Talk:Marcello Pirani

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Principle of the Pirani gauge

"In particular, it employs the change in resistivity of the heated wire ... with temperature to determine the heat loss."

The change of resistivity with temperature has no role in the functioning of a Pirani gauge, since the heated filament is held at constant temperature. The power supplied to the filament in order to achieve this is related (rather intricately) to the ambient pressure. The pressure is thus inferred from the power necessary to keep the filament at the set temperature. --Lupercus (talk) 00:13, 12 December 2010 (UTC)[reply]