Stainless Steel Pirani Vacuum Gauge for Helium Leak Detector

Introduction of Pirani Vacuum Gauge

The Pirani vacuum gauge is a key sensor in the vacuum system of a helium mass spectrometer leak detector, used to measure pressure in the medium to low vacuum range (particularly during the rough pumping stage). Its core sensing element is typically made of metals such as tungsten or nickel, while the overall housing is constructed of stainless steel.

Function of Pirani Vacuum Gauge

The Pirani vacuum gauge plays the roles of "process monitor" and "system protector" in helium mass spectrometer leak detectors, with its specific functions as follows:
Monitoring Rough Pumping (Foreline) Vacuum Pressure:
When the leak detector starts up, the mechanical pump must first evacuate the vacuum system from atmospheric pressure to a relatively low pressure (typically on the order of 10 Pa to 0.1 Pa). The Pirani gauge monitors pressure changes during this stage in real time and displays them on the instrument interface.
Providing an Interlock Signal for High Vacuum Valve Opening (Core Protective Function):
The core mass spectrometer chamber of the leak detector can only operate under high vacuum conditions (typically below 0.1 Pa). If the high vacuum valve (connecting the mechanical pump to the diffusion pump/turbomolecular pump) is opened before the foreline pressure is sufficiently low, it can severely damage the high vacuum pump and contaminate the entire system.
The Pirani gauge is interlocked with the instrument's control system. The control system will only permit the high vacuum valve to open and the turbomolecular pump to start when the Pirani gauge detects that the foreline pressure is below a preset safety threshold. This is a critical safety measure to protect the expensive high vacuum pump and mass spectrometer.
Assisting in System Status and Leak Location Diagnosis:
By observing the rate of pressure drop during pumping and the final stable pressure achievable, it is possible to preliminarily determine whether the system has a large leak (pressure consistently fails to drop) or significant internal outgassing (pressure drops slowly).
During leak testing, if spraying helium not only triggers a mass spectrometer signal response but also causes a noticeable rise in the Pirani gauge reading, it usually indicates the presence of a relatively large leak.