Short for micron of mercury, the pressure of a mercury column one micrometre high, which equals one millitorr or about 0.133 Pa. US vacuum furnace operators, coating shops and refrigeration techs read their thermocouple and Pirani gauges in microns, and pulling a refrigeration system down to 500 microns is a standard evacuation target. Apart from the origin of the name it has nothing to do with the micron as a length.
Furnace pulled down to 40 microns but the leak-up is 15 microns an hour, that won't pass.
Heat-treat and HVAC techs think in microns while fab engineers say millitorr; it is the same number, so 300 microns is 0.3 Torr.
Also heard as
- millitorr
- mTorr
Related terms
Torr
Pressure unit equal to 1/760 of a standard atmosphere, about 1.333 mbar, and the default in US labs and fabs.
Rate of rise
Test that isolates a pumped chamber and tracks how fast the pressure climbs, to estimate leaks and outgassing.
Pirani gauge
Thermal conductivity gauge that reads pressure from how quickly gas carries heat away from a hot wire.