Fuel level sensors

When a company decides to deploy a fleet management system it’s very often that AVL device is installed with additional sensor that measures fuel level in vehicle’s tank.

It is not an overstatement to say that using fuel level sensors are the most popular way to control fuel consumption for today. This method is accurate (the best systems give precision up to 2-3%) and reliable, as well as universal: it matches almost every vehicle that drives on flat roads.

Coban GPS105A

Refuellings and drains can be easily monitored as well, including their volume, date, time and exact place evaluated by GPS.

A fleet manager can also get fuel consumption data, analyzing the change of fuel level and mileage with a simple formula: consumption is equal to the fuel level difference in two waypoints multiplied by tank volume index and divided by the distance between these points.

How does it work?

Indicative measurements may be arranged with the use of fuel floater, thus, more accurate data may be gathered only with electric capacity fuel sensors. Fuel fills up the space between capacitor plates and changes the system’s elastance.

Coban GPS302

Capacitor plates usually are made as coaxial tubes or one tube with a strand of wire in a middle. A sensory picker is placed in a sensor’s upper part. All types of fuel sensors should be installed vertically inside a tank, but should not get beyond its depth at least 2-4 centimeters.

Types of output interfaces

Information about fuel level is transmitted from sensor to vehicle GPS tracker. Most commonly wires are used for that, but it’s important that signal can be modulated in different ways:

  • Analog modulation (voltage represents fuel level)
  • Frequency modulation
  • Transmitting digitized data (quite often with the use of serial interfaces RS232 or RS485).

While analog sensors are very simple digital units provide more “accurate” data thanks to the antinoise protection. The main disadvantage of digital equipment (sensors and tracker) is higher price.

coban

Fuel sensor calibration

Sensor calibration is a very important stage of the installation process for fuel control systems. As previously mentioned, a fuel sensor shows only the fuel level, but not the real volume of gasoline in a tank. Whereas vehicle tanks may not have a regular shape.

The problem of fuel level and volume correlation may be solved by the calibration process. A small and very precise portion of fuel (for example, 10 liters) is doped to a tank. A gained fuel level is equal to this volume. The procedure is repeated a few times (up to 20 efforts) and all correlated parameters are put in a calibration table. Now, you will definitely know what does your fuel level actually mean.

After that, your tracking service may read this sensor calibration table data and provide you comprehensive statistics and reports. Without this table, you will only know the percentage of tank’s load from 0 to 100 percents.

You should remember that there are possible to use many fuel sensors simultaneously. For example, if your truck is equipped with two or more tanks the data from installed fuel sensors is summarized. If fuel sensors are used in a single tank, they should be placed in different corners. In this case, the averaged data will help to avoid the uncertainty of fuel slashing.

What data can be shown to a fleet manager?

There may be some type of reports provided by a good fleet tracking software:

  • Fuel level on-line (level-to-time and level-to-milage graphs) with engine status and current speed
  • Fuel efficiency is fuel consumption level for 100 kilometers (you will see that a loaded truck spent fuel faster)
  • Refueling data (volume, time, place) that is detected with fuel level spike
  • Fuel draining reports (same as refueling)