Dräger Polytron SE Ex

The Dräger Polytron SE Ex ... DD sensing heads are gas detectors for the continuous monitoring of flammable gases and vapors in the ambient air. The measurement is based on the heat of reaction principle, where a chemical reaction takes place in a catalytic bead (so-called pellistor) inside the sensor.

Product Information

Benefits

  • Large temperature range
    • The Dräger Polytron SE Ex sensing head can be used at ambient temperatures of -50 °C to +85 °C, the special HT version even up to +150 °C.
  • Comprehensive explosion protection
    • The sensing heads Polytron SE Ex ... DD are labeled acc. to the Directive 94/9/EC (Atex 95) as II 2G/ II 2D and thus are suitable for operation in areas with potentially explosive atmospheres of zone 1 and 2 as well as zone 21 and 22. In the same way, for world-wide applications, an IECEx-approval allows to operate these sensing heads in hazardous areas.
  • Pellistors sensors Type DD
    • A pellistor is a small bead made of very porous ceramic material which is impregnated by a special catalyst and embedding a small platinum filament. By means of an electrical current of approx. 255 mA on the one hand the platinum filament heats up the ceramic bead to roughly 450 °C, on the other hand this platinum wire acts as a measuring resistor dependent on the bead’s temperature. When molecules of a flammable gas penetrate into the catalytic bead they react with the activated airborne oxygen which is adsorbed in the porous ceramic and release heat of reaction causing the pellistor’s temperature rising. The resulting resistance increase of some milli-Ohms is proportional to the gas concentration.
  • Poison resistance
    • The pellistors which are manufactured since decades are of type PR, which means poison resistant. Based on their special construction these sensors have a longer lifetime compared to conventional sensors when being exposed to industrial atmospheres containing catalyst poisons such as sulfur-, phosphor-, lead- or siliconcompounds.
  • Eight housing variants
    • The sensing heads Dräger Polytron SE Ex PR ... DD and SE Ex LC ... DD are available as four variants each, which differ by their junction boxes, specified by the following code:
      • M1 - small standard housing
      • M2 - midsize standard housing
      • M3 - big GRP plastic housing
  • Measuring signal
    • The flame-proof encapsulated gas sensor produces a mV-signal which is proportional to the gas concentration and can be evaluated by a suitable central controller (e.g. Dräger REGARD or Polytron SE Ex). Connected to the sensing head via a shielded 3-core cable of several hundreds of meters length, the central controller is intended to activate alarms if dangerous gas concentrations occur.
  • Environmental conditions
    • By means of a second, entirely uniform pellistor, which is especially encapsulated, any parameter affecting precise measurement is optimal compensated. This is particularly true in respect to humidity and ambient temperature. During manufacturing these pellistors are matched in respect to optimum compensation characteristics. Since both these pellistors are catalytic the sensor is called type DD, standing for double detector with a resulting long-term stable sensor signal being nearly unaffected by ambient temperature changes.

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