Inductive measuring arrangement for determining the position of a movable core member

Claim 1

An inductance measuring arrangement comprising: (a) an inductive coil; (b) a movable core member variably positionable within said inductive coil such that, the electrical characteristics of said inductive coil vary according to such position of said movable core member; (c) a voltage source coupled at times, to said inductive coil such that a voltage of predetermined amplitude is imposed on said inductive coil, and thereby develops a charging current thereacross as a function of such electrical characteristics when such position of said movable core member is to be determined, such charging current being selectable in value to at least one of a predetermined charging current level and a predetermined charging current time duration; (d) evaluating means coupled to said inductive coil for evaluating such charging current developed therethrough and deriving such position of said movable core member therefrom; (e) current-limiting means coupled between said voltage source and said inductive coil for limiting such charging current to a predetermined peak value, said evaluating means evaluating the time duration to reach such predetermined peak value and thereby deriving the position of said movable core member therefrom; and (f) said current-limiting means having a control voltage portion and a current source portion, said current source portion having a first transistor being biased upon initiation of an enabling signal from said evaluating means such that such charging current can flow thereover to said inductive coil, said first transistor being disabled upon removal of such enabling signal to thereby block the flow of such charging current to said inductive coil such that said inductive coil then discharges, said control voltage portion having a second transistor with a second base lead connected to a first base lead of said first transistor such that such enabling signal is received at said base leads by said first and second transistors simultaneously, said second transistor further having a collector lead connected to said second base lead thereby establishing a blocking condition of said second transistor which prevents said second transistor from turning on until such charging current exceeds a first predetermined value lesser in magnitude than said predetermined peak value, said second transistor being turned on establishing a control voltage value across a control resistor connected between said voltage source and an emitter lead of said second transistor, such control voltage value being applied to a first resistor associated with said current limiting portion to establish such predetermined peak value for such charging circuit.