How to measure diesel tank level by pressure sensor, tank area and diesel paramenters

[esm.]

Hi.

I have two diesel tanks here, used both in trucks and buses, they have around 250 liters of diesel when full filled (250 liters capacity). They have retangular format.

I want to make an electronic measurement to them, of how many liters of diesel is present inside them, using these parameters:

- Pressure measure (in PSI), obtained from an electronic sensor placed at the internal bottom of theses tanks.
- Tank base area (if really needed to use it in the equation)
- Data from the diesel (density and other necessary paramenters)

The diesel tanks have these dimensions:

Base dimensions: 125cm x 60cm
Height: 40cm
OBS: 1cm (centimeter) = 2.54 inches


All I need to know is what would be the aproximate pressure measurement given by the sensor, in PSI (pound per inch) [the measurement unit may be other, I could convert between them], when the tank is nearly filled and nearly empty. I am stuck on this doubt because the selection of a electronic pressure sensor (dedicated IC) will be based on its pressure measurement range (Ex: 3 to 50 PSI, or Ex 10 to 150 PSI, or Ex 0 to 1.5PSI).

EXAMPLE:
What would be the approximate pressure measure when the tank is nearly filled?
What would be the approximate pressure measure when the tank is nearly empty?

Example os pressure sensors:

1) BMP085 from Bosch -> range from 4.35 to 15.95 PSI - http://search.digikey.com/us/en/prod...5-6-ND/1987016

2) MPX2202 Series from Motorola -> range from 0 to 29 PSI - http://search.digikey.com/us/en/prod...02AS-ND/420527
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3) MPXV5010 Series from Motorola -> range from 0 to 1.45PSI - http://search.digikey.com/us/en/prod...GC7U-ND/412949

4) MPX5100 Series From Motorola -> range from 0 to 14.5 PSI - http://search.digikey.com/us/en/prod...00GP-ND/464061

There are many ICs models available with different measurement ranges.
All I need to know is what is the aproximate pressure present at them bottom of the tank when it is 100% filled and nearly empty. The tank has 250 liters capacity and retangular format. Base dimensions of 125cm x 60cm and height of 40cm.

I am looking for this range of pressure values, in any measurement unit, PSI, KpA, mbar, atm, etc

Somebody may help about this question?
Some better ideias to measure diesel level (in % or in liters directly) in the tanks? I don't want to use a capacitite or ultrasonic transducer method to measure the levels.

Thanks in advance.

 

[jpanhalt]

A column of petro-diesel 10 cm high will exert a pressure of about 8.32 g/cm^2.

John

 

[esm.]

Hi. How do i convert g/cm^2 to PSI?

 

[ronsimpson]

http://www.sensorsone.co.uk/pressure-units-conversion.html
try this

 

[esm.]

Hi.

If the pressure exerted by the diesel is around 0.832 g/cm^2. A tank with 40cm height will give me a maximum of 33.28 g/cm^2.

Using this online converter: http://www.sensorsone.co.uk/pressure-units-conversion.html , 33.28 g/cm^2 = 0.47 PSI.

So I think "MPXV5010 Series from Motorola -> range from 0 to 1.45PSI" is suitable to measure diesel level of these tanks, considering this unit conversion I did wasn't wrong.

I used more three online unit converters to convert 33.28 g/cm^2 to the PSI unit and all of them gave me a value of 0.47.

Please correct me if I'm wrong.

 

[jpanhalt]

40cm = 15.7", and as calculated elsewhere, 10" of diesel gives a pressure of 0.3 psi.

Thus, the pressure of 40 cm would be 1.57x the pressure of 10" or 0.47 psi. So, you answer checks out.

John

 

[MrAl]

Hi,

Diesel fuel could vary a bit from something like 0.82 to 0.95 g/cm^2. You might want to use the mean for the final measurements.

You'll have to consider the shape of the container when you go to convert between bottom pressure and gallons unless the cross sectional shape is perfectly rectangular looking from any direction. For a perfectly rectangular box shape the gallons vary proportionally, but for say a "V" shape the gallons wont vary proportionally.

 

[esm.]

Hi.
The shape of all of these tanks are rectangular.
And all the tanks are sealed, they are not open at the top.

 

[jpanhalt]

You should still run a calibration curve. There are good reasons not to want an entirely linear scale. In other words, are your more worried about running out of fuel when you are 3/4 full or 3/4 empty?

John

 

[esm.]

Hi. Yes. When the prototype PCB be ready, I will run some tests, adding diesel in 0,5 liters parts, measuring the sensor output for each situation. And I will do this procedure with diferrent tanks, using diesel from different suppliers and with different temperatures.

 

[MrAl]

Hi,

Yes, if the tank has an unusual shape then you might want to look at the tank as half empty rather than half full

 

[misterT]

- Pressure measure (in PSI), obtained from an electronic sensor placed at the internal bottom of theses tanks.

Don't place the sensor itself at the bottom of the tank. Use a tube from the sensor to the bottom of the tank. (And use a differential pressure sensor if you need a very good accuracy)
View attachment 61935

 

[jpanhalt]

The tube is a good idea, but how do you keep it from filling partially with diesel? Some factors that can cause that are the solubililty of air in diesel, small leaks in the connections, and atmospheric pressure changes. During a low pressure system, the pressure will equilibrate. Then as you move to a high, the tube will fill partially with fuel and give a false reading. Of course, one could purge the tube periodically. A submersible sensor would also work without that complexity.

John

 

[MrAl]

Hi again,

An interesting idea might be to open a port to the tank, then close the port and fill the tank with air pumped in with a pump. The longer it takes to reach a back pressure of say 5 lbs/in^2 the emptier the tank is

Does the fuel bother the sensor package at all, like degrade it in any way ?

 

[misterT]

The tube is a good idea, but how do you keep it from filling partially with diesel? Some factors that can cause that are the solubililty of air in diesel, small leaks in the connections, and atmospheric pressure changes. During a low pressure system, the pressure will equilibrate. Then as you move to a high, the tube will fill partially with fuel and give a false reading. Of course, one could purge the tube periodically. A submersible sensor would also work without that complexity.

John

- Many pressure sensors are designed to be used with a tube. That is why they have the "nozzle".
- Differential pressure sensors measures the surrounding air pressure and subtract that from the liquid pressure (the pressure at the bottom is hydrostatic pressure + air pressure).
- You will not ever need to "purge the tube". The pressure in the tube will be same as the pressure at the bottom (where the tube end is). Small error is caused by the air compressing and small column of diesel filling the tube. The error is the height of the column and can be calibrated out.
- How would you compensate for air pressure with submerged sensor?
- The air in the tube will keep the tube from filling. Important thing is to keep the diesel out of the sensor and the tube does just that.
- Diesel fumes in the tube do not affect the pressure reading, but they may damage some sensors.
- Material selection (for the tube) and careful sealing of the connections is of course required. Steel tube should work very well.

I don't see how submerging electronic sensor + wiring in diesel is a good idea. If you think diesel fumes might be a problem, what about liquid diesel? And replacing a broken sensor is a pain.

 

[kinarfi]

I've always liked the bubble tube, simple, very accurate, you feed it with more pressure than you need and regulate the air flow down to a slow bubble, then if the tube plugs up, the pressure builds and blows the plug out. It's used a lot where sediment would plug up a tube that entered at the bottom.

 

[Electroenthusiast]

Do you really want to use a pressure sensor? How about using a spring transducer, which are used in conventional petrometers? Another Idea would be float sensors.