How does a cold cathode gauge work?

How does a cold cathode gauge work?

A cold cathode ionization gauge measures vacuum pressure by first ionizing gas molecules inside the vacuum gauge and then measuring the resulting ion current. The amount of ion current generated from the ionized gas is proportional to the pressure in the vacuum system and is dependent on the type of gas used.

What is the working principle of Penning gauge?

The operation principle of penning gauge is similar to that of ion vacuum pump. The gas molecules in vacuum enter the gauge and move between two parallel electrical plates or tube-based anode and cathode biased at a DC voltage of 2,000 V.

Why is magnetic field used in Penning gauge?

The inventor of this type of gauge was Penning in 1937. He used a high voltage of up to 2kV to generate a discharge between cathode and anode. Due to the magnetic field the electron is prevented from going directly to the anode and moves instead in helical paths through the gauge.

What is thermocouple vacuum gauge?

Thermocouple Vacuum gauge is a device that is used for the measurement of pressure in vacuum systems or in the very low-pressure region (below atmospheric pressure). In other words, we can say that thermocouple vacuum gauge measures pressure by measuring the change in the ability of a gas to conduct heat.

What is difference between hot and cold cathode?

A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered “cold” if it emits more electrons than can be supplied by thermionic emission alone. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament.

What is a cold cathode vacuum gauge?

Cold cathode ionization vacuum gauges essentially consist of only two electrodes, a cathode and an anode, between which a high voltage is applied via a series resistor. Negatively charged electrons leave the cathode through field emission, moving at high velocity from the cathode toward the anode.

How does a vacuum gauge work?

A vacuum gauge measures pressure below the atmospheric pressure. Normally the atmospheric pressure is set as zero and the vacuum pressure is given in negative values, so -1 barg (-15 psig) means complete vacuum.

How does a high vacuum gauge work?

This vacuum gauge contains a hermetically sealed, evacuated, thin-walled diaphragm capsule which is located within the instrument. As the vacuum pressure reduces, the capsule bulges. This movement is transferred via a system of levers to a pointer and can then be read off as the pressure on a linear scale.

What is the use of Bourdon tube?

A bourdon tube is used to measure pressure in a system, giving the user visual indication of the pressure level, ensuring the amount of pressure doesn’t exceed the maximum level or stoop too low. There are many pressure gauges, however the bourdon gauge is probably one of the most common.

What is the working principle of a thermocouple gauge?

The thermocouple working principle is based on the Seeback Effect. This effect states that when a closed circuit is formed by jointing two dissimilar metals at two junctions, and junctions are maintained at different temperatures then an electromotive force (e.m.f.) is induced in this closed circuit.

What is a cold cathode lamp?

A cold cathode fluorescent lamp (CCFL) is a type gas-discharge lamp similar to linear fluorescent or compact fluorescent lamps. CCFLs are used in a number of different specialty applications, such as cold-weather lighting, display back lighting, and signage.

How do CCFLs work?

Neon lamps primarily rely on excitation of gas molecules to emit light; CCFLs use a discharge in mercury vapor to develop ultraviolet light, which in turn causes a fluorescent coating on the inside of the lamp to emit visible light. These lamps are commonly used for neon signs.

What’s the difference between hot and cold cathode gauges?

In all Cold Cathode gauges there is considerable higher gas sorption than in the ionization vacuum gauge which operates with a hot cathode. A cold cathode gauge tube, there fore, pumps gases similarly to a sputter-ion pump (S = 10-2 ltr s-1).

How does a cold cathode ionization vacuum gauge work?

Cold Cathode Ionization Vacuum Gauge (Penning) Here the pressure is measured through a gas discharge within a gauge head whereby the gas discharge is ignited by applying a high tension. The resulting ion current is output as a signal which is proportional to the prevailing pressure.

What causes a cold cathode gauge to sputter?

A cold cathode gauge tube, there fore, pumps gases similarly to a sputter-ion pump (S = 10-2 ltr s-1). The ions produced in the discharage are accelerated to the cathode where they are partly retained and partly cause sputtering of the cathode material. The sputtered cathode material forms a gettering surface film at the walls of the gauge tube.

How is the current of a hot cathode measured?

A hot cathode emits electrons which impinge on an anode. The gas, the pressure of which is to be measured, is thus ionized. The resulting positive ion current is detected through the third electrode – the so-called ion detector – and this current is used as the signal which is proportional to the pressure.