User description

The zirconia oxygen analyzer is appropriate for measurements of ppm to % amounts of oxygen in a fuel or combination of gases. The zirconia mobile is an electrochemical galvanic mobile utilizing a large temperature ceramic sensor made up of stabilised zirconium oxide.Within Vacuum gauge is mounted in a temperature controlled furnace with the essential electronics to process the sign from the detection mobile. Typically measurements are shown directly via a digital display as oxygen concentration above the range .01ppm to a hundred%.The principle guiding Systech’s zirconia oxygen analyzerThe zirconia mobile is a higher temperature ceramic sensor. It is an electrochemical galvanic cell comprising of two electrically conducting, chemically inert, electrodes attached to possibly aspect of a reliable electrolyte tube. This is demonstrated schematically in Determine one beneath.The tube is fully fuel restricted and manufactured of a ceramic (stabilised zirconium oxide) which, at the temperature of procedure, conducts electrical energy by indicates of oxygen ions. (Be aware: In sensors of this sort, the temperature has to be over 450°C just before they turn out to be lively as an electrolyte conductor). The likely variation across the mobile is offered by the Nernst equation.Where:E is the possible variation (volts)R is the gasoline constant (8.314 J mol-1 K-1)T is the absolute temperature (K)F is the Faraday continuous (96484 coulomb mol-one)P1 & P2 are the partial pressures of the oxygen on both aspect of the zirconia tubeThe Nernst equation can for that reason be reduced to:Thus, if the oxygen partial stress at one particular of the electrodes is acknowledged and the temperature of the sensor is controlled, then oxygen measurement of the prospective variation amongst the two electrodes allows the mysterious partial pressure to be calculated.Be awareThe partial stress of the gasoline is equivalent to the molar focus of the element in a gas mixture occasions the whole force of the gasoline mixture.PO2 = CO2 P2the place:PO2 = Oxygen partial strainCO2 = Molar concentration of oxygenP2 = Overall stressCase in pointFor atmospheric air:CO2 = 20.nine%P2 = one ambiancePO2 = (.209/a hundred) x onePO2 = .209 atmospheresPrinciple of ProcedureThe zirconia mobile employed by Systech Illinois is made of zirconium oxide stabilised with yttrium oxide as the ceramic with porous platinum electrodes. This mobile is shown in Determine one.Figure 1: Enlarged cross sectional illustration of the zirconia substrateMolecular oxygen is ionised at the porous platinum electrodes.PtO → Pt + ½ O2½ O2 + 2e- → O2–The platinum electrodes on each and every aspect of the mobile supply a catalytic area for the change in oxygen molecules, O2, to oxygen ions, and oxygen ions to oxygen molecules. Oxygen molecules on the higher focus reference gasoline aspect of the cell gain electrons to turn into ions which enter the electrolyte. Simultaneously, at the other electrode, oxygen ions lose electrons and are launched from the surface area of the electrode as oxygen molecules.The oxygen content material of these gases, and as a result the oxygen partial pressures, is different. Therefore, the rate at which oxygen ions are created and enter the zirconium oxide electrolyte at every electrode differs. As the zirconium oxide permits mobility of oxygen ions, the number of ions relocating in every single course across the electrolyte will depend on the price at which oxygen is ionised and enters the electrolyte at each electrode. The mechanism of this ion transfer is intricate, but it is acknowledged to include vacancies in the zirconia oxide lattice by doping with yttrium oxide.The consequence of migration of oxygen ions throughout the electrolyte is a net stream of ions in one particular path dependent upon the partial pressures of oxygen at the two electrodes. For instance in the Nernst equation:If P1>P2 ion movement will be from P1 to P2 i.e. a constructive E.M.F.If P1If P1=P2 there will be no net ion flow i.e. a zero E.M.F.In the zirconia analyzer, the Nernst equation is writtenThe zirconia analyzer uses air as a reference, a constant oxygen concentration of 20.9%, and the zirconia cell is mounted inside a furnace whose temperature is controlled to 650°C (923 K).Thus, our Nernst equation further reduces to:The zirconia analyzer electronically calculates the oxygen partial pressure, and therefore oxygen concentration, of a sample gas with unknown oxygen concentration. This is accomplished by measuring the potential, E, produced across the zirconium cell electrodes, substituting for E in the Nernst equation and anti-logging to obtain PO2. The cell potential output is shown in Figure 2.Figure 2 Graph of cell potential vs. oxygen concentration of zirconia cell.By anti-logging the equation, the output signal can be displayed directly on a digital readout meter as oxygen concentration in ppm or %.CalibrationAs the zirconia instrument uses an absolute measurement principle once built and factory calibrated, it does not require any further factory calibration.Factory calibration consists of calibration of the electronics to accept the millivolt input signal from the detection cell and checking that the instrument then reads correctly on air, 20.9%. The instrument is then further checked for correct reading on ppm oxygen content in nitrogen.Applications of zirconia oxygen analyzersThe zirconia analyzers may be used for measurement of oxygen at any level between 0-100% in gases or gas mixtures.The only restriction on the instrument’s usage is that the gas to be measured must not contain combustible gases or any material that will poison the zirconium oxide detection cell.Any combustible gas, e.g. CO, H2, hydrocarbons such as methane, in the sample gas entering the instrument will combine with any oxygen in the sample gas in the furnace due to the high temperature at which the furnace is kept. This will actually reduce the amount of oxygen in the sample gas and cause the instrument to give an incorrect low reading.Materials that will poison the detection cell are:Halogens e.g. ChlorineHalogenated Hydrocarbons e.g. MethylchlorideSulphur containing compounds e.g. Hydrogen SulphideLead containing compounds e.g. Lead SulphideGases or gas mixtures containing any of the above are not suitable for oxygen determination with a zirconia type oxygen analyzer.