| 摘要 |
An electro-chemical sensor for the measurement of concentrations of gas or vapour in accordance with the limiting current principle comprises an electrolytic cell 1 having a sensing electrode 9, a counter electrode 2, an intervening body of electrolyte 4 and a restriction to the rate of access of gas or vapor to the sensing electrode in the form of a porous diffusion barrier 13. The improvement resides in the feature that substantially all the active pores of the diffusion barrier are sufficiently small as to cause diffusion through them to be in accordance with the Knudsen principle, i.e. the diffusion mechanism is effectively determined solely by collisons between the diffusion molecules and the walls of the pores. The barrier is constituted by a body of porous PTFE which may be in the form of a piece of unsintered PTFE tape or compressed PTFE powder formed by drying a dispersion of PTFE in water.
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