During the optical coating of mirrors for laser resonators the typical process pressure lies above 2e-3 mbar.
A suitable vacuum transducer must be able to monitor both, process pressure during the coating as well as the available minimum pressure of 10-6 mbar in the vacuum chamber. Our client used to work with a Pirani/cold cathode combination gauge, the cold cathode monitoring minimum and process vacuum. However, the continuous operation above 10-3 mbar resulted in early wear and tear of the sensor.
In the VSM transducer the Thyracont Pirani activates the cold cathode only below very low pressures. Further the transition between the two sensors can be configured according to the applications requirements. This way we achieved that the entire coating process is now monitored by the Pirani. The cold cathode is saved because it is active only when the appliance pumps down to minimum pressure. The availability of the coating plant improves significantly.