Kurt J. Lesker 979 Series, Operation And Maintenance Manual

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50 Series 979 ATV Transducer
Pirani Sensor
The Pirani sensor is a type of thermal conductivity sensor. It consists of a hot
wire suspended from supports. This wire loses thermal energy in three ways:
♦
Thermal conduction through the gas, which is pressure dependent
♦
End loss to the supports
♦
Radiation to surrounding surfaces
Pirani sensors use pressure-dependent gas transport from a hot wire to
measure pressure. End loss and radiation loss act as error signals and
determine the low pressure limit of the sensor. Optimizing operational
parameters of the wire length and diameter, thermal emissivity, thermal
conductivity, and wire temperature can decrease end loss and radiation errors.
A standard Pirani sensor usually has a lower reading limit of about 10
-3
Torr,
due to signal lost by end loss and radiation error.
Silicon Cover
Temperature
Measurement
resistors
Sensor
Si Substrate
Si Cover
PECVD
Si
3
N
4
/SiO
2
Ni Filament
Gold Wire
SiO
2
or Si
3
N
4
Passivation