SYSTEMS AND METHODS FOR AN OPEN CIRCUIT CURRENT LIMITER

• US 20090045825A1
• Filed: 08/14/2007
• Published: 02/19/2009
• Est. Priority Date: 08/14/2007
• Status: Active Grant

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: ENG, Benjamin JR.
• Granted Patent: US 7,990,162 B2
• Time in Patent Office: Days
• US Class Current: 324/713
• CPC Class Codes: G01R 15/12 Circuits for multi-testers , i.e. multimeters, e.g. for measuring voltage, current, or impedance at will
• CPC Class Codes: G01R 27/08 Measuring resistance by measuring both voltage and current

Abstract

A resistance measuring circuit includes a current generating component, a current control component, and a voltage measurement component. The magnitude of a target resistance can be measured by connecting the target resistance between first and second measurement terminals of the resistance measuring circuit, applying a current generated by the current generating component to the target resistance, and determining the voltage across the target resistance. When no target resistance is connected between the first and second measurement terminals, the current control component controls the current generating component to reduce current consumption of the resistance measuring circuit.

Claims

1. An electrical apparatus capable of measuring electrical resistance, the apparatus comprising:

first and second measurement terminals configured to be coupled to opposite sides of an electrical component;

a current generating component coupled to at least the first measurement terminal and configured to generate a current for measuring a resistance of the electrical component; and

a voltage detecting component for detecting a voltage level between the first and second measurement terminals; and

a current control component configured to decrease the magnitude of the current provided by the current generating component based on a change in the detected voltage level.

2. The apparatus of claim 1, further comprising:

a current measuring component configured to measure the magnitude of the current generated by the current generating component.

3. The apparatus of claim 2, wherein the current measuring component comprises a level shifter circuit configured to amplify and output a voltage drop across a resistor located along a current path of the current generated by the current generating component.

4. The apparatus of claim 1, wherein the current control component controls the current generating component by modulating a switch connected along the current path in response to the detected voltage level.

5. The apparatus of claim 1, wherein the apparatus comprises a battery-powered handheld electrical multimeter.

6. A method of controlling output current in an electronic apparatus capable of measuring electrical resistance, comprising:

generating an operating current with a first magnitude when a target resistance is connected between a first measurement terminal and a second measurement terminal;

sensing a change in a voltage level when the target resistance is disconnected from the first or second measurement terminal; and

controlling the current generating component to reduce the operating current to a second magnitude to reduce power consumption of the electronic apparatus based on the sensed rise in the voltage level.

7. The method of claim 6, further comprising:

measuring a voltage drop across the target resistance when the target resistance is connected between the first and second measurement terminals.

8. The method of claim 6, further comprising:

computing the magnitude of the target resistance based on the measured voltage drop and the operating current.

9. The method of claim 6, further comprising reducing the operating current to a non-zero magnitude.

10. The method of claim 6, further comprising actuating a switch connected along a current path of the operating current in response to the rise in the voltage level of the first measurement terminal to reduce the operating current to the second magnitude.

11. The method of claim 10, further comprising switching a transistor from a fully-on state to a partially-on state in response to the rise in the voltage level of the first measurement terminal.

12. The method of claim 6, wherein the first magnitude is between 5 and 10 mA and the second magnitude is less than 3 mA.

13. An apparatus for measuring resistance, comprising:

a current generating component configured to generate a first current along a current path passing through a node connected to a first measurement terminal when the resistance measuring circuit is in a closed-circuit configuration, and further configured to generate a second current along the current path when the resistance measuring circuit is in an open-circuit configuration, wherein the second current has a lower magnitude than the first current;

a current control component configured to control the current generating component based on a voltage level of the first measurement terminal,

wherein the current generating component generates the first current when the resistance measuring circuit is in the closed-circuit configuration and generates the second current when the resistance measuring circuit is in the open-circuit configuration; and

a voltage measuring component configured to measure a voltage drop across the target resistance when the resistance measuring circuit is in the closed-circuit mode.

14. The resistance measuring apparatus of claim 13, further comprising:

a current measuring component configured to measure the magnitude of the first current.

15. The resistance measuring apparatus of claim 14, wherein the current measuring component comprises a level shifter circuit configured to amplify and output a voltage drop across a resistor of known resistance located along the current path.

16. The resistance measuring apparatus of claim 14, wherein the current generating component comprises a voltage source.

17. The resistance measuring apparatus of claim 13, wherein the current control component controls the current generating component by actuating a switch connected along the current path in response to the a voltage level of the first measurement terminal.

18. The resistance measuring apparatus of claim 17, wherein the switch comprises a field effect transistor (FET).

19. The resistance measuring apparatus of claim 13, wherein the magnitude of the first current is between 5 and 10 mA and the magnitude of the second current is less than 3 mA.

20. The resistance measuring apparatus of claim 13, further comprising a battery-powered handheld electrical multimeter