JPH0216461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for monitoring liquid leakage in the event of a liquid leakage accident, and more specifically, the present invention relates to a device for monitoring liquid leakage when a liquid leakage accident occurs. The present invention relates to a liquid leakage monitoring device that uses a liquid leakage detection cable whose width changes and is capable of measuring the leakage width of the liquid.

In order to detect liquid leakage accidents from liquid transport pipes, storage tanks, and their auxiliary equipment (hereinafter referred to as liquid transport pipes, etc.), for example, oil spill accidents from oil pipelines and tanks, infiltration of the liquid being handled or The TDR method uses a detection cable whose characteristic impedance changes due to penetration, and periodically injects pulses from one end of the cable to observe the reflection from within the cable.
A liquid leakage monitoring device that applies reflectionmetry is used. In such devices, when a liquid leakage accident such as oil occurs, the detection cable is immersed in the leaked liquid and the characteristic impedance of the leaked part changes, causing reflections at that part when the pulse propagates. By injecting a pulse from the observation end and measuring the time it takes for this pulse to reflect back at the oil leak point, it can be calculated from the pulse propagation speed of the detection cable, which is known through prior measurement. The distance from the pulse input end to the leak point can be measured.
However, the reflected waveform of the pulse signal from the liquid leakage part is a combination of reflections at the start and end points of the cable's characteristic impedance change, and the waveform is further distorted due to the propagation characteristics of the cable before reaching the observation point. It was difficult to find out.

In view of the above-mentioned problems, the purpose of the present invention is to focus on the fact that the propagation speed of pulses changes in the characteristic impedance changing portion of the detection cable, and to detect the occurrence of a liquid leakage accident by using a liquid leakage monitoring device that applies the TDR method. Based on the concept of measuring the width of liquid leakage by measuring the difference in pulse propagation speed between the current state and the accident-free state, the width of liquid leakage can be measured relatively easily.

The present invention involves laying a liquid leak detection cable whose characteristic impedance changes due to infiltration of leaked liquid from a liquid transport pipe, etc. along the pipe, and injecting a pulse signal from one end of the cable to detect the pulse signal. In a device that monitors leakage in a pipe or the like using reflected waves, the cable includes a terminating resistor that reflects a pulse signal incident on the cable at the other end, and a terminating resistor that reflects the pulse signal incident on the cable by the terminating resistor. It is characterized by comprising means for measuring the leakage width by measuring the difference between the reciprocating time and the similar reciprocating time when there is no infiltration by the leaked liquid.

The present invention will be explained using mathematical formulas as follows.

Let L be the total length of the cable, l be the width of liquid leakage, and V be the pulse propagation speed of the detection cable in a normal state without leakage. Furthermore, when the detection cable is immersed in liquid, the liquid permeates into the insulator, changing the effective dielectric constant of the insulator and changing the characteristic impedance.
At the same time, the pulse propagation speed also changes. This speed change starts from the start of immersion, gradually increases, and follows a process of asymptotic to a constant value Vc, but since this can be measured experimentally in advance, it is expressed as a function v(t). Then, the time T ₁ for a pulse to travel back and forth along the entire length of the cable without leakage is: T ₁ = 2L/V − (1) Time for a pulse to travel back and forth along the entire length of the cable after t time has elapsed since leakage occurred. T ₂ is T ₂ = 2 (L-l/V+l/v(t)) - (2) Therefore, the difference ΔT between the leakage time and the normal state in the time it takes for the pulse to travel back and forth along the entire cable length is ΔT = T ₂ -T ₁ = 2 {L-l/V+l/v(t)-
L/V}=2l(1/v(t)-1/V)-(3) Therefore, l=ΔT/2(1/v(t)-1/V)-(4) Here, v (t) and V can be known in advance by actual measurement or calculation, so if ΔT is measured by a liquid leakage monitoring device, the liquid leakage width l can be determined from the above equation (4).

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 schematically shows an oil pipeline leak monitoring device according to an embodiment of the present invention. This device is TDR
A similar conventional leak monitoring device that digitally processes the reflected waveform according to the law can be used. In the figure, 1 is a pulse generator, and a control device 2
A pulse is applied to a detection cable 3 laid along an oil pipeline (not shown) according to the command. Reference numeral 4 indicates a section where the characteristic impedance of the cable 3 changes due to oil infiltration, and the pulse is reflected at both ends of this section. Reference numeral 5 denotes a terminating resistor, which is normally provided to match the characteristic impedance of the cable to prevent reflection at the terminal end, but in the present invention, reflected waves from this part are required.
Use one with a different value from the characteristic impedance to obtain a sufficient reflected waveform. The reflected wave within the cable or at the end returns to the pulse input end, is amplified by an amplifier 6, and is sent to a sample-and-hold circuit 7.
The level is fixed, converted into a digital value by the A/D converter 8, and read into the control device 2. In this device, the reflected waveform over the entire length of the cable can be collected as a digital value by repeating the above operation while gradually increasing the time from pulse input to sample hold.

FIG. 2 shows the sample values collected in the apparatus shown in FIG. 1 continuously as solid lines, where a indicates the case where there is no leakage and b indicates the case where there is leakage.
10 is a reflected wave from the leakage section, and 9 is a reflected wave from the terminating resistor. The difference in pulse waveform propagation time in the leakage section appears at the end as ΔT. By reading this ΔT, the leakage width l can be measured using the above-mentioned equation (4) and the known values v(t) and V. Furthermore, by observing the change in ΔT over time, it is also possible to calculate the rate of expansion of the leakage width l. If v(t) cannot be determined accurately because the leakage start time is unknown, v(t) = Vc (constant) after a certain period of time, so
Calculation can be performed using Vc after that time has elapsed.

Although petroleum was mainly used as an example of the liquid in the explanation above, it goes without saying that the present invention can be implemented in the same manner with other liquids other than petroleum.

As described above, according to this method, the liquid leakage width can be easily and accurately measured.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an oil pipeline leak monitoring device according to an embodiment of the present invention, and FIG.
The figure shows pulse reflection waveforms observed with the apparatus of FIG. 1 in cases a when there is no liquid leakage and cases b when there is leakage of liquid. DESCRIPTION OF SYMBOLS 1...Pulse generator, 2...Control device, 3...Detection cable, 4...Oil leakage part, 5...Terminal resistor, 6...Amplifier, 7...Sample and hold circuit, 8...
A/D converter.

Claims (1)

[Claims] 1. A liquid leak detection cable whose characteristic impedance changes due to infiltration of leaked liquid from a liquid transport pipe, etc. is laid along the pipe, etc., and a pulse signal is input from one end of the cable, and the reflected wave of the pulse signal is detected. In a device for monitoring leakage of the pipe, etc.,
A terminating resistor that reflects a pulse signal incident on the cable at the other end, the time it takes for the pulse signal incident on the cable to be reflected by the terminating resistor and travel back and forth along the cable, and a similar situation when there is no infiltration by the leaked liquid. A leak monitoring device comprising means for measuring a leak width by measuring a difference from a round trip time.