Patent ID: 8153067

Claim:
A circuit comprising: a supply voltage; and a catalytic measuring element connected to said supply voltage without a protective resistor and without a thermal safety device arranged upstream, said catalytic measuring element comprising a pellistor dimensioned to have a temperature-dependent variable resistance that limits the current at any point in time to a value that prevents ignition by sparks in an environment with explosion hazard and does not change beyond limits to ensure a sufficient limitation of the current at any time whereby an ignition by spark is effectively prevented in an environment with explosion hazard and said pellistor is dimensioned to act as a thermal safety device to limit the output that can be fed to said pellistor and wherein said pellistor contains a wire coil consisting of platinum or a platinum alloy with a wire diameter of 0.01 mm to 0.08 mm and a catalytic bead consisting of γ-aluminum oxide or a mixture of γ-aluminum oxide and zirconium oxide with catalysts from precious metal particles and is dimensioned such that its resistance is in the range between 3 Ohm and 25 Ohm at an applied voltage of 500 mV to 2,500 mV.