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Hazardous area temperature sensor application guidelines from Pyrosales

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Pyrosales outlines two main methods used in Australia that conform to the applicable standards when installing sensors in a hazardous area, and are approved for use in those areas. The two methods include:

  1. Intrinsically safe Ex ‘ia’:
  • An Intrinsically safe installation is one in which any spark or any thermal effect produced in the conditions specified in AS-NZS 60079.11-2002, which include normal operation and specified fault conditions, is not capable of causing ignition of a given explosive gas atmosphere
  • In principle an “intrinsically safe” apparatus  does not require an enclosure as the method of protection is embodied within the circuits themselves. It is generally accepted that a standard weatherproof enclosure will be suitable
  • Thermocouples and Resistance  thermometers are classified as “simple apparatus” when being assessed for use in an intrinsically safe circuit. An RTD is classified as a simple apparatus as it is a “passive device”. A thermocouple is so classified, as it is not able to produce enough energy to cause the ignition of any flammable atmosphere that may be present
  • Where it is necessary that the simple  apparatus maintains the integrity of the isolation from earth of the intrinsically-safe circuit, it shall be capable of withstanding a 500V a.c. rms test voltage to earth. This will only be applicable if the barrier or transmitter being used is non-isolated
      2.    Explosion-proof (Ex ‘d’) :
  • An Ex ‘d’ installation provides the type of protection for electrical equipment in which the enclosure will not suffer any damage  if there is an internal explosion of a flammable mixture, which has penetrated  into the interior
  • In the event of an explosion occurring, the flamepath to the outside atmosphere needs to be of sufficient length to ensure that the  escaping gases cannot ignite the gases in the external atmosphere

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