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Fuel level

Discussion in 'Automotive Electronics' started by elecLear78, Jan 11, 2016.

  1. elecLear78

    elecLear78 Member

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    Generally if a vehicle is moving in uneven surfaces fuel inside will be fluctuating a lot, but how is it possible that on the meter it is almost constant. What kind of algorithms will be applied to make it constant is it hardware specific or software specific?
     
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Averaging.

    Before computer they simply used a very slow meter.

    In my truck it takes 9 hours of driving to empty a tank. So I will not have a problem with 5 seconds of delay (averaging).
     
  3. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Many modern cars with fuel injection also monitor instantaneous and average fuel flows. I have found the average to be quite accurate. That is, set a trip odometer when you fill up and compare the estimated tank reserve from the fuel gauge with what you calculate from total distance/average mpg (or whatever unit it reads in). I can also switch to a "miles before empty" display. I do not know what that display uses for inputs, but it is also fairly accurate.

    John
     
  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The integrated time the injectors are open per RPM would make the most sense.

    I too have a computer in one of the vehicles that has:
    compass - Just NSEW and the modifiers like NE, NW etc.
    Outside Temp

    Range (miles to empty); If to low it just says LO rather than e wrong.
    Range updates with fuel level. So, you get gas and range updates.

    You get average MPG (reset is available for this function)
    Instantaneous MPG

    Fuel used (reset available) for this.
    Distance traveled (reset available for this too)
     
  6. rumpfy

    rumpfy Active Member

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    In my car, the fuel gauge is a meter which is a hot wire type of unit. The drive current is obtained from a voltage regulator in the dashboard display unit. The supply voltage is passed through the float variable resistance unit (or sender), in the fuel tank. The current from this unit passes through the meter. because the fuel does slosh around in the tank, the current in the meter does vary somewhat. However, because the meter is a thermal meter, then short term variations in the meter current does not show up as a a temperature variation in the meter. The thermal time constant is long, and this is how the meter reading is stabilised. You will note with this type of fuel gauge, that when the ignition switch is turned to ON, it takes a long time for the meter to reach the proper fuel level reading.
    Some of the posts above talk about actual fuel useage and this is done through an algorithm which measures the fuel injection open time. Because the fuel system runs at a constant pressure, Open time of the injectors will correlate with actual fuel consumption. The odometer system will then be able to give fuel useage in Litre per km. (apologies to KISS if I have repeated his post)
    Hope this helps.
     

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