GB1182115A - Improvements relating to Automatic Test Equipment - Google Patents

Abstract

1,182,115. Comparators. BRITISH AIRCRAFT CORP. Ltd. 21 July, 1967 [21 July, 1966], No. 32878/66. Heading G4M. In test equipment, a binary number representing a measured value MV is compared with upper and lower tolerance limits UL, LL, the comparator comprising two multi-bit banks of stages C1-C20, and the outputs from the two banks are compared to check the operation of the comparator. Initially, comparison with UL takes place, an EQ output from a pair of stages e.g. C1a, C1b enabling the next lower pair of stages e.g. C2a. C2b until C20a, C20b produce an EQ output or a Hi or Lo output is obtained. Circuit 11 compares the Hi, Lo and EQ outputs and stops the comparison, if a discrepancy occurs. Circuits 3a, 3b take into account the polarities of MV and UL and produce a Go Hi output if UL is not exceeded, thereby setting 5a, 5b to the 0 state. A comparison with LL is then effected, circuits 3a 3b again taking polarities into account and producing a Go Lo output if MV is not less than LL. Gate 13 produces an output if gates 7a, 7b are enabled, otherwise an indication of which limit is violated is obtained from the NoGoHi or NoGoLo gate. Circuit 12 checks that there is no discrepancy in the settings of 5a, 5b and 6a, 6b. Each bit comparator C1-C20 includes bistable circuits storing corresponding bits of ML, UL and LL and gates effecting the comparisons, the output gates for the Hi, Lo and EQ outputs being enabled by an EQ and EQ input respectively from the preceding stage.