Abstract: A gas sensing assembly from which a number of gas sensing devices can be constructed for determining the concentration of an active gas in a gas mixture. The assembly comprises a self-contained sensing unit including a sensing element at which active gas reacts and is consumed, an output signal being produced proportional to the rate of reaction of active gas. A number of different control members are provided each defining a respective gas diffusion barrier, each member being separately securable to the sensing unit and detachable therefrom while leaving the sensing unit intact to enable gas sensing devices of different sensitivities to be constructed from the same sensing unit.

Abstract: A gas sensor comprises a substrate on which are mounted three cells. Each cell includes an interdigitated capacitor defined by a pair of comb structure, electrically conductive tracks with the fingers of the combs interleaved. The tracks of each capacitor are covered by an insulating and chemically inert protective coating of an electrolyte. A monitor monitors one of a resistive component and a capacitive component of the relative dielectric constant of the electrolyte independently of the other component.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.