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This
is a cold cathode ionisation Gauge consisting of two
electrodes anode and cathode. A potential difference of
about 2.2 KV is applied between anode and cathode
through current limiting resistors. A magnetic field is
introduced at right angles to the plane of the
electrodes by a permanent magnet having nearly 800 gauss
magnetic field which will increase the ionisation
current.
The
electrons emitted from the cathode (gauge head body) of
the gauge head are deflected by means of magnetic field
applied at right angles to the plane of the electrodes
and are made to take helical path before reaching the
anode loop. Thus following very long path, the chance of
collision with gas molecule is high even at low
pressures. The secondary electrons produced by
ionisation themselves perform similar oscillations and
the rate of ionisation increases rapidly. Eventually,
the electrons are captured by the anode and equilibrium
is reached when the number of electrons produced per
second by ionisation is the sum of positive ion current
to the cathode and the electron current to the anode and
is used to measure the pressure of the gas.
The
Cold Cathode Penning gauge is designed on this detection
method to read vacuum from 10-2 to 10-6 m.bar. The vacuum reading efficiency
is enhanced by utilizing cross coupled static magnetic
and electron fields of the gauge head. The gauge is
stabilized to high voltage DC power supply of about 2
KV. The ionization current in terms of vacuum can be
noted from the front panel micro-ammeter. All the high
voltage points in the penning gauge are well insulated
to eliminate any accidental contact by the user.
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