High linearity, low offset interface for hall effect devices

• US 20030006753A1
• Filed: 09/06/2002
• Published: 01/09/2003
• Est. Priority Date: 10/08/1998
• Status: Active Grant

• Current Assignee: Itron Global Sarl (Itron, Inc.)
• Original Assignee: Schlumberger Electricity, Inc.
• Inventors: Gervais, Michel, Goodwin, Wendell, Kobbi, Farah, Heinz-Buethe, Karl, Lancaster, Andrew
• Granted Patent: US 6,628,114 B2
• Time in Patent Office: Days
• US Class Current: 324/117R
• CPC Class Codes: G01R 15/202 using Hall-effect devices Hall elements in arrangements for measuring electrical power G01R21/08
• CPC Class Codes: G01R 21/08 by using galvanomagnetic-effect devices, e.g. Hall-effect devices

Abstract

A Hall effect sensor or device may be used in a variety of embodiments, such as measuring current within an associated conductor by helping to measure flux density within a gap of a ferromagnetic power meter core, such as in a power meter. A high linearity interface for a Hall effect device is provided for minimizing offset effects without using complicated electronic circuits. First and second levels of modulation relative to line frequency are used to synchronize Hall effect device input switching circuits and feedback loops for improved elimination of offset signals or noise from the ultimate system output. The substrate of the Hall effect device may be connected electrically to an output pin of the Hall device or to a separate virtual ground to eliminate any effects caused by asymmetry of the voltage appearing in the channel relative to the substrate. The net effect of the high linearity interface is to eliminate any adverse effects to linearity of the system, especially at low magnetic flux levels where the output voltage of the Hall device would be relatively small compared to the offset voltage levels involved. The interface virtually eliminates adverse effects from operational amplifier input offset voltages, Hall effect device output offset voltages, and any common mode voltages.

Claims

1. A Hall effect sensor with improved output interface for high linearity and low offset performance, as associated with a given line voltage, comprising:

a Hall effect device of the type having a substrate, first and second device inputs and first and second device outputs, wherein said substrate is electrically connected to one of said device outputs and capacitively coupled to said Hall effect device;

a biasing current supplied to said device proportional to the line voltage with which said device and interface are associated; and

a biasing circuit including said substrate, wherein said substrate is electrically interconnected to one of said device outputs.

2. A Hall effect sensor with improved output interface as in claim 1, further including a differential drive circuit for inverting an input voltage appearing at one of said Hall effect device inputs and applying such inverted signal to the other of said Hall effect device inputs.

3. A Hall effect sensor with improved output interface as in claim 1, further including:

plural pairs of inverting and non-inverting switch components connected between a given line voltage and said Hall effect device inputs, having controlled respective switching inputs commonly controlled by a modulation signal; and

modulation means operative with the associated line frequency for generating said modulation signal with reference to line frequency.

4. A Hall effect sensor with improved output interface as in claim 1, wherein said biasing circuit is capable of eliminating undesirable offset effects due to non-symmetries in the Hall effect device and for eliminating common mode voltages.

5. A Hall effect sensor with improved output interface as in claim 4, wherein said biasing circuit includes a differential drive circuit for inverting an input voltage appearing at one of the Hall effect device inputs and applying such inverted signal to the other of the Hall effect inputs.

6. A Hall effect sensor with improved output interface as in claim 4, wherein said biasing circuit includes an in-line biasing resistor for supplying to said Hall effect device said biasing current.

7. A Hall effect sensor with improved output interface as in claim 1, wherein one of said Hall effect device outputs is interconnected to a virtual ground.

8. A power meter arrangement, comprising:

a laminated ferromagnetic power meter core having a designated region thereof defining a core gap; and

a Hall effect sensor residing in said core gap of said power meter core for sensing magnetic flux from which power consumption data may be derived concerning current flow through an associated conductor line, said Hall effect sensor including a Hall effect device of the type having a substrate, first and second device inputs and first and second device outputs, said sensor further including interface means for providing a high linearity low offset sensor output signal and a biasing circuit including said substrate, wherein said substrate is electrically interconnected to one of said device outputs.

9. A power meter arrangement as in claim 8, wherein said interface means includes:

switch means, responsive to switching control input thereto, for selectively switching line voltage, a parameter of which is to be sensed, to the inputs of a Hall effect device;

modulation means for controlling the switching characteristics of said switch means by providing said switching control input thereto; and

output converter chip means for receiving the outputs of the Hall effect device and providing a selectively processed digitized output therefrom.