Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
  • G01M3/22—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
  • G01M3/226—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators

Definitions

• the present invention relates to a method and a device for the detection and localization of leakages in vacuum systems typically operating under negative pressure with respect to the atmospheric pressure. They are based upon the use of sensors to detect alcohols and/or solvents and/or hydrocarbons and/or C0 2 that are characterized by a great sensitivity and very small size.
• the peculiarity of the invention is the detection and the localization of leakages in vacuum systems under the following vacuum range: 760 Torr ⁇ l*10 ⁇ 12 Torr having a leakage amount in the following range: 1*10 5 mbar.l/sec ⁇ l*10 "10 mbar.l/sec such peculiarity being not provided by the state of art .
• any (accidental) opening in the system that connects the inside to the outside thereof is detected as an increase in the inner pressure caused by an air flow from the outside (at higher pressure) to the inside (at lower pressure) .
• the sensitivity to C0 2 allows a vacuum leakage to be detected by monitoring the change in the concentration of gas that will be clearly lower under vacuum conditions than the concentration in the atmosphere.
• the sensitivity to alcohols, solvents, hydrocarbons and C0 2 allows the device of the invention to localize the leakage.
• the injection of one of the elements mentioned above (by nebulization and/or vaporization and/or gasification) along the surfaces of the system under detection will be sufficient to detect a change in the signal of the sensor when one of the above-mentioned elements is sprayed to the opening which is the cause of the vacuum leakage.
• METHOD OF OVERPRESSURE The system or the component is pressurized with air and dipped into water. The detection and the localization of a leakage is made by a flow of air bubbles coming out of water. Further advantages (in terms of capability of detection of lower leakages) are achieved if the gas used is lighter than air and the liquid has a lower surface tension than water. To this purpose, it is demonstrated that helium bubbles in alcohol detect leakages which are one hundred times lower than leakages detected by air bubbles in water. 2.
• DETECTOR OF THERMAL CONDUCTIVITY This technique is based on the different thermal conductivity of air and a gas used as monitor detecting the leakage.
• the analysed system is placed also in this case under overpressure and a probe senses the surface of the analysed system to detect the leakage.
• a change in the temperature of a sensor placed under the flow of the monitoring gas is produced with respect to a similar sensor placed under a controlled air flow. Such change in the temperature is treated to give the operator a leakage signal.
• MASS SPECTROMETER This technique is based upon the detection of helium ion ionised one time (He + ) by mass spectroscopy. As the whole system is tuned to such specific element, extremely small helium concentrations can be detected by this technique.
• the operating mode is to place the analysed system under depression (vacuum) with respect to the outside environment, whereupon helium is sprayed by a probe along the whole surface of the system.
• vacuum depression
• helium will penetrate to the inside of the system and will be detected by the mass spectroscopy.
• the detection of a vacuum leakage can be carried out by inputting helium inside the system and, at the same time, by searching outside traces of helium by a "nose" that enters helium inside mass spectrometer.
• the first limit (if the first mentioned technique of the preceding section is used) is caused by the size of the investigated system that of course cannot be excessively large; actually, such technique is mainly provided for little systems that can be dipped into basins.
• Such limit is overcome extremely well by using techniques 2 and 3 (the latter is used with the "nose") .
• the limit is given by the system engineering. Actually, when a system is designed to guarantee a vacuum tightness, it will absolutely assure the tightness only if the inside pressure is lower than the outside pressure; in contrast, i.e. if the inside pressure is higher than the outside pressure, additional leakages will add unavoidably to the already existing leakages.
• the present invention seeks to overcome all limits of the conventional systems. This has been accomplished by the use of a sensor capable of detect a tracing gas without modifying its state of neutrality. In this way the detection system cannot suffer from the limits due to ionisation. On the other hand, also the limits of the systems operating under overpressure have been well overcome by that operating conditions under lower pressure than the outside environment are provided.
• Fig. 1 shows schematically the mode of use of the device for the detection and the localization of vacuum leakages according to the invention
• Fig. 2 is a diagram of the two modules forming the device for the detection and the localization of the leakages.
• a sensor 3 capable of detecting the presence of a particular gas or vapour is positioned inside such system 1.
• element 5 that can be sensed by the sensor is sprayed or vaporized by suitable means 2 on the surfaces to be investigated in order to locate easily the vacuum leakage.
• element 5 will penetrate inside the system and will be sensed by the sensor. This allows to locate the leakage in system 1.
• a suitable control device 4 of the sensor will facilitate the operation.
• control device 4 is able to measure the change in the concentration of the element inside system 1 because of the leakage on the basis of the change in the concentration of the gas with respect to a typical environmental basic condition.
• This method provides that the gas and/or vapour used to detect the position of the leakage can also be an element usually present in the atmosphere.
• the leakage detection and localization device essentially consists of two modules.
• the first module designated in the figure by MOD. 1, connected to sensor assembly 3 includes an A/D converter and a codec for the dialogue with MOD. 2. According to the type of microcontroller used, A/D converter and codec can be integrated in one and the same chip.
• the second module, MOD. 2 in the figure, includes the semiautomatic offset system, the variable gain amplifier (block OA) and display (block D) in addition to codec as well as the acoustic alarm (block AA) and a data log system (RS232) . Also in this case such module can be integrated in one and the same chip.
• Sensor 3 is a transducer the output signal of which (which is variable as a function of the gas and/or vapour concentration to which it is responsive) is applied to a voltage divider supplied with a voltage of 12 Volt fed after the modules have been recognized.
• the signal consisting of the voltage variations due to the change in the gas concentration is converted to a digital signal fed to module 2 by cable.
• the digital signal received by module 1 only after the two modules have recognized each other is available after about two minutes, a time necessary for the system to be stabilized. Thereafter, it is sampled to represent the zero of the instrument (automatic offset) from that time on. The next changes in the voltage will form the useful signal for the operator.
• the gain of the signal can be adjusted according to several fixed amounts by on/off keys and shown on a display of the current settings.
• the signal is shown on a graphic display and can be heard in the form of an acoustic signal at a frequency and/or loudness which is variable as a function of the magnitude of the signal.
• a log system which can be downloaded to a computer by RS232 as well as a dedicated software able to display the logged variations are available.
• the signal can also be displayed in real time by RS232.
• Module 2 is fed by cells P and has a jack for recharging purposes.
• the voltages in module 1 are supplied by module 2.
• module 1 is fixed to the system in which the detection is made, and module 2 is portable and connected to module 1 by cable.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Examining Or Testing Airtightness (AREA)

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Cited By (26)

Citations (4)

• 2003
  • 2003-09-30 IT IT000451A patent/ITRM20030451A1/it unknown
• 2004
  • 2004-09-10 WO PCT/IT2004/000489 patent/WO2005031297A1/en active Application Filing

Patent Citations (4)

Non-Patent Citations (2)

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