RU2523765C1 - Photo-ionisation detector for gas analysers - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: proposed detector comprises UV lamp with flat outlet opening. Flow-through chamber is arranged above said opening and composed by two disc electrodes. These are arranged one above the other and made of metals with different work function and separated by ring-like fluoroplastic washer. Besides, it comprises electrometer whereto connected are electrodes and signal detector registrator connected to electrometer output. Lower electrode has central bore while upper electrode has analysed gas flow intake channel. In compliance with this invention, said detector incorporates extra flat heater arranged at upper electrode for heat contact therewith. Cylinder made of heat-insulating dielectric material is arranged between lower electrode and lamp flat outlet opening so that cylinder mirror axis is aligned with that of flow-through chamber. Said cylinder has central bore and analysed gas discharge flow communicated with said opening. Note here that upper electrode bottom surface is coated with palladium-bearing material.

EFFECT: higher precision.

2 cl, 1 dwg

Description

The invention relates to the field of analytical technology, namely to means for measuring the concentrations of components in gas analysis.

Known photoionization detector of gases and vapors (Farzane N.G., Ilyasov L.V., Azim-Zade A.Yu. Automatic detectors of gases and liquids. M: Energoatomizdat, 1983, p.96), consisting of an ionization chamber equipped with two electrodes for creating a corona discharge, a polarizing electrode and a collector electrode for measuring the amount of ions formed. Also in the chamber are openings for the input and output of the analyzed gas. The detector’s principle of operation is that in a stream of additional gas, for example argon, a direct current corona gas discharge is excited. As a result of the discharge, metastable argon atoms are formed, which when illuminated create a stream of ions, in the path of which a collector electrode is placed. Photoions either directly ionize the molecules of the components of the mixture, or ionization occurs due to the transfer of photon energy through newly formed metastable argon atoms. The ion current between the polarizing and collector electrodes, to which a potential difference of 240 V is applied, is measured using an electrometer.

The disadvantage of this photoionization detector is the high noise level of the signal, which arises due to the fact that a corona gas discharge is excited in the detector chamber.

The closest in technical essence is a photoionization detector for gas analysis equipment (RU 115072, 04/20/2012, Ilyasov L.V., Evlanova N.I. Photoionization detector for gas analysis equipment.), Containing a UV lamp equipped with a flat exit window, over which a flow chamber is placed, formed by two disk electrodes located one above the other, made of metals of various electron work function and separated by an annular fluoroplastic gasket, electro emp to which the electrodes are connected, and the detector signal recorder connected to the output of the electrometer, wherein the lower electrode has a central opening into which is encased window of a transparent material to ultraviolet radiation, and the upper electrode is provided with openings for entry of the sample gas stream.

The disadvantage of this detector is its relatively low sensitivity to sulfur-containing substances.

The objective of the invention is to increase sensitivity to sulfur-containing substances.

The technical result - the creation of a photoionization detector with increased sensitivity to sulfur-containing substances.

The stated task and the indicated technical result are achieved by the fact that in the photoionization detector for gas analysis equipment, containing a UV lamp with a flat exit window, over which there is a flow chamber formed by two disk electrodes located one above the other, made of metals with different electron work function and separated by an annular fluoroplastic gasket, an electrometer to which the electrodes are connected, and a detector signal recorder connected which is connected to the output of the electrometer, the lower electrode being made with a central hole, and the upper one provided with a channel for inlet of the analyzed gas stream. According to the invention, the detector further comprises a flat heater placed on the upper electrode with the possibility of thermal contact with it, and a cylinder made of heat-insulating dielectric material placed between the lower electrode and the flat output window of the ultraviolet lamp so that its axis of symmetry coincides with the axis of symmetry of the flow chamber, while p is provided with a central opening and a channel for output of the sample gas stream is connected to this opening.

This design of the detector provides an increase in the sensitivity of the detector to sulfur-containing substances due to the fact that the lower side of the upper electrode is covered with a layer of palladium-containing material and the temperature of its flow chamber can be set at 300-400 ° C, while the temperature of the UV lamp can remain no higher than permissible by technical conditions. This is ensured by the fact that a cylinder of heat-insulating dielectric material is placed between the window of the ultraviolet lamp and the lower disk electrode.

Compared with the prototype of the claimed design has a distinctive feature in the combination of elements and their relative position.

A diagram of a photoionization detector for gas analysis equipment is shown in the drawing.

The photoionization detector contains an ultraviolet lamp 1 with a flat exit window 2, above which a flow chamber 3 is formed, formed by two disk electrodes 4 and 5, located one above the other, made of metals with different electron work function and separated by an annular fluoroplastic gasket 6, electrometer 7 , to which the electrodes are connected, and a detector 8 of the detector signal connected to the output of the electrometer. The lower electrode 4 is made with a Central hole 9, and the upper electrode 5 is provided with a channel 10 for the entrance of the flow of the analyzed gas. The detector further comprises a flat heater 11 located on the upper electrode 5 with the possibility of thermal contact with it, and a cylinder 12 of insulating dielectric material, located between the lower electrode 4 and the flat output window 2 of the ultraviolet lamp 1 so that its axis of symmetry 13 coincides with the axis of symmetry of the flow chamber 3, while the cylinder 12 is provided with a Central hole 14 and a channel 15 for the exit of the flow of the analyzed gas connected to this hole 14. The lower side of the upper electrode 5 washed with a layer 16 of palladium-containing material. The detector is equipped with PTFE insulation 17 and a metal protective shield 18.

The operation of the photoionization detector is as follows.

The analyzed gas is continuously pumped through the inlet 10 of the flow chamber 3 of the photoionization detector. In the space of the chamber 3 between the lower disk electrode 4 and the upper disk electrode 5, covered with a layer 16 of palladium-containing material, the analyzed gas is ionized by the ultraviolet radiation of lamp 1. Since the electrodes 4 and 5 are made of different metals with different electron work functions, between them a potential difference occurs and an electric field arises in the flow chamber 3. Under the influence of this field, the ions move in the chamber 3. The value of the detector signal is measured and recorded using an electrometer 7 and a recorder 8. The resulting signal is proportional to the microconcentration of the determined components of the analyzed gas. Since the detector additionally contains a cylinder 12 of heat-insulating dielectric material, when the temperature of the flow chamber 3 is equal to 300-400 ° C, the temperature of the lamp 1 of ultraviolet radiation does not exceed the allowable technical specifications.

It was established experimentally that the proposed photoionization detector for gas analytical equipment, using nickel electrochemically treated with palladium and aluminum, a cylinder made of heat-insulating dielectric material, an ultraviolet lamp with a wavelength of 170-200 nm, allows microconcentrations of sulfur-containing substances to be measured in fractions r.r..m.

The advantage of the proposed technical solution is:

- simplicity of design;

- the possibility of using microconcentrations of sulfur-containing substances in analyzers.

The proposed device can be implemented on the basis of standard electronic devices and ultraviolet sources.

The detector can find application for measuring microconcentrations of sulfur-containing substances in air and in gas chromatography.

Claims (2)

1. A photoionization detector for gas analysis equipment, containing an ultraviolet lamp with a flat exit window, over which there is a flow chamber formed by two disk electrodes located one above the other, made of metals with different electron work function and separated by an annular fluoroplastic gasket, electrometer, to which the electrodes are connected, and a detector signal recorder connected to the output of the electrometer, the lower electrode being made with a central hole rstium, and the upper one is provided with a channel for the entrance of the analyzed gas stream, characterized in that the detector further comprises a flat heater placed on the upper electrode with the possibility of thermal contact with it, and a cylinder of heat-insulating dielectric material placed between the lower electrode and the flat exit window of the ultraviolet lamp radiation so that its axis of symmetry coincides with the axis of symmetry of the flow chamber, while the cylinder is equipped with a central hole and a channel for the flow of the analyzed about gas connected to this hole. 2. The photoionization detector according to claim 1, characterized in that the lower side of the upper electrode is coated with a layer of palladium-containing material.