Pirani gauge (English spelling)

Japanese: Pirani gauge（英語表記）Piranigauge

...The volume of the compressed gas is ax if the cross-sectional area of the capillary is a and the distance from the mercury surface to the tip of the sealed tube is x . From the relationship PV = pax and p = P + h ρg (ρ is the density of mercury, g is the acceleration of gravity) according to Boyle's law, P = h ρg･ ax / ( V - ax ) can be calculated. The Pirani vacuum gauge has a simple structure of a thin metal wire as shown in Figure 2, and the phenomenon in which the thermal conductivity of gas changes depending on the pressure in the low pressure region is read from the change in the electrical resistance of the metal wire. The metal wire is usually a thin wire of tungsten or platinum, and is heated electrically. ...

*Some of the terminology that refers to "Pirani gauge" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…圧縮された気体の体積は，毛管の断面積がa，水銀面から封管の先端までの距離がxであればaxであり，ボイルの法則によるPV＝paxとp＝P＋hρg(ρは水銀の密度，gは重力の加速度)の関係から，P＝hρg･ax/(V－ax)が求まる。ピラニ真空計Pirani gaugeというのは，図2のように，細い金属線を張っただけの単純な構造をしており，低圧領域で気体の熱伝導が圧力によって変わる現象を金属線の電気抵抗の変化から読みとる。金属線は通常タングステンや白金の細線で，電気的に加熱してある。…