GB801923A - Electro-magnetic control device - Google Patents

Abstract

801,923. Non-contactmaking relays. STANDARD TELEPHONES & CABLES, Ltd. June 24, 1955 [June 28, 1954], No. 18344/55. Class 40 (9). Two saturable cored transformers have primary windings connected in series or parallel and secondary windings connected in series opposition the cores and windings being such that an A.C. signal in the primary windings above (or below) a threshold value of current, voltage, or frequency produces an output in the secondary windings whereas a signal below (or above) that threshold produces substantially no output. The cores and/or windings of transformers 1 and 2, shown in Fig. 1, are such that one saturates before the other as the amplitude of A.C. applied to terminals 3, 4 is increased. The amplitude at which one core saturates being the threshold below which the cores are balanced and above which an output appears across rectifier 5. Alternatively, the cores may be such as to balance when both are saturated so that with an increasing input the output is cut off above a threshold value. The threshold value may be varied by means of a variable resistor 8 or by means of bias windings on either or both transformer cores. If the primary windings are fed in parallel a voltage threshold is obtained. As the current in the primary windings is a function of frequency the threshold may be made to coincide with a predetermined frequency.