Cartridge with fill level detection
A cartridge ( 2 ) with a fill level detection system ( 10, 10′, 10″ ), the cartridge comprising a substantially rigid containing wall ( 4 ) having a tubular wall portion ( 12 ) surrounding a chamber ( 18 ) for receiving liquid therein, a plunger or piston ( 8 ) mounted inside the chamber and configured to seal one side of the chamber, the plunger or piston being displaceable in the chamber towards an outlet end ( 14 ) of the cartridge, characterized in that the fill level detection system comprises a plurality of discrete fixed electrodes ( 24, 24′ ) positioned along the tubular wall portion in a juxtaposed manner in a direction of displacement D of the plunger or piston ( 8 ), and a mobile electrode member ( 28 ) fixed to the plunger or piston and displaceable therewith.
1. A cartridge with a fill level detection system, the cartridge comprising a substantially rigid containing wall having a tubular wall portion surrounding a chamber for receiving fluid therein, a plunger or piston mounted inside the chamber and configured to seal one side of the chamber, the plunger or piston being displaceable in the chamber towards an outlet end of the cartridge, wherein the fill level detection system comprises a plurality of discrete fixed electrodes positioned along the tubular wall portion in a juxtaposed manner in a direction of displacement D of the plunger or piston, and a mobile discrete electrode member fixed to the plunger or piston and displaceable therewith, the average thickness (t) of the mobile discrete electrode member in the direction of displacement of the mobile electrode member being equal to, or less than, two times a spacing (s) between adjacent said discrete fixed electrodes.
2. The cartridge with fill level detection system according to claim 1 , wherein the fill level detection system comprises a signal processing circuit connected to the plurality of discrete fixed electrodes, the signal processing circuit comprising a multiplexer for sequentially transmitting and/or receiving signals to each of the plurality of discrete fixed electrodes.
3. The cartridge according to claim 1 wherein the mobile discrete electrode member is directly electrically connected by means of a conductor to a signal processing circuit.
4. The cartridge according to claim 1 wherein the mobile discrete electrode member is connected to a signal processing circuit via a capacitive coupling to a complementary electrode conductor electrically connected to said signal processing circuit.
5. The cartridge according to claim 4 wherein the complementary electrode conductor extends along the tubular wall portion in the direction of displacement D of the mobile discrete electrode member on a side of the cartridge containing wall essentially opposite the plurality of discrete fixed electrodes.
6. The cartridge according to claim 1 wherein the mobile discrete electrode member comprises an electrically conductive disk shaped element assembled to the plunger or piston.
7. The cartridge according to claim 1 wherein the plurality of discrete fixed electrodes each comprise an electrode portion wrapped around the tubular wall portion more than 180°.
8. The cartridge according to claim 1 wherein the plurality of discrete fixed electrodes each comprise an electrode portion wrapped around the tubular wall portion less than 180°.
9. The cartridge according to claim 1 wherein the plurality of discrete fixed electrodes are formed on a substrate assembled to the cartridge containing wall.
10. The cartridge according to claim 9 wherein the substrate is a flexible thin film.
11. The cartridge according to claim 9 wherein the substrate is in the form of a housing injected or molded from an insulating material such as plastic.
12. The cartridge according to claim 1 wherein the plurality of discrete fixed electrodes have electrode portions ( 24 a , 24 a ′) formed directly on or in the cartridge containing wall ( 4 ).
13. A method of determining the fill level of a cartridge comprising a mobile plunger or piston, including:
providing the cartridge with a plurality of discrete fixed electrodes positioned along a tubular wall portion of the cartridge in a juxtaposed manner in a direction of displacement D of the plunger or piston, and a mobile discrete electrode fixed in, on or to the plunger or piston, and
reading a capacitance value between each of the plurality of fixed electrodes and the mobile discrete electrode, whereby the fixed electrode that provides the strongest capacitance value indicates the position of the plunger or piston,
wherein the average thickness (t) of the mobile discrete electrode member in the direction of displacement of the mobile electrode member being equal to, or less than, two times a spacing (s) between adjacent said discrete fixed electrodes.
14. The method according to claim 13 wherein the capacitance value between each of the plurality of fixed electrodes and the mobile electrode are read sequentially by means of a multiplexer.