Possible explanations and actions:

1. Outliers of data.

To detect such outliers, build a track of unit movement for the appropriate period. Outliers of data will be seen on the track as dashed lines.

Ways to overcome outliers:

• Enable filtration of unit positional information in messages (on the Advanced tab of unit properties). This will not affect old messages but applied to new ones.
• To correct data in reports, change settings of trip detection, in particular, reduce Maximum interval between messages and increase Minimum satellites.

2. Incorrect settings or operation of the mileage counter.

• Check the mileage counter settings on the General tab of unit properties.

Yes, but only if the driver has not had other assignments since they were last assigned to the unit.

1. Mileage-based calculation

In a standard situation, all calculations of fuel level are mileage-based. That means data from the FLS is taken only during intervals of movement (trips). Those trips are defined according to parameters set in the trip detector.

Drains and fillings are detected if there is a difference between the fuel level on the following movement interval (X) and the fuel level on the previous movement interval (Y). If (X — Y) > 0, it is a filling; if (X — Y) < 0, it is a drain; if X = Y, it is neither. Of course, there can be some inaccuracy in data coming from the FLS. That is why, to avoid false drains and fillings, set the following parameters in the FLS properties:

• minimum fuel filling volume,
• minimum fuel drain volume,
• minimum stop duration to detect a fuel drain,
• and some others.

2. Time-based calculation

This type of calculation is more complicated and is based on the following algorithm: the speed of the decrease of fuel level according to the FLS is compared with the consumption calculated mathematically. The time-based calculation is necessary for stationary units. It is also widely used for moving units for controlling drains during the movement, for example.

Example

A vehicle stayed at a parking lot during 10 hours. Defueling was made in small portions over the whole parking period. As a result, 60 liters of fuel were drained. It is possible to determine if it was a drain o fuel consumption according to the state of the unit's ignition sensor. ​

Since the consumption math mechanism is based on the values of the ignition sensor, check its properties and operation. You may not have this sensor created or there may be 0 l/h indicated for the fuel consumption in its properties.

You may use one of the approaches described below.

Variant 1

Create a virtual ignition sensor. We recommend that you use average speed (speed+#speed)/const2 as its parameter.

Variant 2

Even if you haven't installed an ignition sensor in the unit or are not sure of the name of the parameter that responds for the ignition, in the parameters of the device there may be some characteristic that corresponds to the operation of the engine. To use it, compare two messages from the unit: one — when the ignition the most probably off; the other — when it's on.

Example

During a long time interval the unit sends approximately the following set of parameters:

hdop=1, odo=0, adc2=2.0475, adc12=1037, c1=0, c2=0, c3=0, c4=0, mcc=260, mnc=2, lac=56720, cell_id=43811, ta=1,
gsm_lvl=55, total_fuel=407154, can_fls=101, can_taho=4797, can_engine_hrs=230420, can_mileage=137603392, engine_temp=123,
srv_dist=0, j1939_air_temp=9072, J1708_eng_hrs=230420, J1708_fl_used=430282, J1708_fl_lvl=101, I/O=80/0

While moving at some speed — approximately the following:

hdop=1, odo=847.358764648, adc2=2.3595, adc12=1117, c1=0, c2=0, c3=0, c4=0, mcc=260, mnc=2, lac=56720, cell_id=60167, 
ta=1, gsm_lvl=71, total_fuel=407178, can_fls=101, can_taho=9940, can_engine_hrs=230447, can_mileage=137609550, 
engine_temp=124, srv_dist=0, j1939_air_temp=9353, J1708_eng_hrs=230447, J1708_fl_used=430307, J1708_fl_lvl=101, I/O=d1/0

Straight before the start of the movement, as a rule, the ignition turns on:

hdop=1, odo=0, adc2=1.4937, adc12=895, c1=0, c2=0, c3=0, c4=0, mcc=260, mnc=2, lac=56720, cell_id=60268, ta=2, 
gsm_lvl=64, total_fuel=407166, can_fls=100, can_taho=996, can_engine_hrs=230439, can_mileage=137605711, engine_temp=120, 
srv_dist=0, j1939_air_temp=9369, J1708_eng_hrs=230439, J1708_fl_used=430295, J1708_fl_lvl=100, I/O=80/0

Discard the parameters that are obviously imprecise: hdop (precision), adcN (it's difficult to determine the regularity), odo (relative odometer in meters), mcc mnc cell_id and lac (LBS data section), gsm_lvl (the level of the GSM signal), etc. The parameter J1708_eng_hrs for this unit seems the most probable, as it doesn't change during the night parking. As a rule, it is also possible to use pwr_ext. Is the ignition is digital, you can follow the values' changes in the block 'I/O =' (see more details in the Inputs and outputs section).

Variant 3

If you have already connected the ignition, find out its parameter by means of the method described above or from the manual of the manufacturer.

Possible reasons:

• In some cases, the system may consider that during the interval with no messages from the unit its ignition was on. Adjust the default value '0 seconds' on the Maximum interval between messages option on the Advanced tab of unit properties. The influence of the option on the fuel calculation is described in the documentation.
• Several engine efficiency sensors can be created. Check up their values. The easiest way to evaluate it is to create in a report a simple chart with one of the curves Fuel consumption by math.

Let us suppose that the fuel consumption in the urban cycle is 10 l/100 km and 7 l/100 km — in the suburban cycle.

• Create an ignition sensor (as in the example above) and set 1 l/h for the consumption during idling.
• The average consumption in the urban cycle is 36 km/h, in the suburban — 80 km/h.
• The unit will cover a distance of 100 km driving at a speed of 36 km/h in 2.8 hours. 10 l / 2.8 = 3.57. Let us calculate the value of the increasing coefficient when moving in the city: 3.57 / 1 (idling) = 3.57.
• As a result of a similar calculation for the suburban cycle, we obtain the coefficient equal to 5.6.
• Create an engine efficiency sensor, taking into account the fact that the unit cannot consume less fuel than during the idling, and that it is stationary before the beginning of the movement. As a parameter we use the average speed (speed + # speed) / const2 and fill in the calculation table (manually or using the calculation table wizard):

Note that the last pair of points is how the system calculated before (the fuel consumption was considered constant for a speed above 80 km/h). You cannot use this method and change the set of points. Also '3' in this example is the minimum speed from the unit's trip detector, consequently, this parameter can be different for your unit.

Result: in our example, the average consumption has been calculated for the unit. It has been calculated relative to the speed and time between messages and taking into account the values of the vehicle operation.

During the mathematical calculation, fuel consumption is computed separately for each pair of messages.

The following algorithm is used:

1. The status of each engine sensor (engine ignition, absolute and relative engine hours sensors) in the current message is determined.
2. For the operating sensors the values indicated in the field Consumed, l/h of their properties are summed.
3. The values of the engine efficiency sensors bounded to the engine sensors are calculated.
4. The received values are summed according to the formula k1 + (k2 - 1) + (k3 - 1) + … + (kn – 1). In that way, the coefficient is formed. If the sum of the coefficients is less than 0 or invalid, the total coefficient will be 1.
5. To determine the current fuel consumption of the unit, the value from point 2 is multiplied by the value of point 4.
6. The value from the previous message till the current one is multiplied by the value from point 5.
7. The consumption for each message pair for the indicated interval is summed and in that way, the fuel consumption is determined by consumption math.