MKS 943 Series, Инструкция по эксплуатации

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5 Operation
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Series 943 Cold Cathode Vacuum Sensor
Instruction Manual - #100009887
Chapter 5
1 Operation
5.1 Theory of a Cold Cathode Ionization Sensor
In a cold cathode sensor, gas molecules are ionized by a high voltage discharge of electrons.
Sensitivity is enhanced by a magnetic field.
MKS cold cathode sensors are not standard Penning sensors. The inverted magnetron design
includes an isolated collector, making the sensor less susceptible to contamination and allowing a
wider range of pressure measurement. The MKS IgniTorr™, an optional cold cathode starting device
initiates the ionization process in cold cathode sensors, starting UHV pressure readings in seconds.
(see Section 6.7 Accessories.
A cold cathode ionization sensor has a number of inherent advantages over a hot cathode sensor.
These include:
• No filament to break or burn out, which makes it immune to inrushes of air, and it is relatively
insensitive to vibration damage
• No x-ray limit for lower pressure measurement
• No adjustment for emission current or filament voltage is needed
• Degassing is not needed
• Properly designed sensor tubes can be cleaned and reused almost indefinitely
With only one current loop, the control circuit is simple and quite reliable, as opposed to a hot
cathode sensor, which has three.
The cold cathode sensor consists of a cathode and anode with a potential difference of several
kilovolts. The electrodes are surrounded by a magnet, arranged so that the magnetic field is
essentially perpendicular to the electric field. The crossed electric and magnetic fields cause the
electrons to follow long spiral trajectories increasing the chance of collisions with gas molecules,
thereby providing a significant increase in ionization efficiency relative to a hot cathode sensor.
Figure 5-1: Inverted Magnetron, Cold Cathode Sensor Design