Abstract: An apparatus and method for analysing a gas of the kind adapted to produce an interference pattern displacements of which are indicative of changes of the constitution of the gas involves exposing an array 8 of photosensitive elements to the interference pattern. Respective digital indications of the intensity of the interference pattern falling of the elements are produced by means of a timing circuit 16 adapted to clock data out of the array 8 as a series of analogue pulses which are held by a fast peak detector 17 and converted by an analogue-to-digital converter 18 into digital indications. The position of a principal peak of the interference pattern is then determined by means of a microprocessor (not shown) adapted to determine the best fit of the digital indications with appropriate pre-stored values.

Abstract: Gas mixing and flow smoothing apparatus for use in for example an anaesthesia system comprises a mixing chamber (8) which receives the flow of two or more gases via control valves (6,7). The mixing chamber (8) is adapted to absorb fluctuations in the pressure of the gases therein through the provision of for example a spring-loaded piston (not shown) which forms one wall of the chamber, and the pressure at the outlet (30) from the chamber (8) is maintained at a substantially constant pressure by means of a valve (9). If desired, further attenuation of the gas flow may be achieved through the provision of a second series arrangement of surge damper (11) and back pressure valve (10) located downstream from the valve (9).

Abstract: In a method of electrochemically sensing the presence of O.sub.2, N.sub.2 O and halothane in a fluid, a gold or platinum electrode and a silver electrode are exposed to the fluid through a permeable membrane.both electrodes are held at a first potential and the currents due respectively to reduction of oxygen at the gold or platinum electrode and reduction of oxygen and halothane at the silver electrode are sensed,the silver electrode is held at a second potential and the current due to reduction of oxygen and halothane and nitrous oxide is sensed,and from the three currents the presence and/or concentration of any of the three gases is determined.