(DE3635513-C)      Method for detecting constituent of combustible gases in an air mixt. using measuring unit equipped with an indicator, which works according to the tempering method as well as the heat conductivity method, carried out with the existence of a measurement signal below a specified reference value (R1), and changed over from the heat tempering method to the heat conductivity method, as soon as the measurement signal has reached a limiting value (C).    A single sensor element catalytically active at high temp. is used so that: the sensor is held constant at a first temp. (T1), sufficiently to begin the measurement for the heat conductivity measurement, the resulting measurement signal is compared with the reference value (R1), if it fails to reach this value (R1), the temp. of the sensor (1) is increased to a second temp. (T2) to facilitate the heat tempering measurement.    The measurement signal delivered from the sensor, with which a loading limit value (G) corresp. to a high gas concn. than the reference value (R1) is compared and its temp. lowered to the temp. and is held constant with failure to reach value (G).    ADVANTAGE -   Very accurate. Unambiguous measurement in total concn. range of 0-100%. Compact, small number of parts. (7pp)i    (US4804632-A)      Proportion of combustible gases in an air mixt. is detected by a sensor (1), suitable for thermal conductivity and heat tone measurements, connected to a controllable current source (2) and load resistance (3). Resistance across the sensor is measured with the aid of an amplifier (4) and converted to temp. in a computer (5,6), the signal passing via a lead (7) to the input of a measurement amplifier (8), whose output passes to a computer (5). The computer continuously interrogates reference values or load limit value in a comparator (6), which controls current source (2) via feedback (12), supplying the sensor with current required to maintain its temp. or to switch over between temps. for the different measurements. Desired value is corrected by a probe (15) as a function of ambient temp.    ADVANTAGE -   Unambiguous measurement of combustible gas over total concn. range, with lowest possible power consumption. (8pp)s    (DE3777854-G)      The proportion of combustible gases is detected by a meter with indicator (13) operating by both the heat tone and heat conduction methods, giving only a heat tone reading below a set ref. value. The meter uses a single sensor element (1) catalytically active at higher temps. At the start of measurement the se