Fuel Sensor Project

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Guys

Right some basic information to start with. I am currently trying to design a system to sense the amount of fuel left in a tank. The system needs to measure in litres and indicate continuously how much fuel is left in the tank. The tank is also not moving so no sloshing of the fuel needs to be considered.

The main aspect I am stuck on at the moment is the sensing device to use. After searching on this forum I found information on a variety of sensors such as capacitive resistive weight pressure etc.

From this information I believe the best solution would to use a capacitive sensor would you agree?

If so how would I go about designing a simple capacitive sensor?

Any help is appreciated

Mark
 




If your application need a precision measurement, you have to go with capacitive type sensors. or if you are looking for cheap and does not require a precision measurement (you would like to sense a particular level) you can go ahead with resistive type sensors...
 
You could induce a spark and measure the resulting explosion and heat produced .............


On a more serious note, how about ultrasonic distance sensing to detect the distance between the fuel and top of the tank ?
 
Capacitive sensors vary widely with the amount of ethanol in the gasoline, unless there's an always-immersed "reference" at the bottom of the tank.

Gasoline itself has a fairly consistent capacitive coefficient. Ethanol, however, is 10x greater than gasoline. Gasoline blended with 10% ethanol reads twice as high than 0% blend- so a half tank will read full. Unless you've got that immersed reference at the bottom which reads the same regardless of level, sensing only the fuel's capacitive coefficient. Also, note that capacitance varies somewhat significantly with the fuel temp. Either temp compensation- or that immersed reference- will compensate for it.

Nowadays, most gasoline is blended with ethanol UP TO 10%, but there's no telling what the actual content will be. Might be 5%, might be 10%. Depends on the season, for one.
 
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picbits said:
On a more serious note, how about ultrasonic distance sensing to detect the distance between the fuel and top of the tank ?
Click to expand...

This is what I was thinking too. That would be terribly easy. Rangefinders are cheap and are pretty accurate too. Although, finding one that is moisture proof might be tough.

How do car gas tanks do it?
 
Sorry Double post

Oh I think I got it. You could get a pressure transducer, and measure the pressure. The change in hydrostatic pressure will correspond to a volumetric change.

That would be really easy, and you could just toss that in the tank and not have to worry, as long as it hits the bottom. Although that might be decently expensive. The pressure transducers I have seen look expensive.


EDIT: I should read the OP D: -No I dont know how you would use a capacitive sensor, unless that is how a pressure transducer or load cell works.
 
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We also need to know if the tank level is linear from empty to full or if its not. Square tank VS round tank or odd shaped tank.
How big of tank volume are you measuring?

A simple float and potentiometer is fairly accurate unless its a very big tank. Using a simple float and string system with a multi turn potentiometer can give a rather precise reference from minimum to maximum. Most likely with the same average levels of error as any other method will.
 
Hey Guys'

Thanks for your quick reply's they've been really helpful. KMoffet your info was especially helpful.

In answer to your question tcmtech, our tank is a 25L plastic tank based on a rectangular screw top, industrial detergent bottle.

Thanks again for your help guys and any more info will be greatly appreciated.

Cheers,

Mark
 
Avatar1 said:
our tank is a 25L plastic tank based on a rectangular screw top, industrial detergent bottle.
Click to expand...


Then there should be a screwed hole at the bottom of the tank where the tap is/was. If this outlet is blanked off just get an elbow and length of clear plexi tube and install it on the elbow. Make a bung to go into the plexi tube and fix a magnet ontop of it,, then put 2 off reed switch's on the plexi tube where you want the high/low points.

Not only a visual indicator but also electrical too.

Too Easy
 
Cheers for all the good stuff guys,

I did look into using reed switches but these can only be used to give high/low points or sections of level.

I am aiming for continuous accurate measurement in litres. I think the only 3 realistic options that i might be able to make with a budget of only £50 ($80) will be either capacitive or ultrasonic or resistive.

Thanks againd guys and anymore ides or advice will be greatly appreciated.

Cheers, Mark
 
Bryan1- (sorry to go off topic) what's the trick to getting the animated GIF to work as an avatar?

I tried uploading my binary clock GIF but it won't animate, its just stuck on 3:39.

Is it a size issue, or do i need to set something in my UserCP?? I saw someone else had an animated GIF but it was only 40x40 pixels or so.
 
Hey Guys

Right I have now made a capacitive fuel sensor with an oscillating op amp and have a nice square wave coming out with a frequency ranging from 100 Hz for a full tank to 1500Hz for an empty tank and have produced a graph for varying amounts of water so thus can program the PIC accordingly.

The PIC I am using a PIC 16F877 and have a development board and chip ready to go. I have been advised to use the capture and compare feature on it to sample the square wave and thus give a read out to my LCD display would you recommend this? Also how do I go about using this feature on my PIC?

The display that I am using is Everbouquet MC16011a-SYR 16 x 1. How would I connect this to my PIC?

Sorry about so many questions guys as I’m only a beginner and this is my first project that I have made.

Thanks Again

Mark
 

Be aware!

If the fuel is petrol (gasoline), the results you will get are totally different from the results for water.
Petroleum has a relative permitivity of 2.2 compared to 80 for water.
On your capacitive sensor, the reading for petroleum will be only about 3% of that of water.

These properties are used in the offshore oil industry for devices such as Subsea Leak Detectors and Wet Gas Flowmeters.

JimB
 
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