JPH0897781A - Cable search device - Google Patents

Abstract

PURPOSE: To prevent a search function from being lost even when a high voltage cable is close to a search cable by connecting a filter blocking a disturbing component of a commercial frequency and passing the search signal with a prescribed frequency between a transmitter and one end of a cable. CONSTITUTION: A filter 2 is inserted between a transmitter 1 and one-side end of search cables 4B, 4C. Through the constitution above, when the transmitter 1 sends search signals whose frequencies are respectively f1 , f2 , the signal passes through the filter 2 without loss of the filter 2 and is fed to cables 4B, 4C. The search signals f1 , f2 are received at a prescribed position of the cables 4A-4C to attain searching depending on the presence of the signal. Then an electromotive force is induced to the searching cables 4A-4C from the high voltage cable 3. The frequency component below 40Hz in the electromotive force receives a negative gain by the filter 2 and especially the commercial frequency component is substantially and completely blocked. Thus, a current based on the electromotive force is given to an output amplifier of the transmitter 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable exploration device, and more particularly to a cable exploration device which prevents a commercial frequency interference component from entering an output amplifier of a transmitter.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional cable exploration device,
It has a transmitter 1 which outputs a probe signal of f ₁ = 625 Hz and f ₂ = 875 Hz and injects into one end of the cables 4B, 4C among the probe cables 4A, 4B, 4C. The other end is short-circuited and grounded by a lead wire 5. A high voltage cable 3 in which a large current is flowing is arranged adjacent to the exploration cables 4A, 4B, 4C.

In the above cable exploration device, the exploration signals of f ₁ and f ₂ are injected from the cable transmitter 1 into the exploration cables 4B and 4C, and received at the other end by a receiving means (not shown) such as a search coil. This allows cable exploration to be performed.

[0004]

However, according to the conventional cable probe device, the electromotive force of the commercial frequency f _{D having} a large level shown in FIG. 4 is generated in the probe cables 4A, 4B and 4C by the induction from the high voltage cable 3. As a result, a disturbing current enters the output amplifier of the transmitter 1 and impairs the cable search function. According to the inventor's confirmation, when the electromotive force reaches 20V, its function is impaired, and it is necessary to suppress it to 18V or less.

[0005]

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a cable exploration device in which the exploration function is not impaired even if the high voltage cable is adjacent to the exploration cable.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a search means such as a search coil at a predetermined position of a cable for a search signal of a predetermined frequency injected from a transmitter to one end of the cable. In the cable exploration device for exploring the cable by receiving at, between the transmitter and one end of the cable, a filter for blocking the interference component of the commercial frequency and passing the exploration signal of the predetermined frequency is connected. The present invention provides a cable exploration device.

[0007]

When the filter is designed to have a gain of -50 dB at 60 Hz, even if the induced commercial frequency electromotive force reaches the level of 280 V, the insertion of the filter causes the output amplifier of the transmitter to have a voltage of 18 V or less. Suppressed and charged. As a result, the function of cable exploration can be maintained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, in which the same parts as in FIG. 3 are designated by the same reference numerals. However, the filter 2 is inserted between the transmitter 1 and one ends of the search cables 4B and 4C. The filter 2 is composed of two capacitors and one inductance, and its characteristics are
As shown in FIG. 2, it has a gain of −50 dB at 60 Hz and a gain of 0 dB in the frequency band of 400 Hz and above.

In the above configuration, when the transmitter 1 outputs the search signals of f ₁ and f ₂ , it passes through the filter 2 without loss and is injected into the cables 4B and 4C. The search signals f ₁ and f ₂ are transmitted to the cables 4A, 4
The signal is received at the predetermined positions of B and 4C, and the cable is searched depending on the presence or absence of the signal.

On the other hand, the high voltage cable 3 to the exploration cable 4
Electromotive force is induced in A, 4B, and 4C. 4 of this electromotive force
Frequency components below 00 Hz are negatively gained by the filter 2, in particular commercial frequency components are virtually completely blocked. Therefore, the current based on the electromotive force does not enter the output amplifier of the transmitter 1.

[0011]

As described above, according to the cable probe device of the present invention, since the filter for cutting off the commercial frequency component is inserted between the transmitter and the probe cable, the electromotive force is induced in the probe cable by the induction of the high voltage cable. The cable exploration function will not be impaired even if the above occurs.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a pass characteristic of the filter of FIG.

FIG. 3 is an explanatory diagram showing a conventional cable exploration device.

FIG. 4 is an explanatory diagram showing the relationship between the signal frequency of FIG. 3 and the frequency of electromotive force induced in the search cable.

[Explanation of symbols]

 1 transmitter 2 filter 3 high-voltage cable 4A, 4B, 4C display 5 short-circuit ground lead wire

Claims (1)

[Claims] 1. A cable search device for searching a cable by receiving a search signal of a predetermined frequency, which is injected from a transmitter to one end of a cable, at a predetermined position of the cable by a receiving means such as a search coil, wherein the transmitter A cable exploration device, characterized in that a filter for blocking an interference component of a commercial frequency and passing the exploration signal of the predetermined frequency is connected between one end of the cable and the cable.