摘要 |
PCT No. PCT/GB81/00064 Sec. 371 Date Nov. 25, 1981 Sec. 102(e) Date Nov. 25, 1981 PCT Filed Apr. 10, 1981 PCT Pub. No. WO81/03071 PCT Pub. Date Oct. 29, 1981.The invention concerns the detection of contaminant in a stream of gas. Previous methods have either been insufficiently sensitive or have been slow and needed skilled operatives. The present invention allows speedy operation with relatively unskilled operatives. A piezo electrical crystal oscillator (1) is allowed to oscillate for a known period of time and the number of oscillations is counted. For a known time the crystal is exposed to contaminant, and is then allowed to oscillate again for the same period of time as before and the oscillations again counted. The difference in number of oscillations is a measure of the mass of contaminant deposited on the crystal (1). The period of oscillation of the first crystal is determined by a second matched crystal oscillator (2) in which the crystal is exposed to the same environment but not in contaminant. The apparatus has the advantage of being self-zeroing, and the exposed crystal (1) does not need cleaning after each use. The invention has special application to the testing of medical gases, for example oxygen and nitrous oxide.
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