AIC Technology
In the engine fuel consumption measurement world, two principles are competing, each with its benefits and inconveniences: The Direct Measurement, which AIC Systems pioneered more than 30 years ago and was at that time revolutionary. The Direct Measurement principle is AIC System technology. Differential measurement, which is the oldest principle.
With the Direct Measurement principle, the installation of only one AIC Fuel Flowmeter is required. The fresh and cool fuel consumed is aspirated from the tank and its volume measured by the AIC fuel Flowmeter before arriving in the AIC vortex head. In the Vortex head, the fresh fuel from the tank is mixed with the fuel returning from the engine. From the AIC Vortex head, the fuel is pumped to the engine by the fuel pump. With this solution no fuel is going back to the tank and  the fuel passing through the AIC Volumetric measuring chamber represents precisely the real engine consumption. The great benefit is that an AIC fuel consumption measuring system is ready to use right after installation.
Tank 908 EngineCAT Text
Direct Tank Engine Text
There is another solution out there for measuring fuel consumption which consists of measuring the quantity of fuel going to the engine and subtract from it what returns to the tank. This principle is mostly named the "Differential Measurement principle". Such solution necessitates the installation of two flowmeters. One for measuring the fuel flow going from the tank to the engine and a second one for measuring the fuel flow returning from the engine to the tank. When passing through the engine the fuel warms up and changes in volume. This physical modification requires the use of a compensation factor in the calculation algorithm of the consumption. As a consequence, the engine consumption obtained with Differential Measurement is the result of a calculation which accuracy and reliability greatly depends of the compensation factor used. With AIC Systems Direct Measurement principle, the fuel flow measured by the flow Sensor represents exactly the volume of fuel burned by the engine. No calculation and compensation factor are used, thus providing reliable values.