Double-cell oxygen sensors

It is apparent that the double-cell sensor can be operated in the limiting current mode (which corresponds to large values of Vg, of the order of 600 to 800 mV). The advantage of this mode of operation is that errors associated with the measurement of small values of Vg (e.g, less than 100 mV) are avoided. However, limiting current operation is generally undesirable since the problems associated with complete depletion of oxygen at the cathode of the pump cell can seriously limit the performance of the device. It is... 

Of the various types of oxygen pumping sensors, the double-cell devices appear to have the best overall performance characteristics. These devices can be constructed to achieve the best combination of response time, independence of temperature and absolute pressure, insensitivity to electrode properties and operation not limited by the resistance of the Zr02 material. 

Figure 20.6 A Clark sensor for oxygen determination. Cell housing two concentric electrodes. The Teflon membrane, permeable to oxygen, must be very close to the cathode so that the double diffusion process through the membrane and subsequently the liquid film will lead to a stable signal after a few seconds.

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