JP2956917B2 - Ultrasonic detection and position detection method and device for cable defect - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus used to detect cable defects such as breaks in insulation.
In particular, the present invention relates to a method and an apparatus using ultrasonic wave propagation for detecting a cable defect.

[0002]

BACKGROUND OF THE INVENTION Monitoring cables, wires, etc. for defects that cannot be determined by visual inspection is important in some industries, particularly in the nuclear power and aerospace industries. In these and other applications, large volumes of cables are frequently used, and these cables are generally accessible, but in the form of coils, loops, etc. Inspection is usually difficult. Therefore, without moving or separating cables,
Furthermore, there is a great need for an apparatus and method for inspecting such cables while maintaining the cables in operation.

One conventional method developed by the Applicant uses ions generated by a high piezoelectric field, in which case the ion source is substantially directed at the cable under test. In addition, sensing conductors are used that are located close to the cable under test. For example, US Pat. No. 4,891,5
No. 97 describes that the current flowing through the sensing conductor due to ions from the ion source varies depending on the presence of defects in the cable insulation.

[0004] Other conventional methods for detecting cable defects are also known. According to a typical method among them,
A high voltage generator is attached to one end of the cable and the cable is moved across the acoustic detector to obtain an indication of a break or defect. In this technique, a corona, arc, spark or other electrical discharge is induced at the defect location and such dielectric breakdown is detected by either an acoustic pickup or VHF (ultra high frequency) detection. Problems with this method include, as is well known, the danger of using high voltages, the risk of cable damage, and the inability to move cables in many situations. Accordingly, there is a great need for an efficient method and apparatus for inspecting accessible cables, wires, etc. to detect the presence of a rupture or defect condition and its exact location.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for detecting faults and defects in cables and their locations, which is efficient and, in some applications, for industrial applications. It is an object of the present invention to provide an apparatus and a method that can be implemented without cutting a used cable.

In order to achieve the above-mentioned object, according to the present invention, there is provided an apparatus and method for detecting a defect in a cable actually used in an industrial application and for locating the defect. Provided. The apparatus includes an ultrasonic source that emits an ultrasonic signal that is coupled to a cable at one or more defects. In one embodiment of the invention, the ultrasound source may be an omni-directional ultrasound source, and in another embodiment, the ultrasound emitted from the ultrasound source may be substantially Can be focused. The cable to which the invention applies is characterized in that metal wires or strips capable of acoustically coupling sound waves without contact extend along the length of the cable.
By moving the ultrasonic source along the cable, efficient coupling of acoustic waves is achieved, even for small gaps or the like in the coating of the electrical cable. An acoustic transducer is placed at the end of the cable to receive and detect the combined transmitted acoustic signal, and an electronic transducer is used to time the sound waves traveling from the defect to the end of the cable. Timing means is provided. This makes it possible to detect the position of the defective portion.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus and method of the present invention are directed to industrial applications where cable defects need to be detected. In many such industrial applications, the cable is an electrical cable, but the invention is equally applicable to other types of cables and similar structures. Such cables are generally in the form of one or more wires and are characterized by having a metal conductor covered by a sheath or other coating, in which case the integrity of the coating is is important. If the cable breaks or becomes defective, the metal is exposed and the acoustic signal can be coupled to the metal. Sound waves in air have a strong property of coupling to surface waves (Rayleigh waves) or Lamb waves in metal. The effective coupling is greatest within a relatively narrow range of angles of incidence, i.e., within about 6 degrees from the normal to the cable surface.
Thus, when the ultrasonic or acoustic source is moved past a defect or opening in the cable coating, acoustic coupling occurs. If the cable is a straight single-wire cable, the break can be physically detected at the position of the sound source when the signal is detected at the end of the cable. Further, if the cable is wound in a coil shape and the position of the sound source is unclear when determining the position of the defect, the position of the defect with respect to the strip length of the cable is determined from the occurrence of the pulse of the sound source. It can be determined by measuring the elapsed time or progress time until the leading edge of the received signal reaches the receiving transducer. Of course, the running time in the air between the sound source and the strip must also be considered. Furthermore, it is necessary to block the direct path in the air between the sound source and the receiving transducer in order to avoid measurement indications of errors.

One preferred embodiment of the device of the present invention is shown in FIG. The cable 30 may be an inner metal strip or wire (metal portion) surrounded by an insulating coating or sheath 34
32 are shown. Defects or breaks in the coating are indicated by reference numeral 35 where the metal strips or wires in the cable are exposed. Defect sizes are exaggerated for illustrative purposes.

A transmission transducer (signal or ultrasonic source means) 36, which is an acoustic source or acoustic transmitter, is moved along or near the cable so that the acoustic signal is substantially incident on the defect. And the acoustic signal 37 is transmitted to the end of the cable coupled to the metal strip, where the acoustic signal 37 is detected by a receiving transducer (ultrasonic detection means) 38 acoustically coupled to the end of the cable. Can be. Of course, if the location of the transducer can be uniquely associated with a location on the cable, it is possible to simply identify or identify the location of the defect. However, the transmitting transducer 36 may be an omni-directional transmitter that transmits incident acoustic energy to a wide variety of cable locations that are typically wired in a maze in industrial applications. In fact, the transmitting transducer 36 couples the acoustic signal to the cable imperfections encountered in certain applications. Alternatively, the transmitting transducer 36 can include a focusing cavity 39 for focusing the direction of the sound waves from the spark gap 52.

In practice, in many applications,
The sound source is moved along the cable while the transducer detects whether a signal has been detected. If the sound source is moved at a relatively low speed, the detection of the signal can be associated with the position of the sound source that directly approximates the defective portion.
However, it is also possible to transmit an additional acoustic signal after slightly altering the position of the acoustic source in order to accurately identify the exact location of the defect on the cable. If the cable is in coil form, the location of the acoustic source may be uncertain with respect to locating the defect. In this case, reliable detection is achieved by using a time measuring circuit. Also, where possible, individual loops of the coil may be acoustically separated and isolated to determine the location of the defect.

The remaining elements of FIG. 1 constitute an electronic processor that measures distance and provides an indication thereof. A timing circuit 40 is provided for generating a sharp timing signal or trigger signal that is coupled to the transmission pulse generator 41. When pulse generator 41 is triggered, pulse generator 41 applies a drive pulse to transducer 36 to generate a sound wave, preferably having a sharp leading edge, as described below. At the same time, the trigger signal is
6 is also applied. The time difference circuit comprises a conventional time measuring circuit or a time measuring circuit for measuring a time interval. The timing circuit starts timing in response to reception of the trigger signal, and stops timing when an input signal is received at another terminal. The trigger signal is also provided to a gate circuit 42, which is preferably a multivibrator that generates an enabling signal coupled to a signal conditioning circuit 44. The enable signal from gate circuit 42 is a signal that enables processing of the signal from receive transducer 38 during a predetermined time interval or window following the generation of the trigger signal. The signal conditioning circuit preferably comprises an amplifier, a filter and a detector or peak detector to provide an indication as to the reception of the transmitted acoustic signal and its magnitude. The output of the signal conditioning circuit can be coupled to a signal monitor 48 for directly monitoring the received signal. The output of the signal conditioning circuit 44 is also coupled to a comparator 45 that compares its amplitude to a predetermined threshold. If the signal amplitude exceeds the threshold, this means a reliable detection of a defect, where the comparator produces an output that is coupled to a time difference circuit 46 to stop timing. On the other hand, the output of the time difference circuit is coupled to a distance indicator 47. The distance indicator 47 gives an indication of the distance at the video terminal or the like and thus the position of the defect. Here, in determining the position of the defect, the transmission time in the air from the transmission transducer 36 to the defect must be taken into consideration. This can be accomplished by an operator making adjustments according to the approximate distance of the transmit transducer 36 from the cable.

Referring now to FIG. 2, there is shown a typical spark gap generation circuit for generating a spark and an associated acoustic pulse. High pressure (typically 1.5-2 KV)
Power supply 51 energizes an RC circuit, shown as R ₁ , C ₁ . As is known, the pulse repetition rate depends on R ₁ , C ₁ and the gap breakdown voltage. A voltage dividing circuit composed of resistors R ₂ and R ₃ is connected in parallel with the capacitor C _1, and a trigger output for starting time measurement or time measurement is obtained at a terminal between R ₂ and R _3. . Spark gap 52 is provided in parallel with the R ₂ and R _3. The spark gap produces an acoustic wave front with a sharp leading edge with a very short rise time. This is beneficial to the device of the present invention in that the detection will be accurate. Sparks are an effective source of sound, where air expands rapidly and creates wave crests in the medium it constitutes. However, other types of acoustic sources can be utilized, as described below. In practice, it has been found that a spark sound source is an effective sound source when it is located within a range of about 1 to 6 inches (about 2.5 cm to 15 cm) from a defective portion of the cable. Can also. The received signal exhibits a clearly recognizable envelope linearity, which allows reliable detection.

In applications where the use of a spark acoustic source is unsuitable or where a more controllable or direct acoustic source is desired, an electroacoustic transducer is the preferred acoustic source. In applications where a wire at the center of the cable is available at the receiving end, a receiving transducer can be coupled to the wire to receive the acoustic waves, as shown in FIG. For this purpose, the metal strip 56 is folded around the wire 32 and pressed against the wire, forming a robust mechanical and acoustic coupling. Receiving transducer 5
4 may be coupled to a strip 56, although not shown, a coupling force may be applied between the top of the transducer 54 and the bottom of the strip 56. However, it should be noted that the acoustic coupling need not be by direct metal contact, but any suitable detection means can be used to detect the sound waves reaching the end of the cable. Further, the term "end of cable" as used herein can be understood as any point on the cable for receiving an acoustic signal coupled to the cable at a spaced apart point.

The present invention is particularly useful for inspecting wires and cables that are repeatedly bent in an aerospace environment such as an aircraft door. It is also useful for hole detection and location in protective coatings that are important for keeping moisture out. The position of such a hole or a defective portion may have a two-dimensional property when a plate or a sheet material is used instead of a wire. The method and apparatus of the present invention can also be used in a submerged arrangement, in which case the acoustic source (other than the spark) and the receiving transducer can be used without direct contact with the cable or wire. , Can be combined by a liquid.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a basic device for ultrasonic detection and location of cable defects according to the present invention.

FIG. 2 is a basic circuit diagram of a spark gap ultrasound source that can be used in implementing the apparatus and method of the present invention.

FIG. 3 is a perspective view schematically illustrating an example of a method of connecting a receiving transducer to a wire of a cable in applying the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 30 cable 32 wire (metal part) 34 exterior 35 defective part 36 transmitting transducer (signal source or ultrasonic source means) 37 acoustic signal 38 receiving transducer (ultrasonic detecting means) 40 timing circuit (distance measuring means) 44 signal adjusting circuit ( Distance measuring means) 45 Comparator (distance measuring means) 46 Time difference circuit (distance measuring means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 29/00-29/28 G01M 3/24

Claims (2)

(57) [Claims] 1. A cable having a metal portion extending along a length of a cable, the metal portion usually being covered with an insulating material such as an armor, and a metal portion being detected at a defective portion of the cable at a point to be detected. A method for ultrasonically detecting and locating a substantially exposed defect in the cable, the method comprising: a) generating an acoustic signal using a signal source; and b) applying the acoustic signal to a portion of the cable. Transmitting along the length of the cable and continuously transmitting the light to be incident on the cable, and during the traveling process, causing the acoustic signal to be incident on the defect; and c) sound at a certain length end of the cable. C) detecting the presence of a signal acoustically; d) determining the distance from the defect to the edge by measuring the transmission time of the acoustic signal from the defect to the edge. Section ultrasonic detection and position detection Law. 2. A cable having a metal portion extending along a length of the cable, the metal portion usually being covered with an insulating material such as an armor, and the metal being substantially removed at a defective portion of the cable at a point to be detected. A device for detecting and detecting a position of a defect of the cable by ultrasonic waves which is exposed to the outside, comprising: a) an ultrasonic source for emitting the ultrasonic signal so that the ultrasonic signal is incident on the defect portion; Means; b) ultrasonic detecting means acoustically coupled to an end of the cable for detecting an acoustic signal; c) connected to the ultrasonic source means and the ultrasonic detecting means. A distance measuring means for determining a position of the defective portion by measuring a distance from the defective portion to an end of a certain length of the cable when the ultrasonic source is located close to the defective portion; Inspection of defective cable Out
Position finder.