GB1400348A - Self-checking analogue-to-digital converter - Google Patents

Abstract

1400348 A/D converters B E B MAX and B G MARTHINSSON 21 Aug 1973 [30 Aug 1972] 39652/73 Heading H3H An A/D converter is provided with automatic indication of erroneous results of conversion and comprises a measuring signal input which is preceded by a switching circuit to which is also applied a reference input whereby either of these inputs can be supplied singly or in combination to the converter, and a control circuit arranged to control the switching and converter circuits so that different outputs of the switching circuit are converted into successive sub-measurements, and has a checking circuit to combine all sub-measurements together and with the reference signal to produce a signal indicative of the error in the A/D conversion. As shown, a single-ramp integrating type A/D converter AD is fed with an input V i from differential amplifier F where the gains A, B of each side are such that A+B= 1. The inputs Eo, Uo, O, being reference, measurement and ground potentials respectively, are applied to amplifier F as signals Ua,Ub via a transistor switching circuit OMK controlled by signals So from central control CU, and 4 measurements are made consecutively, namely: (1) with Ua, Ub, Vi all equal to Uo which is the measurement of Uo; (2) a first check measurement with Ua=Uo, Ub=O, Vi=AUo; (3) a second check measurement with Ua=Eo,Ub=Uo, Vi=AEo+BUo; (4) and a last check measurement with Ua=O, Ub=Eo, Vi=BEo. These are made successively and are stored in registers BM1- BM4 by commands g 1 -g 4 , the output of register BM1 being the converter output and being taken via a decoder AVK to an indicator IND of the measured value. The four measured values are combined at DS1 so that (2)-(4) are added and the result taken from Eo+Uo, Uo being as measured by (I). The result Us is shown to be an error signal indicative of the error in Uo and if this is greater than a threshold, an error indication is provided, e.g. by causing the indicator to flash, or by audible alarm. Signals g 5 and g 6 at appropriate parts of the measurement cycle cause zero- and gain-errors in the converter to be checked and remedied.