Sensors Nemst-type

The fuel-lean region (A > 1) is economical for fuel consumption. However, the EMF output for the normal Nemst-type oxygen sensor does not change appreciably in this range, as can be seen from fig. 8. 

In the potentiometric-type sensor, a membrane (glass, solid state, liquid) selectively extracts a charged species into the membrane phase, generating a potential difference between the internal filling solution and the sample solution (enzyme layer). This potential is proportional to the logarithm of the analyte concentration (activity) following the well-known Nemst equation. 

Most gas sensors that use solid electrolytes are operated potentiometrically. Configurations for potentiometric gas sensors have been reported (Yamazoe and Miura 1998 Miura et al. 2000). The simplest scheme for such sensors is represented in Table 6.1 as Type I. In this diagram illustrating the potentiometric sensor mechanism, A is the analyte with variable activity/concentration, is the constant activity of analyte A on the reference side of the solid electrolyte membrane, AB is a solid electrolyte membrane (A+ ion conductor), and the electrodes facilitate the reaction A +e =A when the activity of A is different on each side of the membrane, a potential, V, is observed. The voltage produced is from the concentration dependence of the chemical potential, which at equilibrium is represented by the Nemst equation ... 

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