Photo-ionization detector for gas-analysis equipment

FIELD: instrument-making industry.

SUBSTANCE: detector has ultraviolet lamp with port for outputting ultraviolet radiation and ionization chamber. Inner volume of chamber is limited by space between surface of ultraviolet lamp port and surface of cylindrical bushing of electric-isolation material, having central inner channel. In the channel polarizing and collecting electrodes are mounted. Electrodes are made in form of rods. Outer surface of rods excluding ends, placed near end surface of bushing, is covered by layer of electric isolation material. Lamp on the side of port for outputting ultraviolet radiation is provided with cylindrical metallic cap. In middle portion of cap inner ring shelf is present, one surface of which is pressed to edges of lamp port, and another surface contacts end surface of bushing. Bushing is made of elastic polymer material and is screwed into hollow of cap, remote from lamp port.

EFFECT: higher efficiency.

4 cl, 3 dwg

 

The invention relates to the field of analytical instrumentation and can find application in the control of impurity substances in gases and, in particular, in the air.

Known photoionization detector containing the radiation source is a UV light with a window for output of ultraviolet radiation, ionization chamber placed in front of the window lights, the channel for supplying a sample gas into the camera, polarizing and collector electrodes installed in the volume of the ionization chamber and separated by an insulator, and the channel to the gas outlet formed by the gap between the insulator and the camera window (see ed. mon. USSR N 1444659, G 01 N 27/62, 1987). Known detector can be used in gas chromatographs, but is not applicable in gas analyzers, working with forced air sampling where required ensure the integrity of the ionization chamber.

The closest to the essential features for the proposed detector is a photoionization detector manufactured by the company, CHROMPET-ECOLOGY as part of the detector COLIN-1. The detector contains UV light with a window for output UV radiation, ionization chamber, the internal volume of which is limited by the space between the window surface and end surface of the cylindrical sleeve of insulating material mounted in front of the window with the or in relation to its surface, polarizing and collector electrodes, mounted in the Central passage in the cylindrical sleeve of insulating material, and the line inlet and the gas outlet, connected to the Central channel of the sleeve (see the Instruction manual of the detector COLIN-1, M: HRADEC-ECOLOGY, 1997).

The disadvantage of this detector is that in the analysis of air with high relative humidity (>70%) on the surface of the insulating bushing material separating the electrodes, and a thin film of water, and there are leakage currents, leading to an increase in the current between the electrodes, i.e. to the occurrence of a false signal. This disadvantage is particularly noticeable while minimizing the internal volume of the ionization chamber when the distance between the electrodes on the surface of the insulating material of the bushing does not exceed 5 mm

The invention consisted in the exclusion of the influence of humidity analyzed air signal photoionization detector while reducing the internal volume of the ionization chamber and ensuring its integrity.

This task is solved in that proposed photoionization detector for gas-analyzing equipment containing UV light with a window for output UV radiation, ionization chamber, the internal volume of which is limited to simple what anstam between the window surface and the surface of the cylindrical sleeve of insulating material, having a Central internal channel and installed in front of the window with a gap relative to its surface, polarizing and collector electrodes, mounted in the Central channel of the sleeve, and the channels for the supply and withdrawal of the sample gas, connected to the Central channel of the sleeve, in which, according to the invention, the electrodes are designed in the form of rods, the outer surface of which except for the ends, placed near the end surface of the sleeve opposite the open lamp, covered with a layer of insulating material, and the electrodes are mounted parallel to each other, and the outer surface layers of insulating material, which serves as a plating electrode, separated from each other by a gap.

Due to the above peculiarities of the electrodes, active (not isolated) the ends of the electrodes, between which flows the ionization current are at a small distance from each other (less than 5 mm), but are separated from each other on the surface of the insulating material of relatively great length the plot of this surface (>30 mm). This leads to the fact that even if on the surface of the insulating material, which covers the majority of electrodes, and a thin film of water, leakage currents are negligibly small value (on the level of share picoampere) and almost never affects the I on the useful signal.

Another difference detector is that the UV lamp from the window to output radiation with metal cylindrical base portion of the inner surface of which covers the side surface of the lamp and hermetically connected with it, and in the middle part of the cap internal annular ledge, one surface of which is pressed tightly against the edges of the window, UV lamp, and the other surface of the protrusion is in contact with the end surface of the bushing of insulating material, and a portion of the inner surface of the cap remote from the lamp, hermetically covers the outer side surface of a sleeve of insulating material.

Another difference detector is the fact that, as the insulating material of the sleeve used polymeric material, and on the inner surface of the cap covering the nut, the thread used for the sealed connection of the cap with the sleeve, and on the surface of the inner annular projection of the cap facing the sleeve is made annular projection having a pointed edge and serves to seal the inner volume of the ionization chamber.

These features perform detector provides reliable sealing of the ionization chamber detector at its minimum volume.

This greatly simplifies the Assembly is a separate estimate of the detector.

Among the differences of the detector should be noted that the lamp cap from the bushing wears a cylindrical metal casing surrounding the outer surface of the sleeve and the shielding electrodes of the ionization chamber from the effects of external electric fields.

The invention is illustrated by drawings.

Figure 1 shows the proposed detector in the longitudinal section.

Figure 2 presents a view of the detector in the cross-section a-a figure 1.

Figure 3 presents a view of the detector in section In figure 1.

Photoionization detector UV lamp 1 with a window 2 for output UV radiation. As an example execution of the drawings presents a gas discharge UV lamp 1 with the electrodes 3 and 4 installed in the internal volume. However, this detector can be used and electrodeless discharge UV lamp in which the discharge that serves as a source of UV radiation is excited by high-frequency inductive or capacitive generator (not shown). Lamp housing 1 from the side window fixed cylindrical metal cap 5, which is connected to a part of its inner surface with the outer surface of the lamp 1 with an adhesive, for example epoxy compound.

In the middle part of the cap 5 has an internal annular ledge 6, one surface of which is pressed tightly against the edges of the window 2 to output UV) is the treatment of the lamp 1, and the other surface of the protrusion 6 is in contact with the end surface of the sleeve 7 of insulating material. As the material of the sleeve 7 is used elastic polymeric material, preferably Teflon. On the inner surface of the cap 5 made the thread so that the sleeve 7 is screwed into the cavity of the cap 5 and its end face is pressed against the surface of the annular protrusion 6 having a pointed edge 8. The space between the surface of the window 2 and the inner surface of the sleeve 7 forms an inner volume of the ionization chamber 9. In the Central part of the sleeve 7 is made of the channel 10, which has electrodes 11, one of which serves as a polarizing electrode and the other serves as a collector electrode. The electrodes 11 made in the form of thin rods 12, the outer surface of which with the exception of the ends 13, installed near the end surface of the sleeve 7, is covered with a layer 14 of insulating material, for example PTFE. In the body of the sleeve 7 is made a channel 15 for the supply of the sample gas (air)connected with the Central channel 10 of the sleeve 7, which has electrodes 11, and the channel 16 to output the sample gas from the volume of the ionization chamber 9. Channels 15 and 16 are connected to respective nozzles 17 and 18 for the supply and withdrawal of the sample gas. The electrodes 11 connect the tive with the appropriate cables 19 and 20, one of which (19) is connected to the power source, and the second (20) is connected with electrometric amplifier (not shown). The electrodes 11 are mounted parallel to each other so that the outer surface of the layer 14 of insulating material serving external coating of the electrodes 11, are separated from each other by a gap (see figure 3). Active (non-isolated) the ends 13 of the electrode 11, between which, in operation, the detector ionization current flows, are at a small distance from each other (less than 5 mm). However, they are separated from each other on the surface of the insulating layer 14 is large enough for the length of the area of this surface (>30 mm), which provides a high electrical resistance and considerably reduce the leakage currents even at high humidity analyzed air.

On the base 5 of the lamp 1 from the side of the sleeve 7 worn a cylindrical metal casing 21 surrounding the outer surface of the sleeve 7 and the shielding electrodes 11 of the ionization chamber 9 from the effects of external electric fields. The casing 21 is pressed against the base 5 by means of a clamp 22.

The detector works as follows.

The flow of the sample gas (air) enters the ionization chamber 9 on channel 15 under the influence of the microcompressor (not shown)connected to the pipe 18. Under the action of UV radiation, p is acting in an ionization chamber 9 of the UV lamp 1 through the window 2, in the ionization chamber 9 is ionization of the molecules of the components of the sample gas having an ionization energy less than energy of photons. The resulting ions and electrons move in an electric field to the active sites of the edges 13 of the electrodes and generate a current signal proportional to the concentration of the molecules of an ionisable components of the sample gas. Due to the fact that the distance between the active (non-isolated) parts (ends) 13 of the electrode 11 on the surface of the insulating layer 14 is more than 30 mm, the leakage current is extremely small (sub of picoampere) even with significant (>80%) relative humidity of the sample gas (air). It almost does not distort the magnitude of the useful signal detector.

1. Photoionization detector for gas-analyzing equipment containing UV light with a window for output UV radiation, ionization chamber, the internal volume of which is limited by the space between the window surface and the surface of the cylindrical sleeve of insulating material having a Central internal channel and installed in front of the window with a gap relative to its surface, polarizing and collector electrodes, mounted in the Central channel of the sleeve, and the channels for the supply and withdrawal of the sample gas, the United Central to the cash sleeve, characterized in that the electrodes are designed in the form of rods, the outer surface of which except for the ends, placed near the end surface of the sleeve opposite the open lamp, covered with a layer of insulating material, and the electrodes are mounted parallel to each other and the outer surface layers of insulating material, which serves as a plating electrode, separated from each other by a gap.

2. The detector according to claim 1, characterized in that the UV lamp from the window to output UV radiation with metal cylindrical base portion of the inner surface of which covers the side surface of the lamp and hermetically connected with it, and in the middle part of the cap internal annular ledge, one surface of which is pressed tightly against the edges of the window, UV lamp, and the other surface of the protrusion is in contact with the end surface of the bushing of insulating material, and a portion of the inner surface of the cap remote from the lamp, hermetically covers the outer side surface of a sleeve of insulating material.

3. The detector according to claim 2, characterized in that, as the insulating material of the sleeve used elastic polymer material, and on the inner surface of the cap covering the nut, the thread used for the sealed connection of the cap is about the sleeve, and on the surface of the inner annular projection of the cap facing the sleeve is made annular projection having a pointed edge and serves to seal the inner volume of the ionization chamber.

4. The detector according to claim 2 or 3, characterized in that the lamp cap from the bushing wears a cylindrical metal shell surrounding the outer surface of the sleeve and the shielding electrodes of the ionization chamber from the effects of external electric fields.



 

Same patents:

The invention relates to instrumentation, and more particularly to the field of isotope analysis of chemical elements in the mass-spectrometric method

FIELD: instrument-making industry.

SUBSTANCE: detector has ultraviolet lamp with port for outputting ultraviolet radiation and ionization chamber. Inner volume of chamber is limited by space between surface of ultraviolet lamp port and surface of cylindrical bushing of electric-isolation material, having central inner channel. In the channel polarizing and collecting electrodes are mounted. Electrodes are made in form of rods. Outer surface of rods excluding ends, placed near end surface of bushing, is covered by layer of electric isolation material. Lamp on the side of port for outputting ultraviolet radiation is provided with cylindrical metallic cap. In middle portion of cap inner ring shelf is present, one surface of which is pressed to edges of lamp port, and another surface contacts end surface of bushing. Bushing is made of elastic polymer material and is screwed into hollow of cap, remote from lamp port.

EFFECT: higher efficiency.

4 cl, 3 dwg

FIELD: measurement technology.

SUBSTANCE: method of measuring ion concentration is based upon storage of charge in capacity of aspiration chamber while ions of tested gas deposit onto its collecting electrode during specified period of time. After it the charge is measured by means of registration of voltage pulse emerging at output of input device when capacitance of aspiration chamber discharges after charge-discharge cycle. Then the second cycle is performed at which moment of discharge of capacitance of aspiration chamber lags moment of discharge during first cycle being equal to period of signal introducing error into measurement of ion concentration. Ion concentration is found by means of combined processing of voltage pulses emerging at discharges of aspiration chamber due to subtraction of voltage pulses during first and second discharges.

EFFECT: improved precision of measurement.

2 dwg

FIELD: investigating or analyzing materials.

SUBSTANCE: device comprises flowing passage that has ionization chamber, unit for separating ions , and system for collecting ions. The ionization chamber has inlet branch pipe for supplying the gas to be analyzed and source of ionization. The ion-separating unit is made of a drift space defined by the coaxial central and outer electrodes connected with the sources of direct compensating voltage and alternating asymmetrical voltage. The additional flowing passage is made of conducting material, is connected with the outer electrode, and is interposed between the drift space and system for collecting ions coaxially to the drift space. The inlet of the additional passage is connected with the outlet of the drift space. The outlet of the additional passage is connected with the inlet of the system for collecting ions. The length of the additional passage should be sufficient to exclude the effect of alternating asymmetrical voltage of the drift space on the system for collecting ions.

EFFECT: enhanced sensitivity.

2 cl, 2 dwg

FIELD: physics.

SUBSTANCE: invention concerns impurity indicators for gas medium, primarily to leakage detectors. Gas impurity detection process is based on change of current flowing in the medium. For that purpose a cell consisting of metal anode and cathode with voltage applied between them is placed into the analysed medium. The cell is irradiated by vacuum UV radiation, that knocks photoelectrons out of the cathode surface and ionises impurity gas, which adds medium conductivity. The voltage applied to inter-electrode gap generates a flow of free electrons in that gap, as well as positive and negative ions left from photoionisation of the gas and from electron attachment to the electronegative gas. Change in the gas content causes change in electric current between the electrodes. Sensitivity of the process can be adjusted by such parameters as voltage in the gap between electrodes, distance between lamp aperture and irradiated cathode surface, lamp frequency content.

EFFECT: obtaining of information on changes in a gas medium and impurity source.

1 dwg

FIELD: medicine.

SUBSTANCE: technique provides preparing dilution series of wound fluid of different concentrations in distilled water: 1:1, 1:2 and 1:3; current 0.005, 0.01 and 0.02 mA is passed through a flow electrode of a joulemeter. The current work and time dependence is determined for each specimen; the current-voltage characteristic dynamics is assessed. A current work value from 0.003 to 1 mcJ shows the absence of anaerobic microorganisms in the wound fluid. If the current work ranges from 100 to 820 mcJ, the presence of anaerobic microorganisms in the wound fluid is stated.

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4 dwg, 2 ex

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