richardn wrote: ↑
Mon Dec 02, 2019 1:18 pm
My understanding is that they use time of flight fuel flow metering rather than doppler effect which could measure continuously but would need to be calibrated to the precise properties of the fuel..
Yes, they use time-of-flight, as well as temperature (I guess Doppler effect is unusable in this case because, tmk, it would need the presence of particulate within the liquid). And yes, the measurements are made at about 2.2kHz frequency, which has been at the basis of some conjectures in this forum not long ago. Here is a description of the FFM from racecar-engineering.com, in an interview with the director of Sentronics, the F1 supplier:
《Located at either end of a thin tube are two piezoelectric transducers. These are effectively ceramic discs, suspended in a fuel resistant housing, which convert electrical energy into ultrasound pulses. In principle, a pulse is sent from one transducer to the other, in the direction of flow. This is then followed by another pulse sent back to the original transducer in the opposite direction. With the distance between transducers known, the time of flight of both pulses is measured and then subtracted to determine the velocity. As the tube diameter is also known, the flow rate of the fuel can be easily calculated. [...] One problem with ultrasonic flow measurement is its fundamental principle is volumetric, this means to calculate mass flow accurately a density measurement is required. [...], the best option at present is to calculate density using a very accurate temperature measurement and calculate density based on fuel samples which have had the density properties very accurately measured under laboriatory conditions. [...] Once the temperature of the fuel has been identified, the necessary look-up is performed and mass flow rate is calculated, which is the final figure all the engineers are after. [...] Acoustic energy takes time to decay away, less time between measurements means you need techniques and algorithms to deal with any unwanted ultrasonic signals that have not had time to fully decay. Our patented technology allows us to achieve highly accurate time of flight measurements even with all these interfering signals being present.’》