| SSIG-17 IONISATION GAUGE SSIG-18 | |||||||||||||||||||||||||
 |
SSIG-17 & SSIG-18 are new, improved Bayard Alpert ionisation
gauges specifically designed for long life and reliability.
As well as using high specification materials, the surface area
of the grid structure has been reduced, and the collector plus
collector shield are of an improved design.
Compared to standard BA gauges, these improvements mean
that the SSIG-17 / 18 has a lower x-ray limit (see technical
note) that enables pressure measurement down to 3 x 10-11
mbar.
At higher pressure operation (up to 10-2
mbar), the rugged, robust characteristics of the gauge
construction ensure a long-life of reliable, repeatable pressure
measurement.
Whatever the application, the very competitive price of the
SSIG-17 / 18 ion gauge make it a must for all vacuum systems.
OVERVIEW
· Bayard
Alpert Gauge
· Nude
Head
· Conflat®
Flange
· Low
X-Ray Limit to 3 x 10-11
mbar
· High
Reliability
· Long
Life
· Robust,
Efficient Design
· Twin
Filaments: Tungsten or
· Bakeable
to 400ºC |
||||||||||||||||||||||||
|
 |
||||||||||||||||||||||||
|
PRINCIPLE OF OPERATION
A hot cathode ionisation gauge comprises three electrodes: a
filament, grid and collector.
Electrons are produced from the filament by thermionic
emission. A
positive potential on the grid attracts the electrons away from
the filament, causing them to oscillate through the fine
structure many times, until eventually they collide with the
grid.
Alternatively, the electrons collide with gas molecules
producing a positively charged ion, which are collected at a
negative electrode (Collector) at the centre of the grid
structure. The
current depends upon the number of ions which is directly
proportional to the pressure in the gauge. X-RAY LIMIT The low pressure limit of the gauge is restricted by the ‘x-ray limit’. Electrons hitting the grid produce soft x-rays which in turn produce photoelectron emission (‘photoelectric noise’) from the collector. Since the measurement electronics cannot distinguish between collecting a positive ion or losing a photoelectron, a theoretical minimum detectable pressure is set. The effect is small and is kept to a minimum by careful design of the gauge. |
GAUGE LEADS
To connect a SSIG-17 / 18 ion gauge head to a controller, a lead
is required.
Bakeable leads are available for both gauges, which means that
the gauge can be operated (and pressure monitored) whilst the
system is being baked.
Also, the gauge heads can be degassed whilst the system
remains hot.
The standard lead is 3 metres long (connections shown below),
but any length can be supplied to order.
GAUGE CALIBRATION
Ionisation gauges have different sensitivities for different
gases and are usually calibrated for nitrogen.
Many users accept the inaccurate pressure measurement for
a gas mixture and rely on the long-term reproducibility of the
gauge.
For accurate pressure measurements the gauge head should be
calibrated for the gas species being measured.
The sensitivity of a gauge is defined as:
S =
Collector current (A) Grid current (A) x Pressure (mbar) |
||||||||||||||||||||||||
