Method and apparatus for measurement of AC and DC electrical current

• US 5,479,095 A
• Filed: 06/30/1994
• Issued: 12/26/1995
• Est. Priority Date: 06/30/1994
• Status: Expired due to Fees

• Current Assignee: Power Corporation
• Original Assignee: Power Corporation
• Inventors: Michalek, Jan K., Shahrodi, Ebrahim B.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): KHOSRAVI, KOURO
• Application Number:
  US08/269,145
• Time in Patent Office: 544 Days
• Field of Search: 324/117 H, 324/117 R, 324/127, 324/115, 324/142, 324/96, 307/128, 340/661, 340/664, 340/870.28
• US Class Current: 324/117.00H
• CPC Class Codes: G01R 15/202 using Hall-effect devices Hall elements in arrangements for measuring electrical power G01R21/08
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence

Abstract

The present invention involves measurement of an electrical current by means of a current transformer having the current to be measured passing in an axial direction through the current transformer, and the voltage induced thereby in the windings of the current transformer are used to produce a first voltage. A Hall effect is used in series with the current transformer to produce a second voltage measurement corresponding to the current measured by the Hall effect sensor. When the two measurements agree to within a predetermined value (typically 5% of the root-mean-square current values measured by each sensor) then the current transformer reading is used as the more accurate. Otherwise, the Hall effect current sensor is used as the more accurate current measurement.

Claims

1. An apparatus for measuring electrical current comprising:

a) a current transformer having the current to be measured passing axially therethrough and producing a first voltage corresponding to a first measured value of said current; and

,

b) a Hall effect current sensor having said current to be measured passing axially therethrough, in series with the passage of said current through said current transformer, and producing a second voltage corresponding to a second measured value of said current; and

,

c) a comparison device receiving substantially simultaneously said first and said second voltages and selecting a selected voltage from said first and said second voltages, said device comparing said first and second measured current values wish each other and with a predetermined error limit, and said device selecting said first voltage if said measured currents agree to within said predetermined error limit, and selecting said second voltage otherwise; and

,

d) a switch directing said selected voltage to an output terminal.

2. An apparatus as in claim 1 wherein said comparison device is a microprocessor.

3. An apparatus as in claim 1 wherein said predetermined error limit is 5% of root-mean-square current values.

4. A method for measuring electrical current comprising the steps of:

a) measuring said current by passing said current axially through a current transformer producing thereby a first voltage corresponding to said first measured current; and

,

b) measuring said current by passing said current axially through a Hall effect current sensor producing thereby a second voltage corresponding to said second measured current value; and

,

c) comparing said first and said second measured current values with each other and with a predetermined error limit; and

,

d) selecting said first voltage if said first and second measured current values agree to within said predetermined error limit, and selecting said second voltage otherwise.

5. A method as in claim 4 wherein said predetermined error limit is 5% of the measured root-mean-square current values.