MPG400 is a member of full range vacuum gauge (gauge that can measure both low vacuum and high vacuum). It applies a Pirani detector for low vacuum (>1Pa) and a cold cathode for high vacuum (<1Pa).
Here are two very good videos for how Pirani gauge and cold cathode gauge work.
The electronics is separated.
The tiny tube at the center is the cold cathode, and the golden tube at the side is the Pirani element.
Pirani element:
Cold cathode: the triangle piece with many teeth is used for ignition (arc caused by the high voltage appears at the shape edge).
The contaminated parts are washed using IPA and reinstalled. This improves the accuracy and the reduces the time used for cold cathode ignition.