CN109884165B - Ionization chamber of photoionization detector and photoionization detector - Google Patents
Ionization chamber of photoionization detector and photoionization detector Download PDFInfo
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- CN109884165B CN109884165B CN201910181731.3A CN201910181731A CN109884165B CN 109884165 B CN109884165 B CN 109884165B CN 201910181731 A CN201910181731 A CN 201910181731A CN 109884165 B CN109884165 B CN 109884165B
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Abstract
The invention discloses an ionization chamber of a photoionization detector and a photoionization detector, and relates to the technical field of inspection and detection. The ionization chamber of the ionization detector comprises a polytetrafluoroethylene deceleration sheet, a PID ultraviolet lamp, a polar plate, an air inlet and an air outlet. The ionization chamber body is of a cylindrical structure with an ionization cavity, the top of the ionization cavity is provided with a polytetrafluoroethylene circular deceleration sheet with an air inlet, the side of the ionization chamber body is provided with an air outlet, and the bottom of the ionization chamber body is provided with a light inlet. The whole ionization chamber is designed to flow axially, the gas direction is antiparallel to the irradiation direction of the ultraviolet lamp and perpendicular to the electric field direction, and the gas is fully ionized. The invention has the advantages of simple assembly structure, stable mechanical structure, good electrical connectivity, convenient disassembly and replacement of the ultraviolet lamp, and the like.
Description
Technical Field
The invention belongs to the technical field of gas detection, and particularly relates to an ionization chamber of a photoionization detector and a photoionization detector.
Background
PID (Photo Ionization Detection photo-ionization detection) technology is becoming increasingly widely used as an accurate and effective means of detecting Total Volatile Organic Compounds (TVOC). The basic principle of PID is that ultraviolet rays generated by inert gas vacuum discharge phenomenon are utilized, and when gas molecules with ionization potential less than or equal to ultraviolet energy absorb one photon, ionization occurs to generate positively charged ions and electrons. In the ionization chamber, ions and electrons rapidly move to the metal electrode under the action of an externally applied electric field, a micro-current signal is generated between the two electrodes, and the concentration of an organic substance is obtained by detecting the amplified current signal through a weak signal amplifying circuit. The photoionization technology has the characteristics of portability, safety, resolution real-time performance and the like, and after the volatile organic compounds are detected, ions are recombined into the original gas, that is to say, the photoionization technology is a detection technology which is not destructive to the detected objects
The existing photoionization ionization chambers are all parallel polarization plate structures. Comprises two parallel flat bias electrodes and parallel collecting polar plates for collecting charges. The design makes the ionization chamber limit the contact area of the polar plate and charged particles and weaken the collection efficiency of the polar plate under the condition of ensuring that the original volume is not changed. The contact area has a great influence on the detection precision of the PID detector, so that how to increase the contact area of the gas and the polar plate to enable ionization to be sufficient is an important factor for preparing the PID detector. In addition, the speed reducing sheet that the photoionization detector on the market set up in the air inlet department is the rectangular array of circular air vent, but its ionization chamber inner chamber is cylindric often, and when gaseous entering cylindric ionization chamber through rectangular speed reducing sheet, the gaseous inhomogeneous in space that awaits measuring, because PID light source self congenital reason, output light wavelet length, the decay is fast in the atmosphere, plus PID light source manufacturing process's degree of difficulty is big, this structure hardly improves the light utilization efficiency of light source by a wide margin, leads to gaseous ionization inhomogeneous, influences photoionization detector's detection sensitivity and measurement accuracy.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an ionization chamber of a photoionization detector, which enables gas molecules to be detected to be fully and uniformly ionized.
The invention is realized by the following technical scheme:
The ionization chamber of photoionization detector comprises a cylindrical ionization chamber main body with an ionization chamber, electrode plates fixedly arranged in the ionization chamber, an air flow inlet and an air inlet are formed at two ends of the ionization chamber main body, an air flow outlet is formed at the side part of the ionization chamber main body, the electrode plates are vortex-shaped positive polarization plates and vortex-shaped negative polarization plates which are arranged at intervals in parallel correspondingly, the negative polarization plates are made of non-conductive materials and are plated with conductive layers, and the conductive layers form a collecting plate
The invention has the advantages and beneficial effects that:
the ionization chamber adopts a circular array speed reducing plate structure arranged at the upper part of the ionization chamber main body, so that gas to be detected entering the ionization chamber can uniformly and uniformly flow into the ionization chamber at a constant speed, thereby being fully irradiated by ultraviolet light and increasing the probability of ionization of gas molecules; the design of the vortex-shaped polar plate in the middle of the ionization chamber and the design of the polar plate electroplating collecting plate increase the contact area of the polar plates and charged particles under the condition of not changing the volume of the original sensor, so that gas ions to be detected are completely deflected between the polar plates to the collecting plate, at the moment, the gas molecules to be detected can be fully and uniformly ionized and deflected in the ionization chamber, meanwhile, the ionization and collecting efficiency is improved, and the performances of the photo-ionization sensor such as sensitivity, repeatability, anti-interference capability, response time and the like can be improved.
The symmetrical PCB layout adopted by the current signal amplifying circuit improves the accuracy of the circuit by placing the original parts on the top layer and the bottom layer. The amplifier adopts a high-performance logarithmic amplifier or a precision operational amplifier to amplify weak voltage signals, the logarithmic amplifier has different amplifying capacities on voltage signals of different orders of magnitude due to the self structure, the precision operational amplifier can measure a wider range of signals, and the precision operational amplifier can minimize errors, so that the circuit network can be more precise. The design of the ionization chamber and the amplifier greatly improves the detection rate of the detector and the signal processing quality.
Drawings
FIG. 1 is a schematic cross-sectional view of a preferred embodiment of a photoionization detector for detecting total amount of volatile organic compounds according to the present invention.
Fig. 2 is a schematic perspective view of the ionization chamber enclosure shown in fig. 1.
Fig. 3 is a schematic perspective view of the ionization chamber enclosure shown in fig. 1.
Fig. 4 is a schematic perspective view of the entire ionization chamber polarizing plate shown in fig. 1.
Fig. 5 is a schematic perspective view of a speed reducing plate at the gas inlet of the whole ionization chamber shown in fig. 1.
Fig. 6 is an enlarged schematic circuit diagram of the ionization chamber shown in fig. 1.
Other relevant drawings may be made by those of ordinary skill in the art from the above figures without undue burden.
Detailed Description
In order to make the person skilled in the art better understand the solution of the present invention, the following describes the solution of the present invention with reference to specific embodiments.
Example 1
The invention relates to an ionization chamber of a photoionization detector, which comprises a cylindrical ionization chamber main body with an ionization chamber, electrode plates fixedly arranged in the ionization chamber, wherein an air flow inlet and an optical inlet are formed at two ends of the ionization chamber main body, an air flow outlet is formed at the side part of the ionization chamber main body, the electrode plates are vortex-shaped positive polarization plates and vortex-shaped negative polarization plates which are arranged at intervals in parallel correspondingly, the negative polarization plates are made of non-conductive materials and are plated with conductive layers, and the conductive layers form a collecting plate. A plurality of tail gas discharge through holes are further formed below the side wall of the ionization chamber wall, and the diameter of each through hole is preferably equal to that of the gas inlet.
Specifically, the positive electrode plate material may be a common conductive material, preferably stainless steel, copper or other metals; the negative electrode plate material can be a common non-conductive material and is easy to electroplate, preferably polytetrafluoroethylene, polyether ether ketone and polyimide, and further preferably polyimide with high insulating property; the vortex-shaped electrode plate comprises a positive electrode plate made of stainless steel and a negative electrode plate made of conductive polyimide film, and the vortex-shaped collecting plate is made of polyimide film materials with gold plating layers on two sides.
For the collecting plate, it is preferable to plate on the negative electrode plate in double-sided plating, which is a polarizing plate and a vortex structure; preferred materials may be common conductive plating materials, preferably copper, nickel, chromium, tin, silver, gold, further preferably gold; preferably, the collecting plate is located on the center line of the negative polarizing plate with its upper and lower edges each spaced 1-2mm from the edges of the polarizing plate.
As one embodiment, for one end of the ionization chamber, the shape of the housing; preferably, one end of the ionization chamber of the shell is of a cylindrical structure; preferably, the inner diameter of the cylinder at one end of the ionization chamber of the shell is 6-7mm, the outer diameter is 8-10mm, the height is 7-10mm, the further preferred inner diameter is 6-6.5mm, the outer diameter is 9-10mm, the height is 7-8mm, the most preferred inner diameter is 6mm, the outer diameter is 10mm, and the height is 7mm;
for one end of the ultraviolet lamp, the shape of the shell is that; preferably, one end of the ultraviolet lamp of the shell is in a round table and cylindrical structure; preferably, the inner diameter of the cylinder at one end of the ultraviolet lamp of the shell is 6-7mm, the outer diameter is 8-9mm, the height is 10-20mm, the further preferred inner diameter is 6-6.5mm, the outer diameter is 8-8.6mm, the height is 10-15mm, the most preferred inner diameter is 6mm, the outer diameter is 8.6mm, and the height is 15mm.
The positive polarization plate is made of stainless steel and has the thickness of 0.1-0.5mm, the negative polarization plate is made of a vortex-shaped conductive polyimide film material with the thickness of 0.1-1mm, the collecting plate is a gold plating layer plated on two sides of the polyimide film material with the thickness of 0.1-1mm, and the electrode plates are vortex-shaped to increase the contact area; the depth of the positive electrode plate is 7-8mm, the thickness is 0.1-1mm, and the screw pitch is 1.5-2.5mm.
The negative electrode plate is a polyimide film with the thickness of 0.1-1mm, the depth of 7-8mm and the screw pitch of 1.5-2.5mm; the collecting plate is a polyimide film with Au plating layers at two sides with the thickness of 0.1-1mm, the plating layer thickness is 0.01-0.1mm, the depth of the collecting plate is 5-6mm, and the screw pitch is 1.5-2.5mm; the first electrode plate and the second electrode plate are parallel to each other and are arranged in a vortex shape, and the distance between the two electrode plates is 1-4mm.
The depth of the positive polarization plate and the negative polarization plate is 7-8mm, the thickness is 0.1-0.15mm, the pitch is 1.5-2.5mm, the depth of the pole plate is 7mm, the thickness is 0.1mm, and the pitch is 2mm.
For the distance between the electrodes in the prior art, the distance between the electrodes is 2-4mm, and the preferred distance between the two electrodes is 0.1-1mm, and the setting greatly reduces the distance between the two electrodes, so that the dead volume of an ionization chamber is reduced, the primary electron capturing efficiency is improved, the detection sensitivity is improved, in addition, the carrier gas flow rate can be greatly reduced, the carrier gas flow rate of the traditional PID (proportion integration differentiation) is reduced from 30-50ml/min to 3-10ml/min, and the miniaturization of the PID detector is facilitated.
The ionization chamber body is of a cylindrical structure formed with an ionization chamber, the top of the ionization chamber is provided with an airflow inlet, the side part of the ionization chamber is provided with an airflow outlet, the bottom of the ionization chamber is provided with a light inlet, the cross sections of two polar plates are in a vortex shape and are symmetrical to the axis of a cylinder, the two polar plates are positioned in the middle of the ionization chamber and are stuck inside a corrosion-resistant and oxidation-resistant polytetrafluoroethylene shell, the collecting plate is a coating on the negative plate, the whole ionization chamber is designed to flow axially, and the gas direction is antiparallel to the irradiation direction of an ultraviolet lamp and is perpendicular to the electric field direction. The design of the vortex-shaped polar plate in the middle of the ionization chamber and the design of the polar plate electroplating collecting plate increase the contact area of the polar plates and charged particles under the condition of not changing the volume of the original sensor, so that gas ions to be detected are completely deflected between the polar plates to the collecting plate, at the moment, the gas molecules to be detected can be fully and uniformly ionized and deflected in the ionization chamber, meanwhile, the ionization and collecting efficiency is improved, and the performances of the photo-ionization sensor such as sensitivity, repeatability, anti-interference capability, response time and the like can be improved.
The ionization chamber is characterized in that a positioning groove is formed in the inner wall of the ionization chamber main body, and the electrode plate and the collecting plate are fixed in the positioning groove in a matched mode to achieve positioning.
Example two
Further, a speed reducing plate is fixedly arranged at the air flow inlet, and a plurality of circular ventilation holes with caliber are arranged on the speed reducing plate for ventilation. The circular holes with the diameter of 0.5mm are formed in the way that a plurality of circular air holes of the speed reducing plate are arranged in a circular array; and the total ventilation aperture of the speed reducing plate is the same as the diameter of the inner cavity of the ionization chamber.
The ionization chamber adopts a circular array speed reducing plate structure arranged at the upper part of the ionization chamber main body, so that gas to be detected entering the ionization chamber can uniformly and uniformly flow into the ionization chamber at a constant speed, thereby being fully irradiated by ultraviolet light and increasing the probability of ionization of gas molecules; for the speed reducing plate, circular flat plates and rectangular array vent holes are preferable, and circular flat plates and circular array vent holes are further preferable; the material of the speed reducing plate can be a common outer packing material, preferably corrosion-resistant and oxidation-resistant polytetrafluoroethylene; preferably, the diameter of the vent holes of the speed reducing plate is 0.2-0.5mm, the distance between vent hole arrays is 0.5-1mm, the total vent hole diameter is 6-7mm, the further preferred vent hole diameter is 0.5mm, the distance between vent hole arrays is 0.7mm, and the total vent hole diameter is 6mm.
Example III
The photoionization detector comprises an ionization chamber of the photoionization detector, an ultraviolet lamp fixedly connected with the ionization chamber of the photoionization detector, and a signal amplification processing circuit, wherein an exit window of the ultraviolet lamp, an air flow inlet and an axis of the vortex-shaped polarizing plate are coaxially arranged.
The symmetrical PCB layout adopted by the signal processing circuit improves the accuracy of the circuit by placing the original parts on the top layer and the bottom layer. The amplifier adopts a high-performance logarithmic amplifier or a precision operational amplifier to amplify weak voltage signals, the logarithmic amplifier has different amplifying capacities on voltage signals of different orders of magnitude due to the self structure, the precision operational amplifier can measure a wider range of signals, and the precision operational amplifier can minimize errors, so that the circuit network can be more precise. The design of the ionization chamber and the amplifier greatly improves the detection rate of the detector and the signal processing quality. For an amplifying circuit; the preferred amplifier is log114; the preferred resistor is the three star 0603 package and the preferred capacitor is both 0603 and 0805 packages. The signal amplifying circuit network is integrated on a special PCB layout double-layer board, weak current signals collected by the collecting board pass through the I/V conversion part, the signal amplifying part is connected again through the noise filtering network in the figure, the original placement of the whole circuit is strictly consistent according to the line length of the positive and negative input ends of a design chip, the PCB pursues symmetrical distribution, the bottom of the chip is hollowed and covered with copper, the wiring is strictly standardized, welding and proofing materials are processed according to requirements, and an FR4 copper-clad plate is adopted.
The photoionization ionization chamber further comprises a dehumidifying device, so that the gas to be detected enters the ionization chamber after passing through the dehumidifying device. The dehumidifier is a common dehumidifier, the filling material of the dehumidifier is preferably a water absorbing material, and the further preferred filling material is silica gel.
Example IV
As shown, a photoionization detector ionization chamber for total volatile organic compound detection, the ionization chamber comprising: the vacuum ultraviolet lamp 2 with the outer diameter of 6mm, the ionization chamber 6, the airflow inlet 8, the light inlet 20, the positive polarization plate 12, the negative polarization plate 13, the collecting plate 14 laid on the negative polarization plate, the electrode plate positioning groove 5, the speed reducing plate 16, the speed reducing plate positioning groove 7 and the through type tail gas outlet 4. Both ends of the polarization plate 1213 of the ionization chamber are fixed by the positioning grooves 5. The speed reducing plate 16 of the air inlet 8 is fixed up and down with the positioning groove 7 of the shell through the upper positioning column 15.
Wherein the positive plate center 11, the negative plate center 11, the collecting plate center 11, the ultraviolet lamp 2, the airflow inlet 8, the speed reducing plate 16 and the light inlet 20 are all positioned in the inner cavity 19 of the cylindrical ionization chamber on the same axis.
The polarization plate 1213 adopts a vortex structure, the preparation material of the positive polarization plate 12 is stainless steel, the depth of a polar plate is 7mm, the thickness is 0.1mm, the screw pitch is 2mm, the preparation material of the negative polarization plate 13 is polyimide, the depth of the polar plate is 7mm, the thickness is 0.1mm, the screw pitch is 2mm, and the distance between two electrodes is 0.1-1 mm. The positive electrode plate 12 is fixed by the fixing groove 5 of the side wall of the ionization chamber, and the negative electrode plate 13 is also fixed by the fixing groove 5 of the side wall of the ionization chamber.
The ionization chamber shell adopts a cylindrical structure, the preparation material of the ionization chamber shell is polytetrafluoroethylene, the inner diameter of one end of the polarization plate of the shell is 6mm, the outer diameter of the polarization plate of the shell is 10mm, the height of the polarization plate of the shell is 7mm, the inner diameter of one end of the ultraviolet lamp of the shell is 6mm, the outer diameter of the ultraviolet lamp of the shell is 8.586mm, and the height of the ultraviolet lamp of the shell is 15mm. The negative polarization plate 13 is provided with a collecting plate 14, the collecting plate 14 adopts a plating layer structure, double sides of the collecting plate are plated on the center line of the negative polarization plate 13, and the upper and lower boundaries of the collecting plate are 1.5mm away from the boundaries of the polarization plate. The preparation material is Au.
The ionization chamber shell 6 lateral wall below is equipped with tail gas outlet 4, adopts a hole penetrating type tail gas emission mode, and tail gas outlet 4 adopts cylindrical structure, and its inside diameter is 3mm, and the outside diameter is 4mm, thickness 1mm, and its vent aperture is polar plate 1213 extreme to the light inlet 20 extreme.
The ultraviolet lamp 2 is arranged at the lower part of the inner cavity 19 of the ionization chamber shell and is in a cylindrical structure, and light rays are parallel to the axis of the inner cavity and are antiparallel to the air flow direction and are perpendicular to the direction of the polar plate electric field; a Heraeus PKR 106-6-14 krypton lamp was used, the diameter of the light source was 6mm, and the photon energy was 10.6eV.
The speed reducing plate 16 is a circular sheet, and four positioning columns 15 are respectively arranged on the upper, lower, left and right sides of the speed reducing plate so as to be conveniently fixed with the positioning groove 7 of the ionization chamber shell; the speed reducing plate 16 is arranged at the air inlet 8, the center of the speed reducing plate is provided with a plurality of vent holes 18 with the diameter of 0.5mm, the vent holes 18 take the center point of a thin sheet as a circular array, the diameter of the circular array is 6mm as same as the diameter of the inner cavity 19 of the ionization chamber, the distance between the vent holes 18 is 0.7mm, and the total vent hole diameter is 6mm.
When the ionization chamber 6 operates, gas to be measured enters from the gas flow inlet 8, after passing through the circular array vent hole 18 and the speed reducing plate 16, the gas to be measured uniformly enters the ionization chamber cavity 19 at a constant speed, the gas to be measured is uniformly distributed in space, at the moment, the light of the ultraviolet lamp 2 is injected into the ionization chamber cavity 19 through the light inlet 20, the gas molecules to be measured are ionized under the irradiation of the ultraviolet lamp 2, a deflection electric field is formed between the positive electrode plate 12 and the ground plate negative electrode plate 13, ions generated by ionization deflect to the negative electrode plate 13 in the electric field, the ions are emitted to the collecting plate 14, namely a double-sided Au plating layer on the negative electrode plate 13, microcurrent signals are collected on the collecting plate 14, the data can be processed and cited, and the rest gas is discharged through the tail gas outlet 4.
Spatially relative terms, such as "upper," "lower," "left," "right," and the like, may be used in the embodiments for ease of description to describe one element or feature's relationship to another element or feature's illustrated in the figures. It will be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "under" other elements or features would then be oriented "over" the other elements or features. Thus, the exemplary term "lower" may encompass both an upper and lower orientation. The device may be otherwise positioned (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Moreover, relational terms such as "first" and "second", and the like, may be used solely to distinguish one element from another element having the same name, without necessarily requiring or implying any actual such relationship or order between such elements.
The foregoing has described exemplary embodiments of the invention, it being understood that any simple variations, modifications, or other equivalent arrangements which would not unduly obscure the invention may be made by those skilled in the art without departing from the spirit of the invention.
Claims (10)
1. An ionization chamber of a photoionization detector, characterized by: the ionization chamber comprises a cylindrical ionization chamber body with an ionization cavity, an air inlet and an optical inlet are formed at two ends of the ionization chamber body, an air outlet is formed at the side part of the ionization chamber body, the electrode plates are vortex-shaped positive polarization plates and vortex-shaped negative polarization plates which are arranged at intervals in parallel, the negative polarization plates are made of non-conductive materials and are plated with conductive layers, the conductive layers form a collecting plate, the cross sections of the two electrode plates are vortex-shaped and symmetrical to the axis of the cylinder, the whole ionization chamber is designed to flow axially, the contact area between the electrode plates and charged particles is increased under the condition that the volume of an original sensor is not changed, so that gas ions to be measured are completely deflected onto the collecting plate, at the moment, gas molecules to be measured can be fully and uniformly ionized and deflected in the ionization chamber, the ionization and collection efficiency are improved, and an exit window of an ultraviolet lamp, the air inlet and the axis of the vortex-shaped polarization plate are arranged coaxially.
2. A photoionization detector ionization chamber as defined in claim 1, wherein: the collecting plates are conductive layers on two sides of the polyimide film material.
3.A photoionization detector ionization chamber as defined in claim 1, wherein: the collecting plate is positioned on the central line of the negative polarization plate, and the distance between the upper edge and the lower edge of the collecting plate and the edges of the polarization plate is 1-2mm respectively.
4. A photoionization detector ionization chamber as defined in claim 1, wherein: the inner wall of the ionization chamber main body is provided with a positioning groove, and the electrode plates are fixed in the positioning groove in a matching way to realize positioning.
5. A photoionization detector ionization chamber as defined in claim 1, wherein: the distance between the positive electrode plate and the negative electrode plate is 0.1-1mm.
6. A photoionization detector ionization chamber as defined in claim 1, wherein: the depth of the positive electrode plate and the negative electrode plate is 7-8mm, and the screw pitch is 1.5-2.5mm.
7. A photoionization detector ionization chamber as defined in claim 1, wherein: the air inlet is fixedly provided with a speed reducing plate, and a plurality of circular ventilation holes with caliber are arranged on the speed reducing plate for ventilation.
8. A photoionization detector ionization chamber as in claim 7 wherein: the circular air holes of the speed reducing plate are arranged in a circular array; the diameter of the total vent holes of the speed reducing plate is the same as the diameter of the inner cavity of the ionization chamber.
9. A photoionization detector comprising a photoionization detector ionization chamber of any one of claims 1-8, an ultraviolet lamp fixedly connected to the photoionization detector ionization chamber, and a signal processing circuit, wherein the exit window of the ultraviolet lamp, the gas flow inlet, and the electrode plate axis are coaxially disposed.
10. The photoionization detector of claim 9 wherein the signal amplification processing section employs a high performance logarithmic amplifier or a precision operational amplifier to amplify weak voltage signals.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4377749A (en) * | 1981-02-25 | 1983-03-22 | Young Robert A | Photoionizer |
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