Here you are going to find some answers to the tank calibration questions most people ask when they deal with fuel level sensor installation.

1. What is the difference between fuel level sensor calibration and tank calibration?

Many people confuse these concepts. We make sensor calibration after the sensor has been cutted . To calibrate the sensor we have to immerse it it in fuel to teach sensor about the new length.  While fuel tank calibration is completely different process and is needed to turn the fuel level into volume.

2. Why do I need to calibrate the tank?

All existing sensors measure the fuel level, but not its volume. To recalculate fuel height into volume, you need to know the shape of the tank. The tank calibration procedure is to determine how the volume of fuel in the tank depends on the height, in essence it is to determine the geometric shape of the tank.

Tank calibration is made by filling the tank in measured portions from empty to full and is a relatively time-consuming procedure. Someone may try to look for other fuel level sensors in an attempt to avoid this procedure, but  without success because tank calibration procedure is related to the fuel tank, not the sensor.

3. Why do I need to calibrate the sensor? And how to do it?

To calibrate the fuel level sensor you do not need a lot of fuel – a piece of plastic pipe closed on one side and filled with 1-2 liters of fuel will help. The length of the pipe must be longer than the length of the calibrated sensor. (Fig. 1).

Fig. 1. Fuel level sensor calibration “Full”

4. Tank calibration by filling it in portions from empty to full is very time consuming. Is there any way to avoid it?

There are several cases where this is possible.

4.1 We are satisfied with the level, not the volume of fuel. For example, we need to know if it is time to fill up the fuel tank. In this case the information about the fuel level is enough.
4.2 We have a ready calibration table for this tank (usually in level – volume format).

We can use this data to calculate the tank calibration with the eurosens configurator. These tables are often found with owners of fuel storage tanks and gasoline tankers.
So if you work with such objects, the first thing to do is to ask the customer about the availability of calibration tables.

4.3 We have such a tank shape that we can calculate the fuel volume for any level using a formula.

For example, a perfectly rectangular tank (parallelepiped without rounding) or a vertical cylinder.

Fig. 2. Ideal tank shapes. We don’t need to calibrate such tanks.

The results of tank calibration can be plotted on a graph (sensor output is the volume of fuel in the tank). For the tanks shown in Fig. 2 the graph will be a straight line. Thus, it makes no sense for us to calibrate the tank by filling portions, because on the graph all these points will fall on this straight line and we can calculate them without filling portions as well.

Fig. 3. Calibration table for tanks with constant width

Other popular forms of tanks are the horizontal cylinder (Fig. 4) and the tank (Fig. 5).

Fig. 4. Cylindrical tank, widely used on vehicles

Fig. 5. Horizontal cistern tank chape

The calibration table for such tanks can be calculated with the eurosens configurator. All that is required is to calibrate the sensor to the actual length using a pipe (see chapter 3) and enter the tank dimensions (Fig. 6).  For a horizontal cylinder, enter the tank size E=0.

Fig. 6. Math calibration of the cistern using eurosens Dominator configurator

5. We have a calibration table from a very similar tank. Can we use it?

For example, we install fuel level sensors on 20 identical trucks  with identical tanks. Our first intention is to calibrate one vehicle and use this calibration everywhere.

But this would be a mistake, because the fuel tanks have slightly different volumes, and the sensors are cutted slightly differently. We will end up with incorrect filllings, especially when refueling to a full tank.

But we can use the calibration tool to compare and process the calibration tables from the eurosens configurator (Fig. 7 ).

Fig. 7. Morphing the calibration from one tank to another.

To get calibration tables for our 20 trucks  we need the following:

1. Calibrate first vehicle with first fuel level sensor.
2. Determine the exact tank volume of each truck (by filling to full condition).
3. Calibrate all sensors in the tube (see chaper 3).
4. Edit the sensor calibration curve by stretching and squeezing on the two axes so that the sensor calibration values “full”-“empty” match the calibration values and the tank volume matches the measured volume.
5. Then save the resulting table into a file and load it into the appropriate sensor.

6. How to choose the right number of portions to calibrate the fuel tank?

Many people think that the more portions used to calibrate the tank, the more accurate the result. In many cases this is true – for example, for tanks whose cross-section constantly changes from the bottom to the top (Fig. 8).

Fig.8. Fuel tank with irregular shape

What advantages this method of a

If we try to get it by taring with 8 portions (Fig. 9) and with 16 portions (Fig. 10), the difference is significant (red graphs).

Fig. 9. Calibration by 8 points

Fig. 10. Calibration by 16 points

If we calibrate an ordinary rectangular tank (Fig. 11), then it has rounded bottom and top, and in the middle part is symmetrical with almost vertical walls.

Fig. 11. An ordinary rectangular fuel tank

It is reasonable to calibrate such tanks with variable volume of the dose, in the upper and lower part of the portion volumes make less, and in the middle part you can make them more. This way we will not lose in accuracy (as you can see in Fig. 12 we can reconstruct the graph on these points), but we will increase the calibration speed. Usually it is 20-30 points, but their number can be reduced by parts of the fuel tank of a constant width.

Fig. 12. Tank calibration with a good accuracy but decreased amount of points.