B-A真空計

B-A (vacuum) gauge

[目次：真空系]

熱陰極電離真空計の一種。加熱したフィラメントから放出される電子を加速し残留気体に当ててイオン化し、イオン電流を測ることから中～高真空での圧力を測定する真空計。測定範囲は0.1～10^-5Pa。ペニング真空計より低真空を計れる。ガラス管でできているので破損しやすいこととガス放出の問題があるので、測定子を直接真空にさらす方式の方がよく採用される。これをヌードゲージという(～10^-9Pa)。出力電流は圧力に比例する。電顕では超高真空試料室の圧力測定などに使われている。

A thermal-cathode ionization gauge. In the B-A (vacuum) gauge, a heated filament emits electrons and the emitted electrons are accelerated, and these electrons ionize residual gasses, then the produced ion current is measured. The B-A gauge measures the pressure of the middle to high vacuum region. The measurable range is 0.1 to 10^-5Pa. The gauge can measure lower pressures than the Penning gauge can. Since the gauge is made of a glass tube, it is likely to be damaged. In addition, the gauge has a gas emission problem. Thus, the B-A gauge adopts, in many cases, a design where the gauge head is directly exposed to the vacuum. This is called a nude gauge (measurable pressure: ～10^-9Pa). The output current is proportional to the pressure. For a TEM, the gauge is mainly used to measure the pressure in the ultra-high vacuum specimen chamber.

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