Dräger PEX 3000 Manual Del Usuario página 27

The ex-sensor is a transducer for measuring the partial pressure of combustible
gases and vapours present in the atmosphere. It functions according to the
heat-of-reaction principle. The monitored ambient air is diffused through the
wire mesh disc into the ex-sensor. This is where the combustible gases and
vapours are catalytically burned at a heated detector element (pellistor). The
oxygen required for combustion is taken from the ambient air. The combustion
heat generated heats the detector element up further. This heating up results in
a change in the resistance of the detector element. This change is proportional
to the partial pressure of the combustible gases and vapours.
The ex-sensor accommodates another heated, diffusion-limited detector
element which, in contrast to the first detector element, reacts significantly less
to the presence of combustible gases and vapours. Both detector elements,
however, are similarly affected by environmental influences such as
temperature, humidity or air pressure. Because both detector elements are part
of a Wheatstone bridge circuit, the environmental influences are compensated
for in the sensor's bridge signal.
The voltage measured on the ex-sensor is amplified by the electronics,
indicated on the display and converted into a 4 to 20 mA signal which is
transmitted to the controller.
The refresh rate of the measured values in the display and the 4 to 20 mA signal
is 80 ms.
3.2 Intended use
The PEX 3000 transmitter is intended to be used for the stationary, continuous
monitoring of mixtures of combustible gases and vapours with air under
atmospheric conditions. The full scale value is 100% or 10% of the lower
explosion limit (LEL). The transmitter is connected to a suitable controller by
means of a 3-core-cable, the measured signal during normal operation is
between 3.8 and 20.5 mA.
The PEX 3000 type XTR 0090 and XTR 0091 transmitters (remote version) are
intended to operate a remote Dräger sensing head.
Dräger sensing head
Polytron SE Ex PR M1 DQ
Polytron SE Ex PR M2 DQ
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Measuring range Order number
100% LEL 6812711
100% LEL 6812710
Dräger sensing head
Polytron SE Ex LC M1 DD
Polytron SE Ex LC M2 DD
Polytron SE Ex PR NPT1 DQ
Polytron SE Ex HT M DQ
The operation of the PEX 3000 in combination with the above-mentioned
remote sensing heads does not differ from the operation of the PEX 3000 with
integral sensor and is not explicitly considered in these instructions for use.
Likewise, the operation of further housing versions, e.g. of the types XTR 0001
and XTR 0011 (drilling templates, see page 45) is not explicitly described.
The transmitters must not be operated at ambient temperatures of less than -
40 °C. For PEX 3000 type XTR 0000, XTR 0001, XTR 0010 and XTR 0011
transmitters, the upper maximum permitted temperature depends on the
temperature class. For the T6 temperature class, this is 40 °C, or 55 °C for T5
and 65 °C for T4. For PEX 3000 type XTR 0090 and XTR 0091 transmitters, the
upper maximum permissible temperature is generally 65 °C.
The transmitter is approved for device categories II 2G and II 2D and can be
installed in zones 1 or 2 and in zones 21 or 22. Observe the installation
instructions.
The transmitter is not suitable for use in oxygen-enriched atmospheres.
In conjunction with a suitable controller unit with preset alarm thresholds
acoustic or optical alarm devices can be activated or automatic
countermeasures can be initiated before the detected gases or vapours can
form dangerous flammable mixtures with air.
3.3 Information for safe use
WARNING
In gas explosion-hazard areas (zones 1 and 2) the transmitter's cover is only
permitted to be opened for maintenance purposes.
Principles of operation
Measuring range Order number
10% LEL 6812722
10% LEL 6812721
100% LEL 6812800
100% LEL 6812720
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