City Technology Limited

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Coal Industry (Patents) Limited

The Governor and Company of the Bank of Scotland

Yat S Chan

Anthony D Tantram

Bryan S Hobbs

John Robert Finbow

William J Aston

An electrochemical gas sensor comprises sensing and counter electrodes (1,2). A conduit (15) permits access of gas to the sensing electrode (1). An electrolyte reservoir (23). A porous, block-like body (24) is positioned in the reservoir (23) for conveying electrolyte to the sensing and counter electrodes and at least partly supporting other components of the sensor.

Electrochemical gas sensor

A gas diffusion control assembly comprises a gas inlet; a restriction to the rate of flow of gas or vapor from the gas inlet in the form of a porous diffusion barrier extending across the gas inlet; and a polythene disc for causing all gas or vapor passing out of the inlet into the diffusion barrier to diffuse through part of the barrier along a path with a lateral outward component relative to the direction of action through the gas inlet.

Gas diffusion control assembly

An electrochemical gas sensor for sensing an alkaline gas such as ammonia. The sensor comprises at least sensing and counter electrodes provided in a cell containing an aqueous electrolyte, the cell further including a diffusion barrier to restrict the access of gas to the cell, and a chemical species with which the gas reacts in use to form a product which is more electrochemically active than the gas. The chemical species is one of iodine, Nesslers reagent and a solution of manganous and silver nitrates.

Gas sensor

The housing 1 of a gas sensor carries a diffusion barrier 2 for restricting the access of gas to the sensing element 4 and a filter 3 mounted between the diffusion barrier 2 and the sensing element 4. As a result, gas reaching the filter 3 must first pass through the diffusion barrier 2 so that its flux is substantially reduced and the life of the filter is increased correspondingly.

An electro-chemical cell has porous sensing and counter electrodes S, C mounted on porous PTFE tapes 4, 5 and contacting the electrolyte of the cell which is drawn from a reservoir by a wick 12. Gas passes directly to the electrode S at 14 and any gas which does not react passes through the electrode S to the electrode C, passing across the electrolyte space by way of a porous insulating separator 10 which is partly hydrophilic and partly hydrophobic, thus providing a path for gas while preserving the electrolyte path between the electrodes. The current flowing between the electrodes is measured in the usual way. The electrode C will not see any particular gas which reacts fully at the electrode S since it will be removed by this electrode first. The electrode C will, however, see any other gas which only partially reacts at the electrode S, thus achieving partial or even complete elimination of the effect of an interfering gas.

An electro-chemical cell for quantitatively detecting an acidic or an alkaline gas, e.g. carbon dioxide, includes a sensing electrode 9 which is connected to a top cap 12 by a contact strip 8 and is accessible to the gas to be tested through a hole 13. The electrode 9 comprises an electro-chemical couple whose potential is pH-dependent (e.g. silver/silver oxide for carbon dioxide) the active material being supported by a nickel gauze to give good current collection. A counter electrode 2 without significant gas access is immersed in an electrolyte 3 whose pH is such that it will change following adsorption of the gas being tested for. A wicking separator 7 ensures an electrolytic path between the two electrodes. The components are contained within a metal can 1, the top cap 12 being held by folding over the rim 5. An insulating grommet 6 is fitted between the two electrodes. When using silver/silver oxide for the sensing electrode 9, the counter electrode may be of the same material and the electrolyte may be potassium carbonate. The current flowing between the electrodes is a measure of the concentration of gas being detected. A reference electrode 14 may also be included.

A gas sensor cell assembly has planar electrodes separated by a planar hydrophilic wick which extends through the electrode into an electrolyte expansion chamber where it contacts an electrolyte. The cell is extremely compact and operates in all orientations.

An electro-chemical sensor for the measurement of concentrations of gas or vapour in accordance with the limiting current principle comprises an electrolytic cell 1 having a sensing electrode 9, a counter electrode 2, an intervening body of electrolyte 4 and a restriction to the rate of access of gas or vapor to the sensing electrode in the form of a porous diffusion barrier 13. The improvement resides in the feature that substantially all the active pores of the diffusion barrier are sufficiently small as to cause diffusion through them to be in accordance with the Knudsen principle, i.e. the diffusion mechanism is effectively determined solely by collisons between the diffusion molecules and the walls of the pores. The barrier is constituted by a body of porous PTFE which may be in the form of a piece of unsintered PTFE tape or compressed PTFE powder formed by drying a dispersion of PTFE in water.

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London, United Kingdom

Yat S Chan