Pressure gauge

Japanese: 圧力計 - あつりょくけい

This refers to a general gauge for measuring the pressure of gases or liquids. There are many types, and based on the principle, they can be broadly classified into liquid column type, weighted piston type, elastic element type, and physical property type. The quantity of pressure to be measured is the magnitude of the force acting perpendicularly to the surface considered to be the measurement point per unit area, and its unit in the International System of Units (SI) is pascal (Pa). A pressure gauge is an instrument or device that balances the force generated by pressure with gravity or elastic force, and indicates the magnitude of pressure by the magnitude of the balanced force or the amount of movement of the balance point. A pressure gauge that places the reference point of pressure in a vacuum is called an absolute pressure gauge, a pressure gauge that places the reference point at atmospheric pressure is called an ordinary pressure gauge, and a pressure gauge that indicates the difference between two pressures is called a differential pressure pressure gauge. A pressure gauge that measures atmospheric pressure is specifically called a barometer, and a pressure gauge that measures pressure lower than atmospheric pressure is called a vacuum pressure gauge.

[Mitsui Kiyoto]

Principle and Features

Liquid column manometers have been widely used since the 17th century, and are simple devices that can provide highly reliable measurement results. There are various types, but a typical one is one in which mercury or water is placed in a U-shaped glass tube, a measurement pressure is applied to one end, and the other end is connected to a reference pressure source. Liquid is pushed by pressure from one end, moves to the other side, rises up the straight tube, and comes to a stop at a position where the gravity acting on the liquid and the pressure are balanced. At that time, the difference in height of the liquid columns on both sides is proportional to the pressure, and the pressure value is calculated by multiplying this height difference by the density of the liquid and the acceleration of gravity.

The deadweight piston type pressure gauge is used to measure high pressures that are difficult to measure with the liquid column type, and as an accurate reference pressure gauge. It has a structure in which a precisely manufactured piston-cylinder is installed vertically, and an adjustable weight is loaded onto the piston. When the pressure applied from below the piston and the weight of the weight are balanced, the magnitude of the pressure is the weight of the weight divided by the effective cross-sectional area of the piston-cylinder.

Elastic element type pressure gauges are also called aneroid (liquid-free) type pressure gauges, and account for the majority of practical pressure gauges. They are instruments that indicate the magnitude of pressure by the amount of deformation of Bourdon tubes, bellows, diaphragms, etc. that undergo elastic deformation in response to pressure, and the pressure value is read from a scale marked based on a liquid column type or deadweight piston type pressure gauge. Since around 1990, digital display pressure gauges using small (a few millimeters) pressure-sensitive elements made of piezoelectric ceramics have been widely used, and are also used as altimeters that estimate altitude from changes in air pressure.

In addition to the above, there are many other types of pressure gauges or their detection parts (sensors), and among them, those that utilize physical properties have a wide range of applications. Changes in electrical resistance due to pressure, the piezoelectric effect, and the pressure coefficient of ultrasonic propagation velocity are values that are specific to each material, and depending on the material, they can be effectively used to measure pressure. Examples include manganin resistance pressure gauges, which are used to measure high pressures of around 10,000 atmospheres.

[Mitsui Kiyoto]

[Reference item] | Differential pressure gauge | Vacuum gauge

Main types and principles of pressure gauges
©Shogakukan ">

Main types and principles of pressure gauges

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

気体や液体の圧力を測るための計器全般をいう。きわめて多くの種類があり、原理のうえでは、液柱型、重錘(じゅうすい)ピストン型、弾性素子型、物性利用型などに大別される。測定対象である圧力という量は、測定箇所とみなす面に垂直に作用する力の単位面積当りの大きさであり、国際単位系（SI）の単位はパスカル（Pa）である。圧力計は圧力によって発生する力を重力や弾性力などとつり合わせ、つり合う力の大きさやつり合い点の移動量によって、圧力の大きさを指示する器械、装置である。圧力の基準点を真空に置くものを絶対圧力計、大気圧に置くものを普通圧力計、二つの圧力の差を指示するものを差圧圧力計（差圧計）という。また、大気圧を測る圧力計をとくに気圧計といい、大気圧より低い圧力を測るものを真空圧力計（真空計）という。

［三井清人］

原理と特徴

液柱型圧力計は17世紀以来広く用いられ、簡単な装置で信頼度の高い測定結果が得られる。種々の形式があるが、代表的なものとして、U字形のガラス管に水銀や水などを入れて一端に測定圧力を加え、他端を基準圧力源につないで用いるものがある。一端からの圧力によって押された液体は、他方へ移動して直管部を上昇し、液体に作用する重力と圧力とがつり合う位置で静止する。そのとき両側の液柱の高さの差は圧力に比例しており、この高さの差に液体の密度と重力の加速度を乗じたものが圧力の値となる。

　重錘ピストン型圧力計は、液柱型では測定困難な高圧力の測定用および正確な基準圧力計として用いられる。精密につくられたピストン・シリンダーを鉛直に設置し、大きさを調節できる重錘をピストン上に負荷する構造をもっている。ピストンの下方から加えられた圧力と重錘の重量とがつり合っているとき、圧力の大きさは、重錘の重量をピストン・シリンダーの有効断面積で除した値である。

　弾性素子型圧力計はアネロイド（無液）型圧力計ともよばれ、実用圧力計の大部分を占める。圧力に応じて弾性変形をおこすブルドン管、ベローズ、隔膜（ダイアフラム）などの変形量によって圧力の大きさを指示する計器で、圧力の値は、液柱型または重錘ピストン型圧力計を基準としてつけられた目盛りによって読み取られる。1990年ごろから、圧電性のセラミックスでつくられた小形（数ミリメートル）の感圧素子を用いたデジタル表示の圧力計が広く利用されるようになり、気圧の変化から高度を推定する高度計としても利用されている。

　このほかにも、圧力計あるいはその検出部（センサー）には多くの種類があり、なかでも物性利用型は応用範囲が広い。圧力による電気抵抗の変化、圧電効果（ピエゾ効果）、超音波伝搬速度の圧力係数などは物質に固有の値をとり、物質によっては圧力測定に有効に利用できる。1万気圧程度の高圧力の測定に用いるマンガニン抵抗圧力計などがある。

［三井清人］

[参照項目] | 差圧計 | 真空計

圧力計のおもな種類と原理

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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