18m2 touch a potential solution to fule out sensor?

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Wrenow

Senior Member
18m2 touch a potential solution to fuel out sensor?

An ongoing project on my back burner is determining if fuel is flowing through a line (or present within a fuel line) without physically interrupting/breeching/penetating the line.

Basically a sensor that warns when the fuel has run out (the feed line is empty).

I remember there being some discussion of using a capacitance sensor to do this. It now occurs to me that the 18m2, with its touch sensors, might fill this need.

I believe the fuel tube is a "rubber" tube, but it could be metal (I can confirm with the end user). Anyway, I would think that the capacitance would change as the tube is full or empty, would it not? Would you just need a wire or plate wrapped around the outside of the tube (or if metal, attached to it?

Am I totally off-base or getting close to a possible solution?

Cheers,

Wreno
 
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InvaderZim

Senior Member
I think it'll take some extensive testing. It sounds like a clever use, but I'd be concerned about how responsive and how reliable it is. Only testing can prove those points.

Shooting from the hip, I think you might have something to work with on the rubber hose. Is the fuel electrically conductive? If so, is it wired to something, or could it's potential vary a lot over time? If the potential of the fuel could vary, you might not be able to get something consistant.

If it's metal you might be...hosed. I don't see how that would work, since the metal is likely wired to a constant potential and that will be all you ever read, fuel or no fuel. But hey, get a rig and give it a shot.
 
D

Dippy

Moderator
I'll leave others to do the "Warning Will Robinson!".

Sounds good. Why not try it? Why not experiment and report back here?
It could be a really useful exercise.
You can easily rehearse it with a cup of fuel and a pad.
 
techElder

techElder

Well-known member
What is a Magnetic Flow Meter?

A magnetic flow meter (mag flowmeter) is a volumetric flow meter which does not have any moving parts and is ideal for wastewater applications or any dirty liquid which is conductive or water based. Magnetic flowmeters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions). Magnetic flowmeters are also ideal for applications where low pressure drop and low maintenance are required.
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"Fuel" probably is a hydrocarbon.
 
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Jeremy Leach

Senior Member
What if there was a section of strong glass or other transpararent pipe, then optically sense if fuel is passing through the pipe?
 
hippy

hippy

Technical Support
Staff member
I think you're in the 'you'll have to try it' territory. The touch sensors are conceptually based around how fast an oscillator runs which varies with capacitance so there may also be issues in an electrically noisy environment such as a vehicle which I guess is where this fuel line would be.

I don't know if there'd be any danger of inducing charge into a fuel line but that generally isn't considered a good thing, especially if something sparks. Probably worth doing some research as well.
 
D

Dippy

Moderator
Yes, a simple solution for that application where there is little background and vibration.

I think you should think twice before trying this approach in this application.

That demo on instrucatable had the advantage of plenty of water woosh noise in an environment with little ambient noise/vibration.
i.e. a lovely signal to noise ratio.
I didn't hear any mention of electronic processing/filtering which leads me to infer that this wasn't even considered.

In this fuel application the slower, non turbulent fuel flow may not provide the wooshing noise you need. i.e. a poor S:N.
I'm not saying it's impossible, but if there is significant ambient noise (e.g. pump) then you may have problems.
(If it had involved an active sonic/ultrasonic method then I'd change my mind).


For me, it's all down to reliability and trust in the device, so I think you should persue the capacitive or optical approach for detecting fuel presence.

And when I hear people repeatedly using the word 'sustainable' then I just KNOW they are after my money :)
 
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westaust55

Moderator
Maybe to know what the fuel is may be helpful. :confused:

ULP, diesel, LPG, liquid oxygen, even water for a PEM cell in electrolysis mode.
 
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gengis

New Member
Optical sensors should work. We managed to sense liquid in a milky 1/8" teflon tube to shut down a pump when if the liquid ran out. Just the usual IR interrupter with a holder to position the tube. It would trigger as the meniscus of a bubble went by.

Larger glass tubes 1/4-3/8" we used the refractive index of the clear liquid - opto emitter and sensor at an angle and the liquid bent the light to the sensor.

Another method we experimented with that showed promise for opaque liquids was a piece of silicon tubing epoxied to a piezo transducer. The self oscillating disc would go up in frequency when the tube was empty. Noisy. The same idea might work at a higher or lower frequency and avoid the noise.

I seem to remember reading about a sensor that drives a tube to vibrate then senses the energy required to move it to sense the mass present. Senses flow rate as well as liquid.

The capacity sensor might work too. I looked up mineral oil and it has 2-3 times the dielectric constant of air. The downside is most plastics have a higher dielectric constant, so a thick tube wall may cause problems.
 
K

KingsJester89

New Member
Why not measure the fuel level in the fuel tank?
You could use something like a Ballcock in a toilet, (although smaller and connected to a microswitch etc) then using trial and error, set a delay to finish off the last of the fuel. It’s not ideal but may be simpler than trying to measuse it through the fuel line.
 
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Dippy

Moderator
We haven't heard from Wreno since his first post.

He was really just casting an idea.
Personally I would use a method with a good signal to noise ratio and no chance of drift.

And as we don't know the situation for this device then I'm not sure if a ballcock is appropriate. Can't imagine it being very good if the end-user wants it on his space rocket or motocross bike :)
 
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BeanieBots

Moderator
As Wrenow is into large scale model boats I'd hazard a guess at an application involving either two-stroke fuel or nitroxed methanol;)
Fuel tank probably about 1 pint in size.

For model aircraft use we get very good results with a simple egg-timer alarm to indicate end of fuel. With my generator, the increase in speed as it leans out gives about 20 seconds warning.
The water coolant on a £MM peice of industrial equipment I worked on used an optical device. It was a hemisperical lense with both Tx and Rx inserted into the hemisphere which in turn was inserted into the fuel line. With no fluid, there was very large internal reflections. When covered with fluid, the refractive changed and the light simply exited the hemisphere with very little picked up by the Rx.

I can't see the 18M2 touch input being very effective unless the fluid is electrically conductive which would be a requirement to have much effect on the capacitance of the "touch" sensor.
 
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KingsJester89

New Member
Dippy, Ballcocks are used in analog car fuel gauges (such as my own car) which is where I got the idea, it was just a suggestion or at least a last resort. If you think a Ballcock is a bad idea in a space rocket imagine if your only indication of low fuel was when the line ran dry:

Space rocket: Houston, we have a problem. :(

Houston: You’re F***ed.

Space rocket: If only we had a Ballcock or other such measuring device! Curse you Dippy!!! :D
 
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Dippy

Moderator
Oh, they'd curse me anyway :)

Yes, a ballcock would be really excellent when you don't know which way is up or in Zero-G....
"Houston, we've lost control of our ballcocks. How we wish we had some other measuring device like an optical method."

Cars tend to stay one-way-up and we all know what the accuracy of the fuel guage is when the tank is nearly empty i.e. it isn't.
... or even when going around a sharp bend.

Motocross bikes, no chance. Your ballcocks would be rattling around like a claustrophobic in a lift.

To be honest we don't know the details so all these suggestions are airy-fairy really, but keep them going as one may work a treat.;)
 
slimplynth

slimplynth

Senior Member
Dippy said:
To be honest we don't know the details so all these suggestions are airy-fairy really, but keep them going as one may work a treat.;)
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A small (strong) magnet, covered in suitably solvent resistant material that floats in a vertical tube, which is connected to the main tank at it's base. The tube would need a suitable valve at the tip?

A few hall effect sensors (to explain idea simply) arranged top, middle and bottom of the tube. (or at the lower end to indicate low >>> very low >>> critical.)

[replace hall effect sensors if touch function can sense a floating magnet or anything else used as a float] - I dunno, not tried it, am just wasting 10 mins while i wait for my career saving miracle to reach 100% complete.
 
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boriz

Senior Member
Depends on the capacitance difference with the presence/absence of fuel, and upon the pipe material. I’d wrap two coils of enamelled copper wire around the tube, say 1cm apart, say each 10 turns and try it.
 
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Wrenow

Senior Member
The person who brought this project up to me mentioned that the mere flowing of fuel through the line induces a charge (why they ground the full lines). Hence, fuel flowing through the line may be creating a change of charge in the line.

As for the noisy environs - that would be a consideration, though it is a pretty simple craft with few EMF generators other than the motor mags and starter.

The fuel line is two pieces - one is metal (aluminum) the other "rubber." Specs are set and cannot be changed, and penetrations/obstructions/wet. are not permissible. Adding something to the outside of the tube, however, are OK.

Cheers,

Wreno

hippy said:
I think you're in the 'you'll have to try it' territory. The touch sensors are conceptually based around how fast an oscillator runs which varies with capacitance so there may also be issues in an electrically noisy environment such as a vehicle which I guess is where this fuel line would be.

I don't know if there'd be any danger of inducing charge into a fuel line but that generally isn't considered a good thing, especially if something sparks. Probably worth doing some research as well.
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Wrenow

Senior Member
westaust55 said:
Maybe to know what the fuel is may be helpful. :confused:

ULP, diesel, LPG, liquid oxygen, even water for a PEM cell in electrolysis mode.
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The fuel is avgas (aviation grade gasoline/petrol).
The normal methodology of checking fuel is to put a stick in the fill opening and see how high the fuel is on the stick - much like the dipstick is used to check your oil level.

The craft has no fancy shmancy fuel gages etc., and it would be nice to know if you no longer have fuel flow from the tank (which means you have a few minutes to start looking for a spot to land - better than the engine simply stopping). This is a plane designed on the 30s and last produced in the 70's.

As for the safety caveats - being a passive sensor acting as a backup to the primary systems and procedures, total failure leaves you no worse off than you started.

That may answer some questions, hopefully.

Not my usual model warship gig.....

Cheers,

Wreno
 
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flyingnunrt

Senior Member
I have an 'ifm efector' capacitive sensor that works ok through a plastic bottle with Methanol and would probbably work ok on the fuel tank, to sense a cut off level, but not neccesarily on a fuel line unless it was of a fairly large diameter, like on a surge tank for example. And no inverted flying!
They say that the unit will work through a metal tank too.
Anyhow you can google ifm and check it out they are not cheap but sometimes similar units are offered on ebay fairly cheaply.
 
techElder

techElder

Well-known member
How about dieing the fuel dark?

Then a simple optical sensor could be used on a clear fuel line like Tygon.
 
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Wrenow

Senior Member
Texasclodhopper said:
How about dieing the fuel dark?

Then a simple optical sensor could be used on a clear fuel line like Tygon.
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Either would be frowned on by the FAA, methinks. According to the A&P mechanic who broached this with me, we have to use the already certified parts (you can strap something to the outside of them, but cannot 'modify" them).

Cheers,

Wreno
 
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Wrenow

Senior Member
Dippy said:
Briefly going back to Post Number 1; have you tried the capacitive method?
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Hi Dippy,

Nope, haven't even gotten around to ordering in a supply of 18M2s to play with yet. :(

One reason I have been quiet on the board - tones of work issues over the past couple of weeks, plus social events like weddings in 3 different cities (not any of my kids, praise be - my daughter's was a couple of years ago), two charity events, and just got the graphics done for the local Library fundraiser today. Along with launching a new web site, son's graduation and move home from college this month. And a couple of Model Warship battles, of course. Things look to be calming down a bit, now (I hope).

Mainly was wondering it it was a possibility. Since it seems to be, I will have to snag some 18M2s and give it a whirl.

Thanks,

Wreno
 
M

MPep

Senior Member
One reason I have been quiet on the board - tones of work issues over the past couple of weeks, plus social events like weddings in 3 different cities (not any of my kids, praise be - my daughter's was a couple of years ago), two charity events, and just got the graphics done for the local Library fundraiser today. Along with launching a new web site, son's graduation and move home from college this month. And a couple of Model Warship battles, of course. Things look to be calming down a bit, now (I hope).
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Okay okay Wrenow, so what's the real excuse :eek:??
 
techElder

techElder

Well-known member
This is a plane designed on the 30s and last produced in the 70's.
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The plane must be something like a Piper J3 or Cub. Heck you don't have to worry about getting to the ground very fast. Just point it into the wind and hover there! :D
 
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