The electrochemical sensor principle of operation is described as follows:
Gas molecules from the sample are adsorbed on an electrocatalytic sensing electrode, after passing through a diffusion medium, and are electrochemically reacted at an appropriate sensing electrode potential. This reaction generates an electric current directly proportional to the gas concentration. This current is converted to a voltage for meter or recorder readout.
The diffusion limited current, ilim, is directly proportional to the gas concentration according to the simplified equation…
ilim = nFADC
where ilim is the diffusion limited current in amps, F is the Faraday constant (96,500 coulombs), A is the reaction interfacial area in cm2, n is the number of electrons per mole reactant, δ is the diffusion path length, C is the gas concentration in moles/cm3, and D is the gas diffusion constant, representing the product of the permeability and solubility coefficients of the gas in the diffusion medium.
An external voltage bias maintains a constant potential on the sensing electrode, relative to a nonpolarizable reference counterelectrode in the two-electrode Interscan sensor. Nonpolarizable means that the counterelectrode can sustain a current flow without suffering a change in potential. Thus, the counterelectrode acts also as a reference electrode, eliminating the need for a third electrode and a feedback circuit, as would be required for sensors using a polarizable air counterelectrode.
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