Device to determine volume of fluid dispensed

An apparatus for determining a volume of fluid dispensed comprising:

• an acoustic volume sensor comprising:
• a structure containing a fixed-volume chamber, a first port, and a measurement chamber, wherein the first port comprises a first tube portion and acoustically couples the fixed-volume chamber to the measurement chamber to form an acoustically contiguous region, the measurement chamber having a gas-filled measurement region;
• a printed circuit board disposed within the structure, the printed circuit board defining the fixed-volume chamber within the structure and the printed circuit board including:
• a loudspeaker acoustically coupled to the fixed-volume chamber, wherein the loudspeaker excites the acoustically contiguous region;
• a reference microphone acoustically coupled to the fixed-volume chamber, the reference microphone producing a first pressure signal based on the response of the fixed-volume chamber to excitement by the loudspeaker;
• and
• a sensing microphone acoustically coupled to the measurement chamber via a second port comprising a second tube portion, the sensing microphone producing a second pressure signal based on the response of the measurement chamber to excitement by the loudspeaker;
• a dispensing chamber, containing a variable fluid volume, an exit channel and a resilient membrane, wherein the dispensing chamber is attached to the structure and the resilient membrane defines a boundary of the gas-filled measurement region;
• and
• a processor in communication with the loudspeaker, the reference microphone and the sensing microphone, the processor comprising:
• receiving the first pressure signal and the second pressure signal at a first instance;
• receiving the first and second pressure signals at a second instance;
• determining a change in volume of the gas-filled measurement region associated with the first and second pressure signals at the first instance and the first and second pressure signals at the second instance;
• and
• determining the volume of fluid dispensed from the dispensing chamber to the exit channel associated with the change in the volume of the measurement region.