JPH09145658A - Noise suppressing method in damage monitoring system in burried pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the damage of a burried pipe by the excavating blade of an excavator securely without the effect of noises. SOLUTION: In this system, a monitoring AC signal, which is applied on a burried pipe 2 at a transmitting part, is received by a receiving part 12 separated from the transmitting part 11, and the damage of the burried pipe is monitored by the change in received voltage. The monitoring AC signal has the constitution so as to include a plurality of frequency components. At the same time, the monitoring of the change in received voltage is performed for each frequency component. The damage of the burried pipe is detected by the decreases of all the received voltages of a plurality of the above described frequency components. The monitoring AC signal can be the signal including a plurality of the frequency components at the same timer can be the signal, wherein a plurality of the frequency components are arranged in a time series, or can be the signal, wherein these methods are combined. By the means described above, the decrease in received voltage caused by the damage of the burried pipe can be securely detected so as to distinguish the decrease from the voltage decrease caused by noises.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise suppressing method in a damage monitoring system for a buried pipe.

[0002]

2. Description of the Related Art In excavation work, a buried pipe may be damaged by an excavating machine, and various systems have been proposed for monitoring this. As one of the conventional systems for monitoring such damage to the buried pipe, an AC signal for monitoring is applied from the transmitter to the buried pipe to be monitored, and the AC signal for monitoring is received by a remote receiver. Then, there is a monitoring system that detects the occurrence of damage to the buried pipe from the decrease in the received voltage.

This monitoring system is shown, for example, in a schematic diagram as shown in FIG. Reference numeral 1 is a transmitter, and this transmitter 1
At, a monitoring AC signal is applied to the buried pipe 2. The monitoring AC signal is, for example, 225H, 525 from the range of 200 to 2500 Hz.
A suitable frequency such as Hz or 2025 Hz is selected, and the voltage is appropriately set and applied in the range of 1.0 to 4.0 V according to the installation environment of the buried pipe.

Reference numeral 3 denotes a receiver installed at a position appropriately separated from the transmitter 1, for example, a position of the buried pipe 2 separated by 2 to 3 km, and the monitoring AC signal transmitted from the transmitter 1 is received by the receiver 3. It is received at and is monitored by the fluctuation of the received voltage (effective value).

That is, in the excavation work currently being carried out between the transmitting section 1 and the receiving section 3, if the conductive excavating blade 5 of the excavating machine 4 damages the insulating coating of the buried pipe 2, the damaged portion will be damaged. Is grounded through the excavating blade 5, the impedance of this portion is lowered and the monitoring AC signal leaks into the ground. For this reason, the reception voltage of the monitoring AC signal in the receiving unit 3 decreases, so that the damage to the buried pipe 2 can be detected by monitoring the decrease in the reception voltage.

For example, FIG. 6 shows monitoring in the receiving unit 3 when a simulated signal of damage is given by grounding one point of the buried pipe 2 between the transmitting unit 1 and the receiving unit 3 with a conductor at appropriate intervals. It shows the measurement result of the voltage level (effective value) of the AC signal for use. In addition, this measurement was performed with the frequency of the monitoring AC signal being 2025 Hz in the buried pipe 2 in which the distance from the transmitter 1 to the receiver 3 was 2.7 km.

As shown in FIG. 6, when a simulated signal of damage is given to the buried pipe, the received voltage at the receiving section becomes a normal value V ₁
From To decreases to V _2, it can be seen that can detect damage to the buried pipes by detected using the voltage drop appropriate method. For example, Japanese Patent Laid-Open No. 4-194742 discloses a method of detecting the occurrence of damage by sampling a reception voltage at every unit time and sequentially comparing the difference between voltages at adjacent sampling points with a set value. There is. For example, the sampling interval is about 0.1 seconds.

[0008]

The above-mentioned monitoring method has the following problems. When viewed as a transmission line for a monitoring AC signal, the buried pipe has a large signal attenuation at a connection portion of magnesium as a galvanic anode, a buried portion in the ground, and the like. Therefore, the distance between the transmitter and the receiver, that is, the monitorable distance is limited. The AC signal for monitoring flowing through the buried pipe is mixed with a drainer, external power, and other electrical noises, so that the received voltage fluctuates greatly as shown in FIG. 7, and pulses due to these noises occur. There is a risk of mistakenly recognizing that a temporary voltage drop will cause damage to the buried pipe. In excavating machines, especially boring machines, the ground resistance value at the time of damaging the insulating coating of the buried pipe may be large.In this case, the voltage drop of the receiving part due to damage will also be small, so this voltage drop is due to noise There is a possibility that the damage cannot be detected because it is buried in the fluctuation. The present invention has been made in view of the above points, and it is an object of the present invention to prevent erroneous detection of damage due to a voltage drop caused by noise.

[0009]

In order to solve the above-mentioned problems, according to the present invention, the monitoring AC signal applied to the buried pipe in the transmitting unit is received by the receiving unit remote from the transmitting unit, and the received voltage In the system for monitoring the damage of the buried pipe due to the change, the monitoring AC signal is configured to include a plurality of frequency components, and the change of the reception voltage is monitored for each frequency component, and all of the plurality of frequency components are monitored. We propose to detect the damage of the buried pipe due to the decrease of the received voltage.

According to the present invention, in the above structure,
The monitoring AC signal is configured to include multiple frequency components at the same time, multiple frequency components are arranged over time, or a portion containing multiple frequency components is arranged over time with different frequency components. You can

According to the present invention, when a plurality of frequency components are arranged with time, the monitoring AC signal is alternately switched to a plurality of preset frequencies with time, and the frequency is changed stepwise. Multiple frequency components can be arranged over time.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram conceptually showing a damage monitoring system for a buried pipe to which the present invention is applied. The same components as those in FIG. 5 described above are designated by the same reference numerals and duplicate description will be omitted. . Reference numeral 11 denotes a transmitter, and the transmitter 11 is configured to apply a monitoring AC signal including a plurality of frequency components to the buried pipe 2 as described in detail later. Further, reference numeral 12 is a receiver installed at a position appropriately separated from the transmitter 11, for example, a position of the buried pipe 2 separated by 2 to 3 km as described above, and the receiver 12 is, as described in detail later, This is a configuration in which a monitoring AC signal including a plurality of frequency components is received, and monitoring is performed by fluctuations in the received voltage (effective value) thereof.

In the first embodiment, the transmitter 11 is configured to apply an AC signal containing a plurality of frequency components simultaneously to the buried pipe 2 as a monitoring AC signal. In FIG.
By the notation that a plurality of (three in the embodiment) oscillators as AC signal sources are connected in parallel to the transmitting unit 11, a plurality of AC signals of different frequencies f ₁ , f ₂ and f ₃ are generated at the same time and the buried pipe is used. 2 shows a configuration in which the voltage is applied to 2. These frequencies are, for example, 300 Hz, 52 Hz from the range of 200 to 2500 Hz described above.
Like the combination of 0Hz, 1025Hz, etc., set each frequency separately.

Corresponding to the frequency components of the monitoring AC signal applied from the transmitter 11 to the buried pipe 2, the receiver 12 is configured to be able to measure the received voltage for each of these frequency components.
In FIG. 1, a plurality of receivers 12 (three in the embodiment) are provided.
The measurement units V ₁ , V ₂ and V ₃ are connected in parallel to represent the configuration for measuring the reception voltage of the AC signals of a plurality of different frequencies f ₁ , f ₂ and f ₃ . In the configuration of such an embodiment, each measuring unit V ₁ , V ₂ , V ₃ is provided with a filter means for passing only the corresponding frequency component.

FIG. 2 shows an operation example in the above-described embodiment, in which the transmitting section 11 simultaneously and continuously transmits alternating signals of _three different frequencies f ₁ , f ₂ and f ₃ to the buried pipe 2. A monitoring AC signal is applied to the buried pipe 2 and the receiving AC signal received by the receiving unit 12 is a measuring unit V corresponding to each of the AC signals of _three different frequencies f ₁ , f ₂ , and f _3.
Measure the received voltage of each frequency component with ₁ , V ₂ and V ₃ . Needless to say, the receiving unit 12 performs analog pre-processing such as lock-in measurement processing and appropriate signal processing such as analog or digital filter processing at appropriate places. Further, the applied voltage of the AC signals of the respective frequencies f ₁ , f ₂ , and f ₃ may be set to be the same, or may be different in advance in consideration of the frequency characteristic of the buried pipe 2 as the transmission path of the AC signals.

As shown in FIG. 2, in the AC signal of frequency f ₁ , the received voltage is greatly reduced at the time points t ₁ , t ₂ , and t ₃ , but in the AC signal of frequency f ₂ , the time points t ₁ , At t ₃ , the reception voltage drops significantly, but at time t
_No significant decrease in the received voltage is seen in 2. In AC signal of a frequency f ₃ is greater reduction of reception voltage at the time of any point t _1, t ₂ are not observed, a large reduction of only the reception voltage at time t ₃ can be seen.

When the buried pipe is damaged by the digging blade and is grounded, the drop in the received voltage of the monitoring AC signal should appear for all frequency components regardless of the difference in frequency, so the receiving unit. The damage determining means at 12 assumes that the decrease in the received voltage at the times t ₁ and t ₂ is due to noise, and the time t ₃ at which the received voltages of the AC signals of all the frequencies f ₁ , f ₂ and f ₃ greatly decrease. The damage judgment output is generated only at. In order to make such a determination,
As the damage determination means in the receiving unit 12, each measuring unit
It suffices to configure a logical product means of signals corresponding to the decrease of the received voltage detected by the appropriate threshold value set in advance for each of V ₁ , V ₂ and V ₃ .

In the above-described embodiment, the number of alternating-current signals having different frequencies constituting the frequency component of the monitoring alternating-current signal is three, but it may be four or more, or in some cases, two with different frequencies. You can also do it. Further, the configuration in which the reception voltage can be measured for each frequency component of the monitoring AC signal in the reception unit 12 has a plurality of measurement units V ₁ , V ₂ , V corresponding to each frequency component as in the above embodiment. Instead of the configuration in which ₃ is provided, it is also possible to apply a configuration in which the received monitoring AC signal is subjected to processing such as FFT to obtain a spectrum and the reception voltage of each frequency component is obtained from the spectrum. In addition, in the method of generating the monitoring AC signal including a plurality of frequency components in the transmission unit 11, in addition to the configuration using a plurality of oscillators as described above, for example, an astable multivibrator or the like is used to periodically generate a plurality of frequency components. A pulse can be generated and this periodic pulse can be used as a monitoring AC signal. In this case, the receiving unit 12 includes a plurality of measuring units V ₁ , V ₂ , as described above, for a plurality of typical frequency components of a large number of frequency components of the preset periodic pulse. V ₃ , ... Is provided and configured so as to detect the drop in the received voltage by the threshold value set corresponding to each, or by providing the means for obtaining the spectrum of the monitoring AC signal as described above, It is also possible to configure to detect a decrease in the received voltage of a plurality of typical frequency components based on the spectrum.

Next, in the second embodiment, the transmitter 11 is configured to apply an AC signal having a plurality of frequency components arranged over time to the buried pipe 2 as a monitoring AC signal. Such a monitoring AC signal can be generated by alternately switching over time to a plurality of preset frequencies using a programmable oscillator with a plurality of frequencies that can be set, and changing the frequency stepwise. .

In FIG. 3, a programmable oscillator is configured in the transmitter 11, and this oscillator generates a monitoring AC signal whose frequency is sequentially switched to _three different frequencies f ₁ , f ₂ and f ₃ at each duration t. 2 schematically shows an operation example in the case where the voltage is applied to the buried pipe 2 after that. In this example, the monitoring AC signal is a signal of a cycle T (= 3 × t) in which the frequencies f ₁ , f ₂ , and f ₃ are sequentially switched at each time t, and the voltage applied to the buried pipe 2 is irrespective of the frequency. It is constant. However, in addition to this, the buried pipe 2 as a transmission line for AC signals
Of the frequencies f ₁ , f ₂ , f
The applied voltage of the AC signal of ₃ can be made different in advance. It is also possible to insert a pause time between the AC signals of the respective frequencies f ₁ , f ₂ and f ₃ .

In the embodiment shown in FIG. 3, the reception voltage of the monitoring AC signal is substantially constant in the normal state although the frequencies f ₁ , f ₂ and f ₃ are different, but at times t ₄ and t _6. , T
Are significantly reduced at _8, t _10. Analyzing the drop in the received voltage at these time points, first, the drop at time point t ₄ returns to time point t ₅ after 2t time has elapsed corresponding to frequencies f ₁ and f ₂ , and the reception of the AC signal at frequency f ₃ is received. The voltage has not dropped. The reduction in the time t ₆ is returned at time t ₇ in the duration of the frequency f ₂ t, receiving voltage of the AC signal of frequency f _1, f ₃ is not decreased. Similarly, the decrease at the time point t ₈ is restored at the time point t ₉ when the duration t of the frequency f ₃ has elapsed, and the reception voltage of the AC signals of the frequencies f ₁ and f ₂ has not decreased.

As described above, the drop in the received voltage generated at each of the times t ₄ , t ₆ and t ₈ does not occur for all frequencies f ₁ , f ₂ and f ₃ of the monitoring AC signal. The damage determination means in the receiver 12 determines that the decrease in the received voltage is due to noise.

On the other hand, the decrease in the received voltage generated at the time point t ₁₀ continues at the time point t ₁₁ when the period T of the monitoring AC signal elapses, that is, the received voltage decreases at all frequencies f. Since the damage occurs at ₁ , f ₂ , and f ₃ , the damage determining means in the receiving unit 12 detects the earliest time point t ₁₁ at which it can detect that the decrease in the received voltage has passed the cycle T, or the detection method. A damage determination output is generated at an appropriate time thereafter.

As a first example of the damage determining means for obtaining such a determination output, a timer that measures the elapsed time from the time when the decrease in the received voltage is detected, and the time measured by this timer is the cycle T And means for determining whether or not the value has exceeded. Further, as a second example, the frequency at the time of detecting the decrease in the received voltage is obtained by the spectrum analysis or the like, the flag for each frequency is turned on for one cycle T, and the flag corresponding to all frequencies is set. It can be configured by means for determining that the ON states have been completed by a logical product means.

The monitoring AC signal is configured to include a plurality of frequency components as described in the first and second embodiments above, and a plurality of frequency components are combined to form a plurality of frequency components in the third embodiment. It is also possible to arrange the portions that simultaneously include the frequency component of 1) with different frequency components and to arrange them over time. That is, FIG. 4 shows an example of such a monitoring AC signal, which uses a square wave containing a large number of frequency components and generates square waves of different periods T ₁ , T ₂ , T _3. The monitoring AC signals having the cycle T (= T ₁ + T ₂ + T ₃ ) are arranged sequentially with time.

When such a monitoring AC signal is used, the damage determination methods applied in the receiving section 12 are appropriately combined with the monitoring AC signals of the first and second embodiments, respectively. Focusing on a plurality of typical frequency components among a large number of frequency components included in the square wave having the periods T ₁ , T ₂ , and T ₃ , damage is caused at the time when all the received voltages of these frequency components are reduced. It is possible to generate the judgment output of.

As described above, the decrease in the received voltage of the monitoring AC signal when the buried pipe is damaged by the digging blade and grounded appears in all frequency components regardless of the difference in frequency, but noise is generated. In view of the fact that the decrease in the received voltage due to the above does not appear for all frequency components, the present invention monitors the change in the received voltage for each frequency component in the receiving unit, and decreases the received voltage for all frequency components. In that case, even if the damage occurs or the received voltage drops, if not all frequency components, it can be determined as noise.

[0028]

As described above, according to the present invention, the monitoring AC signal applied to the buried pipe in the transmitter is received by the receiver remote from the transmitter, and the damage of the buried pipe is monitored by the decrease of the received voltage. In the system, the monitoring AC signal contains multiple frequency components, and if all the received voltages of these multiple frequency components drop, it is determined to be damaged, so the drop in received voltage due to damage is caused by noise. There is an effect that the damage can be surely determined by distinguishing from the above.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration example of a buried pipe damage monitoring system to which the method of the present invention is applied.

FIG. 2 is a schematic diagram showing a damage determination operation in the first embodiment of a monitoring AC signal.

FIG. 3 is a schematic diagram showing a damage determination operation in a second embodiment of a monitoring AC signal.

FIG. 4 is a schematic diagram showing a third embodiment of a monitoring AC signal.

FIG. 5 is a schematic diagram showing a configuration example of a conventional buried pipe damage monitoring system.

FIG. 6 shows the measurement results of fluctuations in the received voltage level of the monitoring AC signal in the receiver when a damage simulation signal is applied to the buried pipe in the system of FIG.

FIG. 7 is a diagram showing a case where trains are frequently operated during the daytime and drainers are frequently operated in the system of FIG.
7 shows the measurement result of the voltage level of the monitoring AC signal in the receiving unit.

[Explanation of symbols]

 1,11 transmitter 2 buried pipe 3,12 receiver 4 excavator 5 excavator 6 drainer

Claims (5)

[Claims] 1. An AC signal for monitoring applied to a buried pipe in a transmitter is received by a receiver distant from the transmitter,
In the system for monitoring the damage of the buried pipe by the change of the reception voltage, the monitoring AC signal is configured to include a plurality of frequency components, the change of the reception voltage is monitored for each frequency component, A noise suppression method in a damage monitoring system for a buried pipe, characterized in that damage to the buried pipe is detected by a decrease in received voltage for all 2. The method for suppressing noise in a damage monitoring system for a buried pipe according to claim 1, wherein the monitoring AC signal includes a plurality of frequency components at the same time. 3. A noise suppression method in a damage monitoring system for a buried pipe according to claim 1, wherein a plurality of frequency components are arranged with time in the monitoring AC signal. 4. The noise in the damage monitoring system for a buried pipe according to claim 1, wherein the monitoring AC signal is arranged such that a portion containing a plurality of frequency components at the same time has different frequency components and is arranged over time. Suppression method 5. The monitoring AC signal is characterized by alternately switching to a plurality of preset frequencies over time, and arranging a plurality of frequency components over time by changing the frequency stepwise. A noise suppressing method in the damage monitoring system for a buried pipe according to claim 3 or 4.