Dräger Polytron SE Ex PR NPT1 DD Instructions For Use Manual page 28

The following hints in respect to the measuring
function have to be observed:
– Behaviour at very high gas concentrations
Basically, the measuring principle of heat of reaction
which is based on the catalytic oxidation of a flam-
mable gas, is ambiguous because at high gas con-
centrations there is not enough oxygen in the sensor
necessary for the oxidation process. So the measur-
ing signal decreases at high gas concentrations and
even can lead to measuring signal within the meas-
uring range again. A connected controller must be
operated with alarm devices, outputs, and alarm
thresholds operating as latched if the measuring
range is exceeded.
In this case do not reset latching alarms without hav-
ing ensured a safe condition by means of an inde-
pendent gas concentrations measurement.
– Minimum oxygen concentration
The measuring principle of heat of reaction needs a
minimum oxygen concentration of 12 % by vol., oth-
erwise the measuring values will be too low because
of oxygen deficiency.
Although the transmitter has been factory-tested be-
fore delivery, the commissioning after installation must
include the zero- and span-adjustment.
The commissioning has to be terminated by a function
test of the complete gas detection system.
28
CAUTION
Measuring function for explosion protection
The following sensing heads
– Sensing head Polytron SE Ex PR M1 DD,
– Sensing head Polytron SE Ex PR M2 DD,
– Sensing head Polytron SE Ex PR M3 DD,
– Sensing head Polytron SE Ex PR NPT1 DD,
– Sensing head Polytron SE Ex HT M DD,
fulfil the essential health and safety requirements of the
Directive 94/9/EC with respect to the measuring
function for explosion protection by application of the
standard EN 60079-29-1 in combination with the central
units REGARD (7th supplement to the EC type
examination certificate DMT 02 ATEX G002 X) and
REGARD-1 (2nd supplement to the EC type
examination certificate BVS 03 ATEX G011 X) for the
gases and vapours given on page 41.
Special notes:
In the event of strong air flows no measurement value
errors occur. However, in case of strong flows of
50 %LEL span gas the measurement values may be up
to 13 %LEL higher.
Above a concentration of 70 %LEL, the measurement
values displayed for hydrogen and ammonia are
reduced by more than 15 %, and for methane by more
than 10 %.