SU787974A1 - Heat conduction detector - Google Patents

Description

(S) THERMAL CONDUCTIVITY DETECTOR

one

The invention relates to analytical instrumentation and serves both for gas analysis and for gas chromatography.

Thermal conductivity detector designs are known, consisting of a metal body with cylindrical chambers placed in it / each of which is connected to the upper and lower parts with channels through which the analyzed gas flows, and placed inside the chambers. vitality elements electrically connected to the bridge measurement circuit l.

The disadvantage of such detectors is not quite identical to the thermal sensitivity of sensing elements placed in different chambers, due to the inaccuracy of their installation. The indistinguishability of the thermal mode leads to a different reaction of sensitive elements: to fluctuations in the body temperature, the supply voltage, the flow rate of the gas being analyzed, and is the main cause of the appearance in the electrical signal of the noise detector, which limits its sensitivity threshold.

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The closest technical solution to the proposed one is a thermal conductivity detector, made in the form of a metal body, in

5 which are located in the lower part of the supplying Gas channel, and in the upper part of the outlet are cylindrical chambers in which sensitive elements are placed, surrounded by heat shields installed with a gap relative to the chamber walls. On one side of each heat shielding screen opposite to the supply gas canal 5, there are narrow slits located along the generator of the cylinder. Ngshichie thermal screens aligns the thermal mode of sensing elements placed in different chambers, and

20 reduces the effect of destabilizing factors on the electrical signal of the detector t, 2J.

Claims (1)

The disadvantages of this detector are a significant decrease in sensitivity and an increase in inertia due to the diffusion character of the flow of the analyzed gas along the sensitive elements of the detector. The deterioration of these characteristics is unacceptable when using thermal conductivity detectors in gas chromatographs. The purpose of the invention is to increase the sensitivity and reduce the inertia of the thermal conductivity detector while simultaneously ensuring the stability of the electrical signal. This goal is achieved by having two transverse channels in each heat shield, the lower axis coinciding with the feed and the upper axis with the outlet channels of the housing, and Sensitive elements are located between the transverse channels of the screen. The presence of transverse channels in heat shields leads to a semi-diffusive nature of the gas flow along sensing elements, in which part of the gas flow, not dependent on the total gas flow, under the simultaneous influence of diffusive and convective factors passes inside the heat shield, which increases the sensitivity and inertia the detector. The drawing shows a thermal conductivity detector. Four; Sensing elements are installed in chambers of housing 1. Sealing is provided with cap nuts 2 and gaskets 3. Heat shields 4 have an annular groove in a region exceeding the length of the sensing element, which forms a gap between the screen and the wall of the chamber. To ensure the alignment of the screen 4 and the camera part of the screen has a diameter that provides a sliding fit. The transverse channels b and 7 in the screen are formed by two pairs of holes, the axes of which coincide with the axes of the channels in the body of the detector. The distance between the axes of the channels exceeds the length of the sensitive energy 5, placed in the inner cavity of the heat shield 4. The system of gas channels in the housing 1 and heat screens 4 forms, together with the chambers, two independent gas paths 8 and 9 for comparative and measuring flows. The detector works as follows. A pure carrier gas flows through two comparative chambers, and two measuring gates flow through the gas leaving the chromatographic column. In each chamber, the gas flow is divided into two parts: one flows through the annular gap between the gauge screen 4 and the wall of the chamber, and the other inside the heat shield, OMiaiBaH sensing element 5. Sensitive elements 5 form a four-arm bridge and are heated by a constant electric current. The difference in thermal conductivity of gases forming the comparative and measuring flows leads to a difference in temperature and electrical resistance of the sensitive elements 5 installed in the comparative and measuring chambers, which causes the appearance of an electrical signal in the measuring diagonal of the bridge. The sensitivity of the proposed detector is about 2 times higher, and the inertia is two times lower than that of other diffusive thermal conductivity detectors, though; (e Bpei-ui, its stability is an order of magnitude higher than that of a semi-diffusion thermal conductivity detector screens The invention of the thermal conductivity for gas analysis, for example for gas chromatography, made in the form of a metal case in which the inlet gas channel is connected to the lower part and to the outlet , cylindrical chambers in which sensing elements are placed, surrounded by heat shields installed with a gap in relation to the chamber walls, characterized in that, in order to increase sensitivity and reduce inertia while simultaneously ensuring stability, two thermal transverse axes are made in each heat shield the lower one coincides with the feed and the axis of the upper one with the outlet channel of the body, and the sensitive elements are located between the transverse channels of the screen. Sources of information taken into account during the examination 1. USSR Author's Certificate No. 54693, cl. G 01 N 27/18, 1937. 2, Automatic and semi-automatic gas analyzers. Issue, 1, Instrumentation. Means of automation and control systems, M., 1966, p. 7374 (prototype).