A dedicated instrument with its own pumps and a magnetic sector or quadrupole mass spectrometer fixed on mass 4, used with helium as the tracer gas. Helium is scarce in air, about 5 ppm, as well as light and inert, so even a tiny flow through a leak stands out against the background. Good units detect leak rates around 10⁻¹² mbar·L/s in vacuum mode and read the rate directly once calibrated against a known leak.
Wheel the helium leak detector over to chamber 3, base is off and we need to find it before second shift.
Also heard as
- MSLD
- helium mass spectrometer leak detector
- leak checker
- leak detector
Related terms
Counterflow
Leak detector layout in which helium travels backward through a turbo pump's exhaust to reach the mass spectrometer.
Helium spray test
Outside-in leak test: helium is sprayed on an evacuated part while a detector watches for it inside.
Sniff
To hunt for helium escaping from a pressurized part by sweeping a sniffer probe slowly over joints and welds.
Calibrated leak
Reference leak with a certified helium flow, used to calibrate and check a leak detector's readings.
Hang-up
Helium that lingers in a leak detector or system after a big hit, holding the signal high and masking small leaks.