A method is described for metering electrical energy. The method includes sensing each phase of a circuit to generate analog voltage signals and analog current signals associated with each phase. The analog voltage signals and said analog current signals are converted into digital voltage signals and digital current signals, respectively, using time division multiplexing to provide three digital outputs. The digital outputs comprise at least one digital voltage signal and at least one digital current signal associated with the same phase. The digital outputs are processed to generate signals representative of real power, the magnitude of reactive power, and apparent power, wherein the signals representative of the magnitude of reactive power are generated from the signals representative of real power and the signals representative of apparent power.
RELATED APPLICATION DATA
This application is a continuation of U.S. patent application Ser. No. 08/259,578, filed Jun. 14, 1994 (now abandoned), which is a continuation of U.S. patent application Ser. No. 07/839,182, filed Feb. 21, 1992, now abandoned.
An isolated current shunt transducer includes a current shunt that produces a voltage difference between the current shunt's first and second ends, with the voltage difference being related to a current flowing through the current shunt. The transducer also includes an isolation barrier positioned between the current shunt and a processing circuit to isolate the processing circuit from a voltage that is common to both ends of the current shunt. Two or more transducers may be included in a power meter for measuring power delivered to a load by a multiple phase power distribution circuit. In such a power meter, a processing circuit is connected to the current shunts through the isolation barriers and is operable to produce multiple phase power measurements based on the differences between the voltages at the first and second ends of the current shunts.
A system and method for improving the ability of an electronic meter to make measurements on signals to determine content of different frequencies, and harmonics of the fundamental frequency, of AC signals (voltages and currents). The line frequency is determined and compensated for prior to performing frequency-dependent parameter measurements or determining frequency-dependent parameters.
A security system for programmable revenue class electricity meters. Each programmable revenue class electricity meter includes a metering portion or stage that couples to a power line. The metering portion is responsive to and senses the electricity in the power line and provides a digital output. The programmable revenue class electricity meter includes a processor that runs programming that records, calculates, and/or stores data relating to the electricity sensed by the metering portion. In particular, the programming records, calculates, and/or stores revenue-related data that can be used for calculating charges for the electricity. The programming can be changed by authorized persons to modify the types of data that can be measured, calculated, recorded, displayed, communicated, and/or stored for any desired purpose and in particular for revenue-related purposes. Modification of the programming and access to information is limited to authorized persons by means of the security system. The security system includes security system programming in the meter that checks for a code word that is required to be input prior to any changes to the revenue-related programming can be effected. The security system programming compares the input code word to a code word stored in the meter and unlocks restrictions on modification of the revenue-related programming if the input code word matches the stored code word.
An analog to digital converter system includes first and second delta sigma converters, a calculation engine, and a serial interface on a single chip. The calculation engine is configured to calculate energy, power, rms current and voltage for single phase 2 or 3 wire power meters. Voltage and current are measured with a shunt or transformer, and a divider or transformer, respectively. The serial interface is bidirectional for communication with a microprocessor or controller, and provides a fixed width programmable frequency output proportional to energy. The digital converter system is user system calibratible.
A signal generator controls power output on the basis of the output from a .DELTA.-.SIGMA. modulator or oscillator. That output may be generated in real time by the modulator or oscillator and fed to a switch control logic unit which controls a power switching stage to output switchably switched power from a power supply to an output, preferably via a filter. Alternatively the output of a .DELTA.-.SIGMA. oscillator or modulator may be stored in a switchable memory to be retrieved when needed. A further alternative is to control the power switching stage by a processor with a program which reproduces the control effect of the .DELTA.-.SIGMA. oscillator/modulator. Feedback from the output may be used to control the .DELTA.-.SIGMA. modulator/oscillator and/or the power supply.
