Importance

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Abstract

An apparatus and method is disclosed for determining the amount of drug remaining in a bellows type or bladder type drug reservoir. With a bellows type drug reservoir, a strain gauge is connected to one end of the bellows and to the bulk head to which the bellows reservoir is attached. With a bladder type drug reservoir, a strain gauge is connected at one end to an end plate attached to the bladder and at the other end to a bulk head. In a variant of these embodiment, the strain gauge is attached at one end to either the bellows or end plate and at the other end to an anchor point that has a fixed distance from the bulk head. In a further embodiment with a bladder type drug reservoir, the reservoir is constrained between a bulk head and an immovable end plate. A strain gauge is attached at one end to a point on the reservoir that moves in response to the filling or depletion of drug from the reservoir. The other end of the strain gauge is attached to an immovable point.

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First Claim