Systems and methods for an open circuit current limiter

• US 9,116,177 B2
• Filed: 08/01/2011
• Issued: 08/25/2015
• 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.
• Primary Examiner(s): Natalini, Jeff
• Application Number:
  US13/195,681
• Publication Number:
  US 20110285414A1
• Time in Patent Office: 1,485 Days
• Field of Search: 324/713
• US Class Current: 1/1
• 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. A resistance measuring circuit with power saving capabilities, comprising:

a first measurement terminal and a second measurement terminal;

a voltage measuring component configured to measure a voltage drop across the first measurement terminal and the second measurement terminal;

a current generating component configured to generate a first current along a current path to the first measurement terminal responsive to a target resistance couplable to the first measurement terminal and the second measurement terminal; and

a current control component configured to reduce power consumption by decreasing a magnitude of the current generated by the current generating component from the first current to a second current lower than the first current in response to a measured increase in the voltage drop caused by a disconnection of the first measurement terminal or the second measurement terminal from the target resistance, wherein the measured increase in the voltage drop is measured by the voltage measuring component.

2. The resistance measuring circuit of claim 1, further comprising:

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

3. The resistance measuring circuit of claim 2, wherein the current measuring component comprises a level shifter circuit configured to generate a level-shifted voltage drop across a resistor of known resistance located along the current path.

4. The resistance measuring circuit of claim 2, wherein the current generating component comprises a voltage source.

5. The resistance measuring circuit of claim 1, wherein the current control component is configured to decrease the magnitude of the current generated by the current generating component from the first current to the second current by actuating a switch connected along the current path.

6. The resistance measuring circuit of claim 5, wherein the switch comprises a field effect transistor (FET).

7. The resistance measuring circuit of claim 5, wherein the switch comprises a transistor that is actuated from a fully-on state when the target resistance is present between the first measurement terminal and the second measurement terminal to a partially-on state when the voltage measurement component measures the increase in the voltage drop.

8. The resistance measuring circuit of claim 1, 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.

9. The resistance measuring circuit of claim 1, wherein the second current has a non-zero magnitude.

10. A method of reducing power used by a resistance measuring circuit, comprising:

measuring a voltage drop between a first measurement terminal and a second measurement terminal;

generating a first current along a current path to the first measurement terminal, wherein the generating is responsive to a target resistance couplable to the first measurement terminal and a second measurement terminal; and

reducing the current along the current path from the first current to a second current responsive to measuring an increase in the voltage drop between the first measurement terminal and the second measurement terminal caused by a disconnection of the first or second measurement terminals from the target resistance, wherein said reducing the current reduces an amount of power consumed.

11. The method of claim 10, wherein reducing the current along the current path from the first current to a second current comprises actuating a switch connected along the current path of the generated current in response to the increase in the voltage drop.

12. The method of claim 11, wherein the switch comprises a field effect transistor (FET).

13. The method of claim 11, wherein the switch comprises a transistor that is actuated from a fully-on state when the target resistance is present between the first measurement terminal and the second measurement terminal to a partially-on state when the voltage measurement component measures the increase in the voltage drop.

14. The method of claim 11, wherein the first current is between 5 mA and 10 mA, and the second current is less than 3 mA.

15. The method of claim 11, wherein the second current has a non-zero magnitude.

16. A resistance measuring circuit with power saving capabilities, comprising:

a first measurement terminal and a second measurement terminal;

a voltage measuring component configured to measure a voltage drop across the first measurement terminal and the second measurement terminal;

a current generating component configured to generate a first current along a current path to the first measurement terminal responsive to a target resistance couplable to the first measurement terminal and the second measurement terminal; and

means for reducing a magnitude of the current generated by the current generating component from the first current to a second current responsive to a measured increase in the voltage drop caused by a disconnection of the first or second measurement terminals from the target resistance, wherein the measured increase in the voltage drop is measured by the voltage measuring component, and wherein said reducing the magnitude of the current generated by the current generating component from the first current to the second current reduces an amount of power consumed.

17. The resistance measuring circuit of claim 16, wherein reducing a magnitude of the current generated by the current generating component from the first current to a second current comprises actuating a switch connected along the current path of the generated current in response to the increase in the voltage drop.

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

19. The resistance measuring circuit of claim 16, wherein the first current is between 5 mA and 10 mA, and the second current is less than 3 mA.

20. The resistance measuring circuit of claim 16, wherein the second current has a non-zero magnitude.