Abstract: The present invention involves a thermal compensation procedure for magnetic circuits, such as those used in security devices detecting metallic masses, whose losses increase as a function of ambient temperature. According to the invention a body is placed in the immediate proximity of the magnetic circuit, the body being made of a material whose magnetic permeability is a decreasing function of temperature and whose Curie point equals the maximum possible ambient temperature.

Abstract: The invention pertains to a logic circuit with threshold and built-in safety such that any change in the characteristics of its components produces a relative increase of the threshold value. It comprises a comparator (7) one input of which receives a reference d-c voltage (VR) whereas the other input is connected to the junction point of a first and a second resistance (1, 2). A first d-c voltage (V1) of low relative value is applied to the free terminal of the first resistance (1), and a second d-c voltage (V2) of high relative value is applied to the free terminal of the second resistance (2) by means of a third resistance (3). According to the invention, there is applied at the junction point (A) of the second and third resistances (2, 3) a third d-c voltage (V3) of intermediate relative value by means of a fourth resistance (4) in series with a chopping commutator (6).