CN105736953A - Pressure sensing based liquid ammonia pipeline leak detection system with cladding layer and detection method - Google Patents

Abstract

The invention discloses a liquid ammonia pipeline leakage detection system with a coating layer based on pressure induction and a method thereof. Including cladding device, pressure sensor, cable, liquid ammonia pipeline and data processing system; the cladding device is wrapped around the periphery of the liquid ammonia pipeline, and an independent airtight chamber is set in the cladding device, and a pressure sensor is installed in the airtight chamber. When a leak is sent somewhere in the pipeline, the pressure sensor detection signal is sent to the data processing system, and the data processing system calculates and analyzes the leaking part. The system also has a self-inspection unit, which is used to detect line faults and ensure the normal operation of the system. The principle of the working circuit of the invention is simple, and the circuit is in an open circuit state when no leakage occurs, which improves the safety of the system. At the same time, two valid data, the length of the single cable and the resistance value of the pressure sensor resistance sheet, can be measured when leaking, and the long-distance liquid ammonia pipeline can be monitored by processing fewer sensor numbers.

Description

A leak detection system and method for a liquid ammonia pipeline with a cladding layer based on pressure sensing

technical field

The invention relates to the research field of leakage detection of liquid ammonia pipelines, in particular to a leakage detection system and method for a liquid ammonia pipeline with a cladding layer under unconventional conditions based on pressure induction.

Background technique

In recent years, with the rapid development of my country's social economy, cold storage has been widely used in people's daily life as a tool for storing food and some special products. As a refrigerant (code R717) in the refrigeration system of cold storage, its thermodynamic properties are the best among all refrigerants, and it is currently the most widely used medium-temperature and medium-pressure refrigerant. In my country's large and medium-sized cold storage refrigeration systems, the use of ammonia as a refrigerant accounts for more than 80%.

Measuring gas parameters based on pressure sensing is a safe and efficient measurement technique. It exhibits different measurement modes depending on the gas physical properties. However, when the working environment is a liquid ammonia pipeline with a coating, the traditional pressure detection faces a more embarrassing situation. Through the design of the detection circuit and the improvement of the pressure sensor, relying on computer technology, the problem that the traditional pressure sensor cannot be measured has been overcome, and at the same time, real-time monitoring can be completed in the case of leakage of the liquid ammonia pressure pipeline with the coating and positioning.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention proposes a pressure-sensing-based leakage detection system and method for a liquid ammonia pipeline with a cladding layer.

A pressure-sensing-based liquid ammonia pipeline leakage detection system with a cladding layer includes a cladding device, a pressure sensor, a cable, a liquid ammonia pipeline, and a data processing system;

The cladding layer device is wrapped around the periphery of the liquid ammonia pipeline, and the cladding layer device includes a cladding layer, an isolation member, and a support member, and the isolation member is arranged between the cladding layer and the liquid ammonia pipeline, and the cladding layer and the liquid ammonia pipeline The space between the pipes is divided into airtight chambers isolated from each other, and support members are installed between the isolation members to ensure the free flow of gas in the airtight chambers;

The cable includes several first solenoid valves, resistors connected to the first solenoid valves, connecting wires, and a control switch connected to the pressure sensor; the first solenoid valves are controlled by the data processing system;

A pressure sensor and a control switch connected to the sensor form a pressure sensor unit, a first solenoid valve and a resistor connected to it form a self-test unit, and each airtight chamber is equipped with a pressure sensor unit and a self-test unit. unit,

The data processing system includes a pc, an ammeter, a stabilized power supply, a second solenoid valve, and a third solenoid valve;

All the pressure sensor units are connected in parallel, and the pressure sensor units connected in parallel are connected in series with the ammeter, the stabilized power supply, and the third solenoid valve to form a circuit; the self-test unit and the pressure sensor unit in the same airtight chamber are connected in parallel connected, one end of the second solenoid valve is connected to the stabilized power supply, and the other end is connected to the control switches of all pressure sensor units and the first solenoid valve;

The pc is connected with the ammeter, the regulated power supply, the second solenoid valve, the third solenoid valve and all the first solenoid valves.

Preferably, the pressure sensor includes a shell., a rubber sheet., a resistor sheet., an electric wire, and two metal sheets. The electric wire is in close contact with the shell. It is divided into two strands, and the two strands are respectively Connected with two metal sheets, the rubber sheet is in seamless contact with the shell, and makes the sensor have a certain pressure of gas inside. The inner side of the rubber sheet is in close contact with the resistance sheet, the outer side of the rubber sheet is exposed in the airtight chamber, and there is a distance between the resistance sheet and the metal sheet.

Preferably, the resistors in the different pressure sensor units have different resistances, and the resistors in the different self-checking units have different resistances.

Preferably, the connecting wire is a three-core wire, and the first solenoid valve has two terminals connected to the neutral wire and the live wire on the cable respectively.

Preferably, one strand of the electric wire is connected to two strands of the connecting wire, and the other strand of the electric wire is connected to the remaining strand of the connecting wire.

The shell is made of non-combustible material, the middle of the shell is hollow, the protruding part of the upper part of the shell is seamlessly connected with the electric wire, and a part protrudes from the inside of the shell, so that the electric wire goes deep into the inside;

The rubber sheet is tightly bonded to the inside of the casing, and the gas containing a certain pressure is isolated from the inside of the casing, and the inside of the rubber sheet is tightly connected to the resistance sheet;

The stabilized power supply provides a stable voltage for the entire monitoring circuit;

The second electromagnetic valve receives a signal from the computer system when the circuit is connected, so that the valve is closed to provide protection for the system to measure the second set of data;

The ammeter measures the size of the two currents passing through the circuit when the circuit is connected, so as to provide a basis for the computer system to analyze the leakage situation;

The computer system receives the statistical data from the ammeter, and calculates the type and position of the pressure sensor that is active according to the set calculation program, and at the same time issues a warning to the staff.

The detection method of the liquid ammonia pipeline leakage detection system comprises the following steps:

Step 1. After the liquid ammonia pipeline leaks, the internal high-pressure liquid ammonia will be released from the leak point quickly and gasified, causing the pressure inside each independent airtight chamber to rise;

Step 2. Under the action of high-pressure gas, the pressure sensor deforms the rubber sheet and drives the resistance sheet to rise gradually until it touches the upper metal sheet, that is, the control switch in the pressure sensor unit is closed, so that the pressure sensor where the pressure sensor is located The circuit connection path of the sensor unit, taking the conduction of the first pressure sensor unit as an example, that is, the circuit connection path of "regulated power supply-ammeter-third solenoid valve-resistor sheet 1-control switch 1-regulated power supply", The distance between the resistor sheet and the metal sheet in the pressure sensor can be determined according to the following calculation method:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; )</span>}$

In the formula: h-the distance between the pressure sensor resistance sheet and the metal sheet;

S-area of pressure sensor rubber sheet;

ΔP- pressure sensor working pressure change value;

P ₀ - the initial pressure value of the pressure sensor;

n - the amount of gaseous substance in the pressure sensor;

k-correction factor;

R - gas constant;

T - absolute temperature;

Step 3. Under the action of the regulated power supply, the resistance sheet inside the pressure sensor will cause the line to generate a specific current value I ₁ , the current value I ₁ is measured by the ammeter and sent to the PC, and then the PC controls the second electromagnetic The valve works, so that the connection line between the regulated power supply and the pressure sensor is connected in parallel to a same connection line. Due to the internal resistance of the connection line, the current transmission in the circuit changes, and the current value I ₂ is generated, and the current value I ₂ is determined. The ammeter measures and sends to the PC;

Step 4. Different current values are collected by the PC, and the installation distance L of the pressure sensor in the circuit and the resistance value R _i of the sensor resistor sheet are calculated according to the magnitude of the current. Since each pressure sensor is connected with the data processing system (5) The cable lengths between them are different, and the resistance value of each pressure sensor is not painful, so that the position of the pressure sensor of the leaking airtight chamber can be determined, and the monitoring personnel can be warned, and the reasoning can be simplified.

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

The calculation method is:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula: R _i - the resistance value of the resistance sheet of the pressure sensor, i takes 1, 2...n;

U- the voltage of the regulated power supply;

I ₁ - the current value of the circuit before the solenoid valve does not work;

I ₂ - the current value of the circuit after the solenoid valve works;

L-the installation distance L of the pressure sensor in the working circuit;

S-The cross-sectional area of the cable;

ρ-resistivity of the cable;

Step 5. When the current values I ₁ and I ₂ are uploaded to the PC, the PC sends an instruction to the third solenoid valve located in the main circuit of the circuit, and the third solenoid valve disconnects the circuit, so that the system is in a non-energized state to ensure leakage In the end, there will be no hidden danger of accidents. After the technicians repair the liquid ammonia pipeline, the third solenoid valve will be restored to the original state through the PC;

Step 6. The computer sends instructions to the first solenoid valves located on the cables inside the cladding layer, so that all the first solenoid valves work successively from near to far to check the integrity of the circuit. After confirming that the circuit is intact, the system is in the detection state again.

Compared with the prior art, the present invention has the following advantages:

(1) In the present invention, the independent airtight cavity formed by the isolation cladding layer outside the liquid ammonia pipeline can enhance the effect of heat insulation.

(2) The pressure sensor invented in the present invention, as the terminal sensor of the monitoring system, has the advantages of simple manufacture, sensitive reflection, and different resistance characteristics, which is convenient for making different types of pressure sensors.

(3) The principle of the working circuit of the present invention is simple, and the circuit is in an open circuit state when no leakage occurs, which improves the safety of the system. At the same time, two valid data, the length of the single cable and the resistance value of the pressure sensor resistance sheet, can be measured when leaking, and the long-distance liquid ammonia pipeline can be monitored by processing fewer sensor numbers.

(4) The present invention utilizes computer system, can realize real-time data processing and warning in time, and is convenient for the statistic work of liquid ammonia pipeline leakage situation data.

(5) The present invention uses a common cable as a signal transmission line, and at the same time, a device for detecting whether the cable is damaged can ensure the monitoring effect and facilitate daily maintenance work.

Description of drawings

Fig. 1 is a schematic diagram of a liquid ammonia pipeline leakage detection system of the present invention;

Fig. 2 is a schematic diagram of a working principle circuit in the present invention;

Fig. 3 is a structural schematic diagram of a pressure sensor in the present invention;

Fig. 4 is a schematic diagram of layout of liquid ammonia pipeline leakage detection elements in the present invention

Fig. 5 is a flowchart of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figures 1-4, the pressure-sensing-based liquid ammonia pipeline leakage detection system with a coating layer of the present invention includes a coating device 1, a pressure sensor 2, a cable 3, a liquid ammonia pipeline 4 and a data processing system 5;

The cladding device 1 is wrapped around the liquid ammonia pipeline 4, and the cladding device 1 includes a cladding layer 1.1, an isolation member 1.2, and a support member 1.3, and the isolation member 1.2 is arranged between the cladding layer 1.1 and the liquid ammonia pipeline 4 The space between the cladding layer 1.1 and the liquid ammonia pipeline 4 is divided into mutually isolated airtight chambers, and a support member 1.3 for ensuring the free flow of gas in the airtight chamber is installed between the isolation members 1.2;

The cable 3 includes several first solenoid valves 3.1, resistors connected to the first solenoid valves 3.1, connecting wires, and control switches connected to the pressure sensor 2; the first solenoid valves 3.1 are controlled by the data processing system 5 controls;

A pressure sensor and a control switch connected to the sensor form a pressure sensor unit, a first solenoid valve 3.1 and a resistor connected to it form a self-test unit, and each airtight chamber is equipped with a pressure sensor unit and a self-checking unit. inspection unit,

Described data processing system 5 comprises pc machine 5.1, ammeter 5.2, voltage stabilized power supply 5.3, second solenoid valve 5.4, the 3rd solenoid valve 5.5;

All the pressure sensor units are connected in parallel, and the pressure sensor units connected in parallel are connected in series with the ammeter 5.2, the stabilized power supply 5.3, and the third electromagnetic valve 5.5 to form a circuit; The device units are connected in parallel, one end of the second solenoid valve 5.4 is connected to the stabilized power supply 5.3, and the other end is connected to the control switches of all pressure sensor units and the first solenoid valve 3.1 respectively;

The pc 5.1 is connected with the ammeter 5.2, the stabilized power supply 5.3, the second solenoid valve 5.4, the third solenoid valve 5.5 and all the first solenoid valves 3.1.

Preferably, the pressure sensor 2 includes a shell 2.1, a rubber sheet 2.2, a resistance sheet 2.3, an electric wire 2.4 and two metal sheets, and the electric wire 2.4 is in close contact with the shell 2.1 and is divided into two strands, two strands They are respectively connected with two metal sheets, and the rubber sheet 2.2 is in seamless contact with the shell 2.1, and makes the sensor have a certain pressure of gas inside. The inner side of the rubber sheet 2.2 is in close contact with the resistance sheet 2.3, the outer side of the rubber sheet 2.2 is exposed in the airtight chamber, and a distance is set between the resistance sheet 2.3 and the metal sheet.

Preferably, the resistors 2.3 in the different pressure sensor units have different resistance values, and the resistors in the different self-test units have different resistance values.

Preferably, the connecting wire is a three-core wire, and the first solenoid valve 3.1 has two terminals connected to the neutral wire and the live wire on the cable 3 respectively.

Preferably, one strand of the electric wire 2.4 is connected to two strands of the connecting wire, and the other strand of the electric wire 2.4 is connected to the remaining strand of the connecting wire.

The pc 5.1 can upload data and issue instructions with the ammeter 5.2, the second solenoid valve 5.4 and the third solenoid valve 5.5.

The ammeter 5.2 is located on the main circuit of the circuit and can measure the magnitude of the current in the circuit.

The stabilized power supply 5.3 can provide stable voltage for the whole monitoring system.

The second solenoid valve 5.4 and the third solenoid valve 5.5 complete the circuit opening and breaking actions according to the instructions of the PC.

As shown in Figure 5, a pressure-sensing liquid ammonia pipeline leak detection system with a coating layer, the specific working principle includes the following steps:

Step 1. After the liquid ammonia pipeline leaks, the internal high-pressure liquid ammonia will be released from the leak point quickly and gasified, causing the pressure inside each independent airtight chamber to rise;

Step 2. Under the action of high-pressure gas, the pressure sensor will deform the rubber sheet and drive the resistance sheet to rise gradually until it touches the upper metal sheet, that is, the control switch in the pressure sensor unit is closed, so that the pressure sensor where the pressure sensor is located The circuit connection path of the sensor unit, taking the conduction of the first pressure sensor unit as an example, that is, the circuit connection path of "regulated power supply-ammeter-third solenoid valve-resistor sheet 1-control switch 1-regulated power supply", The distance between the resistor sheet and the metal sheet in the pressure sensor can be determined according to the following calculation method:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; .</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; )</span>}$

In the formula: h-the distance between the pressure sensor resistance sheet and the metal sheet;

S-area of pressure sensor rubber sheet;

ΔP- pressure sensor working pressure change value;

P ₀ - the initial pressure value of the pressure sensor;

n - the amount of gaseous substance in the pressure sensor;

k-correction factor;

R - gas constant;

T - absolute temperature;

Step 3. Under the action of the regulated power supply, the resistance sheet inside the pressure sensor will cause the line to generate a specific current value I ₁ , the current value I ₁ is measured by the ammeter and sent to the PC, and then the PC controls the second electromagnetic The valve works, so that the connection line between the regulated power supply and the pressure sensor is connected in parallel to a same connection line. Due to the internal resistance of the connection line, the current transmission in the circuit changes, and the current value I ₂ is generated, and the current value I ₂ is determined. The ammeter measures and sends to the PC;

Step 4. Different current values are collected by the PC, and the installation distance L of the pressure sensor in the circuit and the resistance value R _i of the sensor resistor sheet are calculated according to the magnitude of the current. Since each pressure sensor is connected with the data processing system (5) The cable lengths between them are different, and the resistance value of each pressure sensor is not painful, so that the position of the pressure sensor that leaks the airtight air chamber can be determined, and a warning is issued to the monitoring personnel. The calculation method is simplified by reasoning as follows:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula: R _i - the resistance value of the resistance sheet of the pressure sensor, i takes 1, 2...n;

U- the voltage of the regulated power supply;

I ₁ - the current value of the circuit before the solenoid valve does not work;

I ₂ - the current value of the circuit after the solenoid valve works;

L-the installation distance L of the pressure sensor in the working circuit;

S-The cross-sectional area of the cable;

ρ-resistivity of the cable;

Step 5. When the current values I ₁ and I ₂ are uploaded to the PC, the PC sends an instruction to the third solenoid valve located in the main circuit of the circuit, and the third solenoid valve disconnects the circuit, so that the system is in a non-energized state to ensure leakage In the end, there will be no hidden danger of accidents. After the technicians repair the liquid ammonia pipeline, the third solenoid valve will be restored to the original state through the PC;

Step 6. The computer sends instructions to the first solenoid valves located on the cables inside the cladding layer, so that all the first solenoid valves work successively from near to far to check the integrity of the circuit. After confirming that the circuit is intact, the system is in the detection state again.

Claims (6)

1. the liquefied ammonia pipeline leakage checking system with clad based on pressure sensitive, it is characterised in that include clad device (1), pressure inductor (2), cable (3), liquefied ammonia pipeline (4) and data handling system (5)；

It is peripheral that described clad device (1) is wrapped in liquefied ammonia pipeline (4), clad device (1) includes clad (1.1), insulating element (1.2), supporting member (1.3), insulating element (1.2) is arranged between clad (1.1) and liquefied ammonia pipeline (4), space between clad (1.1) and liquefied ammonia pipeline (4) is divided into mutually isolated sealed gas chamber, the supporting member (1.3) for ensureing free flow of gas in sealed gas chamber is installed between insulating element (1.2)；

Described cable (3) includes resistance that several first electromagnetic valves (3.1) are connected, connecting line and the control switch being connected with pressure inductor (2) with the first electromagnetic valve (3.1)；Described the first electromagnetic valve (3.1) is by the control of data handling system (5)；

One pressure transducer and the control switch being connected with this sensor constitute a pressure inductor unit, one the first electromagnetic valve (3.1) and coupled resistance constitute a self-test unit, one pressure inductor unit and a self-test unit are installed in each sealed gas chamber

Described data handling system (5) includes pc machine (5.1), ammeter (5.2), regulated power supply (5.3), the second electromagnetic valve (5.4), the 3rd electromagnetic valve (5.5)；

Described all pressure sensor unit are connected in parallel, and the pressure sensor unit after being connected in parallel and ammeter (5.2), regulated power supply (5.3), the 3rd electromagnetic valve (5.5) are connected into loop；The described self-test unit in same sealed gas chamber and pressure inductor unit are connected in parallel, one end of described the second electromagnetic valve (5.4) is connected with regulated power supply (5.3), and the other end switchs with the control of all of pressure sensor unit respectively and the first electromagnetic valve (3.1) is connected；

Described pc machine (5.1) is connected with ammeter (5.2), regulated power supply (5.3), the second electromagnetic valve (5.4), the 3rd electromagnetic valve (5.5) and all of first electromagnetic valve (3.1).

2. the liquefied ammonia pipeline leakage checking system with clad based on pressure sensitive according to claim 1, it is characterized in that described pressure inductor (2) includes shell (2.1), sheet rubber (2.2), resistor disc (2.3), electric wire (2.4) and two sheet metals, described electric wire (2.4) and shell (2.1) close contact, it is divided into two strands, two strands are connected with two sheet metals respectively, described sheet rubber (2.2) is seamless with shell (2.1) to be contacted, and makes the gas having certain air pressure inside induction apparatus.Sheet rubber (2.2) inner side and resistor disc (2.3) close contact, sheet rubber (2.2) outside is exposed in sealed gas chamber, is provided with distance between resistance sheet (2.3) and sheet metal.

3. the liquefied ammonia pipeline leakage checking system with clad based on pressure sensitive according to claim 1, it is characterized in that the resistance of resistor disc (2.3) in described different pressure inductor unit is different, the described resistance in different self-test unit is different.

4. the liquefied ammonia pipeline leakage checking system with clad based on pressure sensitive according to claim 1, it is characterized in that described connecting line is triple core wire, the first electromagnetic valve (3.1) has two lugs zero line on cable (3) to be connected with live wire.

5. the liquefied ammonia pipeline leakage checking system with clad based on pressure sensitive according to claim 2, it is characterized in that a described strand of electric wire (2.4) is connected with two strands of connecting line, one remaining with connecting line of another strand of electric wire (2.4) is connected.

6. the detection method of liquefied ammonia pipeline leakage checking system as described in any one of claim 1-5, it is characterised in that comprise the following steps:

After step 1, liquefied ammonia pipeline leak, the liquefied ammonia of internal high pressure can discharge from leakage point rapidly and the pressure within the sealed gas chamber causing each independent that gasifies rises；

Step 2, pressure inductor are under the effect of gases at high pressure, sheet rubber produces the dynamic resistor disc of deformation band and is gradually increasing until contacting with the sheet metal on top, the i.e. switch of control in pressure sensor unit Guan Bi, so that the circuit ON path of this pressure inductor place pressure inductor unit, in pressure inductor, the distance between resistor disc and sheet metal can be determined according to method calculated as below:

$h=k\frac{nRT}{S}.\frac{\mathrm{\&Delta;}P}{P_0(P_0+\mathrm{\&Delta;}P)}$

In formula: the distance between h-pressure inductor resistor disc and sheet metal；

The area of S-pressure inductor sheet rubber；

The change value of pressure of Δ P-pressure inductor work；

P₀The force value that-pressure inductor is initial；

The amount of gaseous matter in n-pressure transducer；

K-correction factor；

R-gas constant；

T-absolute temperature；

Step 3, under the effect of regulated power supply, the resistor disc within pressure inductor can make circuit produce specific current value I₁, current value I₁Recorded by ammeter and be sent to pc machine, then pc machine controls the second electromagnetic valve work so that connecting line between regulated power supply with pressure inductor in parallel upper one just as connecting line, owing to connecting line exists internal resistance, make electric current in circuit send change, produce current value I₂, current value I₂Recorded by ammeter and be sent to pc machine；

Step 4, different current values are collected by pc machine, and the size according to electric current calculates the mounting distance L of pressure transducer in circuit and the resistance R of induction apparatus resistor disc_iOwing to the length of cable between each pressure transducer from data handling system (5) is different, and the resistance of each pressure transducer is not bitterly, may thereby determine that the position occurring to reveal the pressure inductor of sealed gas chamber, and monitoring personnel are given a warning, by its computational methods of reasoning abbreviation it is:

$L=\frac{2S}{\mathrm{\&rho;}}(\frac{U}{I_1}-\frac{U}{I_2})$

$R_i=4\frac{U}{I_2}-3\frac{U}{I_1}$

In formula: R_iThe resistance value of-pressure inductor resistor disc, i takes 1,2....n；

The voltage of U-regulated power supply；

I₁-electromagnetic valve do not work before the current value that passes through of circuit；

I₂The current value that after-electromagnetic valve work, circuit passes through；

The mounting distance L of pressure transducer in L-operating circuit, the i.e. length of cable between pressure transducer and power supply；

The sectional area of S-cable；

The resistivity of ρ-cable；

Step 5, as current value I₁And I₂When being uploaded to pc machine, pc machine sends instruction to the 3rd electromagnetic valve being positioned at circuit main line, 3rd electromagnetic valve disconnecting circuit, make system be in no power state thus ensure leak after will not produce accident potential, after technical staff repairs liquefied ammonia pipeline, by pc machine, the 3rd electromagnetic valve is returned to original state；

The first electromagnetic valve that step 6, computer are pointed on clad inside cable sends instruction, allows all first electromagnetic valves gradually work from proximal and distal, checks the integrity of circuit, and after confirming that circuit is intact, system is in detection state again.