Crossover
Crossover turns up in 2 fields: vacuum, forestry. Here is what it means to the people in each one.
Crossover in vacuum
Point in a pump-down where pumping switches from the roughing pump to the high vacuum pump.
The moment, and the pressure, at which the roughing valve closes and the high vacuum valve opens. Crossing over too high hits the high vacuum pump with a slug of gas it cannot handle: a cryopump overloads and warms, a diffusion pump stalls and backstreams, a turbo is braked hard. Cryopumps carry a crossover rating in mbar·L or Torr·L, so the highest allowed crossover pressure is that figure divided by the chamber volume.
"Cryo's rated for 150 torr-litres and the chamber's 500 litres, so cross over at 0.3 torr, not a hair above."
Crossover in forestry
A critical fire weather condition where the relative humidity percentage drops below the ambient air temperature.
In wildland fire monitoring, this threshold indicates extreme fire danger. When the relative humidity number falls below the temperature reading, fine fuels on the forest floor dry out rapidly. Fire behavior becomes highly erratic and aggressive, often forcing crews to halt logging operations or shift tactics.
"Humidity is sitting at twenty percent and the temperature just hit twenty-five, so we've a crossover condition and need to shut down the skidder."