The variable inductor and the comparison inductor of a semi-differential variable inductance both have a pair of coils magnetically coupled together. The output current of an amplitude-controlled oscillator flows through the series combination of one coil of each pair and the other coil of the comparison inductor is used to supply a signal which is rectified in order to regulate the amplitude of the oscillator. The remaining coil, the other coil of the variable inductor, is connected in reverse polarity and in series with the coil last previously mentioned to provide, through a rectifier, an ouptut signal representative of the difference between the variable and comparison inductances normalized to (divided by) the comparison inductance. The output variation corresponds to the displacement of the short-circuiting ring of the variable inductance, which is mechanically linked to the control rod of a fuel injector of a diesel engine as required for a system controlling the fuel injector. The oscillator and the rectifiers can conveniently use operational amplifiers of the same type designation.

System for preventing erroneous operation of control rods for securing a safety control of a nuclear reactor. The erroneous operation preventing system is comprised of a control rod objective position setting means for setting an objective position of a control rod, a control rod position detector for detecting a position of the control rod, and an operation means which operates a difference between the objective position set up and the detected position of the control rod being operated and produces a signal for blocking the control rod operation when the control rod is operated so that the difference goes away from zero. The erroneous operation blocking system stops the control rod at the first possible control rod stopping position. The erroneous operation preventing system includes a return operation commanding unit for compensating for erroneous operation of the control rod when the control rod is erroneously operated.

A winding section includes a primary winding to be excited by a single-phase A.C. signal, and a plurality of secondary windings provided at different locations with respect to a predetermined direction of linear movement. A variable magnetic coupling section includes a plurality of magnetic response members provided in repetition at a predetermined pitch along the direction of linear movement, and allows inductive A.C. output signals, amplitude-modulated in accordance with a varying linear position of an object of detection, to be produced in the individual secondary windings with amplitude function characteristics differing depending on positional differences between the secondary windings. Each of the inductive A.C. output signals produced in the secondary windings varies in its amplitude function in periodic cycles each corresponding to the pitch length of the magnetic response members. The variable magnetic coupling section may include a core section made of a wire, and the magnetic response members in the form of metal pieces provided at the predetermined pitch and secured by caulking to the core section.

The coupling and decoupling of one or more of a plurality of differential transformers comprising a digital position probe assembly develops a phase encoded signal indicative of the position or level of a magnetically permeable element such as liquid metal or a lead screw in a nuclear reactor assembly. The phase encoded signal, which is developed as a Gray code, is processed in a phase decoder and digitally converted into a binary coded decimal to provide a digital representation of the level or position of the magnetically permeable material.

Various forms of hydraulic cylinders having axial bores formed in their piston rods, and probes projecting axially from the closed end of the cylinder body with two spaced coils thereon are disclosed. The coils are connected into external circuitry which responds to change in inductance of either coil whereby to generate a reference signal upon the occurrence of preselected changing conditions of inductance of either coil caused by movement of that coil into or out of mutual induction with a shorted turn arrangement formed by or carried by the piston. The coils may be the drive coils of a displacement transducer arranged to indicate either end of the stroke of the piston. Alternatively either a supplementary shorted turn or an additional drive coil may be provided to generate an intermediate stroke reference signal. The reference signals may be used in operation of a system for effecting automatic continuous reciprocation of the piston.