Short answer
A tank calibration table maps what the sensor reports to real litres, for one specific tank. It is built by measurement rather than calculation, because a real vessel deviates from its nominal shape through dents, internal ladders and hatches, and installation tilt that no formula can anticipate.
Key takeaways
- A calibration table is a measured mapping from sensor reading to litres, valid for one tank only.
- Eurosens names the reason plainly: a real vessel deviates from the ideal shape through dents, internal ladders and hatches, and installation tilt.
- Teltonika documents the method, fill in 5–10% increments, allow about 30 seconds of settling at each step.
- The output is a cubic fit with coefficients a0 to a3, because the underlying height-to-volume curve is not a straight line.
- Recorded values must change monotonically; up-and-down readings mean a physical fault to find, not data to fit.
01What the table actually is
A tank calibration table, often called a strapping table in bulk storage, is a list of paired numbers. On one side is what the sensor reported; on the other is how many litres were actually in the tank when it reported that. Nothing more. It is not a specification, it is not supplied by the sensor manufacturer, and it cannot be downloaded, because it describes a particular vessel rather than a product line. The OMNICOMM listing states a measurement range of 0 to 4,000 millimetres and an accuracy of ±0.5%, and both figures describe how well the device measures a height. The table is the separate artefact that turns that height into the quantity an operator can act on. Without it a platform has a number that moves in the right direction and means nothing quantitative; with it, the same number becomes litres that can be compared against a delivery note.
02Why a formula is not enough
For an idealised tank the mathematics is solvable and exact. A horizontal cylinder holds 19.55% of its capacity at quarter height and 80.45% at three-quarter height, computed from the circular-segment relation, and the maximum error of assuming a straight line instead is 5.77 percentage points near h/D = 0.19. So geometry already tells you the shape of the curve. What it cannot tell you is the shape of your particular tank. Eurosens, which manufactures level sensors and therefore has no incentive to add work, states the reason directly: a real vessel deviates from the ideal shape through dents, internal ladders and hatches, and installation tilt. Each of those is specific and unpredictable. A dent removes litres at one narrow band of heights. An internal ladder displaces volume across a range. Tilt shifts the entire curve sideways, so nominal empty is not empty.
03How the table is built
Teltonika documents the procedure concretely enough to follow. Fill the tank in increments of 5 to 10% of capacity, allow roughly 30 seconds of settling after each addition, and record the sensor reading against the known litres now present. That gives ten to twenty paired points across the working range, which is enough to characterise the curve without an unreasonable amount of fuel handling. The settling pause is not politeness: a freshly added volume is still moving, and a reading taken during that movement records the surface disturbance rather than the level. The increment size matters for a different reason, too coarse a set and the fit smooths over a genuine local deviation such as a dent or a baffle, which is exactly the detail the table exists to capture. Adding fuel is preferable to draining, because a measured delivery is easier to trust than a measured extraction.
04What the platform does with the points
The paired points are not usually stored as a lookup list. Teltonika fits them and produces cubic coefficients a0, a1, a2 and a3, a third-order polynomial rather than a straight line, chosen because the underlying height-to-volume relationship genuinely curves. A cubic has enough freedom to follow the S-shape of a horizontal cylinder while staying smooth between the measured points, which matters when a reading arrives at a height that was never sampled. It is worth understanding what that means for trust: the platform reports litres by evaluating a polynomial, so a level between two calibration points is interpolated rather than measured. That is acceptable when the points are dense enough. It quietly stops being acceptable when a table was built from three points at convenient heights, because the fit then has more freedom than evidence and can bend confidently through regions nobody checked.
05The diagnostic that catches a bad run
Teltonika gives one check that is worth treating as a hard gate: the recorded values must change consistently as fuel is added, and up-and-down values mean a fault to find before continuing. Read that literally. Fuel only went in, so the reading can only go one way. If step six sits below step five, the reason is physical, a probe that shifted in its mount, air trapped in a capacitive gap, the vehicle moved between readings, or a level taken while the surface was still travelling. None of those are fixed by fitting a polynomial through the anomaly. A cubic will pass near the bad point and absorb it into the curve, so the resulting table looks complete and reports litres that are wrong across a whole band of the tank. Stopping the calibration to find the cause is cheaper than discovering the fault six months later through a reconciliation dispute.
06One table per tank, and when it expires
Because the table encodes the deviations of one vessel and one sensor installation, it does not transfer. Two identical tanks from the same production batch will differ once one has been dented and the other mounted on a slope, and the same tank recalibrated after the probe is removed and refitted will differ again, because the probe's depth and angle in the fitting are part of what was measured. Practically, that means a calibration table has events that end its validity rather than an expiry date: the sensor is moved or replaced, the tank is repaired or has a baffle added, or the tank is remounted at a different attitude. Fleet operators sometimes look for a calibration interval instead. There is no measurement basis for one, a manufacturer warranty period is a commercial term, not a statement about how long a fitted curve remains true.
07What the table does not solve
A correct table converts a level into litres in the tank at the moment of reading, and two things sit outside that. The first is temperature. Measurement Canada publishes diesel volume correction factors of 1.0000 at 15 °C, 0.9958 at 20 °C and 0.9873 at 30 °C, about 0.00085 per °C, which is roughly 6.8 litres on a 400-litre tank across a 20-degree swing. Those litres are real in the tank and not real on an invoice corrected to a reference temperature. The second is sampling. Teltonika's data-acquisition settings offer four simultaneous record triggers, time, distance, angle and speed delta, and a level change is only visible if a record was taken while it happened. A perfect table behind a five-minute record interval still gives five-minute resolution.
| Property | Geometry formula | Measured calibration table |
|---|---|---|
| Handles the nominal tank shape | Yes, exactly | Yes |
| Handles dents and internal ladders | No | Yes, that is its purpose |
| Handles installation tilt | No | Yes |
| Transfers to an identical tank | Yes | No, one tank, one table |
| Survives removing and refitting the probe | Yes | No, recalibrate |
| Cost to produce | None | A controlled fill in 5–10% increments |
Figures and sources
- Eurosens manufacturer rationale for requiring a tank calibration table: a real vessel deviates from the ideal shape: dents, internal ladders and hatches, and installation tilt (Source: Mechatronics, Using tank calibration table utility, as of 2026-08-31)
- Teltonika documented calibration procedure and the polynomial it produces: 5–10% tank increments, ~30 s settling; yields cubic coefficients a0, a1, a2, a3 (Source: Teltonika Telematics Wiki, Analog Fuel Sensor, as of 2026-08-31)
- Teltonika monotonicity diagnostic during calibration: voltages must change consistently; up-and-down values mean a fault to find before continuing (Source: Teltonika Telematics Wiki, Analog Fuel Sensor, as of 2026-08-31)
- Volume held by a horizontal cylindrical tank at quarter height (exact circular-segment geometry): 19.55% of capacity at h/D = 0.25, and 80.45% at h/D = 0.75 (Source: Computed from V/Vtot = (θ − sin θ)/2π, θ = 2·arccos(1−2h/D); ENTEK.AI computation, independently reproducible, as of 2026-08-31)
- Maximum error of assuming level is linearly proportional to volume in a horizontal cylinder: 5.45 pp at quarter and three-quarter height; true maximum 5.77 pp near h/D = 0.19; zero only at half height (Source: Computed from the exact circular-segment formula; ENTEK.AI computation, independently reproducible, as of 2026-08-31)
- OMNICOMM measurement range and accuracy, what the sensor side of the table contributes: 0 – 4,000 mm; ±0.5%; capacitive (LLS series) (Source: ENTEK.AI product catalogue, as of 2026-08-31)
- Diesel volume correction factors per API MPMS Ch. 11.1, and the apparent change they imply: VCF 1.0000 at 15 °C, 0.9958 at 20 °C, 0.9873 at 30 °C ≈ 0.00085 per °C (≈6.8 L on a 400 L tank over 20 °C) (Source: Measurement Canada (ISED), Volume correction factors, diesel fuel, as of 2026-08-31)
- Teltonika record-acquisition triggers, a level change is visible only if a record is taken during it: four simultaneous methods: time (Min Period), distance, angle, speed delta; zero disables each (Source: Teltonika Telematics Wiki, FMB120 Data acquisition settings, as of 2026-08-31)
Questions
Can I download a calibration table for my tank model?
No. The table describes one physical vessel, including the dents, internal ladders and hatches, and installation tilt Eurosens names as the reason it is needed. Two tanks from the same batch differ once one is dented or mounted on a slope.
How many calibration points do I need?
Teltonika documents increments of 5 to 10% of capacity, which gives roughly ten to twenty points. Fewer points let the cubic fit bend freely through regions nobody measured, so the table interpolates confidently over heights that were never checked.
Why must I wait about 30 seconds between steps?
Freshly added fuel is still moving. A reading taken during that movement records surface disturbance rather than the settled level, and it enters the table as a point the polynomial then honours. The settling pause is part of the measurement, not a courtesy.
How often should a calibration table be redone?
On events, not on a schedule. Redo it when the sensor is moved or replaced, when the tank is repaired or has internal structure added, or when it is remounted at a different attitude. A manufacturer warranty period is a commercial term, not a calibration interval.
Sources
- Mechatronics, Using tank calibration table utility (the manufacturer's stated rationale)
- Teltonika Telematics Wiki, Analog Fuel Sensor (increments, settling, cubic fit, monotonicity check)
- Teltonika Telematics Wiki, FMB120 Data acquisition settings
- Measurement Canada (ISED), Volume correction factors, diesel fuel