Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Patent
1989-12-01
1991-05-07
Pellinen, A. D.
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
341167, H03M 150
Patent
active
050140582
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and an arrangement for evaluating an analog measurement quantity according to the time divider principle.
In measurement value-processing systems which use the time divider principle, evaluating methods are applied in which, in a fixed integration interval, values equivalent to the measurement quantities are determined, for instance, by counting out clock pulses of constant frequency; thus, a corresponding analog-digital conversion is carried out. The time divider principle contains two integration parts, of which the first part represents a compensation of the measurement quantities by an unbalancing quantity of opposite polarity (up-integration) and the second integration part contains a down-integration. So that at the end of the two integration parts, i.e., at the end of the time divider period, the integration signal has become zero, the time of the first integration part must be adjusted accordingly relative to the total time divider period. Thus, the measurement result can be taken directly from this time divider clock ratio.
In a known method operating according to the time divider principle of this type (German Pat. No. 33 30 841) it was possible to achieve high resolution and conversion accuracy with a relatively small cost for components. The integration circuit for the analog-digital conversion used, however, has several disadvantages; there, the time divider ratio, i.e., the correct adjustment of the time of the first integration part relative to the total time divider period is obtained by an evaluation extending over a multiplicity of time divider periods, of the amplified control deviation signal as well as over its phase-selective rectification and subsequent smoothing by an analog lowpass filter included in a servo control circuit of the time divider adjustment. Thereby, the known method has a rather sluggish response behavior to abrupt changes of the measuring quantity. Here, depending on the resolution, dead times and/or adjustment times t.sub.e of approximately 100 ms <t.sub.e <ls are typical which, in a multiplicity of applications made the practical use of time divider circuits to date at least problematic if not impossible.
It is an object of the invention to provide a method and arrangement which makes possible, while retaining the low cost and the high accuracy and long-term stability of the time divider principle, a considerable improvement of the response behavior of the digital measurement values after abrupt changes of the measurement quantity as well as regarding its evaluation and further processing.
The method according to the invention is advantageously realized in such a manner that in a first step the control deviation .DELTA..sub.1 .alpha. from the correct time divider ratio is determined by definite integration over the measurement and reference signal, for instance, by a Miller integrator, always exactly over a full time divider period T. An analog integration signal .DELTA.U.sub.i obtained thereby serves as a measure for the control deviation which is converted after the end of the time divider period into a digital control deviation signal m.sub.1.
According to the invention, the digital control deviation signal is used for the correction of the time divider clock ratio ##EQU1## in the subsequent second time divider period.
According to another advantageous subidea of the invention, the overall circuit costs can be kept particularly low if the integrator used, for instance, the Miller integrator is utilized twice in the manner of a dual-slope method by up-integrating alternatingly in a first step, first via the time divider T.sub.1, the sum of the measurement signal (input voltage U.sub.m) and reference signal (standard voltage U.sub.n) and subsequently, the deviation signal obtained thereby is digitized by a counting-down integration. The dual-slope method known per se for fast analog-digital conversion is described, for instance, in the book Tietze/Schenk "Halbleiterschaltungtechnik", Fifth Edition, 1980, Springer Verlag, pa
REFERENCES:
patent: 4024533 (1977-05-01), Neumann
patent: 4608553 (1986-08-01), Ormand
patent: 4694277 (1987-09-01), Takahashi
patent: 4739305 (1988-04-01), Naito
"Halbleiterschaltungstechnik", Tietze et al., 5th Edition, Springer-Verlag, pp. 663-664 (1980).
"Uber die Genauigkeit elektrischer Grundnormale und Kompensationsmesseinrichtungen", Angersbach, Archiv fur Technisches Messen (ATM), J930-3 (1964).
Hoff Marc S.
Pellinen A. D.
Siemens Aktiengesellschaft
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