JPS5938537B2 - Leak detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid leakage detection device, and particularly to a leakage detection device suitable for early detection of leakage and local identification of leakage locations in piping systems using heat insulating materials. Regarding.

Leakage detectors include methods that utilize changes in resistance or capacitance when a leak occurs, but capacitance type detectors that utilize changes in capacitance are particularly useful for early leakage detection in pipes wrapped with heat insulating material. It is valid.

FIG. 1 shows the principle of a known capacitive leak detection device.

The pipe 2 through which the fluid 1 flows is used as an inner electrode, and the outer electrode 4 is provided on the outside of the heat insulating material 3 wrapped around the pipe.
and form a capacitor 6. 5 and 5' are detection terminals taken out from the piping 2 side and the exterior electrode 4 side, respectively.

Here, regarding the capacitance Cl (F/m) of the capacitor 6, the following formula holds true: Cl22πε/log(b/
a) ...... (c) However, ε: Dielectric constant of the substance existing between the electrodes a: Outer diameter of the pipe b; Inner diameter of the external electrode If there is no leakage, ε is the dielectric constant of the material existing between the electrodes. dielectric constant,
Its value is relatively small.

On the other hand, when cracks 7 occur in the piping near the electrodes and fluid begins to leak 8 from this portion into the heat insulating material, the dielectric constant increases. Therefore, by detecting an increase in capacitance, leakage can be detected at an early stage when fluid penetration has not yet appeared on the surface of the heat insulating material and has already penetrated inside the heat insulating material. Here, in order to constantly monitor the presence or absence of leakage, it is necessary to automatically measure the capacitance Cl of the capacitor 6, but conventionally,
A self-balancing AC bridge was used for this purpose.

FIG. 2 shows the configuration of a self-balancing AC bridge.

The capacitor 6 of the piping section mentioned above is connected to the bridge circuit 10 via the detection terminals 5, 5'. Cs is the capacitance of a standard capacitor, and R1 and R2 are resistances. The unbalanced output voltage V of the bridge circuit 10 is amplified by an amplifier 12, and a component V1 having the same phase as the voltage E of the AC power source 11 is separated by a phase detector 13. This V1 is the servo amplifier 1
The resistor R2 is adjusted by the servo motor 15 via the servo motor 4 to adjust it to V1-O. If the servo motor is stable and 1=O is established, then CL is established from equation (2).

The above self-balancing AC bridge is suitable for precision measurements, but
It has the following drawbacks.

The first drawback is that it includes mechanical parts such as servo motors and has a complex overall structure, making it prone to failure and expensive.

The second drawback is that the time it takes for the bridge output to reach zero, that is, the time it takes for the servo motor to stabilize, is from several seconds to tens of seconds.
It takes a considerable amount of time to detect leaks at the many critical points in nuclear or chemical plants, and the early leak detection feature inherent to capacitive detection methods is lost. be. In addition to the above-mentioned AC bridge method, there are other capacitance detection methods such as the resonance method, but these methods are used to measure minute changes in capacitance, and are used to measure leakage that causes large changes in capacitance. Not suitable for detection. SUMMARY OF THE INVENTION An object of the present invention is to provide a fluid leakage detection device that can easily detect everything from small fluid leaks to large fluid leaks, and can also determine the amount of leakage.

A feature of the present invention is that the width of the first pulse, which is determined based on the capacitance between the first electrode connected to the pipe and the second electrode attached to the surface of the heat insulating material of the pipe, is based on a predetermined capacitance. A leakage signal is output when the width of the second pulse is larger than the width of the second pulse determined by the width of the second pulse, and when the leakage signal is output, the amount of leakage is determined based on the difference between the time widths of the first pulse and the second pulse.
Embodiments of the present invention will be described with reference to FIGS. 3 to 5.

200 is an interrogation device, 300 is a multiplexer, P,,p
2, . . . , Pn are strip-shaped electrodes that are installed in large numbers near the welding line, for example, at points where caution is required in case of leakage of the pipe 2 wrapped with the heat insulating material 3.

Tl, T2,..., Tn are the aforementioned Pl, p2,...
......, lead wires 11, 12, ...... to Pn.
, 1n. Piping 2 is the other common electrode and is connected to each of the responders via lead wire g. The operation of this system will be explained below using the time chart shown in FIG.

First, the trigger pulse generator 20 of the interrogation device 200 is
As shown in FIG. 4, a pulse i of a constant period CM is generated.

This pulse is transmitted to multiplexer 300 via a transmission line. Now, when the multiplexer 300 has the terminal S1 selected as shown, the trigger pulse i enters the transponder T1 as i1, and the trigger pulse i enters the transponder T1 as i1.
and 42 input signals.

Although mechanical contacts are schematically shown in the multiplexer, a non-contact semiconductor element may actually be used. Furthermore, the monomultis used in 41 and 42 operate as shown in FIG.

The mono-multi element has two types of input terminals, A and B, and two output terminals, Q and Q, as shown in FIG. first,
If a trigger pulse is input to the A input terminal,
As shown in the figure, a pulse with a time width τ determined by equation (3) from the rise time of the input pulse is output to the Q output terminal. τ＝
α・RC・・・・・・・・・・・・・・・・・・
(3) However, α: proportionality constant Also, as shown in the figure, the Q terminal outputs a signal with a polarity completely opposite to the Q output.

On the other hand, when a trigger pulse is input to the B terminal, a pulse with a time width determined by equation (3) is output to the output terminal.
As shown in the figure, this differs from the A input case in that the output pulse rises when the trigger pulse falls.

Now, since the trigger pulse i1 becomes the A input in the monomulti 42, it outputs a rectangular pulse H with a time width determined by the resistor Rs and the capacitor Cs.

This h1 becomes a control signal for the switch circuit 43, turning on the switch for a predetermined period of time. As a result, the capacitor made up of the exterior electrode P1 and the pipe 2 is connected to the monomulti 41. Therefore, the monomulti 41 is B
From the fall time of the trigger pulse i1 input to the input terminal, a pulse with a time width τ determined by the resistance RL and the capacitance CL is output. Here, since RL is a fixed resistance, τ1 is always proportional to CLl. As described above, only when the transponder T1 is selected, the switch circuit 43 is turned on and the capacitance CL between the electrode Pl and the pipe 2 is converted into a pulse width. Therefore, if leakage occurs and the capacitance increases, the pulse width will also increase in proportion to this.
This pulse is transmitted to the interrogator 20 as a response signal via a transmitter circuit 44 and a transmission line γ common to each transponder.
Returned to 0. The time chart shown in FIG. 4 generally shows the operation when the transponders Tk-1, Tk, Tk+1 are sequentially selected by a multiplexer, and the response signal γ is generated in response to the interrogation signals 1k-1, ik, ik+1. ,-1
, γK, γk+, are returned.

Now, in the interrogator 200, the aforementioned trigger pulse i generated by the trigger pulse generator 20 also enters the monomulti 23, and has a time width W as shown in FIG.

A negative logic pulse p of +τo is output. This pulse width is also determined by the resistance Rp and the capacitance Cp. In addition, W.
corresponds to the pulse width of the trigger pulse i, and τo is set to be the maximum value of the γ pulse when no leakage occurs. The AND gate 24 performs a logical product of the pulse p and the response pulse γ, and only the portion of the γ pulse that exceeds the interval of the logical value "0" of p is output as a pulse d.

Here, since the response pulse γ is returned at the falling edge of the trigger pulse i), each response pulse γk−Drk γk+
The time widths τk-1, τK, and τk+1 of 1 are the above-mentioned τ at the gate 24. The pulses exceeding τo are output as d pulses. In the example of FIG. 4, γk+
, the pulse time width τk+1 is τ. The d pulse is generated at a time significantly exceeding the d pulse, indicating that leakage has occurred near the exterior electrode Pk+. This system measures the time width of the d pulse in order to determine the amount of leakage.

That is, for the d pulse, an AND gate 26 samples the clock pulses output from the clock oscillator 25 to form an e pulse group, a counter 27 counts the e pulse group, and the counted value is displayed on the display 28. I'm starting to do that. On the other hand, the identification number of the transponder that the interrogator 200 is interrogating is determined by the output value m of the counter 21 whose counting input is the trigger pulse i, and the display 2
The number value is displayed at 2. Further, at the same time, the output value m also controls the multiplexer 300. In addition, the counter 21 is one 2t.
3 la o″″″″5n? It is designed so that it can be counted in cycles like 1 2 3 3300. Therefore, by monitoring the indicators 22 and 28 in the operation room, the operator can detect leakage points at the piping site at an early stage and measure the amount of leakage, which changes from moment to moment. Note that in the response signal explained above, the information regarding capacitance is expressed by the time width of the pulse, but the response signal can be a pair of pulses, and the capacitance can be expressed and transmitted by the time interval between the two pulses. is also possible and can be easily realized by those skilled in the art.

As described above, this example has a relatively simple circuit configuration, and
Fluid leakage can be detected over a wide range from micro-leakage to large-scale leakage, and it is possible to detect leakage points and leakage amounts at many points in the piping system at an early stage.

This makes it possible to realize a highly reliable and economical leakage detection system, which can be expected to be applied to plants with a large number of piping systems, such as nuclear plants and chemical plants. According to the present invention, the width of the first pulse determined based on the capacitance between the first electrode and the second electrode is compared with the width of the second pulse determined based on the predetermined capacitance. Therefore, a wide range of fluid leaks from micro leaks to large leaks can be easily detected with a simple structure, and the amount of fluid leaks can also be easily determined.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining a conventional example, and FIGS. 3, 4, and 5 are diagrams for explaining an embodiment of the present invention.

Claims (1)

[Claims] 1. A first electrode connected to a pipe in which a fluid exists, a second electrode attached to the outer surface of a heat insulating material surrounding the pipe, a means for generating a trigger pulse, and a means for generating a trigger pulse. means for transmitting a first pulse having a width determined by a capacitance and a first resistance between the first electrode and the second electrode when the pulse is transmitted; means for transmitting a second pulse having a predetermined width determined by a capacitor; means for outputting a leakage signal when the width of the first pulse becomes larger than the width of the second pulse; and the leakage signal. When the first
A fluid leakage detection device comprising: means for determining a leakage amount based on a difference in time width between a pulse and a second pulse.