| 摘要 |
1286765 Measuring gas pressure photoelectrically VDO TACHOMETER WERK ADOLF SCHINDLING GmbH 6 Jan 1971 [9 Jan 1970] 641/71 Heading G1A The gas-pressure in a chamber 1 is measured by determining the absorption of α-particles from a source 5 using a photo-cell 6, e.g. a semiconductor or scintillation counter, whose output is displayed on a counter 9. By using an essentially mono-chromatic source, e.g. Am-241, the apparatus may be used either as a threshold device or to give a continuous pressure reading. In its threshold form, an un-modified monochromatic source is used. When the count rate falls to zero this indicates that a certain gaspressure has been exceeded. To measure pressure continuously the apparatus is modified so that there is no abrupt pressure/ count-rate cut-off. This may be done by employing a laminar or rod-shaped source, Fig.1, inclined to the detecting surface. Particles from the top of the source then have less far to travel to the detector than those from the bottom. A similar effect may be achieved by placing an absorbing film (11) of wedge cross-section on either the source or the detector, or both, Fig.2 (not shown). Alternatively an absorbing foil may be arranged at an oblique angle between the source and detector. The detector output may be evaluated in accordance with the pulse amplitude using a pulse height voltage converter. Either the source, or the detector, or both may be movable to alter the spacing between the two before a measurement is made. |
