Which kind of table do you need?
A calibration table tells the device how many liters go with each sensor reading. The tool builds it two ways: from the shape of the tank, or from fuel you add and measure.
From the tank shape
Tab 1
- You need
- Inside dimensions and the probe length
- Time
- A few minutes, no fuel
- It misses
- Baffles, bulges and tilt
From a real fill
Tab 2
- You need
- A metered pump and the sensor reading after each batch
- Time
- One to two hours per tank
- It misses
- Little, if the batches are small and the vehicle is level
What does each tank shape need?
Measure the inside of the tank, not the outside. The wall takes away from the volume.
| Shape | Measurements | Rule used |
|---|---|---|
| Horizontal cylinder | Length, diameter, dome depth | Circle segment times length, plus the domed ends |
| Rectangular | Length, width, height | Width times fuel height times length |
| Oval | Length, width, height | Ellipse segment times length |
| Rounded rectangle | Length, width, height, corner radius | Rectangle minus the four corner voids |
| Trapezoid | Length, bottom width, top width, height | Trapezoid area times length |
| Vertical cylinder | Diameter, height | π × radius² × fuel height |
Typical value. Replace with your tank measurement or your sensor datasheet value.
How do you calibrate a tank by filling it?
Level the vehicle and run the tank low
Park on level ground with the engine off. Run the tank as low as is safe, and read the sensor with the tank empty. That is your empty reading.
Choose the batch size
A batch of one tenth to one twentieth of the tank is common. Use smaller batches where the tank shape is irregular.
Add fuel through a metered pump
Add one batch and write down the liters from the meter, not from the pump display of the station.
Wait, then read the sensor
Let the fuel settle for a minute or two and the reading stop moving. Write down the reading in the units your device reports.
Repeat up to full
Continue batch by batch until the tank is full or the reading stops rising. Note the batches where the reading jumps.
Enter the batches
Open the Fill data tab, enter the empty reading and the batches. The tool flags readings that do not rise and slopes that look wrong.
Prove it with a test fill
Load the table, then add a few more measured liters and compare. The Test fill check tab does the comparison for the shape table.
How are the liters worked out?
For a horizontal cylinder the cross-section of the fuel is a circle segment. Multiply its area by the tank length and divide by one million to get liters. The tool then maps each sensor reading to a fuel height: the tip height plus the reading.
Worked example
- Tank: 800 mm diameter, 1,500 mm long, flat ends. Capacity: π × 400² × 1,500 ÷ 1,000,000 = 754.0 L.
- Probe 750 mm long, tip 25 mm above the bottom, dead zones of 20 mm and 30 mm. The probe measures 714.6 L of the capacity, and 7.0 L sits below the tip.
- A reading of 375 mm puts the fuel 400 mm above the bottom, the middle of the tank: 377.0 L.
- With a 25 mm step the table has 31 rows, and each step adds between 12.6 L and 30.0 L.
Common mistakes
- Using outside dimensions. The walls take volume. Measure inside.
- Forgetting the gap under the tip. The fuel below the tip is real, but the sensor cannot read it.
- Calibrating on a slope. A tilted vehicle gives a table that is wrong on level ground.
- Mixing reading units. The table must use what the device sends: millimeters, percent or a raw value.
Assumptions and limits
The shape table is an estimate. Baffles, bulges, tilt and a non-linear sensor are not in it, so confirm it with a test fill. The defaults, including the probe length, the dead zones and the raw range, are typical examples and not the specification of a Tracom sensor. Check the import format and the row limit of your device and platform before you load a table. For the full job, use the calibration field sheet and the cut-length calculator.