Patent ID: 8747391

Claim:
A method of monitoring the amount of fluid remaining in an implantable pump, the pump having a housing; a base plate connected to said housing, said base plate dividing said housing into an electronics chamber and a second chamber; a bellow mechanism connected to said base plate and disposed within said second chamber, said bellow mechanism having an expandable side wall and a bottom plate, said bellow mechanism dividing said second chamber into a medicament receiving portion and a non-medicament receiving portion, said bellow mechanism having a intermediate plate disposed within said medicament receiving portion, the intermediate plate being directly connected to the expandable side wall portion of the bellow mechanism, the intermediate plate being movable within the medicament receiving portion depending upon the amount of medicament remaining in the medicament receiving portion; and a coil disposed on the lower surface of the base plate; the method comprising the steps of: energizing the coil such that a magnetic field, that is affected by the location of the intermediate plate within the medicament receiving portion, is generated by the coil; and determining the amount of fluid remaining in the reservoir based on the electrical characteristics of the coil.