The Pfeiffer ModulLine IMR 420 is a Bayard-Alpert measurement system for connection to an IMG 400 operating unit. The gauge head has a range of UHV down to 1x10-11 Torr. Operation of these passive sensors is based on the hot cathode ionisation effect. Can be baked out up to 400 °C (without measurement cables) or 200 °C (with high-temperature measuring cables). The IMR 420 gauges may only be used for the measurement of total pressures in vacuum systems and this only in connection with Pfeiffer ModulLine Controller IMG 400 Hot Cathode Measuring Unit.