The principle of zirconia sensors is to use zirconia ceramic sensing elements to measure the oxygen potential in various heating furnaces or exhaust pipes, and calculate the corresponding oxygen concentration based on the principle of chemical equilibrium to monitor and control the combustion air ratio in the furnace, thereby ensuring product quality. Furthermore, the measuring element meets exhaust emission standards and is widely used for atmosphere control in various coal-fired, oil-fired, and gas-fired furnaces. It is currently the best method for measuring combustion atmosphere, with a simple structure, fast response, easy maintenance, ease of use, and accurate measurement. Using zirconia sensors for combustion atmosphere measurement and control not only stabilizes and improves product quality but also shortens production cycles and saves energy.
Zirconia sensors are designed to utilize the stable oxygen ion conduction properties of zirconia ceramics in environments of 650°C or higher. Under certain temperature conditions, if different oxygen partial pressures (i.e., oxygen concentrations) exist in the gas on both sides of a bulk zirconia ceramic, a series of reactions will occur inside the zirconia ceramic, and oxygen ions will migrate. At this point, a stable millivolt-level signal can be measured through the lead-out electrodes on both sides of the zirconia, which we call the oxygen potential.
The zirconia sensor follows the Nernst equation: where E is the oxygen potential (mv) output by the zirconia sensor, Tk is the absolute temperature inside the furnace (K), and P1 and P2 are the oxygen partial pressures of the gases on either side, representing zirconia. In practical applications, one side of the zirconia is introduced into a gas with a known oxygen concentration (usually air), which we call the reference gas. The other side is the gas to be measured, which is the atmosphere in the furnace we want to detect. The signal output by the zirconia sensor is the oxygen potential signal. Using the Nernst equation, we can obtain the relationship between the oxygen partial pressure and the oxygen potential in the furnace atmosphere.
When the reference gas is air, it can be expressed as: where E is the oxygen potential output by the zirconia sensor; Tk is the absolute temperature inside the furnace; and PO2 is the partial pressure of oxygen inside the furnace. Our zirconia sensor products are equipped with a self-heating device. The temperature is typically maintained at 700℃, so the Tk value is essentially constant, and therefore the oxygen partial pressure concentration inside the furnace can be directly measured using the above formula. In engineering applications, standard gases are used to calibrate the correspondence between the zirconia sensor output oxygen potential E and the oxygen partial pressure concentration PO2. For the most precise calibration, this method is also the most accurate.
Here we recommend the commonly used British SST zirconia high-temperature oxygen analyzer (zirconia sensor) – OXY-Flex, which can be used to control boiler combustion systems:
High-precision linear output;
Configurable outputs: 4-20mA and 0-10VDC or RS232 COM port;
Selectable output ranges: standard ranges 0-25% and 0-100%, or fully adjustable via RS232 in 0-100% mode;
Externally triggered automatic or manual calibration;
It can be calibrated in ordinary atmosphere or in gaseous atmosphere of known concentration.
A 3.3VDC logic output can diagnose the condition of the sensor pump cycle.
Optional filtering settings allow for suitable fast and dynamic output or slow, stable output.
