Page 253 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Catalytic Converter Functionality Diagnosis by Means of Temperature Measurements 235

Temperature sensors used in monitoring of catalytic converters

Before examining in detail the diagnosing methods that use temperature sensors, it is
worthwhile to describe some temperature sensors and to explain their operation principle.

The use of a simple thermocouple a few centimeters upstream of the converter inlet presents
durability and signal processing problems, as the thermocouple voltage is too low for a typical
vehicle data acquisition system. As mentioned already, the aging reduces the temperature
gradient from the front face of the converter and causes a shift of the main reaction zone in the
direction of the flow, so that different temperature profiles are expected during the course of
aging. Thus, a single temperature measurement in a fixed position would probably not be
sufficient to monitor exothermal heat release over a long operating period. So more
sophisticated temperature sensors are necessary for monitoring the efficiency of catalytic
converters.

temperature sensor

jacket

insulating
layer

A-A

Fig. 99 (from W09114855)