6 u03c9 m were coated with a ceramic composition having dispersed therein platinum with a concentration of 0 75 mole l the ceramic material can be zirconia alumina silica tungsten carbides titanium dioxide silicon nitrides and mixtures thereof the surface area of the porous ceramic layer is enlarged by means of known techniques such as the sol gel technique or in situ precipitation in a pyrolytic cleaning cycle without increasing the power input to the oven and after a stabilization period the applicant has measured a change of temperature of the catalytic wire or element due to the chemical reaction when the temperature reaches a steady value this meant that the pyrolytic cycle was finished the resistance of the sensing wire at 400 u00b0 c was about 52 452 u03c9 and resistance at 500 u00b0 c was about 63 24 u03c9 the applicant experienced a practically linear dependence of resistance from temperature a raise in temperature of about 1 u00b0 c due to catalytic reaction has caused a change of resistance of 63 24 52 452 100 0 108 u03c9 in fig6 and 7 a further embodiment is shown in which the catalytic element 9 a is used as a resistance heating element whose ends 31 a and 31 b are linked to an electric power supply system 30 and to a power meter system 32 in this embodiment the electrical power is supplied to the catalytic element and the power consumed by the element depends on the temperature of the catalytic coated wire and therefore as in the previous embodiment on the chemical reaction.