GB892409A - Digital comparator - Google Patents

Abstract

892,409. Electric calculating apparatus. HAGAN CHEMICALS & CONTROLS Inc. Aug. 24, 1960 [Sept. 23, 1959], No. 29303/60. Class 106 (1). A digital comparator providing an alarm signal if an input leaves a preset range comprises for each decade ten relays with contacts C-0 to C-9 (normally closed) in series and coils 24 (two for each relay), the input digit being presented as an earthing of one of the terminals T-0 to T-9, and the digits of the upper and lower limits by connections between 28 and 31 on one of the banks 12 and 13 respectively. The comparison is effected in two steps; first a positive potential is applied to 42, 43 and terminal 26 of the upper bank 12, and switches 33 of bank 12 closed so that the upper limit digit relay is energized to open the corresponding contacts C. Current will flow in a relay coil 38 if the upper limit digit does not exceed the input digit, and in relay coil 39 if it is not less than the input digit, so that if the digits are equal both relays will be energized to close 55, 56 and 58, 59, and this makes the giving of an alarm at 63 dependant on the next lower denomination, the point corresponding to 60 of which is connected to line 71. If the input digit exceeds the upper limit digit 55, 56 only are closed, and the alarm circuit is directly earthed. After testing of the upper limit a similar test (by energizing 45, 46 and 26 of bank 13) on the lower limit is effected, in which the connections of second coils 41, 42 on the relays are reversed.