| 摘要 |
The electrochemical membrane sensor 20 for immersion in a test fluid, such as wastewater, to sense chemical species such as dissolved oxygen, has a housing sealed from the test fluid by a membrane 28, 38, filled with an electrolyte 30, and containing a cathode 29, 35 and an anode 29a. The sensor 10 includes a device for agitating the test fluid adjacent the membrane 28, 38, so that the test fluid can be stirred and the outer surface of the membrane can be cleaned. The device may comprise a piezoelectric crystal 22 attached to a thin wall 25 of a cavity 23 in the structure supporting the anode and cathode. The crystal may he driven to resonate wall 25 in a drum mode to stir the test fluid or at an ultrasonic frequency to clean the membrane. Alternatively, as shown in figure 6, the membrane 38 may be of piezoelectric film, with a central, selectively permeable area and outer areas polarised and covered with an electrode film. Compressible space 44, sealed by a flexible membrane 43, allows the membrane to vibrate when excited at sonic or ultrasonic frequencies. <IMAGE>
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