Method and apparatus for power measuring
First Claim
1. A method of generating a product of signals proportional to the voltage of an electrical supply and the current flowing through a load connected thereto, comprising the steps of deriving a first signal proportional to the said supply voltage, deriving a second signal proportional to the said load current, frequency modulating two constant frequency carrier signals by the said first and second signals to produce third and fourth signals respectively, normalising the third and fourth signals with reference to frequencies corresponding to zero voltage and zero current, and multiplying the two normalised third and fourth signals to form a product signal which is proportional to the power being absorbed by the load connected to the electrical supply.
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Abstract
A method for generating a product of signals proportional to the voltage of an electrical supply and the current flowing through a load connected thereto, comprises the steps of deriving a first signal proportional to the said supply voltage, deriving a second signal proportional to the load current, frequency modulating two constant frequency carrier signals by the said first and second signals to produce third and fourth signals respectively, normalizing the third and fourth signals with reference to frequencies corresponding to zero voltage and zero current, and multiplying the two normalized third and fourth signals to form a product signal which is proportional to the power being absorbed by the load connected to the electrical supply. The third and fourth signals comprise pulse trains whose instantaneous pulse repetition rate is proportional to the voltage and current. Apparatus is described for performing this method. A 555 timer device is employed for voltage to frequency conversation. A microprocessor is employed for multiplying the fifth and sixth signals and is programmed to compute therefrom not only the apparent power but also the apparent instantaneous power, the real energy and real power and also the reactive energy and reactive power supplied to the load.
39 Citations
24 Claims
- 1. A method of generating a product of signals proportional to the voltage of an electrical supply and the current flowing through a load connected thereto, comprising the steps of deriving a first signal proportional to the said supply voltage, deriving a second signal proportional to the said load current, frequency modulating two constant frequency carrier signals by the said first and second signals to produce third and fourth signals respectively, normalising the third and fourth signals with reference to frequencies corresponding to zero voltage and zero current, and multiplying the two normalised third and fourth signals to form a product signal which is proportional to the power being absorbed by the load connected to the electrical supply.
- 6. Power measuring apparatus adapted to produce an output signal proportional to the product of a supply voltage and current flowing through a load connected thereto, in which a first analogue signal is derived proportional to the said supply voltage and a second analogue signal is derived proportional to the said load current so that a product signal can be produced by a microprocessor corresponding to the power, characterised in that third and fourth signals are produced by frequency modulating two constant frequency carrier signals using the said first and second signals, and the said third and fourth signals are supplied to the microprocessor for multiplication to produce the power product signal, in place of the first and second analogue signals.
- 23. Apparatus for generating a product of signals proportional to the voltage of an electrical supply and the current flowing through a load connected thereto, comprising circuit means adapted to be connected to an electricity supply for producing one output signal proportional to the potential difference betwen the live and neutral wires of the supply, and another output signal proportional to the current flowing in the live wire of the supply, wherein current sensing means is provided for producing a signal relating to the instantaneous magnitude of the current flowing in the live wire, first frequency modulation circuit means is provided for converting this signal into a pulse train whose frequency is representative of the current, voltage sensing means is provided for producing a signal proportional to the instantaneous magnitude of the potential difference between the live and neutral wires of the supply, second frequency modulation circuit means is provided for converting this signal into a pulse train whose frequency is representative of the potential difference, circuit means is provided for obtaining signals representing the mean frequencies of the two pulse trains, and multiplier means is provided for multiplying together the two mean frequency signals in order to obtain the required product.
Specification