Two-wire proximity detector

Claim 1

In a detector of the size of a physical parameter, and more particularly, a proximity detector, capable of operation over a wide range of a.c. mains voltage, of the kind having a probe giving a command signal, a rectifier bridge bridged across the mains through a utilization device, a semi-conductor-controlled rectifier bridged across the direct-current terminals of the rectifier bridge and having a command input, means for connecting the probe to said command input, and an auxiliary supply device connected to the said direct-current terminals, the improvement which comprises the means for connecting the probe to said command input comprises an inhibitor device rendered conducting by the command signal and inhibiting the command of the controlled rectifier, the auxiliary supply device including a first voltage regulator circuit bridged across the said terminals such that the inhibiting device is blocked, the first regulating circuit comprising two complementary conduction paths of which the impedances vary inversely when the mains voltage increases, one of said paths comprising a ballast semi-conductor, the second regulation circuit comprising means for causing delay in the starting of the controlled rectifier and for charging, during this delay, a capacitor to a substantially constant voltage.