Patent ID: 8322229

Claim:
A measurement apparatus to measure a physical amount of a measurement object, the measurement apparatus comprising: a measurement pipe to feed the measurement object; a cylindrical lining body lined on an inner wall surface of the measurement pipe; an electrode insertion hole formed by penetrating a pipe wall of the measurement pipe and the lining body; an electrode inserted in the pipe wall from inside of the measurement pipe with the electrode insertion hole serving as a central axis of the electrode, so as to allow one end portion of the electrode to contact the measurement object; and an electrode fixing unit to be engaged with an opposite end portion of the electrode to fix the electrode by pulling the electrode toward an outer wall of the measurement pipe; wherein: the electrode includes an electrode head portion serving as the one end portion having a first surface exposed to the inside of the measurement pipe so as to contact the measurement object, and a second surface located on an opposite side to the first surface, an electrode anchor portion formed around a peripheral portion of the second surface of the electrode head portion, and an electrode shaft portion serving as the opposite end portion formed integrally with the electrode head portion toward the opposite side to the first surface; the second surface excluding the electrode anchor portion forms a flat surface orthogonal to the electrode shaft portion and a protruding portion is formed around a peripheral edge portion of the second surface, the protruding portion having a semicircular cross-section and a size smaller than a radius of the electrode shaft portion; the lining body is lined on a surface of the electrode insertion hole and further on a pipe-wall outer edge of the electrode insertion hole, and includes a counterbore flat surface portion at an arc portion around a central axis of the electrode insertion hole of an inner surface of the lining body so as to define a flat surface having an area equal to or larger than an area of the second surface; the electrode fixing unit includes a first spacer and a second spacer provided on the electrode shaft portion so as to hold the pipe-wall outer edge of the lining body, a spring inserted between the first spacer and the second spacer, and a nut screwed on the electrode shaft portion from behind the spring; and while uniformly coming into contact with the counterbore flat surface portion of the lining body with pressure, the protruding portion of the electrode anchor portion bites into the counterbore flat surface portion, when the nut is screwed, to uniformly raise a surface pressure between the second surface of the electrode and the counterbore flat surface portion, so as to ensure airtightness between the electrode and the lining body.