A zirconia probe is used to measure very low concentrations of % oxygen in the furnace, typically less than 1 x 10 -20. To supply the required species carbon it is usual for the furnace to be supplied with a base endothermic carrier gas which conditions the furnace, at say 20% CO for a methane based carrier gas.
In the atmosphere loop, the controller uses the carbon potential calculation based on the known oxygen reading to increase the carbon potential by allowing enrichment gas (ie methane) to enter the furnace.
Conversely, to decrease the carbon potential, controlled air is introduced into the furnace. Automatic probe cleaning functions ensure that the reading is accurate, while probe health and sooting alarms warn of a deterioration in the probe performance.