Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1994-10-05
1995-11-28
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
324 7647, 36472406, 342195, G01R 23165, G01R 23167
Patent
active
054711339
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF INVENTION
Digital devices for measuring the frequency of an electrical signal are known, all of which operate basically in the manner that a counter counts pulses introduced by an oscillator during a time period determined by successive passages through zero of an electrical signal the frequency of which is to be measured. The counter reading at the end of the time interval then represents a measurement of the frequency to be measured.
By way of example, reference may be had in this connection to the published German application 31 49 165 A1 in which a circuit arrangement for measuring the frequency of an alternating voltage is described. Upon the commencement of each period of the alternating voltage, a time is started having a duration which corresponds to the shortest expected period of the alternating voltage. After the execution of this time, a following counter is started into which pulses of an oscillator are introduced until the end of the period being monitored is indicated by a control pulse. The frequency is calculated from the reading of the counter.
SUMMARY OF THE INVENTION
The present invention provides a digital arrangement for measuring the frequency of an electrical signal. In accordance with this arrangement a rapid disturbance-free, highly precise determination of the frequency is made possible.
In order to achieve this purpose in accordance with the invention, in a digital arrangement for the measuring of the frequency of an electrical signal, a linear-phase non-recursive digital filter with symmetrically distributed filter coefficients which is acted on by the electrical signal is developed as an all-pass filter, and a further linear-phase non-recursive digital filter with symmetrically distributed filter coefficients which is also acted on by the signal is so developed as a low-pass filter that its transfer function has a value of one for a predetermined frequency of the electrical signal; following the all-pass filter there is arranged a circuit which in one branch on the input side contains a linear-phase transverse filter with symmetrically distributed filter coefficients, a time-delay member connected after it and a following multiplier, and has, in a branch parallel to said one branch on the input side, another linear-phase transverse filter with anti-symmetrically distributed filter coefficients and a value of one of its transfer function at said predetermined frequency, a further time-delay member connected after it and, following the latter, a further multiplier, in which connection said one multiplier on the input side is connected also with an output of the further transverse filter, and the further multiplier is connected also with the output of said one transverse filter and that circuit unit also contains a difference former the inputs of which are connected to the outputs of the multipliers; a circuit device identical in construction to the circuit unit is arranged to follow the low-pass filter, the outputs of the difference former of the circuit unit and the circuit arrangement are connected to a quotient former after which there is a square-root member, and an inverse-function former is connected to the square-root member.
One important advantage of the digital arrangement of the present invention for the measuring of the frequency of an electrical signal is that the frequency can be determined very accurately with it, since the precision is dependent only on the quality of the crystal of the oscillator used and on the resolution of the analog/digital converters which are required. The avoidance of introducing errors into the results of the measurement by component tolerance, aging phenomena and temperature variations furthermore contributes to the high precision. The use of non-recursive filters furthermore avoids problems in stability.
Filters of different order can be used in the digital arrangement of the invention. However, for a rapid carrying out of the measurement and with respect to the expense required, it is advantageous that all filters ar
REFERENCES:
patent: 4403298 (1983-09-01), May, Jr.
patent: 4433422 (1984-02-01), Kurth
patent: 4438504 (1984-03-01), Favin
patent: 5089770 (1992-02-01), Lee et al.
patent: 5198750 (1993-03-01), Prokin
Electrical Design News, vol. 34, No. 2, Jan. 1989, Newton, Mass., US, pp. 149-155, George Dovel: FET analyzers make spectrum analysis a snap.
Do Diep
Siemens Aktiengesellschaft
Wieder Kenneth A.
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