GB917911A - Improvements in or relating to voltage selectors - Google Patents

Abstract

917,911. Magnetic amplifiers. SMITH & SONS (ENGLAND) Ltd., S. Jan. 18, 1961 [Oct. 30, 1959], No. 36972/59. Class 40 (9). [Also in Group XXXVI] Apparatus selecting the median voltage of magnitude intermediate of those of two other voltages of differing magnitudes comprises a negative feedback amplifier with five inputs and a common output, the first and fifth inputs operating on the amplifier in reverse sense to the second, third and fourth inputs; the first input circuit including a voltage selector selecting the smallest of the three voltages applied to the second, third and fourth inputs; the fifth input circuit including a voltage selector selecting the largest of such three voltages; and means for applying 100% negative feedback from the common output circuit to each input, whereby the median voltage appears at the common output. In Fig. 1 three input voltages A, B, C are applied from corresponding transmission channels to input windings 2, 3, 4 of a magnetic amplifier 7 having 100% negative feedback from its output 8 to its input windings 1 to 5, and input windings 1 and 5 are operating in opposition to windings 2 to 4 are respectively energized from the inputs over pairs of rectifiers 10, 13; 11, 14; 12, 15 in opposed polarity, so that the voltages applied to the windings 1 and 5 are the differences between the output voltage and respectively the smallest and the largest of the four voltages constituted by input voltages A, B, C and the output voltage, and it is shown that for an amplifier with a rectangular characteristic (Fig. 2, not shown) stability is achieved when the input voltage represents the median voltage of the three inputs. In a modification (Fig. 3) the common return of the input windings is connected to the slider of a potentiometer 17 energized from a direct voltage source at least equal to the largest input value, and the potentiometer is adjusted by a motor 18 energized from the magnetic amplifier output so that an increase in output voltage produces an increase in feedback voltage and at stability the slider voltage and position represents the median of the three input voltages. Further input windings and rectifier pairs enable the output to represent the median of four or more inputs (Fig. 4, not shown) and it is shown that the apparatus may then be applied to produce an output equal to the mean of all but the smallest and largest of four or more applied voltages. The inputs may be derived from potentiometers driven by respective mechanical signals, and amplifiers other than magnetic may be used.