Testing instrument for detectlng alternating voltages in mains and alternating electromagnetic fields in the vicinity of voltage-carrying conductors

• US 4,724,382 A
• Filed: 10/11/1985
• Issued: 02/09/1988
• Est. Priority Date: 10/11/1984
• Status: Expired due to Fees

• Current Assignee: Hubertus Schauerte
• Original Assignee: Hubertus Schauerte
• Inventors: Schauerte, Hubertus
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Mueller, Robert W.
• Application Number:
  US06/786,518
• Time in Patent Office: 851 Days
• Field of Search: 324/133, 324/51, 324/72.5
• US Class Current: 324/133
• CPC Class Codes: G01R 19/145 Indicating the presence of current or voltage
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage
• CPC Class Codes: G01R 29/085 for detecting presence or location of electric lines or cables fault detection G01R31/50; fault location G01R31/08

Abstract

An electrical measuring or testing instrument is disclosed for detecting alternating voltages in mains, induced voltages in ungrounded conductors, and alternating electrical fields in the vicinity of voltage-carrying conductors. The instrument includes a constant-voltage source, a test prod, which is connected via a protective resistor to the input of an amplification circuit and via a further resistor and a switching transistor to the negative pole of the constant-voltage source, and an LED connected to the constant-voltage source and controlled by the amplifier circuit. The amplifier circuit has a very high amplification factor, so that even weak alternating fields in the vicinity of voltage-carrying conductors can be detected. The amplification is normally reduced with the aid of a resistor connected between the input of the amplifier circuit and the negative pole of the voltage source. If higher amplification is required, the connection between the resistor and the constant-voltage source can be interrupted with the aid of a foil sensor.

Claims

1. A testing instrument for detecting alternating voltages in mains and alternating electromagnetic alternating fields in the vicinity of voltage-carrying conductors, comprising:

a constant-voltage source;

an amplifier circuit;

a test prod connected to an input of said amplifier circuit through a protective resistor;

an amplification reducing circuit connected to said test prod, comprising a resistor and a switching transistor for connecting said test prod to ground through said resistor, when actuated, and means for actuating said switching transistor;

an LED connected to the constant-voltage source and controlled by the amplifier circuit;

wherein the testing instrument is a screwdriver having a blade which forms the test prod and having a handle which receives said constant-voltage source, said amplifier circuit, said protective resistor, and said amplification reducing circuit and wherein said switching transistor is actuatable by a sensor in such a manner that the switching transistor blocks when the sensor is actuated.

2. A testing instrument as defined by claim 1, wherein the switching transistor is an n-p-n transistor, the emitter of which is connected directly to ground and the base of which is continuosly connected through a resistor to a positive pole of the voltage source and is connectable to ground through the sensor and a further resistor.

3. A testing instrument as defined by claim 2, wherein a contact electrode is connected to the constant-voltage source.

4. A testing instrument as defined by claim 3, wherein a Zener diode is disposed between the constant-voltage source and the contact electrode, the blocking voltage of the Zener diode being lower than the voltage of the constant-voltage source.

5. A testing instrument as defined by claim 3, wherein the contact electrode is disposed immediately adjacent the sensor.

6. A testing instrument as defined in claim 3, wherein the contact electrode is disposed on the sensor.

7. A testing instrument as defined in claim 1, wherein the sensor is a foil sensor.

8. A testing instrument as defined in claim 1, wherein the amplification factor of the amplifier circuit, when the sensor is closed, is at least 10⁶.

9. A testing instrument as defined in claim 8, further comprising a housing having an outer wall, and a copper plate disposed in the interior of the testing instrument on the outer wall of the housing, the copper plate being connected to the amplifier circuit via a high input resistor.

10. A testing instrument as defined in claim 9, further comprising a ground electrode connected to the constant voltage source.

11. An electrical multi-purpose measuring instrument having a constant-voltage source, comprising:

a housing having an outer wall;

a device for detecting alternating electromagnetic fields, said device including a copper plate disposed in the interior of the multi-purpose measuring instrument on the outer wall of the housing;

an amplifier circuit connected to the copper plate via a high input resistor and having an amplification factor of at least 10⁶, and an LED connected to the constantvoltage source of the measuring instrument and controlled by the amplifier circuit.

12. A testing instrument as defined by claim 11, wherein a ground electrode is connected to the constant-voltage source.

13. A testing instrument for detecting alternating voltages in mains and alternating electromagnetic alternating fields in the vicinity of voltage-carrying conductors, said instrument comprising:

test prod means for probing said mains and the vicinity around said voltage-carrying conductors;

amplification means coupled to said test prod means for receiving and amplifying a signal received from said test prod means;

amplification reduction means coupled to said test prod means and said amplification means for reducing the amplification of said signal when said test prod means probes said mains; and

indicator means coupled to said amplification means for indicating the reception of said signal.