The Dräger Polytron® SE Ex ... DQ sensing heads are gas detectors for the continuous monitoring of flammable gases and vapours in the ambient air. Measurement is based on the heat of reaction principle where a chemical reaction takes place in a catalytic bead (also known as a pellistor) inside the sensor.
Heat of reaction principle By the heat of reaction principle, concentrations of flammable gases can be detected long before they tend to be ignitable, in other words: before they reach the lower explosive limit (LEL). The sensing heads are intended to be used in the harsh industrial environment and connected to a suitable central controller by means of a 3-core cable. Based on different sensor types Dräger offers three versions for different applications: On the one hand for the detection of up to 100 % LEL (where a special HT-version can be used at ambient temperatures up to 150 °C), on the other hand for the detection of very low concentrations in the range 0 ... 10 % LEL (leak detection).
Six housing variants The sensing heads Dräger Polytron SE Ex PR ... DQ 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
Besides these junction boxes made of glass fiber reinforced Polyester (GRP) with type of protection “e” (increased safety) housing a sensor with metric (“M”) thread, a further variant with type of protection “d” (flameproof enclosure) is available, coded as:
NPT1 - flame-proof metal housing
This variant houses a sensor with NPT-thread and is intended to be used in conduit installations. The variant M2 should preferably be used in outdoor applications since the lateral cable gland may be exchanged by the stopping plug so that the cable can be inserted from the bottom.
Comprehensive explosion protection The sensing heads Polytron SE Ex ... DQ are labeled according to the Directive 2014/34/EU 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.
mV 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.
Pellistor sensors type DQ Since they are operated as precisely measuring temperature dependent resistors, the measuring beads housed in the sensor are called pellistors (from engl. pellet and resistor). 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 heatsup the ceramic bead to roughly 450 °C,on the other hand this platinum wire actsas a measuring resistor dependent on thebead’s temperature. When molecules of a flammable gaspenetrate into the catalytic bead they reactwith 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.
Compensation of 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 DQ (double detector) with a resulting long-term stable sensor signal being nearly unaffected by ambient temperature changes.
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.
Very short response times To achieve short response times the gas entrance of the DQ-sensor is not a conventional sinter disc but a thin wire mesh disc so that the gas to be detected can very quickly enter the pellistors by way of diffusion.
Measuring function for explosion protection In conjunction with some Dräger central controller units the Dräger sensing heads Polytron SE Ex PR ... DQ and HT M DQ are type-approved to be used in pre ventive explosion protection applications acc. to EN 1127-1. This is a customer’s benefit since in case of a dangerous gas concentration a performance approved gas detection system will auto matically activate countermeasures so that explosive concentrations cannot form and the extension of hazardous areas thus decrease. By this, electrical installations can be designed more simply and in some cases even no further explosion protection measures are necessary. This is because potentially explosive atmospheres occur seldom or even not at all when having a gas detection system like this.
These splash-resistant, anti-static, long-sleeved overalls from Tuffsafe® are designed to meet safety standards against a wide range of contaminants. Lightweight and comfortable for prolonged wear, the micro-porous material weighs just 65gsm, making these coveralls ideal for hot and humid working environments.
Features and Benefits • Easy to use, non-woven disposable coveralls that have been designed to zip over neck to above the chin to protect exposed neck areas • Elasticated hood, cuffs, back and ankles for quick and secure usage • Anti-static and liquid repellent protection against a wide range of contaminants • 2-way zip design at front with 1-ply adhesive tape storm-flap for convenience • Flexible diamond crotch gusset to improve movement
Typical Applications • Industrial use • Chemical industry
Standards • EN ISO 13982-1:2004 • EN 13034:2005 • EN 1149-1 • EN 14126:2003
The disposable personal single-gas detection device, Dräger Pac® 6000, measures CO, H2S, SO2 or O2 reliably and precisely, even in the toughest conditions. The robust design, quick sensor response times, and a powerful battery ensure maximum safety for up to two years with virtually no maintenance required.
PRODUCT CODE : N P-F-07N1 COATING MATERIAL : Chloroprene LINEAR MATERIAL : Flocklined EXTERIOR FINISHING : Pebble CUFF STYLE : Straight THICKNESS MM : 0.75 LENGTH MM : 330 COLOUR : Midnight Blue SIZE/WRIST : 7, 8, 9, 10, 11 PACKAGING : Pair packed 12 pairs in a bundle 20 pairs in a master carton