MEASUREMENT ACCURACY FOR THE DIGITAL FUEL PROBE
- One should strictly distinguish between the theoretical accuracy provided in the technical characteristics of digital probes measuring the amount of fuel in the tank and the actual accuracy of the measurement which can be achieved under specific conditions of vehicle or machine use.
- The theoretical accuracy of measuring the amount of fuel in the tank depends on the technology used by the probe manufacturer to measure the level or volume of fuel in the tank and is typically from 0.5% to 0.1%. This is the accuracy that can be achieved in the laboratory conditions.
- In real conditions there are additional factors that impact the accuracy of the measuring the amount of fuel in the tank, such as:
- fuel temperature difference when driving and when stationary (depending on the time of year); one may cautiously assume that the fluctuations are normally in the range of 20 – 30 degrees C (when driving, fuel is additionally heated because it serves cooling the engine injection pump). This causes a change in volume and accounts for an error in measurement of ca. 1.5-2.0%,
- the fuel “sloshing” in the tank even after applying various techniques and mounting the probe centrally causes an additional error of ca. 0.5 to 1.0% (in the case of machinery working in difficult conditions this error may even reach 3%),
- tank calibration error, even with careful installation, is in the range of 0.5-1.0% (in atypical tank shapes this may be as high as 2-3%).
- Construction machines often have tanks of irregular shape and work in very difficult conditions, therefore the error in fuel measurement may be even 2-5% greater than for cars.
- In the case of a vehicle equipped with dual tank, we mount two independent digital probes for fuel measurement; our recorder is designed for simultaneous measurement of fuel level in two tanks.
MEASUREMENT ACCURACY FOR THE FUEL FLOW METER
The flow meter allows you to obtain a very accurate measurements of fuel consumption – the measurement is made to an accuracy of 1/100, 1/200 or even, in some vehicles, 1/1000 litre. Its installation requires some alteration of the fuel system to properly take into account also the fuel returning into the tank. The cost of the meter itself and of its assembly is large – but still this is the most accurate measurement method. This enables extremely accurate accounting for consumption – the results of the measurement are not affected by rocking of fuel in the tank or the number of tanks.
A flow meter does not directly indicate the moment of any fuel theft – shortages are only detected in a long run from summaries accommodating for refuelling. A flow meter may not be mounted on all types of engine and fuel system. A good practice would be to conduct measurement by means of a flow meter in conjunction with data from a floater or probe – this provides an accurate statement of consumption and basic information on refuelling and any shortages or fuel theft – on the summary, the flow meter data will indicate precise shortage amount, and the floater data will indicate the moment where irregularities took place.
MEASUREMENT ACCURACY FOR THE CAN BUS
A CAN Bus communicates data between all electronic devices in the vehicle. The amount of data is large – from the fact of opening the door, over the temperature and engine speed, up to the dose of fuel injection etc. After connecting a GPS device with the CAN module one gains access to all these parameters – with those most important stored and transmitted to the system. Basis on data analysis of the data collected one may designate the engine operating parameters and, above all, the fuel consumption (average, instantaneous, total) and the engine speed. The data requires accurate calibration – but when this is done – the results are highly accurate. The disadvantage of this solutions is that not each vehicle manufacturer allows for permanent connection to the CAN bus in the warranty period and that not all cars make the same data available.
SUMMARY
The quality of the measurements: Flow meter/CAN – very accurate measurement of the total consumption and instantaneous consumption, at the expense of non-detection of refuelling and shortages. Probes – the other way round – provide less accuracy, but allow you to identify the moments where there are certain changes in the level of fuel. The shorter the periods of analysis the less precise is the data from the probe,
The costs are nearly proportional to the accuracy of the measurements – the probe is the cheapest, the flow meter – the most expensive. Obviously, in any case, regardless of the chosen fuel control system, the costs spent on system installation pay great dividends: the awareness of control and monitoring has a mobilizing effect on drivers, your staff members drive more calmly and thus safer; an analysis of routes allows them to be optimized; all of the above directly affects the reduction of maintenance costs for the fleet of vehicles.
| Probe | Flow meter | CAN | |
| Assessment of measurement accuracy | good | very good | average |
| Average measurement error | 3-6% | <1% | <15% |
| Total consumption | good | very good | average |
| Instantaneous consumption | poor | very good | average |
| Detection of refuelling | good | only indirectly | good |
| Detection of pouring out | good | only indirectly | good |
| Cost of assembly | average | average | low |
| ost for tank no. 2 | average | none | none |
| Interference with vehicle electronics | minimal | minimal | large |
| Interference with vehicle fuel system | little | large | none |
| Installation in passenger vehicles | no | yes | yes |
| Installation in transport vehicles | yes | yes | yes |
| Installation in heavy goods vehicles | yes | yes | yes |