RU1779961C - Vacuum system of leak detector - Google Patents

Abstract

Usage: control and measuring vacuum devices. SUBSTANCE: vacuum system contains a mechanical pump 1, a steam-oil pump 2, a nitrogen trap 4, a mass spectrometric chamber 8, vacuum valves 3, 6 and 7, temperature sensors 11 and 12, and a device for supplying heat or pneumatic flow to the cryogenic vessel 5 of the trap 4 Thermal sensors 11 and 12 are located in the lower part of the cryogenic vessel 5 at various heights, corresponding to

Description

The invention relates to vacuum technology, in particular to the design of means for testing products for leaks.

A known leak detector vacuum system comprising a mechanical pump with an inlet valve, a steam-oil pump, the output of which is connected via a line with an electromagnetic valve to the input of the mechanical pump, and a nitrogen trap with a refrigerant vessel, connected through the throttle valve to the input of the steam-oil pump, and using a bypass line with shut-off valves and a mass spectrometric camera, to the input of a mechanical pump. In addition, the system includes a line with a shut-off solenoid valve. It is connected to the cavity of the refrigerant vessel and the steam pump, and the throttle valve is equipped with an electromagnetic actuator with an adjustable switching frequency. The system is connected to the test product using an input line with a control helium flow. The invention reduces the stopping time of the leak detector by intensifying the cooling of the steam-oil pump.

However, during operation of the leak detector, when the cryoagent is evaporated, its level decreases, and the upper parts of the vessel and the vacuum wires are heated. In this case, the protective properties of the trap are degraded and the previously condensed vapors, which fall back into the pumped volume, contaminate it and worsen the vacuum from the heated surfaces. In addition, the cathode and magnetic vacuum sensor are very dirty, which leads to significant fluctuations in the readings

of the latter and large measurement errors, the contamination of the hot cathode filament can lead to burnout of the cathode. All this greatly reduces the reliability of the cathode and the magnetic vacuum sensor, reduces the time of the inter-regulation period, reduces the accuracy of measurements, significantly increases the operational and labor costs when working with the leak detector.

A known fore-vacuum cryogenic trap comprising a Dewar vessel and a pipe for passing a pumped gas is installed. along the axis of the Dewar vessel. The outer surface of the pipe is covered with a layer of porous heat-conducting material, for example, sintered bronze powder. In this invention, a layer of porous material increases the heat exchange surface of the pipe, and due to capillarity, it provides

wetting the entire pipe with refrigerant regardless of the level of refrigerant in the Dewar vessel, which increases the efficiency of the trap. However, upon evaporation of all refrigerant in the Dewar vessel, a sharp

deterioration of the protective properties of the trap, which negatively affects the functioning of devices placed in the mass spectrometer chamber of the leak detector.

Known chilled sorption

a trap containing a housing with an annular copper vessel for liquid refrigerant with an anti-migration barrier and sorbing elements placed in it, and to the lower part of the annular vessel

hermetically attached pipe coated with a layer of sorbent-catalyst, for example titanium oxide. In the absence of liquid refrigerant in the annular vessel, oil peers, migrating along the walls of the trap, fall on

the nozzle coated with a layer of sorbent catalyst is decomposed into light fractions and pumped out by a diffusion pump. However, upon evaporation of all the refrigerant in the Dewar vessel, a sharp deterioration in the protective properties of the trap occurs, which negatively affects the functional and operational characteristics of the mass spectrometric leak detector.

A device is known for cooling an element located in an evacuated volume, for example, to cool a trap of a diffusion pump, comprising means installed outside the volume and insulated with a vacuum casing; these means are connected to the cooled element so that heat can be removed from it. In addition, it comprises a heat sink connection formed by a cooling rod that is integral with the cooling medium. The heat sink connection is introduced into the volume through a tubular part extending from the evacuated casing and connected to the volume so that the vacuum volume and the casing are connected to each other. The tubular part is provided with a vacuum tight flange connecting to a similar flange on the evacuated volume. The cooling rod is made in the form of a hollow element through which the refrigerant flows. The cooling means is in the form of a storage tank for liquid refrigerant. This technical solution significantly reduces the likelihood of evaporation of the entire refrigerant in the nitrogen trap, but still does not exclude the complete emptying of the refrigerant in the Dewar vessel of the cryogenic trap, and, as a result, the pollution of the instruments of the mass spectrometric chamber,

A vacuum trap is known, comprising a housing and a refrigerant conduit located therein, on which louvers are mounted that can be rotated and connected by a drive, the latter being made in the form of a bimetallic element equipped with a heater. This technical solution allows automatically adjusting the conductivity of the trap depending on the magnitude of the vacuum in the system. However, by completely emptying the Dewar vessel of the cryogenic trap, the mass spectrometric chamber is not completely cut off from volatile contaminants desorbed from the trap surfaces, which leads to pollution and damage to the instruments of the mass spectrometric chamber.

A known system for automatic control of a vacuum installation containing

the inlet and outlet controlled valves of a diffusion pump with a heater and a pressure sensor located on the forevacuum pipe, made radiometric and connected to the recording, signaling and command equipment for influencing the valves, the pressure sensor being installed in the zone of the diffusion pump and equipped with

a clip with slots and an infrared receiver associated with command equipment for acting on the inlet valve. This technical solution allows monitoring the operation of the unit by suppression, cooling water flow and power supply through one channel, which generally increases the reliability of the control system. However, this technical solution does not provide and does not imply

protecting the evacuated volume, in particular the mass spectrometric chamber, from the contaminating surfaces of the trap in the event of complete evaporation of the refrigerant.

The closest in technical essence analogue is a leak detector vacuum system containing a mass spectrometric chamber, a steam booster pump, a rotary vane pump, seven valves, a calibrated helium leak, and nitrogen

trap, vacuum sensor and thermocouple gauge transmitter. In this system, upon evaporation of the cryoagent with a decrease in its level, the upper parts of the vessel and the vacuum wires are heated. Wherein

the protective properties of the nitrogen trap are degraded and de-condensation from the heated surfaces of previously condensed vapors, which fell back into the pumped volume, pollute the devices

mass spectrometric camera. As a result, the reliability of the cathode, the magnetic vacuum sensor, the inter-period, the measurement accuracy decrease, and the operational

expenses,

The aim of the invention is to increase the reliability of the cathode of the magnetic vacuum sensor of the mass spectrometric chamber, increase the time of the intergovernmental period and the accuracy of measurements. In addition, the aim of the invention is also to increase the reliability of controlling the drying of the nitrogen trap after the end of the work and its automation, and to reduce the costs and save the life of the compaction system during vacuum drying of the nitrogen trap.

The goal is achieved by the fact that the known vacuum system of the leak detector,

containing a mechanical pump with an inlet clap JM, a steam-oil pump, the output of which is connected via a line with a direct solenoid valve to the input of the mechanical pump, a nitrogen trap with a refrigerant vessel, connected through a throttle valve to the input of the steam-oil pump, mass spectrometer The Richs chamber, connected through a second electromagnetic valve to a nitrogen trap, and with the help of a bypass line with a shut-off element to the input of a mechanical pump, is equipped with at least two temperature sensors, in the lower part of the refrigerant vessel at different heights, the first thermal sensor at the warning level, the second at the critical level, and attached to the vessel wall using brackets made of diamagnetic heat and moisture insulation material, the first recording and signaling equipment and the first command equipment for influencing the second solenoid valve and power supply system of the cathode and magnetic vacuum sensor, and each of the temperature sensors consists of a permanent magnet, a sensitive element nta in the form of a magnet envelope made of ferromagnetic material with a Curie point close to the boiling point of the refrigerant and a magnetically controlled contact reed switch mounted inside the corresponding bracket, contact reed switches of both temperature sensors are connected to the recording and signaling equipment, and the contact reed switch of the second the temperature sensor is connected to the first command equipment. In addition, it is equipped with a switching device for supplying heat or pneumatic flow to the refrigerant vessel, tertiary, a temperature sensor mounted on the bottom of the refrigerant vessel, and connected to it by a second recording apparatus and a second command apparatus for acting on the switching device, and the second thermal sensor is also connected to second command equipment. In this case, the leak detector vacuum system is equipped with a blocking device for the pressure pumping system and a third command apparatus for influencing the blocking apparatus, and the third temperature sensor and the steam jet pump vacuum sensor are connected to the third command apparatus.

The essence of the invention consists in preliminary signaling and subsequent automatic cutting off of the mass spectrometric chamber volume from the rest of the vacuum system of the leak detector and the cathode’s power supply is interrupted, as well as the magnetic vacuum sensor, while the refrigerant level in the cryogenic vessel decreases below the permissible level. In addition, the essence

The invention also consists in automatically stopping the heating of the trap upon evaporation of all the refrigerant and then turning on the blocking of the pressure pumping system, which is triggered after the working pressure of the steam jet is restored.

Comparative analysis with the prototype allows us to conclude that the design of the vacuum system of the leak detector additionally contains at least two temperature sensors located in the lower part of the cryogenic tank at various heights corresponding to the level

warning and critical level, attached to its wall by means of brackets made of diamagnetic heat and moisture insulation material, the sensitive elements of which are made in

in the form of shells enclosing permanent magnets, and the shells are made of ferromagnetic material with a Curie point close to the boiling point of a cryogenic liquid, and magnetically controlled contact reed switch is mounted inside each bracket, one of which is connected to recording and signaling equipment, the other - with recording, signaling and command equipment

act on the electromagnetic valve located between the mass spectrometric chamber and the nitrogen trap, as well as on the power supply system of the cathode and the magnetic vacuum sensor. In this way,

The claimed technical solution meets the criterion of novelty.

A technical solution is known for the design of an automatic control system for a vacuum unit. In this design, the operation mode of the installation is monitored by pressure, flow rate of cooling water and power supply through a single channel, which generally increases the reliability of the system. However, this scheme of protecting the vacuum chamber (mass spectrometric chamber) from contaminants is ineffective in the case of evaporation of the refrigerant in cryogenic

vessel traps and warming its freezing walls. The flow of substances that are condensed from the walls of the trap at the initial moment does not significantly change the pressure in the vacuum chamber, but significantly pollutes the main working elements

a mass spectral camera, namely an ion source and an ion receiver. The ion source contains a cathode, an ionizer box, and a diaphragm. The ion receiver comprises an input diaphragm, a suppressor consisting of two grids and an ion collector. The contamination of the surfaces of the main working elements of the mass spectrometer chamber leads to significant errors in measuring the background, the occurrence of fluctuations in the measurement of pressure by a magnetic vacuum sensor, the formation of oil cracking films on the surfaces of the main working elements, the failure of the cathode, ion receiver, and vacuum sensor, intergovernmental period. With an increase in the flow of decondensable substances in the vacuum chamber, the pressure will change and then the automatic control system of the vacuum unit (6) will interfere with the operation of the system. However, by this time a significant negative impact on the main working elements of the mass spectrometric chamber will already be provided. The claimed technical solution eliminates these drawbacks by monitoring the minimum permissible amount of refrigerant in the cryogenic vessel, ensuring the normal freezing and holding effect of pollutants during the pumping process and the active intervention of the control system during the pumping process of the mass spectrometric chamber and the functioning of the main operating elements contained therein in the event of a decrease in the amount of refrigerant below the minimum acceptable level. Thus, on the basis of the analysis of known technical solutions in the studied area, the solution can be recognized as meeting the criterion of Significant differences.

The drawing shows a diagram of a vacuum system leak detector.

The leak detector vacuum system contains a mechanical pump 1 with an inlet valve, a steam-oil pump 2, the output of which is connected via a line with an electromagnetic valve 3 to the input of the mechanical pump 1, a nitrogen trap 4 with a refrigerant vessel 5, connected through a throttle valve 6 to the steam inlet oil pump 2 and through the solenoid valve 7 to the mass spectrometer chamber 8, and using the bypass line 9 with a shut-off valve 10 and the mass spectrometer chamber 8 to the input of the mechanical pump 1, two temperature sensors 11 and 12, located at the lower part of the cryogenic tank at various heights corresponding to the warning level about the need to replenish the cryogenic product in the nitrogen trap for the latter to function normally and at a critical level at which the nitrogen trap is not able to freeze out liquid vapor and hold it qualitatively condensate previously accumulated on the freezing surface. Temperature sensors 11 and

0 12 are attached to the wall of the cryogenic vessel 5 by means of brackets 13 of diamagnetic heat and moisture insulating material. Sensitive elements of temperature sensors are made in the form of shells

5 to 14, covering the permanent magnets 15, wherein the shells 14 are made of a ferromagnetic material with a Curie point close to the boiling point of the cryogenic liquid. Inside each bracket

0 11 a magnetically controlled contact reed switch 16 is mounted, one of which is connected to the recording equipment 17 and signaling 18, the other to the recording 17, signaling 18 and command 19

5 by means of the latter, it acts on the electromagnetic valve 7 located between the mass spectral chamber 8 and the nitrogen trap 4. In addition to acting on the electromagnetic valve 7, the command cn0 device 19 also affects the power supply system 20 of the cathode 21 and the power supply system 22 of the magnetic vacuum sensor 23. Thus, in block 19 there are three command equipment: command equipment for acting on the electromagnetic valve 7, command equipment for influencing the Osk system; - feeding 20 of cathode 21 and command RPPZ - Rural impact on s.ch: heme

0 power supply 22 is a vacuum sensor 23. In addition, the vacuum system leaks., The boiler contains an additional temperature sensor 24 installed in the bottom of the cryogenic vessel 5 of the trap 4. It is connected to the registration 5, signaling 18 and command equipment for influencing commutation. a thermal device 25 for supplying heat or pneumatic flow to the cryogenic vessel of the trap, while thermal command 12 installed at a critical level is also connected with the command action on the ohm-m device 25; Tor-modatchmk 24, installed by the z.-p. gene vessel 5 trap -t as well

5, the vacuum gauge 26 of the steam-jet cartridges is connected to the command apparatus 27 by influencing the interlock 28 of the pressure pumping system. Interlock 28 s & .hz mon with time relay 29. The time relay switches the power supply system of the mechanical pump 1.

The liquid nitrogen simulator 30 in trap 4 is connected to command equipment 19. The inlet valve 31 communicates with the mass spectrometer camera with the test object. Command device 32 is associated with recording equipment 17 and signaling equipment 18.

The vacuum leak detector system operates as follows.

After evacuation of the volume of the vacuum pump 1 to the operating pressure, the unit for simulating liquid nitrogen in the cryogenic vessel 5 is turned on at a level that exceeds the warning level. Next, the steam-oil pump 2 is pumped out. After pump 2 is pumped out, the heater of the latter is turned on. After heating the steam jet pump 2 through the valve 6, the volume of the nitrogen trap 4 is pumped to a predetermined pressure measured by the sensor 26. Then, liquid nitrogen is poured into the cryogenic vessel 5 of the nitrogen trap 4 and the simulated liquid nitrogen block 30 in the trap 4 is turned off. After cooling the nitrogen trap 4 the electromagnetic valve 7 is opened and the mass spectrometric chamber 8 is evacuated. During the evacuation of the chamber 8, a magnetic vacuum sensor 23 is turned on and after reaching the working pressure in the chamber, the ion is heated th source. After the set emission current has been set, the inlet valve 31 is opened, connecting the leak detector vacuum system to the test object of the cryogenic vessel 5.

In the presence of liquid nitrogen in the cryogenic vessel 5, the sealed contacts of the sensors located below the liquid level are open, since the magnetic fluxes Ph created by the permanent magnets 15 are shielded by the ferromagnetic shells 14 of these magnets, locking their field lines. In order to open the reed contacts, a minimum force of attraction must be applied to them.

Federal Law

  2fio a b

where fio is magnetic constant, equal to 4 lx 107G / m:

a - the length of the overlap springs, m;

b is the width of the springs, m;

Фз - magnetic flux in the gap (in the web pax).

The contacts are kept open under the action of an elastic force directed opposite to the force of magnetic attraction

where X is the gap between the rings of undeformed springs, m;

x-working gap between the springs at

their deformation during operation, m;

S is the stiffness of each spring, N / m2. During operation of the leak detector, as the liquid nitrogen evaporates from the cryogenic vessel 5, the temperature sensor may be above the liquid level. In this case, the sensitive element of the temperature sensor 11 is a shell 14, covering a constant

magnet 15 will begin to heat up quickly. When passing through the Curie point, the material of the shell 14 begins to possess the property of paramagnets and is diamagnetic. The sealed contacts of the sensor 11 are closed. This condition is explained as follows. The magnetic flux Фп created by the permanent magnet 15, penetrating the shell 14, reacts with the reed switch 16. Due to the appearance of a magnetic flux of sufficient power for

lock the contacts of the reed switch 16, the free ends of the springs approach each other, the equilibrium state Fm Fy occurs, which corresponds to the magnetic flux

0

5

Фз о а b S (X - х).

After the magnitude of the gap decreased from X to x under the influence of the increased magnetic field H, the springs continue to approach each other without a critical gap N. To ensure reliable operation of the reed switch and greater sensitivity, it is advisable that the working induction B ft / S be less the saturation induction Bs, a, the coefficients ai and E2 in the expressions Bi Ф1 / 5 а 1 Bs and В2 Фг / S а 2 Bs were within 0.75 ai 0.9; 0.6 32 0.75.

Thus, after the contacts of the reed switch of the temperature sensor 11 are closed, an electrical signal is supplied to the command device 32 for influencing the recording equipment 17 and signaling device 18. When receiving signals from equipment 17 and 18, the operator pours liquid nitrogen into the trap. When nitrogen is evaporated in the cryogenic vessel 5 to a critical level, the contacts of the reed switch of the temperature sensor 12 are triggered, an electrical signal is issued to the command device 19. The command device 19 directs the effect of closing the electromagnetic valves 7 and 31, to the power supply system 20 of the cathode 21c

in order to de-energize it, to the power supply system 22 of the magnetic vacuum sensor 23 in order to turn it off. After the solenoid valve 7 has been activated, the electric closing signal is transmitted to the electro-pneumatic valve 25 and only after receiving the action from the command device 19 does the electro-pneumatic valve 25 installed on the supply line of the pneumatic flow into the cryogenic vessel 5 of the trap 4 automatically open. closing the electromagnetic valve 7. After the heating of the nitrogen trap 4 in the vacuum cavity between the cryogenic vessel and directly the outer walls of the nitrogen trap 5 begins the process of increasing the pressure, which is detected by the vacuum sensor 26. After reaching a certain pressure limit and receiving a signal about the complete absence of liquid nitrogen in the cryogenic vessel 5 from the temperature sensor 24, the command equipment 27 directs the effect of closing the pressure lock 28 on the pumping system . After all the condensate has evaporated from the freezing surface of the cryogenic vessel and is removed by the pumping system, the pressure in the vacuum cavity of the nitrogen trap will begin to decrease. At a certain pressure in the vacuum cavity corresponding to the working pressure in the vacuum system without liquid nitrogen in the blocking trap 28, it gives a command to close the electrovalve 6 and then turn off the steam-oil pump heater 2. After turning off the pump heater 2, the block 28 will turn on the timer 29. After the time required to cool the body of the steam-oil pump 2 has passed, the relay will turn off the mechanical pump 1. The leak detector is automatically stopped.

Thus, the proposed device can significantly increase the reliability of the cathode and the magnetic vacuum sensor, increase the time of the inter-control period of the leak detector, increase the accuracy of measurements, simplify the process of stopping the leak detector by the operator.

Claims (3)

SUMMARY OF THE INVENTION 1. A vacuum leak detector system comprising a pump with an inlet valve, a steam-oil pump, the output of which is connected via a line with the first solenoid valve to the inlet of the mechanical pump, a nitrogen trap with a refrigerant vessel, connected through the throttle valve to the inlet of the steam-oil a pump, a mass spectrometric chamber connected through a second electromagnetic valve to a nitrogen trap, and using a bypass line with a shut-off valve, to the input of a mechanical pump, characterized in that, in order to increase the reliability of the cathode and the magnetic mass-spec vacuum sensor - of the measuring chamber, increasing the inter-regulation period and the accuracy of measurements, it is equipped with at least two temperature sensors located in the lower part of the refrigerant vessel at various heights, the first sensor in ur out 5 warnings, the second at a critical level, and attached to the vessel wall by means of brackets made of diamagnetic heat-moisture-insulating material, the first recording and 0 with the signaling equipment and the first command equipment, act on the second electromagnetic valve and the power supply system of the cathode and the magnetic vacuum sensor, and each of the temperature sensors 5 consists of a permanent magnet, a sensing element in the form of a sheath of a ferromagnetic material enclosing a magnet with a Curie point close to the refrigerant boiling point, and 0 magnetically controlled contact reed switch mounted inside the corresponding bracket, contact reed switches of both temperature sensors are connected to the recording and signaling equipment, and contact5 reed switch of the second temperature sensor is connected to the first command equipment. 2. The system according to claim 1, characterized in that, in order to increase the reliability of controlling the drying of the nitrogen trap after At the end of the work and its automation, it is equipped with a switching device for supplying heat or pneumatic flow to the refrigerant vessel, a third temperature sensor installed at the bottom of the vessel for 5 of the refrigerant, and with the second recording equipment and the second command equipment connected to it, acting on the switching device, and the second temperature sensor is also connected to the second command equipment. 3.Popp system. 1 and 2, characterized in that, in order to reduce costs and save the life of the pumping system during vacuum drying of the nitrogen trap, it is equipped with a blocking device for pressure pumping and a third command device for influencing the blocking device, and a third thermal sensor and a steam jet vacuum sensor pumps are connected to the third command equipment.