Meter for accurately measuring integrated electric power

• US 5,079,510 A
• Filed: 11/02/1990
• Issued: 01/07/1992
• Est. Priority Date: 12/26/1988
• Status: Expired due to Fees

• Current Assignee: Korea Electric Power Corporation (Government of South Korea), NEC Corporation
• Original Assignee: Korea Electric Power Corporation (Government of South Korea), NEC Corporation
• Inventors: Kobayashi, Tadashi, Takagi, Toshio, Nakamura, Hidetake, Komatsu, Masatoshi, Fushimi, Shigeo, Wada, Shigenori
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/608,540
• Time in Patent Office: 431 Days
• Field of Search: 324/142, 324/103 R, 324/107, 324/111, 341/118, 328/160, 364/483
• US Class Current: 324/142
• CPC Class Codes: G01R 21/1331 Measuring real or reactive component, measuring apparent energy

Abstract

In a watt-hour meter in which first and second input signals representing an analog electric current and an analog voltage of an alternating current are converted into first and second digital signals, a first adder produces a sum signal which represents a sum of the first input signal and an additional analog signal of a frequency different from that of the first input signal and which is substituted for the first input signal. The meter may further comprise a second adder which adds another additional analog signal to the second input signal. Alternatively, the meter comprises low-pass filters and oversample-and-convert circuits to produce the first and the second input digital signals. As a further alternative, the meter comprises a first inverter for inverting a selected one of the first and the second input signals into a first inverted signal. In this event, a first selector alternatingly selects one of the first inverted signal and the selected one of the first and the second input signals and the other of the first inverted signal and the selected one of the first and the second input signals at a predetermined time interval as a first selected signal. A second inverter for inverting a product signal representing a product of the first and the second digital signals into a second inverted signal. Ganged with the first selector, a second selector alternatingly selects one of the second inverted signal and the product signal at the predetermined time interval as a second selected signal so that the second inverted signal is selected when the first selector selects the first inverted signal.

Claims

1. An electric power meter comprising:

first processing means (60 and 63;

60, 63, 35, and 36;

or 73 and

     74) for inverting a first input signal representative of the predetermined one of an analog electric current and an analog voltage of an input alternating current into an inverted signal and for processing said first input signal and said inverted signal into an output alternating signal in which said first input signal and said inverted signal alternatively appears at a predetermined period;

converting means (66 and 70;

or

     38) connected to said first processing means and supplied with a second input signal representative of the other of said analog electric current and said analog voltage for converting said output alternating signal and said second input signal into first and second digital signals;

second processing means (27, 71, and 72;

66, 70, 76, and

     78) connected to said converting means for processing said first and said second digital signals into an electric power signal representative of one of first and second products at a time, said first product being an inverted product of said first and said second digital signals when said first digital signal is converted from the inverted signal included in said output alternating signal, said second product being a product of said first and said second digital signals when said first digital signal is converted from the first input signal included in said output alternating signal; and

integrating means (28) connected to said second processing means for integrating said electric power signal into a meter output signal representative of integration of said one of the first and the second products.

2. An electric power meter comprising:

first inverting means for inverting a first input signal representative of a predetermined one of an analog electric current and an analog voltage of an alternating current to produce a first inverted signal;

first selecting means connected to said first inverting means and supplied with said first input signal for alternatingly selecting one of said first input signal and said first inverted signal and the other of said first input signal and said first inverted signal at a predetermined time interval as a first selected signal;

first converting means connected to said first selecting means for converting said first selected signal into a first digital signal;

second converting means supplied with a second input signal representative of the other of said analog electric current and said analog voltage for converting said second input signal into a second digital signal;

multiplying means connected to said first and said second converting means for calculating a product of said first and said second digital signals to produce a product signal representative of said product;

second inverting means connected to said multiplying means for inverting said product signal to produce a second inverted signal;

second selecting means connected to said multiplying means and said second inverting means and ganged with said first selecting means for alternatingly selecting one of said product signal and said second inverted signal and the other of said product signal and said second inverted signal at said predetermined time interval as a second selected signal so that said product signal is selected when said first selecting means selects said first input signal and that said second inverted signal is selected when said first selecting means selects said first inverted signal; and

integrating means connected to said second selecting means for integrating said second selected signal to produce a meter output signal representative of an integrated electric power of said alternating current.

3. An electric power meter comprising:

first inverting means for inverting a first input signal representative of a predetermined one of an analog electric current and an analog voltage of an alternating current to produce a first inverted signal;

first selecting means connected to said first inverting means and supplied with said first input signal for alternatingly selecting one of said first input signal and said first inverted signal and the other of said first input signal and said first inverted signal at a predetermined time interval as a first selected signal;

first sample-and-hold means connected to said first selecting means for sampling said first selected signal into a first sampled signal and for holding said first sampled signal as a first held signal;

second sample-and-hold means supplied with a second input signal representative of the other of said analog electric current and said analog voltage for sampling said second selected signal into a second sampled signal and for holding said second sampled signal as a second held signal;

held signal selecting means connected to said first and said second sample-and-hold means for alternatingly selecting one of said first and said second held signals and the other of said first and said second held signals at a preselected period as a selected held signal;

converting means connected to said held signal selecting means for converting said selected held signal into a digital signal;

separating means connected to said converting means and ganged with said held signal selecting means for alternatingly producing said digital signal as a first and a second separated signal at said preselected period so that said first separated signal is produced when said held signal selecting means selects said first held signal and that said second separated signal is produced when said held signal selecting means selects said second held signal;

first memorizing means connected to said separating means for memorizing said first separated signal as a first memorized signal;

second memorizing means connected to said separating means for memorizing said second separated signal as a second memorized signal;

multiplying means connected to said first and said second memorizing means for calculating a product of said first and said second memorized signals to product a product signal representative of said product;

second inverting means for inverting said product signal to produce a second inverted signal; and

second selecting means connected to said multiplying means and ganged with said first selecting means for alternatingly selecting one of said product signal and said second inverted signal and the other of said product signal and said second inverted signal at said predetermined time interval as a second selected signal so that said product signal is selected when said first selecting means selects said first input signal and that said second inverted signal is selected when said first selecting means selects said first inverted signal; and

integrating means connected to said second selecting means for integrating said second selected signal to produce a meter output signal representative of an integrated electric power of said alternating current.

4. An electric power meter comprising:

first inverting means for inverting a first input signal representative of a predetermined one of an analog electric current and an analog voltage of an alternating current to produce a first inverted signal;

first selecting means connected to said first inverting means and supplied with said first input signal for alternatingly selecting one of said first input signal and said first inverted signal and the other of said first input signal and said first inverted signal at a predetermined time interval as a first selected signal;

first converting means connected to said first selecting means for converting said first selected signal into a first digital signal;

second inverting means connected to said first converting means for inverting said first digital signal to produce a second inverted signal;

second selecting means connected to said first converting means and said second inverting means and ganged with said first selecting means for alternatingly selecting one of said first digital signal and said second inverted signal and the other of said first digital signal and said second inverted signal at said predetermined time interval as a second selected signal so that said first digital signal is selected when said first selecting means selects said first input signal and that said second inverted signal is selected when said first selecting means selects said first inverted signal;

second converting means supplied with a second input signal representative of the other of said analog electric current and said analog voltage for converting said second input signal into a second digital signal;

multiplying means connected to said second selecting means and said second converting means for calculating a product of said second selected signal and said second digital signal to produce a product signal representative of said product; and

integrating means connected to said multiplying means for integrating said product signal to produce a meter output signal representative of an integrated electric power of said alternating current.