Method for detecting a current flowing over the human body between a forward and a return conductor and a circuit configuration for carrying out the method

• US 4,942,313 A
• Filed: 08/17/1988
• Issued: 07/17/1990
• Est. Priority Date: 08/29/1987
• Status: Expired due to Fees

• Current Assignee: Asea Brown Boveri AG (ABB Limited)
• Original Assignee: Asea Brown Boveri AG (ABB Limited)
• Inventors: Kinzel, Helmut
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US07/233,242
• Time in Patent Office: 699 Days
• Field of Search: 307/116, 307/326, 361/42-50, 361/100, 361/110, 361/232, 128/303.13, 128/303.14, 128/303.17, 128/422, 604/20, 324/72, 324/133, 324/514, 324/524
• US Class Current: 307/326
• CPC Class Codes: H02H 5/12 responsive to undesired approach to, or touching of, live parts by living beings

Abstract

The method and circuit detects a current flow over the human body between a forward conductor and a return conductor, and disconnects the network conductors. The output signal emitted by a current sensor connected to a network conductor is detected and a switch for disconnecting the network conductor is then actuated only at a value of the signal of the current sensor between an upper and a lower threshold value.

Claims

1. Method for detecting a current flowing through a human body between forward and return main network conductors at a given network voltage, and for switching off the main network conductors, which comprises detecting a current increase through the human body by means of an output signal emitted by a current sensor connected in one of the network conductors, actuating a switch for switching off the main network conductors only if a value of the output signal of the current sensor is between a lower and an upper threshold value, wherein said lower threshold value represents a current that is of just no danger to a human body, and the upper threshold value represents a maximal allowable current value through a human body, at said given network voltage, rectifying the output signal of the current sensor in a rectifier, differentiating the rectified output signal in a differentiating section, supplying the rectified output signal to a discriminator circuit after differentiation, and limiting a window of the discriminator circuit by the lower and upper threshold values.

2. Method according to claim 1, which comprises supplying the rectified output signal of the current sensor to a peak-value forming circuit and then to the differentiating section.

3. Circuit configuration for detecting a current flowing over the human body between forward and return network conductors, and for switching off the network conductors, comprising a current sensor connected to one of the network conductors, means for setting upper and lower threshold values of an output signal of said current sensor, a switch connected to one of the network conductors, a differentiating section in the form of an RC section connected to said current sensor, and a discriminator circuit having first and second controllable semiconductor switches connected to said RC section, said first controllable semiconductor switch being turned on with a signal of said RC section above the upper threshold value for discharging an output voltage of said differentiating section to ground, and said second semiconductor switch being activated with a signal of said RC section between the upper and lower threshold values for activating said switch.

4. Circuit configuration according to claim 3, wherein said first controllable semiconductor switch is a thyristor having a gate terminal, and including a Zener diode connected to the gate terminal of said thyristor.

5. Circuit configuration according to claim 3, wherein said second controllable semiconductor switch is a transistor having a base terminal, and including an adjustable resistance voltage divider driving the base of said transistor.

6. Circuit configuration according to claim 3, wherein said second controllable semiconductor switch is a threshold-value transistor circuit.

7. Circuit configuration for detecting a current flowing over the human body between forward and return network conductors, and for switching off the network conductors, comprising a current sensor connected to one of the network conductors, means for setting upper and lower threshold values of an output signal of said current sensor, a switch connected to one of the network conductors, a rectifier connected to said current sensor for rectifying the output signal thereof, a differentiator connected to said rectifier for differentiating the rectified output signal, and a discriminator circuit connected to said differentiator having a window limited by the upper and lower threshold values.

8. Circuit configuration according to claim 7, wherein said rectifier, said differentiator, and said discriminator circuit, are formed of comparator and amplifier circuits.

9. Circuit configuration according to claim 7, wherein said rectifier, said differentiator, and said discriminator circuit, are formed of comparator circuits.

10. Circuit configuration according to claim 7, wherein said rectifier, said differentiator, and said discriminator circuit, are formed of amplifier circuits.

11. Circuit configuration according to claim 7, wherein said rectifier is a two-way rectifier, and including an input amplifier with over-voltage and short-circuit protection connected upstream of said rectifier.

12. Circuit configuration according to claim 11, including a smoothing peak-value forming circuit connected upstream of said differentiator.

13. Circuit configuration according to claim 12, including an evaluating circuit, and a block forming circuit connected between said discriminator circuit and said evaluating circuit for protected evaluation of the signal.