Apparatus and method for electrical measurements on conductors

• US 6,828,770 B1
• Filed: 10/11/2001
• Issued: 12/07/2004
• Est. Priority Date: 04/12/1999
• Status: Expired due to Fees

• Current Assignee: CHK Wireless Technologies Australia Pty Limited
• Original Assignee: CHK Wireless Technologies Australia Pty Limited
• Inventors: Sweeting, David Keith, McCauley, Simon Francis
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Dole, Timothy J.
• Application Number:
  US09/958,848
• Time in Patent Office: 1,153 Days
• Field of Search: 324/117.R, 324/117.H, 324/72, 324/72.5, 324/543, 324/529, 324/530
• US Class Current: 324/117.00R
• CPC Class Codes: G01R 15/142 Arrangements for simultaneous measurements of several parameters employing techniques covered by groups G01R15/14 - G01R15/26
• CPC Class Codes: G01R 19/2506 Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values G01R19/003 takes precedence; Details concerning sampling, digitizing or waveform capturing displaying waveforms G01R13/00; analog sampling G01R19/0053

Abstract

A method for measuring at least one characteristic parameter of an alternating current in a conductor, the method including the steps of measuring the magnetic field around the conductor at a point along the conductor; deriving an analogue voltage signal representative of the measured magnetic field; amplifying the analogue voltage signal; converting the amplified voltage signal into a digital voltage signal; measuring the digital voltage signal and, when the amplitude of digital voltage signal reaches a predetermined value, adjusting a gain setting of the amplification; and generating an output signal representative of the parameter of the alternating current based on the amplified voltage signal and the gain setting.

Claims

1. A method for measuring at least one characteristic parameter of an alternating current in a conductor, the parameter of the alternating current comprising at least one of a group of waveform characteristics of the alternating current;

phase of the alternating current;

harmonic content of the alternating current; and

a derivative of the alternating current, the method comprising the steps of;

measuring a magnetic field around the conductor at a point along the conductor to obtain a measured magnetic field value;

integrating the measured magnetic field value to thereby derive an analogue voltage signal representative of the magnetic field;

adding a direct current (DC) offset signal to an alternating current (AC) component of the magnetic field;

amplifying the analogue voltage signal;

converting the amplified voltage signal into a digital voltage signal, the digital voltage signal being within a dynamic range of signal values;

measuring the digital voltage signal including a DC component in the digital voltage signal, and when the amplitude of digital voltage signal reaches a predetermined value, adjusting a gain setting of the amplification to vary the dynamic range of signal values, and varying the DC offset signal in response to the measured DC component in the digital voltage signal;

generating an output signal representative of the parameter of the alternating current based on the amplified voltage signal and the gain setting; and

deriving a second analogue voltage signal representative of the measured electric field in the vicinity of the conductor;

whereby in measuring the variance in the magnitude of the electric field generated by the conductor in conjunction with variance in the conductor, faults in the conductor may be detected.

2. A method as claimed in claim 1, further comprising the step of digitally filtering the digital voltage signal to determine the ratio of a mains voltage signal at a mains frequency of the conductor and a second harmonic of the mains frequency for determining whether a magnetic field signal around the conductor is caused by magnetizing inrush current.

3. A method as claimed in claim 1, wherein the step of measuring the electric field comprises the step of placing a capacitor arrangement in the vicinity of the conductor;

and the method further comprises the steps of;

amplifying the second analog voltage signal;

converting the amplified second voltage signal into a second digital voltage signal;

measuring the second digital voltage signal and, when the amplitude of the second digital voltage signal reaches a second predetermined value, adjusting a second gain setting of the amplification;

and generating a second output signal representative of at least one parameter of a voltage signal in the conductor based on the amplified second voltage signal and the second gain setting.

4. An apparatus for measuring at least one characteristic parameter of an alternating current in a conductor, wherein the parameter of the alternating current comprises at least one of a group of waveform characteristics of the alternating current;

phase of the alternating current;

harmonic content of the alternating current; and

a derivative of the alternating current, the apparatus comprising;

measuring means for measuring a magnetic field around the conductor at a point along the conductor;

integrating means for deriving an analogue voltage signal representative of the measured magnetic field;

trimming means for providing a DC offset signal to an AC component of the measured magnetic field;

amplification means for amplifying the analogue voltage signal;

converting means for converting the amplified voltage signal into a digital voltage signal, wherein the digital voltage signal is within a dynamic range of signal values;

gain control means for adjusting a gain setting of the amplification depending on the amplitude of the digital voltage signal, wherein the dynamic range of signal values is varied;

second trimming means for providing a second DC offset of the amplification means;

means for generating an output signal representative of the parameter of the alternating current based on the amplified voltage signal and the gain setting;

second measuring means for measuring an electric field in the vicinity of the conductor; and

second integrating means for deriving a second analogue voltage signal corresponding to the measured electric field in the vicinity of the conductor;

wherein by measuring the variance in the magnitude of the electric field in conjunction with the variance in current, faults in the conductor may be detected.

5. An apparatus as claimed in claim 4, the apparatus further comprising filtering means for filtering the digital signal and means for determining the ratio of a mains voltage signal at a mains frequency of the conductor and a second harmonic of the mains frequency to determine whether a magnetic field signal around the conductor is caused by magnetizing inrush current.

6. An apparatus as claimed in claim 4, the apparatus further comprising:

second amplification means for amplifying the second analog voltage signal;

second converting means for converting the second amplified voltage signal into a second digital voltage signal;

second gain control means for adjusting a second gain setting of the second amplification depending on the second digital voltage signal;

and a second means for generating an output signal representative of at least one parameter of a voltage signal in the conductor based on the second amplified voltage signal and the second gain setting.

7. An apparatus as claimed in claim 4, wherein the first and/or the second trimming means each comprise a serial to parallel shift register, wherein the outputs of the shift register are connected to a resister network to form a digital to analogue converter.