauge quit working once when
ever the fuel level got down around half tank or so. Then there was no
indication as the tank further emptied.

I removed the sender unit to check it. To my surprise, it was a open frame
wire wound rheostat, directly immersed in the fuel. Half way along it's
length, it had worn through and the element had broken. Since it was fed
electrically from the top, it began to only respond when the tank was half
full or more.

If you have any interest in putting "electricity in your tank", check out
the principles of intrinsic safety first. But... there' no real reason to
reinvent the wheel here.  A little research will show what others are doing
for a solution to the same problem.

BTW, I like the thermistor solution mentioned by Roman. Simple and straight
forward. For a more complex but non invasive method, this can be solved by
ultrasonics - crystal bonded to the bottom of the tank outside. Ping the
crystal, count bananas til the echo is received.  Way too complex though in
the light of simpler systems.

At 08:01 AM 9/21/01 -0700, you wrote:
{Quote hidden}

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2001\09\21@115816 by Harold M Hallikainen

picon face
       You might also try putting an insulated rod in the tank, then measure
the capacity between the insulated rod and the rest of the tank. The
dielectric constant of the fuel is different than that of air, so the
capacity will vary. This technique is usually used to determine the
amount of water in fuel (since water has a much higher dielectric
constant), but if the DC of the fuel is pretty constant, it MIGHT work!

Harold


On Fri, 21 Sep 2001 17:49:00 +1200 Jinx <joecolquittspamspam_OUTCLEAR.NET.NZ>
writes:
{Quote hidden}

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2001\09\21@115819 by Thomas McGahee

flavicon
face
Try Dielectric sensing via capacitance change. As fuel level changes,
air dielectric is replaced with fuel dielectric, causing the capacitance
to change. A simple variable frequency oscillator circuit using this
capacitance as the frequency determining element will suffice. A PIC
(of course) can be used to monitor the period or frequency and convert
this to a suitable output range, such as percentage of tank occupied
by gas, or gallons remaining, etc.

Averaging (using the PIC, of course) can help eliminate some of the
effects of sloshing. The key is to keep sloshing WITHIN the sensor
cell to a minimum. The cell can be fitted with fairly small
gas entry/exit holes that will add a sort of mechanical
averaging mechanism to the sensor.

Fr. Tom McGahee




{Original Message removed}

2001\09\21@123148 by Steven Bakaletz

flavicon
face
> I'm trying to make a simple fuel level indicator for a fuel tank.  I only
> need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).


If your tank is plastic try http://www.qprox.com/products/qt114.php3

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2001\09\21@123717 by Arnold Chord

picon face
Have you thought of using a piezo fluid sensor?
I have found information on a sensor that can be used in any type of fluid.
In the specs that I have it is called a "Singing Tube."
I can scan the info and send to you if you want it.
Arnold
@spam@achord2KILLspamspamhome.com

----- Original Message -----
From: "Gennette, Bruce" <KILLspambruce.gennetteKILLspamspamTAFE.NSW.EDU.AU>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Friday, September 21, 2001 12:55 AM
Subject: Re: [EE]: Conductive Liquid Sensor


> At the bottom of the tank put a stretchy membrane (urethane resists
petrol?)
> and place 3 micro switches below/beside it (depends on where the hole is,
> bottom/lower side of tank).
> Put a little fuel in the tank and clamp #1 micro switch so that it is just
> open.  You have a near empty indicator.
> Put more fuel in the tank and clamp #2 micro switch so that it is just
open.
> You have a part full indicator.
> 7/8 fill tank and clamp #3 micro switch so that it is just open.  You have
a
> near full indicator.
>
> Debounce the switches with a L O N G G G G delay.
>
> Bye.
>
> {Original Message removed}

2001\09\21@124416 by Arnold Chord

picon face
Another idea is to use a pressure sensor. I know that Motorola makes one.
A tube would mount at the bottom of the tank and the senor at the other end.
As the tank fills up the pressure in the tube will increase.
Just an idea.

Arnold
spamBeGoneachord2spamBeGonespamhome.com

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2001\09\21@150748 by Olin Lathrop

face picon face
> Don't hack electric stuff inside your fuel tank.  This is done by the
pros,
> with VERY CAREFUL design and testing, limited energy wiring, special
> coatings, materials and so on.  Yes, we are all pros, but this is
something
> to avoid.

Doh!  I was just thinking you could use the difference in breakdown voltage
between air and gasoline to do the test.


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(978) 742-9014, TakeThisOuTolinEraseMEspamspam_OUTembedinc.com, http://www.embedinc.com

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2001\09\21@150754 by Olin Lathrop

face picon face
> As long as the connections are tight and there are no sparks, it doesn't
> matter if you run electricity in a fuel tank.

Yes, that's what's *supposed* to happen.  Unfortunately this kind of setup
leaves a lot less margin when something goes wrong.  Isn't this exactly what
brought down that airliner near Long Island a few years ago?


********************************************************************
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(978) 742-9014, RemoveMEolinspamTakeThisOuTembedinc.com, http://www.embedinc.com

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2001\09\21@153308 by Don Hyde

flavicon
face
No.  The airliner had wires passing through the fuel tank inside a metal
conduit.  The wires shorted and generated enough heat to ignite vapors in a
nearly-empty tank.

UL has rules for "explosion-proof" circuitry, which basically intends to
ensure that it can produce no sparks and can't carry enough current to
generate enough heat to ignite anything.

It's not all that hard to meet the requirements.  As I understand it, just
about anything powered by a couple of AA batteries will pass the tests.
Basically you're limited to about 3 volts, any current source must have at
least enough internal resistance to limit current to a few milliamps, and
there's a minimum spacing between exposed conductors such as PC board
traces.  I wish I could quote you exactly, but I don't have a written copy
of the spec in my possession.

> {Original Message removed}

2001\09\21@154939 by Misana Enginyeria

flavicon
face
Im sorry my english is horrible.
En depositos de gasolina yo he visto sensores  tan curiosos como una NTC que
al estar sumergida en el combustible se enfria y varia su valor con respecto
cuando esta al aire que se calienta y deja pasar más corriente encendiendo
un piloto. Todo a 12 voltios. Hecho por Honda Motorcycles.
Do you understanding? Best regards.

-----Mensaje original-----
De: pic microcontroller discussion list
[PICLISTEraseMEspam.....MITVMA.MIT.EDU]En nombre de Don Hyde
Enviado el: viernes, 21 de septiembre de 2001 21:32
Para: EraseMEPICLISTspamMITVMA.MIT.EDU
Asunto: Re: [EE]: Conductive Liquid Sensor


No.  The airliner had wires passing through the fuel tank inside a metal
conduit.  The wires shorted and generated enough heat to ignite vapors in a
nearly-empty tank.

UL has rules for "explosion-proof" circuitry, which basically intends to
ensure that it can produce no sparks and can't carry enough current to
generate enough heat to ignite anything.

It's not all that hard to meet the requirements.  As I understand it, just
about anything powered by a couple of AA batteries will pass the tests.
Basically you're limited to about 3 volts, any current source must have at
least enough internal resistance to limit current to a few milliamps, and
there's a minimum spacing between exposed conductors such as PC board
traces.  I wish I could quote you exactly, but I don't have a written copy
of the spec in my possession.

> {Original Message removed}

2001\09\21@161211 by Ian Jordan

flavicon
face
When was the last time you heard of a car exploding? From what I remember,
what happened to the jet was that an A/C pack overheated, causing the
insulation on wires to melt/burn. That's a far cry from a "loose" connection
like we are talking about in a gas tank.

The reality is that in almost all cases, the fuel vapors in a gas tank are
so dense that they are not really combustible. The most dangerous gas tank
is an empty one because it has enough oxygen in it to explode. They always
teach you that if you are going to weld on a steel gas tank, do it full of
gas. Gas burs- vapors (at the right A/F mixture) explode.

The chances of a wire getting loose, sparking, and being in an explosive
environment are almost zero. That's why car manufacturers have been putting
electric fuel pumps and electric fuel senders in tanks for years with no
problems. Remember, if it sparks while it's under fuel, there will be no
fire- there's no oxygen to feed it. If it sparks in the vapor, chances are
very, very low that the vapor mixture will be flammable.

Plus, this is on a race car. The thing will get stuffed into a wall long
before the wire has time to rattle loose ;)

--Ian

{Original Message removed}

2001\09\21@172732 by Jinx

face picon face
> > Isn't this exactly what brought down that airliner near Long Island
> > a few years ago?

> No.  The airliner had wires passing through the fuel tank inside
> a metal conduit.  The wires shorted and generated enough heat
> to ignite vapors in a nearly-empty tank

The story I heard was that the plane was unlucky enough to
have exactly te wrong air-fuel mix in that empty tank. If there'd
been more fuel, the explosion probably wouldn't have happened.
I forget the details, don't they purge with nitrogen or something ?

I know that section of the plane has been re-designed to prevent
(hopefully) it happening again

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2001\09\21@174844 by Dave King

picon face
>I'm trying to make a simple fuel level indicator for a fuel tank.  I only
>need to be able to sense a few levels (i.e. Full, ~1/3 full, Near Empty).
>I'm thinking of having two wires (or other electrical contact) actually -in-
>the gas, and using the fuel to "close the switch".  I'm pretty sure this
>would work for water, but I don't know if the gas will be able to conduct
>electricity well enough.  There is also the ignition issue, but at the
>voltages I'd use it shouldn't matter.  I will be using 94 Octane gasoline
>for my purposes.
There are quite a few people using homemade capacitive fuel sensors.
Basically its two pieces of foil or conductor materials which uses the
fuel/liquid
as the electrolytic media. This is common for experimental or amateurbuilt
aircraft
and it works even with 100/130 octane.* Once its calibrated its very
accurate as well.

Dave

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2001\09\21@195526 by Douglas Wood

picon face
Try using a load cell under the tank/gas can and convert the load (weight of
the gas in the tank) to a level reading.

Douglas Wood
Software Engineer
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{Original Message removed}

2001\09\22@011057 by Raymond Choat

flavicon
face
If the gas is not clear then you could send ledlight from the top (where
float normally is) and have it reflect off a mirror and back up to a sensor.
Average the reading to stop some of the slush, also the idea earlier of a
tube with holes in it would help some more of the slush problem.  This would
keep all the electronics above and out of the tank with a clear glass view
of mirror in tank. Hope that sparks an idea (no pun intended)
Wrong Way Ray (Raymond Choat)

{Original Message removed}

2001\09\22@011918 by Raymond Choat

flavicon
face
Thats what is great about those black boxes. They help so a mistake never
happens twice.

----- Original Message -----
From: "Jinx" <RemoveMEjoecolquittspam_OUTspamKILLspamCLEAR.NET.NZ>
To: <RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU>
Sent: Friday, September 21, 2001 1:29 PM
Subject: Re: [EE]: Conductive Liquid Sensor


{Quote hidden}

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2001\09\22@055306 by Peter L. Peres

picon face
I am sure that with an empty gas tank and an illegal cap fitted the
immersed fuel pumps can be coaxed into producing a small bang. The
ignitable gas/air mixture needs to contain at most 14% afair gas so it
takes a while after the tank is empty to get there, but get there it will
eventually. Add to this a partially worn collector commutator that makes
nice sparks and a fresh battery and it should produce results (I think
that they use some sort of special damping on the commutator to avoid
sparks).

Peter

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2001\09\22@055817 by Peter L. Peres

picon face
Gas does not conduct current. Use a float switch or potentiometer or one
of those graded optical sensors. If the tank is transparent you can use
miniature reflective optocouplers glued to the wall. I have used this and
it works also with model fuel, but only with a level tank. Ignition is a
problem if you have enough Joules to spend on a spark or glow, no matter
what the voltage. Keep it well under 0.0001 Joules and you won't be able
to ignite it probably. This is easy with low voltage. F.ex. 10uF at 5V
decoupling that could discharge through a short in the tank will be
0.00025 Joules, i.e. too much imho. The danger of explosion will be
greatest when the tank is empty. Use an approved tank with an approved air
valve built in (this is important) and screw it on tightly every time.

Peter

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2001\09\22@084321 by Roman Black

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face
I've been a bit disturbed by the number of people
advocating using electricity in contact with the
fuel...

I have a lot of circuit diagrams for modern vehicles,
and often advise people re installing equpment or
modifying these modern vehicles. It's part of my
job. :o)

I see NO modern vehicles using electricity in direct
contact with the fuel!!!!

The 3 main types of fuel level sensing in modern
vehicles are:

* Simple pressure gauge (senses liquid height above
the pressure sensor)
* Sliding float over sealed tube with reed switch.
* Thermistor sensor (senses difference in heatsinking
between fuel and air)

ALL of these 3 types have one thing in common, there
is NO direct contact between fuel and electricity.

Call me a safety freak if you must, but I would NEVER
consider using live electricals in contact with fuel.
If the fuel container is punctured, and some atmospheric
condition causes the fuel to atomise, you have real
danger situation presented.

Surely if the cost/hassle of contruction is similar,
you MUST prefer a system with no direct electics
in the fuel??

Please argue if you think i'm wrong, or argue with all
the modern vehicle manufacturers if you like...
-Roman

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2001\09\22@150009 by Ian Jordan

flavicon
face
Roman,
   You've obviously never taken an electric in-tank fuel pump out of a car.
I've taken at least 10 fuel pumps out of modern, fuel injected cars, and in
each and every one, the wires run down to the fuel pump and are completely
submerged in fuel. In fact, the whole pump is submerged, and uses the fuel
for lubrication, so even the brushes are under fuel.

Here's the picture of a fuel pump out of a Mitsubishi Eclipse. Everything
you see is completely under fuel:
vfaq.moojohn.com/proj-pics/pump/1GAWD/pump12.jpg
You can clearly see the exposed ground wire on the right, and I promise you
that the "seal" on the left is totally ineffective at preventing the fuel
from getting to the positive wire. The positive wire is submerged as well.
Many cars completely forgo the seal around the positive wire.

--Ian

{Original Message removed}

2001\09\23@101310 by Roman Black

flavicon
face
Ian Jordan wrote:
>
> Roman,
>     You've obviously never taken an electric in-tank fuel pump out of a car.
> I've taken at least 10 fuel pumps out of modern, fuel injected cars, and in
> each and every one, the wires run down to the fuel pump and are completely
> submerged in fuel. In fact, the whole pump is submerged, and uses the fuel
> for lubrication, so even the brushes are under fuel.
>
> Here's the picture of a fuel pump out of a Mitsubishi Eclipse. Everything
> you see is completely under fuel:
> vfaq.moojohn.com/proj-pics/pump/1GAWD/pump12.jpg
> You can clearly see the exposed ground wire on the right, and I promise you
> that the "seal" on the left is totally ineffective at preventing the fuel
> from getting to the positive wire. The positive wire is submerged as well.
> Many cars completely forgo the seal around the positive wire.


Good point, my bike fuel pump is in the tank,
although the wiring is insulated I guess the
motor brushes are in there somewhere.

I would still choose a non-contact fuel
sensor if possible. :o)
-Roman

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2001\09\24@061700 by Andrew Hooper

flavicon
face
Why not just use optical sensor's?
Seems to me that the depth of the fuel could be calculated by the amount
of light able to penitrate.

Top of tank with led or ir emitter
|----\_/----|
|~~~~~~~|
|----/^\----|
bottom of tank with ir receiver.

Or another alternative is an ultrasonic sensor in the top.
most industrial ultrasonic units are stainless and work well in fluid.

Or cheap and nasty, pezio transducer stuck to one side of the tank
on the other side a mechanical hammer, strike the tank and pickup
sound vibration from the pezio. :) need better resolution then install
a bigger hammer :)

Andrew

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2001\09\24@093049 by Raymond Choat

flavicon
face
I suggested the same idea with the optical sensor's but use a mirror on
bottom of tank so all electronics is out of tank and in one area. Use of
slush tube with holes would help also as suggested by others.
Wrong Way Ray  (Raymond Choat)

{Original Message removed}

2001\09\24@093254 by t F. Touchton

flavicon
face
I just replaced the fuel pump and sender in my Olds (1992).  The fuel pump
connections on the old pump and the new pump did not appear to be hermetic
in any way.  The fuel tank sender is a wirewound rheostat, open to the
gasoline.  +12V at one end, ground at the other.  I was mystified when I
saw this.  I am used to the marine environment where this is done
magnetically.  However, this rather new car was done the same way my 67
Chevy is done... voltage directly in contact with fuel.

Looks like this is common practice on GM cars and trucks (at least up to
1993... I'd love to hear if GM has changed this).  I haven't looked inside
my truck tank yet, but the schematic in the service manual shows a rheostat
in the gas tank.

This has not made me comfortable, but it has not blown up yet.........

Scott



                   Roman Black
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                   ET.AU>               cc:
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I've been a bit disturbed by the number of people
advocating using electricity in contact with the
fuel...

I have a lot of circuit diagrams for modern vehicles,
and often advise people re installing equpment or
modifying these modern vehicles. It's part of my
job. :o)

I see NO modern vehicles using electricity in direct
contact with the fuel!!!!

The 3 main types of fuel level sensing in modern
vehicles are:

* Simple pressure gauge (senses liquid height above
the pressure sensor)
* Sliding float over sealed tube with reed switch.
* Thermistor sensor (senses difference in heatsinking
between fuel and air)

ALL of these 3 types have one thing in common, there
is NO direct contact between fuel and electricity.

Call me a safety freak if you must, but I would NEVER
consider using live electricals in contact with fuel.
If the fuel container is punctured, and some atmospheric
condition causes the fuel to atomise, you have real
danger situation presented.

Surely if the cost/hassle of contruction is similar,
you MUST prefer a system with no direct electics
in the fuel??

Please argue if you think i'm wrong, or argue with all
the modern vehicle manufacturers if you like...
-Roman

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2001\09\24@111416 by goflo

flavicon
face
Jinx wrote:

> The story I heard was that the plane was unlucky enough to
> have exactly te wrong air-fuel mix in that empty tank. If there'd
> been more fuel, the explosion probably wouldn't have happened.
> I forget the details, don't they purge with nitrogen or something ?

Military aircraft fill the tank dead space with inert
gas as the fuel is pumped out, thus there is never a
combustible mixture in the fuel tank.

Been a mostly under-the-radar argument about requiring
this for civil aviation for many years. If you look into
it you'll find there have been other such incidents, not
involving such loss of life.

regards, Jack

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2001\09\24@145302 by Nick Ray

flavicon
picon face
My dishwasher has a simple optical liquid level sensor... it's a rod of
clear plastic with the end cut at an angle (or maybe a V), the angled end is
toward the liquid, the other end is the viewing window. When the end is
clear of the liquid any incident light is reflected down then back up the
rod; when liquid touches the end the light path is extended into the
reservoir and the viewing window looks dark.

So put a reflective sensor at the "viewing" end... Not sure how well that'd
work with gasoline though.

> {Original Message removed}

2001\09\25@172542 by Peter L. Peres

picon face
> Been a mostly under-the-radar argument about requiring
> this for civil aviation for many years. If you look into
> it you'll find there have been other such incidents, not
> involving such loss of life.

I think that oil tankers have provisions to lead engine exhaust fumes into
the empty cargo hols. Maybe this could be modified for aircraft using a
bleed in the trubine exhaust. I don't think that it could be used in cars,
for fear of CO poisoning inside. Anyway air is only 21% oxygen and if you
get rid of it somehow then it is an inert gas for most purposes.

Peter

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