|Capacitive fuel level sensors are widely used in vehicle monitoring systems. They are versatile and precise. DUT-E sensors can be used to monitor fuel level in tanks of any vehicles and fixed installations.
Fuel tanks come in different shapes and sizes (see Figure 1). It is impossible for a sensor to store all mathematical models of different fuel tanks and automatically calculate the current fuel volume in a tank.
Figure 1 – Fuel tanks come in various shapes
To ensure correct measurement of fuel volume it is important to calibrate the fuel tank where DUT-E sensor is installed.
The Purpose and Requirements of the Calibration Procedure
The calibration procedure is performed to find out the dependence of DUT-E output signal on the current fuel volume in the specific fuel tank.
Before starting the calibration procedure you must install the DUT-E sensor in accordance with the Operation Manual, connect DUT-E to the on-board power supply and to a vehicle monitoring device (see DUT-E Fuel Level Sensor. Operation Manual). Make sure the tank is empty and clean.
A vehicle must meet certain requirements:
- the unloaded vehicle must be placed on a horizontal even ground,
- vehicle wheels must be of standard dimension-type,
- air pressure in the tyres must meet the manufacturer’s requirements,
- the engine must be stopped, ignition switched on.
The Calibration Procedure
To measure the volume of fill-ups, accepted graduated containers, fuel filling columns of refuelling stations, or mobile refuelling units can be used (see Figure 2). For departmental refuelling stations it is required to check using an accepted graduated containers that the fuel is measured accurately. Relative error of measurement must not exceed 0.25 %.
a) graduated container b) fuel filling column of a refuelling station c) mobile refuelling unit
Figure 2 – Equipment for measuring fuel portions
During calibration process a calibration table is built. A vehicle monitoring system will use it later on to calculate the current level of fuel volume in the tank.
The volume of one fill-up must be chosen depending on technical feasibility of a vehicle monitoring device and the shape of a particular tank. The more complex the tank shape is, the less volume must be used for fill-ups. It is recommended to choose such volume of one fill-up that would not exceed 1/10 of the volume of the fuel tank. To achieve accepted precision of fuel measurement a calibration table must have 10-16 checkpoints. During the calibration process portions may be changed if it’s necessary.
While building the calibration table it is important to correctly define the first checkpoint. A vehicle monitoring device will start to display actual data. This initial value, together with the corresponding fuel volume will be the first checkpoint in the calibration table.
Some tanks may have reinforcement ribs and internal partitions. After each fill-up take a pause (sometimes of up to a few minutes) to stabilize fuel level. Proceed with fill-ups until the tank is full.
After the calibration is done, assess the curve you built. It must be ascending. Each value of DUT-E output signal must correspond to a single fuel volume value (see Figure 3).
Figure 3 – Calibration graph
Calibration Process Using Various DUT-E Types
A calibration table for analog (DUT-E A5, DUT-E A10, and DUT-E I) and frequency (DUT-E F) sensors is built with the help of telematics server software and may be stored on the server. The software calculates current fuel volume according to received output signal present in the fuel level sensor reports.
A calibration table for an analog DUT-E sensor connected to an online vehicle monitoring tracker (such as ) is built using SK Online service kit. It is stored in the memory of the tracker (see Figure 4).
Figure 4 – Building calibration table for analog DUT-E sensors using SK Online service kit
For digital sensors (DUT-E 232, DUT-E 485, and DUT-E CAN), a calibration table is built using SK DUT-E service kit. The table is stored in the memory of a sensor (see Figure 5). Digital DUT-E sensors can calculate fuel level independently (in liters or as percentage value of a full tank) and then transmit this data to a vehicle monitoring device.
Figure 5 – Building a calibration table for digital DUT-E sensors with SK DUT-E service kit
Calibration of Fuel Tanks of Various Shapes
For vehicles that mostly operate on complex off-road terrain, sometimes 2 or more DUT-E sensors are required. This allows to visibly mitigate fuel level sensor data dependency on angular position of a car. Calibration of a tank with multiple fuel level sensors will be different from that with only one sensor because of fuel tank shape complexity.
Two separate calibration tables must be created for a tank of regular geometry (see Figure 6). Fuel volume for each resulting checkpoint is found as a sum of two volumes of corresponding separate checkpoints in the calibration tables of DUT-E #1 and DUT-E #2.
Figure 6 – Calibration process of a regular geometry tank with two DUT-E sensors installed
For instance let’s examine a tank of irregular geometry, in “stares”-like shape, with 2 DUT-E sensors installed (see Figure 7). A calibration procedure must include 3 volume ranges that such tank can be divided in. A separate calibration table will be created for each of the sensors installed in the tank.
Figure 7 – Calibration procedure performed for a tank of irregular geometry with 2 DUT-E installed
Calibration of Range 1 and Range 3 of a fuel tank must be performed for a single sensor only. Calibration of these ranges is performed as described in the previous sections, for DUT-E #1 and DUT-E #2.
Calibration of Range 2 of fuel tank is performed for both sensors, for DUT-E #1 and DUT-E #2. The procesure is the same as done for a single fuel level sensor installed in a tank of regular geometry.
Calibration for Vehicles with Multiple Fuel Tanks
In a vehicle with multiple fuel tanks it is requred to perform calibration for all tanks separately. After sucessful calibration, to receive data from multiple tanks you will need a fuel level sensor summator. For instance, for DUT-E 232 fuel level sensors SUMMATOR DUT-E SUM can be used.
Fuel tank calibration is an important step of DUT-E fuel level sensor installation and customization. Once calibration is finished, a fleet owner will always have accurate real-time fuel volume data for any modern vehicle.
And have you already calibrated fuel tanks in your vehicles?