GB1279700A - Improvements in or relating to analogue-to-digital converters - Google Patents

Abstract

1279700 A/D converters ROSEMOUNT ENG CO Ltd 9 Dec 1970 [9 Dec 1969] 60156/69 Heading G4H In a dual ramp digital voltmeter, e.g. for measuring an analogue input 14 representing temperature, a capacitor 13 is charged by input 14 for a period determined by logic 29 and the frequency of clock pulse source 23, counter 24 is then reset to a non-zero datum by store 32, the datum corresponding to the zero level of input 14, and counter 24 is then counted up from the datum until capacitor 13 has been discharged by a reference input 10 to a reference level 21 supplied as the second input to comparator 20. Logic 29 and store 32 may comprise an AND gate and store as shown or may be pre-wired circuit boards, manually set switches or a circuit which is set to different values in sequence corresponding to different inputs being measured by data logging equipment so that different scale ranges and datum levels may be selected. Switch 36 when closed at the end of a digitizing operation holds the amplifier 12 output at a datum which is preferably different from the comparator datum 21. Store 32 may enter a negative number in counter 24 which is bidirectional.