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

Discussion in 'Sensors and Actuators' started by esm., Mar 7, 2012.

  1. esm.

    esm.

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    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
    c
    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.
     
    Last edited: Mar 7, 2012
    esm., Mar 7, 2012
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  2. esm.

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Well, the pressure is related only to the depth in the fluid.

    So, if you create a dummy tank with a very small capacity (think tall and skinny) you can test sensors and calibrate them.

    The pressure will probably be relative to atmospheric and will be given by the density of the diesel and the height of the liquid above the sensor.
     
    (*steve*), Mar 7, 2012
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  3. esm.

    esm.

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    I noticed that after posting.
    Do you have an idea of approximated values for minimum and maximum pressure values for this case?
     
    esm., Mar 7, 2012
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  4. esm.

    davenn Moderator

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    I can see a lot of problems doing it by pressure measurement
    2 that come to mind are....

    changes in altitude is going to cause lots of fluctuations as the vehicles move around the region

    Changes in temperature is going to drastically change the pressure within the tank
    as the diesel expands. Just think what happens when you take the cap off your fuel tank on a hot day... there's a great puff of air/fumes as the inside/outside pressures equalise

    cheers
    Dave
     
    davenn, Mar 7, 2012
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  5. esm.

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The minimum pressure will be approximately 10 tonnes per square metre and it will increases by something a little less than 1 tonne per square metre for every metre of depth of the tank.

    Of course, the 10 T figure can normally be eliminated.

    Davenn points to a number of issues that are relevant. The other issue is that any pressure measuring device which gives a pressure relative to atmospheric pressure requires a port to access atmospheric pressure and this is a source of leaks in the long term.
     
    (*steve*), Mar 7, 2012
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  6. esm.

    duke37

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    It is necessary to know if the tanks are sealed or open.

    If the tanks are open then it is only necessary to measure the pressure at the bottom. Expansion of the fuel will alter the volume of the fuel but not the mass so the pressure will not change with temperature.

    If the tanks are sealed, then it is necessary to either use two gauges, one above the liquid and one at the bottom and subtract the values, alternatively use a gauge with two inputs to measure the pressure difference.

    It is 60 years since I did schoolboy physics but air pressure (15 lb/sq in) can lift water almost 30 feet. Your tanks then will have pressures at the base of about 1 or 2 psi. Given time I could get into the 20th century and use SI units!!

    Doing a Wiki 'hydrostatic pressure' brings me a little towards the present day.
    Pressure = density * gravity * height.
    Density (kg/m3) = About 900
    Gravity= 9.81 m/s2
    Height(m)=0.6

    Therefore pressure=5.3kPa. Is this correct?

    Wiki2 'diesel density'
    Pressure = 832 * 9.81 * 0.4 = 3.3 kPa ???
     
    Last edited: Mar 7, 2012
    duke37, Mar 7, 2012
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  7. esm.

    GreenGiant

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    You would probably be better off using floats or something like that

    pressure will be horribly inaccurate unless you have hundreds of sensors all over each tank, if the truck/bus is parked on a slight slope then a sensor in the middle will read incorrectly, even one in each corner (or quarter for round tanks) you wont get a truly accurate reading of the level of fuel unless you take into account the temperature, the exact listing of additives in it (some places you get diesel from will have additives that others do not, this will affect the density of the fluid)
     
    GreenGiant, Mar 7, 2012
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  8. esm.

    esm.

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    Hi, There is no need of precision measurement.
    And the buses are never parked on a slope.

    The measurement will be very slow, each 10 seconds. There will be a microcontroller reading the diesel level, so I can detect a high variation on fuel level and disconsider it.

    The measurement will be very slow, each 10~20 seconds. There will be a microcontroller reading the diesel level sensor, so I am able to detect a fast variation on fuel level and disconsider its value, mantaining the last conversion value. I can implement some protections in firmware about this issue, and the best: the firmware of this MCU may be upgraded anytime via GPRS network, I can customize the firmware for some vehicles if needed and correct possible errors
     
    Last edited: Mar 7, 2012
    esm., Mar 7, 2012
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  9. esm.

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    One other amusing method to calculate the volume of fuel is to determine the resonant frequency of the fuel tank. It will go up and down as the volume of air in the tank changes.
     
    (*steve*), Mar 8, 2012
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  10. esm.

    hevans1944 Hop - AC8NS

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    I am gonna bump this old thread by suggesting that the simplest method of measuring the volume of fuel in a tank is to weigh the tank. That means the tank(s) must be mounted on load-cells, perhaps more than one for each tank, but at least all the necessary wiring and signal conditioning is external to the fuel tank. Volume will vary with fuel density, which varies with ambient temperature, so some means to measure fuel temperature (or at least ambient temperature) will also be required,

    All this should be an easy task for a modern microcontroller or microprocessor, but a mechanic (and perhaps a mechanical engineer) familiar with how diesel fuel tanks are mounted on trucks and buses should be consulted to determine how, where, and how many load cells are needed for an accurate weight measurement. Load cells today come in a wide range of sizes and accuracy, and for onesie-twosie applications you can even make your own, a real character-building experience if you have never applied strain gauges and wired them up before. Lots more (modern) info is available if someone wants to revive and pursue this ancient thread...

    Hop
     
    hevans1944, Jun 11, 2018
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  11. esm.

    kellys_eye

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    My question would be - why do you want to make a simple task difficult? Will it be an improvement on existing methods? Will it be easily reproducible? Will calibration be a significant issue? Is such accuracy required?

    If content accuracy is a requirement then measuring fuel in and fuel out is the best way to go. The 'fuel in' part could be a manual entry of the figure from the pump (themselves accurate to nationally required standards) and fuel flow measurement is already simple, if not already included in many vehicles. If someone 'forgets' to update the manual fill part then at the next fill make sure the tank is 'topped off' and perform a reset. The actual 'full' capacity of the tank can be easily determined.

    I can't think of a more difficult and pointless exercise than attempting it in the manner the OP is suggesting. :confused:
     
    kellys_eye, Jun 11, 2018
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  12. esm.

    hevans1944 Hop - AC8NS

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    I just happened to dig out of the trash at work the other day a trade magazine, the May 2018 issue of "Fleet Maintenance -- All Maintenance, All Management, All Vehicle Classes, All the Time." The main article discussed the case for on-site fuel management. One option is on-site delivery of diesel fuel by tanker truck to your fleet of vehicles, a lower cost alternative perhaps to on-site storage of diesel fuel favored by some very large fleet operations.

    To manage on-site refueling via tanker trucks requires some means of knowing which vehicles need fuel and how much fuel to deliver to the site to allow efficient scheduling. Some fleets, such as school buses, will have seasonal requirements while over-the-road coast-to-coast operations may be a more steady consumer of fuel. Either way, it could be a significant advantage to know how much fuel is in each vehicle by means of inexpensive wireless remote sensors instead of relying on manual record keeping. I would not be surprised to discover that such systems already exist and are in use, but the article either didn't mention that or I missed it. There might be a short-term niche market to re-fit existing tractors with fuel-tank load-cell weighing systems if newer vehicles already have these installed, or to have an installation option upon purchase.

    Load cells to measure fuel quantity in vehicles apparently is gaining some traction. Without a lot of effort, Google found this article.

    Published October 2017 in the International Research Journal of Engineering and Technology (IRJET) by workers at Dept. Of Electronics and Instrumentation Engineering, Bannari Amman Institute of Technology, Tamilnadu, India, it appears to be a straightforward application of existing Arduino and load cell technology to an in-cab display of current fuel level. Below is the abstract at the beginning of the paper.

    And here is another one, also authored in India, with somewhat more details.
     
    Last edited: Jun 12, 2018
    hevans1944, Jun 12, 2018
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  13. esm.

    kellys_eye

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    That's an interesting proposal, thanks for outlining it Hevans.

    With all vehicles having ODBII (or similar) installed it should be simplicity to get a journey average for mpg and transmit this at source/destination to get 'fuel used'. In fact, coding ODBII to (say) Bluetooth to monitor whole-vehicle status (and potential fault prediction issues) would probably be more productive - but that's expanding the issue beyond the requirements!

    - my bold.

    This is taking the issue too far (imho) as such bunkers are usually certified for accuracy - certainly at domestic refeuling stations it is a legislative and regulatory requirement for accuracy (weights and measures etc) but could be easily overcome by using the simple technique of 'fill er up'! It's not as if the fuel will 'never' be used and the cost of carrying the 'surplus' - or rather INVESTMENT of carrying it given the fluctuations in fuel costs - would easily offset the costs of installing complex and non-standard measurement systems.

    But, once the vehicle is 'fuelled up' then the ODBII recording of mpg will result in an accurate usage. Here in the UK they also use weigh stations to check for load status and these could equally be used to check for fuel.

    I'm not decrying the OP's attempts to resolve a theoretical situation (and solution thereof) but questioning the 'need' if the proposal is intended for real-world use.

    On a ROI basis I can't see any sophisticated system offering payback unless such systems were fitted as standard at the factory.
     
    kellys_eye, Jun 12, 2018
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  14. esm.

    hevans1944 Hop - AC8NS

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    Not sure what the economic incentive to the manufacturer would be. As you noted, most drivers simply "fill 'er up" when re-fueling, and logbook records and receipts could be (and are) used to verify usage and track miles-per-gallon or kilometers-per-liter fuel efficiency, Unless the trucking industry suddenly starts demanding digitally accurate fuel gauges interfaced to cellular (GSM) phones and GPS locators, where is the profit in providing a "feature" that apparently no one realizes they "need?"

    Of course, a good marketing campaign could reverse that attitude. Remember the Nike and Air Jordan basketball/tennis shoes? I stuck with my Converse All Stars for casual footwear. Still have a pair. But... Howsabout a "Big Mack saves you fuel costs" campaign? Or maybe "Peterbilt carries you further for less cost" campaign? Yada, yada, yada. Ads don't have to be fully truthful (Don't confuse me with facts, my mind's made up), but they do need to be repeated often until the idea sinks in.

    I did a brief on-line survey yesterday of existing diesel fuel tank installations on commercial trucks. It appears there is a huge variety of tanks available, and each manufacturer has developed their own choice of tank(s) and method(s) of mounting. It may not be practical, or cost-efficient, to retro-fit load cells to the fuel tanks of an arbitrarily selected vehicle. But load cells, temperature compensated for fuel density fluctuations, are the only way I know of to obtain an accurate and repeatable indicator of the actual amount of fuel onboard. As you noted, weigh stations could provide this information if someone went to the trouble of accounting for all the tare weight involved... assuming that's even possible. Disconnect the trailer and weigh the tractor separately, perhaps? What a PITA that would be!

    Fuel tanks equipped with load cells currently appears to be a solution looking for a problem to solve, much like the early days during the commercial development of lasers. And I sure didn't anticipate the arrival of OBD-II (On Board Diagnostics - II), and its subsequent requirement by law to be installed on all new vehicles manufactured and sold in the United States after 1996. However, that would be the logical interface to use, along with perhaps the CAN (Controller Area Network) bus for digitized data transfer from the load cell signal conditioner.

    I remember a craze during the late 1950s to 1960s for after-market analog meters to measure automobile engine Revolutions-Per-Minute (RPM). These were popular on drag racers for some reason, and the idea spread to be an added-factor of "coolness" for street-legal vehicles because most automobiles did not come factory-equipped with tachometers. There were plenty of DIY articles published in magazines (the Internet didn't exist yet) on how to interface the standard points-and-condenser ignition system to either off-the-shelf after-market tachometers or to DIY-built tachometers. The hardest problem, IIRC, was finding a suitably large, inexpensive, D'Arsonval meter movement and then mounting it in a spiffy-looking (preferably heavily chromed) "bullet" case for installation on the dash. See examples here.

    It is entirely possible, but perhaps unlikely, that a similar craze will develop for fuel-tank weight sensing, maybe among custom car builders or restoration experts. Hopefully, I can be there to help them figure it all out... for a small fee.:D

    Hop
     
    hevans1944, Jun 12, 2018
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  15. esm.

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I think the issue here is that trucks don't carry a significant portion of their load as fuel and don't need to worry about balancing fuel load with payload. In addition, stopping for fuel mid-journey is cheap.
     
    (*steve*), Jun 12, 2018
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  16. esm.

    hevans1944 Hop - AC8NS

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    No, it isn't. Every minute not spent driving on the road represents a cost that cannot ever be recovered. That is why truck drivers back in the 1950s took those "little white pills" to stay awake and "on the road." The lyrics to the song "Six Days on the Road" provide some insight into what the trucking culture was like way back then:

    AFAIK the economics haven't changed, although drug use may be down, and many fleet operations use GPS to keep track of operator time-on-the-road to comply with federal regulations regarding mandatory rest periods.

    Truckers only make money when their trucks are moving down the road, not while parked in a rest area or waiting for fuel to be pumped. You would think this would provide an incentive for team trucking, where someone is always driving and stops are only made when necessary. I haven't noticed this being a widespread mode of operation... possibly because truckers are a fiercely independent lot. Husband and wife teams do exist, as well as other "partnership" arrangements, but I don't believe it is common. However, I think the idea of always knowing the precise amount of fuel available would be of significant financial benefit in planning where and when to re-fuel, especially for those driving long-haul, cross-country rigs.

    Certainly there are after-market fuel-tank level transponders and digital displays for same, but I think the available accuracy is rather poor. Truck fueling in countries like India could very well be like an American Wild West Free-For-All of the 19th Century, where fraud and cheating were something you just had to be prepared for and defend against. I am pretty sure that such fuel dispensing practices cannot occur now, here in the States, because of the intense competition and legal requirements for tested, certified, and sealed fuel-pumping stations. However, I have been shown to be wrong before, so your mileage (or kilometers) may differ considerably.

    Hop
     
    hevans1944, Jun 13, 2018 at 7:11 AM
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  17. esm.

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    In comparison with refueling an aircraft it is. :)

    I'm sure that truck drivers do fuel planning, and of course there are costs (other than the fuel) in stopping to refuel.
     
    (*steve*), Jun 13, 2018 at 8:10 AM
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  18. esm.

    kellys_eye

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    LOL.

    First time I've seen it used in the correct context!

    I don't know about others but even in a family car it's relatively simple/easy to determine when you're ready to 'fill er up'. On board car fuel metering isn't 'accurate' by any measure but seems to be more than adequate for the billions of vehicles currently on the roads.

    The only time fuel measurement would really become apparent is if you were to sell the vehicle and wanted to recoup the cost of the remaining fuel in the tank! Otherwise whatever is in WILL get used regardless of the level. Same goes for trucking.

    But in the case of dispensing it from a central depot and keeping stock levels adequate it's still (imho) irrelevant as the depot doesn't pay taxes on the purchase of a whole storage tank - if, as happens in the UK, you store fuel for dispensing, you pay AS IT IS DISPENSED such that any change in tax, duty or whatever your Government rips you off with is adjustable 'on the fly' so to speak.

    Fuel storage tanks are 'bunded' here in the UK (IIRC) in that the taxes paid on the dispensed fuels is calculated when it is used, not when it is stored.

    Individuals rush to the filling stations at annual tax-adjustment day (due to the usually inevitable increase - never a decrease) but all you can get away with is your personal tank full (and maybe a couple of containers) but you can't take your own tanker in and fill it!

    Besides, running a truck on the basis of keeping the tank as 'close to zero as possible' is far too risky with traffic jams and roadworks being unpredictable.
     
    kellys_eye, Jun 13, 2018 at 9:21 AM
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  19. esm.

    hevans1944 Hop - AC8NS

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    Agreed. I don't think anyone deliberately tries to drive until the tank is virtually empty and the vehicle is "running on fumes"... with the possible exception of teenagers, who are generally loath to fill up (or even add gas to) the family car on their own nickel.

    My wife keeps an eye on the gas gauge while we are traveling. and she wants me to pull over and "top it off" when the gauge indicates less than half a tank, or a quarter-tank, or whatever makes her start to feel uncomfortable, depending on where we are and the distance to the nearest gas station that might still be open. I have been known to wait until the little red light comes on before re-fueling, but that is a dangerous practice that risks running dry in the middle of nowhere. It is of course unsafe (and probably illegal) to carry a reserve container of fuel on-board a passenger vehicle, but we have done that when traveling out west, where you used to be able to drive vast distances without ever seeing a gas station. Not so much anymore... the USA has become overcrowded, coast-to-coast and from Canada to Mexico.

    Yikes! Don't get me started on THAT subject! To re-fuel a small aircraft properly requires climbing on the wings and using a "dip stick" to verify how much fuel is already on-board. Many "day trippers" don't bother and sometimes they run out of fuel in mid-air. The guv'mint, OTOH, uses in-flight re-fueling capabilities on many aircraft to allow for an extended mission profile. Imagine the possibilities if civilian and commercial aircraft could routinely do that! Scheduled commercial trans-Pacific or trans-polar sixteen-hour flights without re-fueling already exist, but who would want to stay in the air that long? Hmmm. Anyone in a hurry and not willing to change planes or stop over maybe?

    Way back in the 20th Century I used to fly domestically for business reasons, but tried to avoid it for personal travel. It seemed to take forever to negotiate airport traffic, both coming and going, and it seems that airports with convenient flight schedules and ticket prices were never located near my origin or destination points. The hassle of procuring a rental car at the destination and parking my personal vehicle at the point of origin added to the inconvenience of flying. And, since the events of 9/11, the delays involved with security processing are also an inconvenience. I wish Elon Musk would hurry up and get his Hyperloop thingy installed and networked 24/7/365. I would love to be able to step into a pod at a terminal near Venice, FL, and step out of it an hour or so later, auto-routed to a terminal near Virginia Beach, VA, or Washington, DC, or New York, NY. This concept kind of reminds me of those little brass cylinders department stores used to use to route paper around, but people-sized with acceleration couches... and no long delays.
     
    hevans1944, Jun 13, 2018 at 4:37 PM
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  20. esm.

    kellys_eye

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    Musk will only deliver what the US taxpayer can be conned in to handing over the cash for....... on a open-ended timescale too.
     
    kellys_eye, Jun 13, 2018 at 7:18 PM
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