In this manual, the word “probe” means the assembly consisting of % oxygen sensor, thermocouple sensor, their protection tube and the cold end termination head.

Two electrodes make contact with the platinum coated zirconium element at the tip of the sensor, one outer electrode, one inner electrode.

The special alloy protection tube is one conductor for the oxygen probe signal, which eliminates the need of a small signal wire normally exposed to the the furnace environment. The protection tube has excellent resistance to corrosion and oxidation at high temperature, and has good mechanical strength (since Hydrogen causes embrittlement).

The AP Probe is suitable for high temperature carburizing heat treating, carbonitriding and endothermic gas generators. The AP Probe is NOT suitable for nitriding applications.

Zirconia is a solid state electrolyte which conducts oxygen ions at temperatures above 1400°F. The ion conduction results in a voltage between the two electrodes. The magnitude of the voltage is dependent on the temperature of the Zirconia and on the ratio of the oxygen partial pressure on the reference side of the electrolyte to the oxygen partial pressure on the process side of the electrolyte.

Two connections to the Zirconia cell conduct the voltage to the four pin connector.