Electronic kilowatt-hour-meter with error correction

• US 4,066,960 A
• Filed: 12/29/1976
• Issued: 01/03/1978
• Est. Priority Date: 12/29/1976
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Milkovic, Miran
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/755,298
• Time in Patent Office: 370 Days
• Field of Search: 324/142, 324/141, 235/194, 307/225, 328/160
• US Class Current: 324/142
• CPC Class Codes: G01R 21/127 by using pulse modulation G01R21/133 takes precedence

Abstract

An electronic kilowatt-hour meter having internal error correction is disclosed for metering electrical power and energy consumption in a single phase or polyphase electrical system. A comparator compares an analog signal which is proportional to the voltage in the system with a relatively high frequency triangular waveform. The output of the comparator which is a pulse width modulated signal having a pulse duration proportional to the amplitude of the voltage in the system is multiplied by a signal which is proportional to the current in a system. The output of the multiplier is integrated to thereby provide a signal which is proportional to the energy consumed in the system. The output of the integrator is converted to a pulse train having a frequency which is proportional to the amplitude of the output signal of the integrator, and hence is proportional to the kilowatt hours consumed in the electrical system. In order to provide error correction, the phase of the analog signal which is proportional to the voltage in the system is shifted with respect to the phase of the triangular waveform by reversing the connections of these respective signals to the input terminals of the comparator. This is done each time an output pulse is generated by the analog-to-pulse-rate converter. Thus the integrator alternately integrates up and down to thereby correct any offset errors in the system.

Claims

1. An electronic meter for measuring energy consumed in an electrical system comprising:

means for generating first and second analog signals, said signals being proportional to a current in said system, and said first analog signal being 180°

out-of-phase with respect to said second analog signal,

means for generating a third analog voltage proportional to a voltage in said system,

means for generating a relatively high frequency triangular waveform signal,

a comparator having an in-phase input and an inverting input,

switching means for selectively coupling said triangular waveform to one input of said comparator and said third analog signal to the other input of said comparator, the output of said comparator being a pulse width modulated signal having a pulse width proportional to the amplitude of the third analog signal,

means for multiplying said pulse width modulated output signal of said comparator with a signal proportional to said first and second current proportional analog signals, the output of said multiplier having an amplitude proportional to the electrical current in said system and having a pulse width proportional to the amplitude of the voltage in said system,

an integrator, said integrator being connected to the output of said multiplier, the output of said integrator being proportional to the energy consumed in said system,

a pulse generator, the input of said generator being connected to said integrator to thereby convert the output of said integrator to a pulse train, each pulse being proportional to energy consumed in said system,

means connected to said pulse generator for recording and displaying the energy consumed in said electrical system, and

error correction means responsive to the output pulses of said generator for operating said switching means to reverse the input terminals of said comparator to which said triangular waveform signal and said third analog signal are connected to thereby correct offset integration errors in said meter.

2. The electronic meter of claim 1 wherein said pulse generator circuit comprises means for determining when the voltage level at the output of said integrator reaches a first predetermined positive level and means for detecting when the output of said integrator reaches a second negative level, and means responsive to said detecting means for generating an output pulse when said predetermined positive and negative levels are reached.

3. The meter of claim 2 wherein said multiplying means comprises a switch, said switch selectively connecting said first or said second analog signals to said integrator in accordance with the output of said comparator.

4. An electronic meter for measuring energy consumed in a polyphase electrical system comprising:

a plurality of means for generating first and second analog signals, said signals being proportional to the current in each phase of said system wherein said first analog signal is 180°

out-of-phase with respect to said second analog signal,

a plurality of means for generating a third analog voltage proportional to the voltage in each phase of said system,

means for generating a relatively high frequency triangular waveform signal, a plurality of comparators, one for each phase of said polyphase system,

a plurality of switching means for selectively coupling said triangular waveform signal to one input of each of said comparators, and one of third analog signals to the other input of said comparator, the output of said comparators being a pulse width modulated signals wherein each signal has a pulse width proportional to the amplitude of the third analog signal coupled to the input of the comparator generating the pulse width modulated signal,

a plurality of means for multiplying said pulse width modulated output signals of said comparators with the corresponding first and second current proportional analog signals for each phase, the output of said multipliers having an amplitude proportional to the amplitude of said electrical current in said system and having a pulse width proportional to the amplitude of the electrical voltage in said system,

means for summing said output of said multiplying means,

an integrator, said integrator being connected to the outputs of said multipliers, the output of said integrator being proportional to the energy consumed in said system,

a pulse generating circuit, the input of said generator being connected to said integrator to thereby convert the output of said integrator to a pulse train, each pulse being proportional to energy consumed in said system,

means connected to said generator for recording and displaying the energy consumed in said electrical system, and

error correction means responsive to the output pulses of said generator for operating said plurality of switching means to reverse the input terminals of said comparators to which said triangular waveform signal and said third analog signal are connected.

5. The electronic meter of claim 4 wherein said pulse generating circuit comprises means for determining when the voltage level at the output of said integrator reaches a first predetermined positive level and means for detecting when the output of said integrator reaches a second negative level, and means responsive to said detecting means for generating an output pulse when said predetermined positive and negative levels are reached.

6. The meter of claim 5 wherein said multiplying means each comprises a switch, said switch selectively connecting said first or said second analog signals to said integrator in accordance with the output of said comparator.

7. An electronic meter for measuring energy consumed in an electrical system comprising:

means for generating first and second analog signals, said signals being proportional to current in said system, and said first analog signal being 180°

out-of-phase with respect to said second analog signal,

means for generating a third analog voltage proportional to the voltage in said system,

means for generating a relatively high frequency triangular waveform signal,

a comparator, said comparator having an in-phase input terminal and a phase inverting input terminal,

switching means for selectively coupling said triangular waveform signal to one input of said comparator and said third analog signal to the other input of said comparator,

means for multiplying said pulse width modulated output signal of said comparator with said first and second current proportional analog signals, the output of said multiplier having an amplitude proportional to the current in said system and having a pulse width proportional to the amplitude of the voltage in said system,

an integrator, said integrator being connected to the output of said multiplier, the output of said integrator being proportional to the energy consumed in said system,

a pulse generating circuit, the output of said generator being connected to said integrator to thereby convert the output of said integrator to a pulse train having each pulse proportional to energy consumed in said system, said pulse generator including means for determining when the voltage level at the output of said integrator reaches a first predetermined positive level, and means for detecting when the output of said integrator reaches a second negative level, and means responsive to said detecting means for generating an output pulse when said predetermined positive and negative levels are reached, and

error correction means responsive to the output pulses of said pulse generating circuit for operating said switching means to reverse the input terminals of said pulse generating circuit to which said triangular waveform signal and said third analog signal are connected, said error correcting means correcting the offset integration errors in said meter, and means for deriving a voltage proportional to the voltage in said electrical system, means responsive to said derived voltage for generating power supply voltages for the comparator, the triangular waveform signal generating means, the switching means, the multiplying means, the integrator and the pulse generating circuit.