The zirconia oxygen analyzer is ideal for measurements of ppm to % degrees of oxygen in a gasoline or combination of gases. The zirconia cell is an electrochemical galvanic cell utilizing a significant temperature ceramic sensor made up of stabilised zirconium oxide.
Inside of an instrument the zirconia cell is mounted in a temperature managed furnace with the vital electronics to system the signal from the detection cell. Generally measurements are exhibited directly by using a digital screen as oxygen focus above the vary .01ppm to a hundred%.
The theory powering Systech’s zirconia oxygen analyzer
The zirconia mobile is a superior temperature ceramic sensor. It is an electrochemical galvanic mobile comprising of two electrically conducting, chemically inert, electrodes hooked up to possibly facet of a reliable electrolyte tube. This is shown schematically in Determine 1 under.
The tube is completely fuel tight and manufactured of a ceramic (stabilised zirconium oxide) which, at the temperature of operation, conducts electric power by implies of oxygen ions. (Notice: In sensors of this form, the temperature has to be higher than 450°C before they turn out to be active as an electrolyte conductor). The opportunity distinction across the mobile is presented by the Nernst equation.
E is the prospective big difference (volts)
R is the gasoline consistent (eight.314 J mol-one K-one)
T is the absolute temperature (K)
F is the Faraday frequent (96484 coulomb mol-one)
P1 & P2 are the partial pressures of the oxygen on both side of the zirconia tube
The Nernst equation can consequently be lowered to:
Consequently, if the oxygen partial force at one particular of the electrodes is regarded and the temperature of the sensor is managed, then oxygen measurement of the opportunity distinction concerning the two electrodes enables the not known partial strain to be calculated.
The partial force of the fuel is equal to the molar concentration of the ingredient in a fuel mixture occasions the overall stress of the fuel mixture.
PO2 = CO2 P2
PO2 = Oxygen partial tension
CO2 = Molar concentration of oxygen
P2 = Full pressure
Case in point
For atmospheric air:
CO2 = 20.9%
P2 = one atmosphere
PO2 = (.209/100) x one
PO2 = .209 atmospheres
Theory of Operation
The zirconia cell applied by Systech Illinois is created of zirconium oxide stabilised with yttrium oxide as the ceramic with porous platinum electrodes. This cell is shown in Determine 1.
Figure 1: Enlarged cross sectional representation of the zirconia substrate
Molecular oxygen is ionised at the porous platinum electrodes.
PtO → Pt + ½ O
>½ O2 + 2e- → O2–
/>The platinum electrodes on every side of the cell provide a catalytic area for the change in oxygen molecules, O2, to oxygen ions, and oxygen ions to oxygen molecules. Oxygen molecules on the superior concentration reference gasoline aspect of the cell attain electrons to grow to be ions which enter the electrolyte. Concurrently, at the other electrode, oxygen ions reduce electrons and are introduced from the floor of the electrode as oxygen molecul
/>The oxygen information of these gases, and consequently the oxygen partial pressures, is distinctive. Thus, the charge at which oxygen ions are developed and enter the zirconium oxide electrolyte at each individual electrode differs. As the zirconium oxide permits mobility of oxygen ions, the selection of ions moving in every single path throughout the electrolyte will rely on the amount at which oxygen is ionised and enters the electrolyte at each individual electrode. The mechanism of this ion transfer is elaborate, but it is recognised to contain vacancies in the zirconia oxide lattice by doping with yttrium oxi
/>The result of migration of oxygen ions throughout the electrolyte is a net flow of ions in a person course dependent on the partial pressures of oxygen at the two electrodes. For example in the Nernst equati
/>If P1>P2 ion move will be from P1 to P2 i.e. Dew-Point Transmitters
a optimistic E.M
/>If P1 />If P1=P2 there will be no net ion flow i.e. a zero E.M
/>In the zirconia analyzer, the Nernst equation is writ
/>The 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
/>Thus, our Nernst equation further reduces
/>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
/>Figure 2 Graph of cell potential vs. oxygen concentration of zirconia ce
/>By anti-logging the equation, the output signal can be displayed directly on a digital readout meter as oxygen concentration in ppm or
/>As the zirconia instrument uses an absolute measurement principle once built and factory calibrated, it does not require any further factory calibrati
/>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 nitrog
/>Applications of zirconia oxygen analyz
/>The zirconia analyzers may be used for measurement of oxygen at any level between 0-100% in gases or gas mixtur
/>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 ce
/>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 readi
/>Materials that will poison the detection cell a
/>Halogens e.g. Chlor
/>Halogenated Hydrocarbons e.g. Methylchlor
/>Sulphur containing compounds e.g. Hydrogen Sulph
/>Lead containing compounds e.g. Lead Sulph
/>Gases or gas mixtures containing any of the above are not suitable for oxygen determination with a zirconia type oxygen analyzer.