Apparatus for electrically determining injection doses in syringes

Claim 1

In combination with a syringe, an apparatus for determining and recording the dose of an agent delivered with said syringe, said syringe being of the type comprising: a) a barrel for holding said agent; b) a plunger arranged inside said barrel for expelling said agent; c) a conducting path for conducting an electric current inside said barrel and parallel to said plunger, said conducting path comprising a conductive strip located inside said barrel and oriented parallel along said plunger, a rim on said barrel made of an electrically conducting material and remaining in electric contact with said conductive strip, and an electrically resistive means in the form of a strip whose resistance changes depending on the position of said plunger inside said barrel, said conducting path having a first end and a second end; d) an input terminal located on the outside of said syringe and in contact with said first end and with said conducting strip; e) an output terminal located on the outside of said syringe and in contact with said second end and with said electrically resistive means; said apparatus comprising: a) a housing; b) a field on the outside of said housing, said field having an input contact for contacting said input terminal and an output contact for contacting said output terminal; c) a voltage generating means located inside said housing for producing a voltage difference across said input contact and said output contact, thereby causing said electric current to flow through said conducting path when said input contact is contacting said input terminal and said output contact is contacting said output terminal; d) an electric response measuring means located inside said housing for measuring said electric current and calculating from said electric current said dose; and e) a recording means located inside said housing for recording said dose.