An ultrasonic flowmeter unit, developed by SAW Technologies, measures the flow rates of syrup and carbonated water with a claimed accuracy of 2%.
Installed in post-mix dispensing machines, the signal from the flowmeter unit feeds a control system that proportions the mix of carbonated water with syrup. As well as allegedly outperforming units that depend on pressure, the system also logs the speed of sound in the syrups, thus making it possible to distinguish between genuine and black market syrup varieties.
The post-mix dispensing equipment contains three flow lines: carbonated water and two syrups. An injection moulded plastic cartridge in each line contains opposing piezo film sensors which act as ultrasonic transceivers. These sensors consist of piezoelectric PVDF film which is overlayed with a barrier layer of ordinary PVDF film. The active area of the piezo film sensors is about 4mm diameter.
An ASIC chip directs the sensors to act alternately as transmitters and receivers, timing ultrasonic pulses in each direction. The difference in time indicates the liquid flow rate through the unit.