In the European Union, the ATEX Directive 94/9/CE is compulsory for plants or machines, in which hazardous substances are processed or produced. It states that only ATEX-approved instruments must be used in hazardous areas within Europe.
One frequently selected explosion protection method for pressure sensors is intrinsic safety. An pressure sensor cerified for hazardous areas, i.e. an ATEX-approved pressure sensor, must be operated together with an intrinsically safe isolated barrier in order to be operated with the explosion protection method intrinsic safety. Additionally the “proof of intrinsic safety” according to the values found in the barrier’s and the sensor’s ATEX Ex i approval must be fulfilled.
By means of the so-called “Proof of intrinsic safety” in the “Explosion protection document” (= part of the total plant documentation), the plant owner has to prove that the instrument combination used (i.e. pressure sensor and PLC input card) is intrinsically safe. In circuits with only one associated apparatus (= instrument in which not all circuits are intrinsically safe, e.g. PLC input card in non hazardous area), usually a “basic” proof of intrinsic safety is sufficient. Normally, the plant owner gives a basic proof of intrinsic safety by comparing individual values from the instrument approvals.