These barometers are sensitive barometers and are used to measure very low pressures such as severe vacuum. They measure pressure indirectly by the electrical ions generated by the electron bombardment of the gas. The lower the gas density, the less ions are formed. This gas can be ordinary air inside a chamber whose pressure is being measured and is being discharged (vacuum) by a pump
. Therefore, the calibration of an ionization barometer (Ionization Gauges) is unstable. Because it is highly dependent on the nature of the gas used. For this reason, they are usually used with McLeod barometers (MacLeod)Which are more stable and independent of the chemical nature of the gas, are calibrated. Ionic barometers are produced in different types and among them, two types of cold cathode and hot cathode are the most widely used
Thermogenic phenomena occurring in hot cathodes or cold cathodes are used to generate electrons. These electrons collide with gas atoms to form positive ions
. These ions are absorbed by a collector electrode connected to a suitable voltage. The current generated in this collecting electrode is proportional to the amount of gas ionization whose pressure is being measured. Therefore, measuring the collecting electrode current can determine the gas pressure. The working range of these barometers from10 -3until the10 -9 Net(torr) Is
In the hot cathode model, the heated filaments generate electron beams. These electrons travel the length of the barometer and ionize the gas molecules around them. The ions produced are collected by a negatively pole electrode, creating a current that is proportional to the number of ions generated and ultimately proportional to the pressure being measured. The most common hot cathode sphygmomanometer is the Bayard Albert sphygmomanometer (Alpert Bayard) Which contains a small ion collector that is located inside a network. An open-ended glass chamber facing the vacuum chamber contains three electrodes
The working principle of the cold cathode model is similar to that of the hot cathode, except that the electrons are generated by the electrical discharge caused by the high voltage. Cold cathode model measurement range is usually10 -3until the10 -9Tour means10Is less than the hot cathode
Two Penning Barometers (created by Michael Penning).And the inverted magnetron (also known as the red head) are two common examples of cold cathode manometers
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