Pulse-duty-cycle-type evaluation circuit for a variable inductance

Evaluation circuit for an inductive transducer of which the inductance varies with a physical magnitude to be measured, such as length of path traveled, pressure, or position of a pedal, comprising, in addition to said transducer:

• a transistor (Tr) having emitter, collectors and base electrodes and having the inductance (L) of said transducer connected in series with the emitter-collector path of said transistor and with a voltage source in such a manner as to carry at least a part of the current passing through said emitter-collector path while the remainder of said current, if any, does not pass through any element having an electrical reactance;
• resistance providing means (R.sub.1) interposed in series with said emitter-collector current path of said transistor, said inductance (L) and said voltage source;
• a comparator (K) having a first input (1) connected to said resistance means and to said voltage source so as to obtain therefrom a voltage derived from the variation of the current through said resistance means, and a second input connected with the tap of a voltage divider R.sub.8 R.sub.9) connected across the output of said voltage source and having an output connected to one of said inputs thereof through a feedback circuit branch comprising a first diode (D.sub.1), said last-mentioned comparator input being a noninverting input, said output of said comparator being also connected for providing alternating voltage step waves to said base electrode of said transistor, and
• a second diode (D.sub.2) connected between said second input of said comparator and a source of periodic trigger signals (T),
• whereby trigger signals from said source produce voltage waves at said output of said comparator of which the duty cycle corresponds to the magnitude of said inductance.