CN100414290C - A safety door detection device based on photoionization detector technology - Google Patents

Abstract

The invention discloses a safety door detection device based on photoionization detector technology, which comprises a vacuum pump, a preheating air chamber, an electromagnetic valve, a photoionization detector, a digital display and a power supply system. The inlet of the preheating chamber is connected with the outlet of the vacuum pump, and the outlet of the preheating chamber is connected with the inlet pipe of the photoionization detector through a solenoid valve. The power supply system is a vacuum pump, a preheating chamber, a solenoid valve and a photoionization detector. , The digital display provides power. The detection of weak ions by the invention can reach the magnitude of ^10-10 ampere, and the signal-to-noise ratio of the gas chromatogram of the gas to be measured is good. The unique sampling and preheating gas chamber technology is used to improve the sensitivity of organic volatile gas detection. The power system adopts an integrated design, with little interference, low noise and good system stability.

Description

A safety door detection device based on photoionization detector technology

technical field

The invention relates to a chemical analysis instrument, in particular to a detection device for trace organic chemical dangerous goods.

Background technique

As we all know, the detection of dangerous goods is playing an increasingly important role in real life, and it is directly related to personal safety and social stability. The detection accuracy of the existing safety detection devices for organic chemical dangerous goods is not high enough, and it is difficult to meet the needs of civil aviation, railway and other system safety inspection departments for the detection of trace substances.

Portable Photoionization Detector (PID) is a detection instrument that works under normal temperature and pressure. The principle is: two electrodes parallel to each other are placed in the ionization chamber, the electrodes are insulated from each other and connected to the positive and negative terminals of the high voltage power supply respectively. After the vacuum pump pumps the gas into the detector, the detection lamp in the detection chamber emits ultraviolet light to bombard the gas molecules, making them ionized into positively charged ions and negatively charged electrons. Under the action of the electric field of the polarized plate, the ions The electrons and electrons drift and collide to the two poles respectively, causing changes in the amount of induced charge on the collecting electrode plate, thus forming a weak ion current that can be detected. According to this principle, a free-air ionization chamber as shown in Figure 1 can be made.

However, due to the direct connection between the collector plate and the power supply, on the one hand, the power supply is easy to burn out the amplifier, and on the other hand, various noises from the power supply are added to the input end of the micro-current amplifier through the collector plate, which has a great impact on the effective signal detected. weakened detection sensitivity.

In addition, due to the tight packaging of dangerous goods and the extremely low concentration of leakage, the conventional sampling method is difficult to meet the detection requirements, so it is particularly urgent to find a suitable sampling method.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of the existing traditional photoionization detectors that the collection plate is directly connected to the power supply, and the conventional sample feeding method is difficult to meet the detection requirements, and to provide a technology based on photoionization detectors. safety door detection device.

The technical solution adopted by the present invention to solve its technical problems is: a safety door detection device based on photoionization detector technology, including a vacuum pump, a preheating gas chamber, a solenoid valve, a photoionization detector, a digital display meter and a power supply system . The air inlet of the preheating chamber is connected with the outlet of the vacuum pump, and the outlet of the preheating chamber is connected with the inlet pipe of the photoionization detector through the solenoid valve. The power supply system is the vacuum pump, the preheating chamber, and the photoionization detector of the solenoid valve And the digital display meter provides power.

The preheating gas chamber adopts a multi-stage structure, and the outer wall of the preheating gas chamber is made of quartz glass material, and an electric heating wire is wrapped around it.

The electromagnetic valve is a two-way valve, and a self-excited multivibrator is formed by a 555 timer to generate an adjustable pulse width breaking voltage to control the opening and closing of the electromagnetic valve.

The photoionization detector includes a vacuum ultraviolet lamp, a photoionization chamber, a compound electrode structure, etc.; the photoionization chamber is connected to the air inlet pipeline and the gas outlet pipeline respectively, and a vacuum pump is installed on the gas outlet pipeline; Composite electrode structure, including zero potential electrode plate, collecting electrode plate and polarization potential electrode plate, the three electrode plates are parallel to each other, neatly arranged in a rectangular structure, and the collecting electrode plate is located between the zero potential electrode plate and the polarization potential electrode plate; The collecting electrode plate is connected to the micro-current amplifier, and the micro-current amplifier amplifies the collected electrical signal, which can be output to the digital display meter, or sent to the computer for analysis and processing through the data acquisition card; the zero-potential electrode plate is connected to the power ground, The polarization potential electrode plate is connected to the negative pole of the negative high voltage circuit, and the polarization voltage is less than -300V; the vacuum ultraviolet lamp is installed on one side of the photoionization chamber, and the irradiation port is located between the zero potential electrode plate and the collecting electrode plate.

There are dehumidification and filter devices on the air intake pipe of the photoionization detector, which are water-absorbing agent silica gel, sponge coarse filter layer, high-precision metal dust filter, double-layer filter composite paper dust bag and glass fiber air filter paper .

The zero-potential electrode plate inside the photoionization chamber has a length of 5-20 mm, a width of 1-5 mm, and a thickness of 0.2-2.0 mm. The collecting electrode plate has a length of 5-20 mm, a width of 1-5 mm, and a thickness of 0.2-2.0 mm. The length of the polarization potential electrode plate is 5-20 mm, the width is 1-5 mm, and the thickness is 0.2-2.0 mm. The distance between the zero potential electrode plate and the polarization potential electrode plate is 3-8 mm. Electrode plates are made of gold, silver, gold-plated, silver-plated or stainless steel and other materials.

The energy of the photons generated by the vacuum ultraviolet lamp is 10.6 electron volts, and the wavelength is ultraviolet light of 117 nanometers.

The input of the power supply system is 220V AC, through the AC-DC module, it outputs ±15V DC voltage pair; at the same time, it outputs +12V DC voltage through the DC switching power supply. The ±15V DC voltage pair output by the AC-DC module is directly connected to the power input terminal of the micro-current amplifier; the +15V DC voltage output by the AC-DC module is connected to the negative high-voltage power supply small module power input terminal and boosted to -1500V. The output voltage is connected to the UV lamp through a 1.5MΩ resistor; the +15V DC voltage output by the AC-DC module passes through the LM7805CV chip to output +5V DC voltage to provide the working voltage for the digital display meter. The +12V DC voltage output by the DC switching power supply supplies power for the vacuum pump, the electric heating wire wrapped around the quartz glass, the 555 timer and the solenoid valve respectively.

Working principle of the present invention is:

When the item to be tested passes through the detection table, if there are dangerous substances inside, it will be pumped to the first-stage air chamber by a powerful vacuum cleaner for primary preheating, and then controlled by the first-stage solenoid valve, and then enter the second-stage air chamber by the vacuum pump. Secondary air chamber and secondary preheating. Since the inlet of the second-stage air chamber adopts adsorption, concentration and adds dimethyl siloxane film, the second-stage air chamber increases the concentration of the gas to be measured, and the number can be increased by about 10 to 100. Controlled by the second-stage solenoid valve, the gas to be measured enters the ionization chamber.

The gas to be measured enters the ionization chamber, and the ultraviolet light emitted by the VUV bombards the gas molecules, so that the organic molecules in it are ionized into ions and electrons. Under the action of the electric field of the polarized plate, ions and electrons collide with the plate, forming a weak ion current that can be detected by a high-sensitivity micro-current amplifier. After the current signal is amplified into a voltage signal by a high-sensitivity micro-current amplifier, under the control of the MCU (single-chip microcomputer), the voltage signal can be converted into a corresponding concentration value according to the fitting curve and sent to the display unit through the sampling of the data acquisition card. It can be sent to the computer through the I/O interface, and the measurement results can be analyzed and processed by the chromatographic workstation.

The present invention uses a vacuum ultraviolet lamp as an ionization source to generate photons of 10.6ev, which can ionize molecules with ionization energy lower than 10.6ev, but cannot ionize molecules with ionization energy higher than 10.6ev, such as _N2 , _O2 , and water vapor, greatly reducing The type of ions produced is clearly defined, and a very clear spectrum of the analyte is obtained, thereby enhancing the detection sensitivity and working stability. In addition, the organic volatile gas will recombine to the original state after being ionized by the vacuum ultraviolet light, and will not destroy the structure and properties of the original gas.

The design requirements for the ionization chamber are: as large a measurement volume as possible and as small an electrode distance as possible, and an appropriate inter-electrode voltage should also be considered. Because the ionization of organic volatile compounds in the ionization chamber produces positive and negative ion pairs, the positive and negative ions move to the two poles under the action of the electrode electric field, and an output current signal is formed in the external circuit. According to the ionization theory, the charge collection efficiency of the ionization chamber increases with the decrease of the electrode distance d, and increasing the collection voltage can improve the collection efficiency (but the high voltage will increase the power consumption.)

Generally, when the electrode spacing of the ionization chamber is 3-8mm, the polarization voltage greater than 200V can make the collection efficiency of the ionization chamber reach more than 99%. In addition, according to the Gaussian law in the electric field and the constitutive relationship in the medium, an important conclusion can be drawn, that is, the collector plate can be made larger in theory, so that more charges q can be generated, so as to improve the ionization chamber sensitivity.

The beneficial effect of the present invention is that the PID ionization chamber design is adopted, which has the characteristics of integration, miniaturization and modularization, strong versatility, high sensitivity and low detection threshold; the detection of weak ions can reach the order of magnitude of ^10-10 amperes, and the gas to be measured The signal-to-noise ratio of the gas chromatogram is good; the unique preheating gas chamber technology is used to maintain the temperature and concentrate the trace concentration of substances, and the solenoid valve is closed to increase the pressure of the preheating gas chamber, and the solenoid valve is connected to ionize Chamber sample injection, greatly improving the sensitivity of organic volatile gas detection. The power supply system adopts an integrated design, with little interference and low noise, which improves the reliability and stability of the system work.

Description of drawings

Figure 1 is a model diagram of a free air ionization chamber.

Figure 2 is a schematic diagram of the structure of the photoionization detector.

Fig. 3 is a cross-sectional structure diagram of the ionization chamber of the photoionization detector.

Fig. 4 is a longitudinal sectional structure diagram of the ionization chamber of the photoionization detector.

Fig. 5 is an embodiment of an ionization chamber in which the VUV lamp is perpendicular to the direction of the gas path.

Fig. 6 is an example of an ionization chamber in which the VUV lamp is parallel to the direction of the gas path.

Fig. 7 is a working principle block diagram of the present invention.

Fig. 8 is a working flowchart of an embodiment of the present invention.

Detailed ways

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

As shown in Figures 1 and 2, the vacuum pump 14 draws the detectable gas 6 into the photoionization chamber 10 through the intake pipe 12, and the vacuum ultraviolet lamp 3 emits ultraviolet light to bombard the gas molecules to ionize them into bands. Positively charged ions 7 and negatively charged electrons 8, under the action of the electric field between the polarized plates 1 and 2, the ions 7 and electrons 8 drift to the two poles respectively, and hit the two poles 1 and 2, causing the induction of the collecting plate 11 The amount of charge changes, creating a small, detectable ionic current. After the current signal is amplified into a voltage signal by the high-sensitivity micro-current amplifier 4, it enters the analysis and processing unit 5. The detected gas is recombined to the initial state gas 9 and discharged through the gas outlet pipeline 13 .

The present invention has adopted the light ionization chamber 10 as shown in Figure 3, and the distance d1 between the polarized potential electrode plate 1 and the zero potential electrode plate 2 is 7 millimeters, and the distance d1 between the collecting electrode plate 11 and the zero potential electrode plate 2 The distance d2 is 5 mm, the voltage difference U between the polarizing potential electrode plate 1 and the zero potential electrode plate 2 is 300 volts, E≈4.286× ¹⁰⁴ volts/meter, between the collecting electrode plate 11 and the zero potential electrode plate 2 The potential difference is about 214.3 volts.

The ionization light source adopted in the present invention is a vacuum ultraviolet lamp 3, which produces photons with an energy of 10.6 eV and a corresponding wavelength of 117 nanometers. The zero-potential electrode plate 2 is grounded, the collecting electrode plate 11 is suspended in the air and does not contact other plates, and the polarizing potential electrode plate 1 is connected to the negative high voltage -1500 volts provided by the auxiliary power supply. The collecting plate electrode 11 is connected with the microcurrent amplifier 4. When the vacuum pump 14 continuously inhales the external gas to be measured from the intake pipe 12, the gas first passes through the metal filter attached to the intake pipe mouth 12 to remove moisture, block dust and foreign matter; then the gas enters the photoionization chamber 10 and is ionized under the irradiation of the vacuum ultraviolet lamp 3 . Positive and negative ions move along the direction of the electric field under the action of a polarized electric field of about -300 volts between the zero-potential electrode plate and the collecting electrode plate, and hit the electrode 11 of the collecting plate to form a weak ionization current. Measure the concentration of the substance. After the signal is amplified by the high-sensitivity micro-current amplifier 4, it can be output to an oscilloscope, a display, and a multimeter for observation, or sent to a platform such as a chromatographic workstation inside a computer through a data acquisition card for processing.

The ionization chamber adopted in the present invention is cylindrical, and nickel sheets or pure stainless steel sheets are placed in parallel in the middle, as shown in FIG. 4 . There is an air inlet pipe 12 at the lower end of the ionization chamber 45, an air outlet pipe 13 on the side, and an electrode rod 46 inside. The ionization chamber 45 is located in the ionization outer cover 47, and the vacuum ultraviolet lamp 3 is located at the upper end of the ionization chamber 45, with spacers 15 and 44 in the middle. There is a stainless steel sleeve 41 outside the vacuum ultraviolet lamp 3, and a polytetrafluoro ring 42 is separated in the middle. The vacuum ultraviolet lamp 3 and the ionization chamber 45 are fixed on the stainless steel sleeve 41 and the ionization outer cover 47 through the total fastening bolt 43 on the stainless steel sleeve 41. formed cavity. In order to improve sensitivity and ion collection efficiency, the volume of the cylinder should be appropriately small, with a diameter of about 20 mm.

Since the optical path of the ultraviolet light column is about 10mm, if the VUV lamp is perpendicular to the direction of the gas path, as shown in Figure 5, the optical path range of the ultraviolet light column will be limited to a limited distance from the surface of the lamp to the wall of the ionization chamber (we use About 3mm), the efficiency of ionization will not be very high. If the ultraviolet beam is parallel to the direction of the gas path, as shown in Figure 6, the probability of ionization of gas molecules will be greatly increased.

Fig. 7 is a working principle block diagram of the present invention. The total input of the power supply system is 220V AC, and the AC-DC module U1 outputs a ±15V DC voltage pair; meanwhile, the DC switching power supply U10 outputs +12V DC voltage. The ±15V DC voltage pair is directly connected to the power input terminal of the micro-current amplifier U3. The +15V DC voltage pair is connected to the input terminal of the negative high-voltage power supply module U2 and boosted to -1500V, and the output voltage is connected to the ultraviolet lamp U5 through a 1.5MΩ resistor. The +15V DC voltage is connected to the input of the LM7805CV chip to generate a +5V DC voltage, which provides the working voltage for the digital display meter U9. The +12V DC voltage output by the DC switching power supply U10 supplies power for the electric heating wire U7 wrapped around the quartz glass, the 555 timer, the solenoid valve U6, the vacuum pump U8 and U4 respectively.

Fig. 8 is a working flowchart of an embodiment of the present invention. When the item to be tested passes through the detection table, if there are dangerous substances inside, it will be pumped to the first-stage air chamber by a powerful vacuum cleaner for primary preheating, and then controlled by the first-stage solenoid valve, and then enter the second-stage air chamber by the vacuum pump. Secondary air chamber and secondary preheating. The inlet of the second-stage gas chamber adopts adsorption, concentration and adds dimethyl siloxane membrane. After the concentration of the gas to be tested is increased in the second-stage gas chamber, the gas to be tested is controlled by the second-stage solenoid valve to enter the ionization chamber. room.

Claims (10)

1. the safety door detection device based on the photoionization detector technology comprises vacuum pump, preheating air chamber, solenoid valve, photoionization detector and power-supply system; It is characterized in that: the preheating air inlet of air chamber is communicated with the vacuum pump gas outlet, preheating air chamber gas outlet is communicated with the photoionization detector admission line by solenoid valve, and power-supply system provides power supply for vacuum pump, preheating air chamber, solenoid valve and photoionization detector, digital indicator.

2. a kind of safety door detection device based on the photoionization detector technology according to claim 1 is characterized in that: described preheating air chamber adopts multilevel hierarchy, and the preheating gas chamber outer wall is a silica glass material, is tied with electrical heating wire outside it.

3. a kind of safety door detection device according to claim 1 based on the photoionization detector technology, it is characterized in that: described solenoid valve is a two-port valve, constitute free-running multivibrator by 555 timers, produce cut-offfing of the adjustable drop-out voltage control electromagnetic valve of pulsewidth.

4. a kind of safety door detection device according to claim 1 based on the photoionization detector technology, it is characterized in that: described photoionization detector comprises vacuum UV lamp, photoionization chamber, combined electrode structure; Photoionization chamber links to each other with admission line, outlet pipe respectively, and a vacuum pump has been installed on the outlet pipe; The photoionization chamber interior adopts combined electrode structure, comprise zero potential electrode plate, passive electrode plate and polarized potential battery lead plate, three battery lead plates are parallel to each other, the rectangular structure of proper alignment, and the passive electrode plate is between zero potential electrode plate and polarized potential battery lead plate; The passive electrode plate links to each other with micro current amplifier, and micro current amplifier both had been output to digital wash after the electric signal of collecting is amplified, and also can deliver to Computer Analysis and processing by data collecting card; The zero potential electrode plate earthing, the polarized potential battery lead plate links to each other with the negative pole of negative high voltage circuit, and polarizing voltage is less than-300V; Vacuum UV lamp is installed in a side of photoionization chamber, and the irradiation mouth is between zero potential electrode plate and passive electrode plate.

5. according to claim 1 or 4 described a kind of safety door detection devices based on the photoionization detector technology, it is characterized in that: be separately installed with dehydrating unit and filtration unit on the described photoionization detector admission line, wherein dehydrating unit is a water absorbing agent silica gel, and filtration unit is sponge coarse filtration layer, high-precision metal micro dust filter net, double medium filtration compound papery dirt bag and glass fibre air filter paper.

6. a kind of safety door detection device based on the photoionization detector technology according to claim 4 is characterized in that: the zero potential electrode plate length of described photoionization chamber interior is 5～20mm, and width is 1～5mm, and thickness is 0.2～2.0mm; Passive electrode plate length is 5～20mm, and width is 1～5mm, and thickness is 0.2～2.0mm; Polarized potential battery lead plate length is 5～20mm, and width is 1～5mm, and thickness is 0.2～2.0mm; Spacing between zero potential electrode plate and the polarized potential battery lead plate is 3～8mm; Battery lead plate all adopts gold, silver, gold-plated, silver-plated or stainless steel material.

7. a kind of safety door detection device based on the photoionization detector technology according to claim 4 is characterized in that: it is that 10.6 electron-volts, wavelength are the ultraviolet light of 117 nanometers that described vacuum UV lamp produces photon energy.

8. a kind of safety door detection device according to claim 1 based on the photoionization detector technology, it is characterized in that: described electric power system is input as the 220V alternating current, right by AC-DC module output ± 15V DC voltage, simultaneously by direct-current switch power supply generation+12V DC voltage.

9. a kind of safety door detection device based on the photoionization detector technology according to claim 8 is characterized in that: AC-DC module output ± the 15V DC voltage is to directly linking to each other with the power input of micro current amplifier; AC-DC module output+the 15V DC voltage links to each other with negative high voltage power source small modules power input and boosts to-1500V, and this output voltage is connected to uviol lamp by the resistance of a 1.5M Ω; The output of AC-DC module+the 15V DC voltage is through the LM7805CV chip, and output+5V DC voltage is for digital wash provides operating voltage.

10. a kind of safety door detection device based on the photoionization detector technology according to claim 8 is characterized in that: the output of described direct-current switch power supply+the 12V DC voltage is respectively electrical heating wire, 555 timers and the solenoid valve that vacuum pump, quartz glass twine outward.

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