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Select the Best Bayard-Alpert
Ionization Gauge for Your Application
An immense amount of research and development work, by many talented scientists and engineers, has
led to a variety of new Bayard-Alpert Gauge (BAG) product designs. In fact, a high vacuum user looking
for a new BAG might be surprised, and possibly overwhelmed, by the large number of new commercial
options that have become available. Standardization of the BAG design has made it possible for generic
ion gauge controllers, such as the IGC100, to control gauges from many different manufacturers.
This application note provides an overview of the current state of BAG technology to help high vacuum
users choose the best hot-cathode ion gauge for their application.
In This Application Note
BAG Designs 3
Glass Tubulated Gauges 3
Broad-Range Glass Tubulated Gauges 5
Nude Gauges 5
High-Accuracy Gauges 7
Tiny Gauges 9
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2 Selecting a Bayard-Alpert Ionization Gauge
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Selecting a Bayard-Alpert Ionization Gauge 3
BAG Designs
This application note provides an overview of the current state of the BAG technology to
help choose the best hot-cathode ion gauge for any application. For detailed information
on the principle of operation of BAGs see the application note, 'Bayard-Alpert Ionization
Gauges'.
Glass Tubulated Gauges
The glass tubulated BAG is the most commonly used gauge design in the world. Glass
tubulated gauges are also the most inexpensive BAGs available.
The tubulated gauge has its electrodes surrounded by a glass envelope with a side tube
that attaches to the vacuum system. The most common construction materials for the
glass envelope are Nonex (an inexpensive glass used in old vacuum tubes) and Pyrex.
Most tubulated BAGs are connected to the vacuum system through an O-ring
compression fitting. Pyrex is the material selected when the side tube must be glass-
blown directly on to the vacuum system. Kovar alloy is the material of choice when
metallic tubulation is required for the side port. The thermal expansion coefficient of
Kovar matches that of Pyrex producing strong glass-to-metal transitions. Kovar
tubulation is sometimes combined with compression fittings, but most often it is welded
to Klein or ConFlat