Triggering circuit for an aerosol drug-dispensing device
An electronic gas flow triggering circuit for use in an aerosol drug dispensing device has a voltage source and a self-nulling circuit to which voltage is supplied from the voltage source. A hot wire anemometer filament forms a component of the bridge circuit which is adapted to maintain a constant resistance of the anemometer filament, the bridge drive voltage being dependent upon the gas flow across the anemometer filament. A comparator compares the bridge output voltage with a reference voltage and provides a triggering signal to operate the device if the bridge drive voltage is greater than the reference voltage.
1. An electronic gas flow triggering circuit for use in an aerosol drug dispensing device, the circuit including:
a voltage source;
a self-nulling bridge circuit to which voltage is supplied from the voltage source;
a hot wire anemometer filament forming a component of the bridge circuit which is adapted to maintain a constant resistance of the anemometer filament, the bridge drive voltage being dependent upon the gas flow across the anemometer filament; and
a comparator for comparing the bridge drive voltage with a reference voltage such that a trigger signal is provided if a certain rate of change of gas flow is exceeded.
2. A triggering circuit according to claim 1 , wherein the bridge circuit is a Wheatstone bridge.
3. A triggering circuit according to claim 1 , wherein the reference voltage is derived from the bridge drive voltage, to prevent erroneous triggering due to changes in ambient temperature.
4. A triggering circuit according to claim 3 , wherein the reference voltage is filtered to pass only low frequency signals. It is requested that multiple dependencies be removed from the application. If any multiple dependencies remain after amendment, said multiple dependencies should be deleted and the claim made dependent on the next previous claim.