OXYGEN PROBE SYSTEM FOR ATMOSPHERE CONTROL
An oxygen probe allows INSITU measurement of atmosphere composition by measuring the level of oxygen traces in a metallurgical atmosphere. The hearth of an oxygen probe consists of zirconia disc on either side of which are the terminals of platinum electrodes . This disc is sealed in a high alumina refractory tube (shell) with one electrode running inside the shell and the other on the outside. A small diaphragm pump constantly feeds ambient air into the shell via a stainless steel reference air tube. When this shell is inserted into the furnace or a gas generator, the two electrodes are subjected to different oxygen partial pressures( The reference air has an oxygen pressure of 20.9 ). As a result , a D>C potential is created between the electrodes which is proportional to the logarithm of the ratio of the two oxygen partial pressure.
With the help of this potential and knowledge of feeds of the gas generator/ furnace, the gas composition can be determined. Typically, the feed to a gas generator are natural gas (mostly methane ), LPG (A MIXTURE OF PROPANE AND BUTANE) and ammonia . Similarly, typical feeds to a furnace are such externally manufactured gases, or liquid methanol, or commercial gases such as hydrogen or nitrogen. (For monitoring and controlling the flow of the liquids we can provide flow control panels.
Generally in metallurgical furnaces, the full composition of gas is seldom required. For most of the processes, it is enough to know the gas dew point or, in the case of carburising atmosphere, its carbon potential. Relationships between these parameters and the oxygen potential are readily available in the form of equations, homographs or charts. Some representative equations are shown in para 2.0 of this spe. And the remaining will be furnished along with the operating instruction of the oxygen probe system installed by us.
With suitable control gear, the gas composition can be controlled by using the oxygen probe system MODEL OXPS. After major settings are made by means of hand operated flow valves ,the fine tuning is done by using an ON/OFF controller to work with solenoid valves, or by using a proportional controller to work as an actuator kit and butterfly valve.
The oxygen probe milivolts out put as well as its relationship with the gas composition depends on the furnace/ generator temperature. A nuiltin thermocouple is therefore supplied along with the probe for accurate determination of the gas composition.