Abstract: The diaphragm comprises a peripheral zone (12) and a central zone (16) in the same plane. Between these zones there is a corrugated zone comprising 2n corrugated portions (18.sub.1 to 18.sub.4) which are separated by connection zones (20.sub.1 to 20.sub.4). Any one corrugated portion may be derived from the adjacent corrugated portion by a rotation through 180.degree. about the connection zone, or else by a rotation of 2.pi./2n about the diaphragm axis followed by a symmetry about the housing plane.

Abstract: A flow meter comprises electrodes (16, 18), induction windings (12, 14), a winding driver circuit (20), and a processor circuit (22). The winding excitation current is a combination of a current of period T.sub.1 and a current of period T.sub.2, where T.sub.2 >T.sub.1. The processor circuit (22) processes the voltage signal sent by the electrodes and generates intermediate measurement signals of periods T.sub.1 and T.sub.2. These signals are then used to generate a correction signal for removing the relaxation effect from the measurement signal S.

Abstract: The temperature of the condensation point of light hydrocarbons in a gas is quickly determined by heating a frosted mirror placed in a gas swept enclosure up to the evaporation temperature of all the heavy and light hydrocarbons. The mirror is first cooled as quickly as possible to a temperature higher than the presumed condensation temperature for the light hydrocarbons. Then is cooled much more slowly until the appearance of the first condensations on the mirror. Another cycle as described above is started, in which the presumed condensation temperature value is taken as being equal to the condensation start temperature value of the previous cycle.

Abstract: A gas analyser of the infra-red radiation absorption type, particularly for measuring the amounts of CO.sub.2 and CO in vehicle exhaust gases, comprises a pair of infra-red radiation sources arranged to direct their radiation along a measurement path and a reference path respectively, the radiation entering each path being periodically interrupted by a rotating commutator. Two measurement chambers for receiving the gas to be analysed and respective detection chambers for CO.sub.2 and CO are alternately disposed along the measurement path, while two reference chambers and two more such detection chambers are alternately disposed along the reference path, corresponding detection chambers being connected to respective differential pressure sensors of the variable capacitance type. The analyser includes a calibration cell containing predetermined concentrations of CO.sub.2 and CO. The cell is selectively interposable in the measurement path, and is connected to a flexible-wall chamber.