Installation Of A - Dräger Polytron Pulsar 2 Technical Manual

certifications. The choice of standard used for the factory
calibration can be varied to special order.
Generally, the relatively small differences in the values
between the calibration standards is of less consequence for
open path instruments than for point detectors, since they do
not normally measure gas concentration directly but with a
weighting according to the size of a spreading gas cloud.
Arising naturally from the way they work, all 'line of sight'
detectors measure the total quantity of gas that the beam
intercepts. A flammable gas detector reads the concentration
in LEL times the length of path that the gas occupies (usually
less than the whole Transmitter-Receiver path), making the
appropriate units for the measurement LEL metres (LELm).
The only exception is when a uniform concentration
completely fills a path of defined length, allowing a true
measurement of concentration and the appropriate units to be
%LEL as for the Duct-Mounted Dräger Polytron Pulsar 2 (see
separate manual).
Each of Dräger Polytron Pulsar 2's linearisation tables covers
the range 0 to 8 LELm and this full range of measurement is
always available in the digital data stream. The user can
configure the span of the 4-20 mA output to any value between
0 4 LELm and 0 8 LELm. Note that a choice other than 0
8LELm does not alter the underlying measurement, but
causes readings between the chosen full scale and 8 LELm to
be clamped at 20mA.
The installation kit includes plastic test sheets which mimic the
infrared absorption of the gases to be detected. They are not
used for calibration but provide a convenient check that the
detector retains its factory-set calibration and is working
correctly. The sheets are marked with their thickness in
micrometres (eg 070
Polytron Pulsar 2's Calibration
response to similar sheets at the factory. Note that different
sheets, each of an appropriate plastic film, are used for the
standard Dräger Polytron Pulsar 2 and for the Ethylene
(ethene ) optimised version.
5

Installation of a

Dräger Polytron Pulsar 2
5.1 Choosing the path of the beam
1 The siting of an open path gas detector is often not as
critical as a point detector, since the released gas only has
to find its way into some portion of the beam instead of to
a particular point. However siting is still an important
consideration. Guidance for siting is contained in EN
60079-29-2.
2 Dräger Polytron Pulsar 2 is immune to sunlight so there is
no need to take account of the sun position when siting
detectors.
3 The density of the gas to be detected has to be considered.
Methane is lighter than air and may be expected to rise,
unless released at a low temperature or in a mixture with a
heavier gas like Carbon Dioxide. Likewise heavier
hydrocarbons may be expected to fall. However such
simple considerations as buoyancy may not be a reliable
indicator of gas movement in practical situations. Gas
leaking from high-pressure systems entrains with it a much
larger volume of ambient air, forming a mixture that may be
flammable and almost neutrally buoyant. In these
circumstances it is the natural air currents or forced
ventilation that control the motion of the plume or cloud.
Where air movements are unpredictable it may be
necessary to use separate beam paths to cover different
possibilities.
Dräger Polytron Pulsar 2
= 0.070 mm). The
Certificate includes
4 The distance between the Transmitter and Receiver should
agree with the model selected (i.e. 4-60m, 30-120m or 100-
200m). Note that the Optical Attenuator should be fitted
below 16 metres.
5 The beam path and immediate surround should be kept
free of obstructions that might hinder the free movement of
air in the protected area or block the infrared beam. A clear
path of 25cm diameter or greater is recommended. For
maximum availability it is also recommended to avoid the
following:
Smoke stacks, chimneys and exhausts.
Steam vents and plumes.
Walkways and areas where personnel muster or col-
lect.
Splash and spray from moving equipment and cooling
towers etc.
Parking, loading, cranes, vehicle temporary stops.
Vegetation that may grow tall enough to impinge on the
path especially with movement by the wind.
Surfaces that may obstruct the beam path with a build
up of ice or snow.
5.2 Mounting the unit
The Dräger Polytron Pulsar 2 should be mounted to a stable
structure free of excessive vibration. Good choices would be a
steel bulkhead, brick wall, concrete lamppost or a rigid steel
structure. Avoid flimsy metal structures that may flex, or
wooden structures that may warp. In open areas a suitable
structure close to the ground would consist of a five inch
nominal (141mm outside diameter) steel pipe driven 1 metre
Dräger
into firm ground or embedded into a concrete foundation. Tall
its
structures should be suitably guyed or braced.
Installation of a Dräger Polytron Pulsar 2
7