IsoPrime User’s Guide
Version 1.01 Background Information Page 143 of 219
For a more detailed description please refer to the pump manufacturer’s manual.
PRESSURE GAUGES
THE PIRANI GAUGE
A Pirani gauge operates in a similar way to a thermocouple gauge, in which gas molecules collide
with a filament and the filament conducts heat away. However in a Pirani gauge, the filament
resistance rather than the temperature is measured.
The filament forms part of a bridge circuit as shown below. In a balanced bridge circuit, the
current flow through paths one and two is equal and a meter placed at the centre reads zero.
When the filament changes resistance, this balance is upset and a voltage difference is
developed at the meter terminals. This results in a flow of current that is calibrated for pressure.
The compensator is very similar to the filament and is held at a constant temperature and
pressure.
The Pirani gauge generally operates in the range 10
3
to 10
-3
mbar.
To Next Page
Loading...