AU692516B2

AU692516B2 - Method and means for signal processing for parameter measurement

Info

Publication number: AU692516B2
Application number: AU16304/95A
Authority: AU
Inventors: Kurt Kugler; Peter Okanik
Original assignee: Maschinenfabrik Reinhausen GmbH; Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen GmbH
Priority date: 1994-07-08
Filing date: 1995-04-06
Publication date: 1998-06-11
Anticipated expiration: 2015-04-06
Also published as: CN1119740A; FI953357L; EP0691545A1; AU1630495A; ES2145172T3; DE4424059C1; FI953357A7; JPH08101235A; FI953357A0; ATE192239T1; DE59508215D1; EP0691545B1; CN1057839C

Abstract

The zero crossing of the measurement signal (U) is detected by superimposing a d.c. voltage (Uref) as a reference voltage onto the actual measurement signal . The zero crossing of the measurement signal is detected in relation to the potential of the reference voltage. A further voltage (Uref*) is generated which continuously increases during the positive half cycle of the measurement signal and continuously decreases during the negative half cycle of the measurement signal. This further voltage is superimposed on the reference voltage and hence onto the measurement signal.

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Maschinenfabrik Reinhausen GmbH Actual Inventor(s): Peter Okanik Kurt Kugler Address for Service: *s PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: METHOD AND MEANS FOR SIGNAL PROCESSING FOR PARAMETER S MEASUREMENT Our Ref 407288 POF Code: 1585/238596 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- 1A- METHOD AND MEANS FOR SIGNAL PROCESSING FOR PARAMETER MEASUREMENT The present invention relates to a method and means for signal processing for parameter measurement, and has particular reference to measuring alternating voltage, alternating current and phase angle of a measurement signal.

A method and device for signal parameter measurement are described in German (Federal Republic) patent specification No. 36 14 419, in which method a direct voltage is superimposed as a reference voltage on the measurement signal so that the signal zero transition is displaced into a riore readily detectable voltage range. In the device, one pole of each of a voltage transformer and a current transformer is connected to the potential of the reference voltage, which is applied to a multiplexer as a reference magnitude. This in turn is connected to an analog-to-digital converter. In this known method and associated device high demands are placed on the accuracy of the analog-to-digital converter, as this constantly operates in the same working point fixed by the level of the reference voltage. If the analog-to-digital converter exhibits inaccuracies or nonlinearities, this can lead to the working point having a certain inconstancy and thus the respective measurement value can be falsified :i 20 by plus or minus one bit. However, in industrial applications it is sought, for reasons of cost, to use commercially available analog-todigital converters which are as simple as possible, inexptnsive and consequently subject to certain non-linearities. The known method, and the associated device realising this method, necessarily result in substantial measuring errors when such commercially available converters are employed.

-2 It is therefore the object of the present invention to provide a method and measuring means by which accurate measurements may be possible even when analog-to-digital converters which are subject to tolerances and drifting about a working point are used.

According to a first aspect of the present invention there is provided a method of signal processing for parameter measurement in a digital system, including the steps of superimposing on a measurement signal a reference voltage in the form of a direct voltage, detecting the zero transition of the signal with respect to the potential of the reference voltage thereby to distinguish positive and negative half waves of the signal, generating a further voltage which continuously increases during said positive half wave and continuously decreases during said negative half wave, superimposing the further voltage on the reference voltage and thus on the measurement signal to provide a resultant signal, and digitally processing the resultant signal to obtain a value of the *9 measurement signal.

.According to a second aspect of the present invention there is S" provided measuring means in a digital system for measuring 20 alternating voltage, alternating current and phase angle of a *,measurement signal by way of a voltage transformer and a current transformer, which are each connected at the secondary side thereof to a multiplexer connected to an analog-to-digital converter, wherein .one pole of the secondary side of each of the voltage transformer and the current transformer lies at the potential of a reference voltage, which is applied to the multiplexer as reference magnitude for the voltage value and current value to be measured, wherein the reference voltage and the other pole of the secondary side of the voltage transformer or of the current transformer are applied as -3inputs to a comparator, the output of which is fed back to the potential of the reference voltage by way of a resistance-capacitance circuit.

A method exemplifying the invention has the advantage that a further voltage changing with time is superimposed on the originally applied direct voltage, so that during a half wave virtually the entire working range of the analog-to-digital converter is run through. Compensation for inaccuracies and non-linearities is thus provided, as the analog-to-digital converter does not remain as usual in the state of the art at the same working point during the entire measuring period, i.e. the entire half wave.

Measuring means embodying the invention enables such a method to be carried out in a particularly advantageous manner, in that a voltage, which continuously increases during one half wave and 15 approximates a sawtooth shape and which is superimposed on the *reference voltage in a simple manner, is generated by a resistancecapacitance member in a feedback branch.

An example of embodiment of the method and an embodirrent of the 0 0 measuring means of the invention will now be more particularly 0.0 described with reference to the accompanying drawings, in which: "Fig. 1 is a diagram illustrating the course of a signal processed by a method exemplifying the invention; and Fig. 2 is a schematic block circuit diagram of measuring means for carrying out this method and embodying the invention.

Referring now to the drawings there is shown in Fig. 1 a measurement signal, in this case a measurement voltage U.on which is superimposed a reference voltage URef. In addition, a further voltage -4- URef* is generated, which continuously increases during the positive half wave of the measurement voltage U and continuously decreases during the negative half wave of the measuremen voltage U. This voltage URef* is also superimposed on the voltage U, so that there is obtained a resultant voltage UM to be measured. The value of the measurement signal, with the detected zero transition to, can be obtained from this voltage UM in known manner by a downstream multiplexer and an analog-to-digital converter connected to the output of the multiplexer.

Fig. 2 shows measuring means particularly suitable for this method. The measuring means comprises a voltage transformer U with poles U1 and U2 at its secondary side, a current transformer J with poles J1 and J2 at its secondary side, a multiplexer M connected at inputs thereof to the poles U1 and J1 and an analog-to-digital 15 converter A/D conected at its input to the output of the multiplexer.

0* Also present in the measuring means is a reference voltage source generating the above-mentioned reference voltage URef, which is applied to the poles J2 and U2 and to a further input of the multiplexer M, a comparator K for comparing a current or voltage B Be 20 magnitude to be measured with the reference voltage, and a resistance -capacitance circuit C,R,R connected to the output of the comparator.

The magnitude to be measured, in this instance the measurement voltage U at the pole U1, is applied to the comparator K, which detects the zero transition of the voltage U with respect to the reference voltage and in dependence thereon generates a direct voltage with two different amplitudes. These are applied to the resistance-capacitance circuit in such a manner that the voltage URef* is generated, which describes an e function in its time course and is superimposed on the reference voltage URef.

.0 0. 0

Claims

1. A method of signal processing for parameter measurement in a digital system, lincluding the steps of superimposing on a measurement signal a reference voltage in the form of a direct voltage, detecting the zero transition of the signal with respect to the potential of the reference voltage thereby to distinguish positive and negative half waves of the signal, generating a further voltage which continuously increases during said positive half wave and continuously decreases during said negative half wave, superimposing tue further voltage on the reference voltage and thus on the measurement signal to provide a resultant signal, and digitally processing the resultant signal to obtain a value of the measurement signal. 0 A method as claimed in claim 1 and substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

3. Measuring means for signal parameter measurement in a digital system, including a voltage transformer, a current transformer, a *00s reference voltage source connected to one pole of each of the transformers at the secondary side thereof so that each of those 20 poles lies at the potential of a reference voltage from the source, a multiplexer connected at inputs thereof to the other pole of each of the transformers at the secondary side thereof and to the reference voltage source, an analog-to-digital converter connected at an input v thereof to an output of the multiplexer, a comparator connected at 7 inputs thereof to the reference voltage source and to said other pole of one of the transformers, and resistance-capacitance means connected to an output of the comparator and arranged to cause a variable further voltage dependent on zero transistion detection by the comparator to be superimposed on the reference voltage.

4. Measuring means substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings. DATED: 23 April 1998 MASCHINENFABRIK REINHAUSEN GMBH By their Patent Attorneys PHILLIPS ORMONDE FITZPATRICK 9*9o S* 9 9 *e 'I- -8- ABSTRACT OF THE INVENTION A method of signal processing for parameter measurement in a digital system comprises superimposing a direct voltage as a reference voltage (URef) on the actual measurement signal generating, in dependence on the zero transition of the signal, a further vnltage which continuously increases or decreases and superimposing the further voltage on the reference voltage and thus on the measurement signal. For carrying out the method, the signal and the reference voltage can be applied to a comparator, the output of which is fed back to the potential of tne reference voltage by way of a resistance- 10 capacitance circuit. 1 Fig. 1- i