Pirani gauge

[2] Marcello Stefano Pirani was a German physicist working for Siemens & Halske which was involved in the vacuum lamp industry.

In 1905 their product was tantalum lamps which required a high vacuum environment for the filaments.

[3] Pirani was aware of the gas thermal conductivity investigations of Kundt and Warburg[4] (1875) published thirty years earlier and the work of Marian Smoluchowski[5] (1898).

[2] The Pirani gauge consists of a metal sensor wire (usually gold plated tungsten or platinum) suspended in a tube which is connected to the system whose vacuum is to be measured.

The connection is usually made either by a ground glass joint or a flanged metal connector, sealed with an o-ring.

The sensor wire is connected to an electrical circuit from which, after calibration, a pressure reading may be taken.

If the gas pressure is reduced, the number of molecules present will fall proportionately and the wire will lose heat more slowly.

[2] Note that keeping the temperature constant implies that the end losses (4.)

The thermal conductivity and heat capacity of the gas affects the readout from the meter, and therefore the apparatus may need calibrating before accurate readings are obtainable.

A special form of the Pirani gauge is the pulsed Pirani vacuum gauge where the sensor wire is not operated at a constant temperature, but is cyclically heated up to a certain temperature threshold by an increasing voltage ramp.

For adequately low pressure, the following first-order dynamic thermal response model relating supplied heating power