New air density and absolute humidity sensors using optical fibre cable and alpha-rays

摘要

A simple sensor for measuring the air density at atmospheric pressure has been developed by the author using common optical fibre cable and a radioactive alpha-ray source. A silver activated zinc sulphide scintillator film and the photomultiplier tube for alpha-ray detection were separated by an optical fibre cable and the scintillator film was connected with the optical fibre cable in order to transmit the light caused by alpha-rays. The effect of the temperature on the photomultiplier tube could be removed in the temperature range from 0 to 60℃. From the relationship between the attenuation of alpha-rays passing through the air and the air density, the air density could be measured with an accuracy of ±4×10{sup}(-6) g cm{sup}(-3) in the range from 1.07×10{sup}(-3) to 1.309×10{sup}(-3) g cm{sup}(-3). Also, a new-type absolute hygrometer sensor has been devised by coupling the two air density sensors. One of the two is for measuring the dry air density of absolute humidity zero and the other is for measuring the humid air density. Absolute humidity could be measured with an accuracy of ±2 g m{sup}(-3) in a range of 0 to 66 g m{sup}(-3) by taking into account the differences in counting rates of alpha-rays from the two sensors.