METHOD AND APPARATUS FOR DETECTING PRE-EXPLOSION CONCENTRATION OF METHANE IN AIR

FIELD: physics. ^ SUBSTANCE: according to the invention, the method and apparatus for detecting methane are based on using a cyclic mode of operation of a micropower thermochemical (catalytic) sensor, consisting of a working and a comparative sensitive element connected into a bridge measurement circuit and placed in a reaction chamber with diffusion access of the detected gas mixture through a microporous explosion-proof ceramic-metal gas-exchange filter. The disclosed method involves forcing heat-mass-exchange of the sensitive elements in a transient process, which is achieved due to that a current (voltage) pulse in each cycle is generated by stepped variation of the pulse amplitude, initially transmitting a pulse whose amplitude is 1.5-2 times higher than the nominal operating value and duration which is sufficient to achieve the working temperature of heaters, the amplitude is then instantly lowered to the operating value and the response (output signal) is measured in the initial phase of thermal equilibrium (ëÑ95% of the steady-state value of the output signal) at a strictly fixed time. The disclosed device includes membrane-type sensitive elements made using micromachining technology from nanoporous anodic aluminium oxide (AAO) with thin-film platinum heaters, current leads and contact pads sputtered on the surface of the membrane, wherein the main part of the membrane, according to its purpose and its functions, on which there is a heater-resistance thermometre and a catalytically active coating on the working element and a passivating coating on the comparative element, is in form of a cantilever separated from the basic mass of the membrane and the connected two cross members made from AAO with sputtered platinum thin-film current leads, wherein the geometric configuration of the cantilever and its defining dimension d' are minimised to values at which a film-type mode of heat transfer is realised, characterised by coefficient of heat transfer =0.5/d', where is the heat conductivity coefficient of the air medium surrounding the cantilever. ^ EFFECT: possibility of designing a sensitive element with a substrate made from anodic aluminium oxide, with minimisation of heat removal by convection and heat conductivity of the material of the platform, as well as shorter time for the transient process of heating the sensitive element to increase its efficiency when operating in pulsed mode. ^ 2 cl, 2 ex, 15 dwg, 2 tbl Способ и устройство детектирования