Method of protecting catalytic converters for exhaust gas purification and heat tone sensor for implementing the method

A method of using a heat tone sensor for protecting a catalytic converter used for exhaust gas stream purification by detecting hazardous operating conditions comprising the steps of:

• providing a heat tone sensor comprising at least two NTC or PTC resistors with a coating of a catalytically active material being provided on the sensor in a region of at least one of the resistors, and with the catalytically active material initiating identical exothermal reactions as those which take place in a catalytic converter;
• disposing the heat tone sensor in at least a part of an exhaust gas stream flowing through the catalytic converter upstream of the catalytic converter so that the catalytically active material initiates identical external reactions as those which take place within the catalytic converter;
• detecting a deviation of the exhaust gas composition from a change in resistance in the resistor disposed in the region of the catalytic coating due to overheating of the resistor resulting from an excessive exothermal reaction;
• and,
• taking countermeasures to protect the converter when a threshold value of resistance change is exceeded.