Precautions that make it possible to use electrical apparatus in explosion-hazard zones.
Sigrist process photometers can be equipped with a pressurized enclosure complying with protection type "p", which is certified under the designation EExpIIT3 according to the standards of CENELEC (European Electrotechnical Standardization Committee) or with an encapsuled enclosure complying with protection type "d" (e.g. chemical industry). This encapsuled system is certified under the designation EEXdIICT6 resp. T3.
The type of protection "p" (pressured enclosure) is based on the principle of housing the electrical apparatus in an enclosure that is slightly pressurized with either air or an inert gas. This prevents the potentially explosive gases surrounding the enclosure from coming into contact with the electrical components. Whenever the enclosure pressure drops below a certain level, an automatic monitor cuts off the power supply. Prior to start-up, the enclosure is purged for a prescribed period of time.
The type of protection "d" (encapsuled enclosure) is based on a housing resisting to an internal explosion, without a spark escaping.