Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Patent
1987-12-01
1989-05-09
Tokar, Michael J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
324111, 324116, G01R 3300
Patent
active
048292397
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a portable multimeter for measuring electrical quantities from the fields of electrical installation engineering. As the essential instrument transducer there is used a clip provided with Hall sensors which, for d.c. or a.c. measurements, embraces the respective current conductor to be measured. Relative thereto, the overall measuring range is divided into at least two switchable measuring ranges.
BACKGROUND
A multimeter of this type has been described on page 104 of the German technical journal "Elektronik", No. 25 of Dec. 16, 1983. In this multimeter the clip is a separate instrument transducer which is connected by cable to the display unit. Moreover, in EP-A No. 67 527, there is described a clip-on measuring device provided with two Hall sensors, which is designed as a one-piece measuring device with a digital measured value display and which, owing to a special opening mechanism of the clips, is particularly suitable for measuring direct currents.
Such clip-on measuring devices have found wide acceptance in the fields of electrical installation measuring engineering because they, as is well known, permit current measurements to be carried out without any opening or stripping of the conductor, hence during normal operation.
It has been noticed as a disadvantage of such clip-on measuring devices that their measuring accuracy still leaves a lot to be desired. Also, different types of clip-on measuring devices are required for d.c. and a.c. measurements, while those which are provided with Hall sensors, as shown above, can be made suitable for both d.c. and a.c. measurements. There are also known clip-on power meters to which, for power measurement, there is additionally applied the voltage which is taken off by the user.
Mostly, the accuracy of the measurement also suffers from the fact that the measured value as displayed depends on the shape of curve, and hence does not correspond to a genuine root-mean-square-value measurement.
It is the object of the invention as characterized in the claims, therefore, to further embody the previously described multimeter in such a way that it, with improved accuracy, permits the measurement of displayed current, voltage, power and frequency values which are all independent of signal shapes, with the possibilities of practical use of the multimeter still not yet being fully exhausted.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention is directed to a multimeter of the type having a clip including at least one Hall sensor; a Hall-effect measuring circuit for measuring a current I flowing in a conductor embraced by said clip; and a display unit for displaying the value of the current I as measured by the measuring circuit. The multimeter has at least two switchable measuring ranges. A voltage-measuring circuit is provided for measuring a voltage U which, as a DC or AC quantity, is supplied to an input means. A microprocessor and storage means for storing data are also provided. The measured current I and voltage U values, together with stored correcting values resulting from an adjusting measurement preceding the actual measurement in terms of time, and with circuit-specific constants as stored by the manufacturer, are stored as data and are selectively processed by means of the microprocessor into values of direct or of alternating current I, of DC or AC voltage U, of apparent power Ps, of real power Pw, of power factor cos (phi), or of the frequency f, with the microprocessor controlling the display unit to display the aforesaid values, by forming the root-mean-square value, being independent of the waveform of the current I to be measured and/or of the voltage U to be measured. Range switching is effected by the microprocessor as soon as it is detected by the latter that a range has been exceeded in the course of a measuring process.
In another aspect, the invention provides a method for measuring electrical signals by means of an electrically operated measuring device, compri
REFERENCES:
patent: 2886779 (1959-05-01), Kuhrt et al.
patent: 4514685 (1985-04-01), Gilker
patent: 4516070 (1985-05-01), Brown et al.
patent: 4517513 (1985-05-01), Brown
patent: 4536706 (1985-08-01), Kemper
Elektronik, Band 25, 16, Dec., 1983, Franzis-Verlag GmbH (Munich), "Stromzange Misst Lageunabhangig", p. 104.
DE, A 3323961 (P. S. Baier et al.), Jan. 10, 1985, siehe Seite 11, Zeile 13-Seite 12, Zeile 6, Seite 12, Zeile 17-Seite 13, Zeile 14.
JEE, Journal of Electronic Engineering, No. 129, Sep. 1977, Dempa Publications Incs. (Tokyo), "Clamp-on-Maters--Ideal Measuring Instruments for Electrical Systems":, pp. 26-27.
Holstein Jorg
Rapp Lothar
Muller & Weigert, GmbH
Peterson Thomas L.
Tokar Michael J.
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