Setting up the instrument
24
The Wöhler A 550 has three pumps. A sample pump sucks the flue gas through the
probe and the cable hose. A purge pump pumps fresh air to all sensors during the cali-
bration phase. As the sample pump is cut-off during the calibration, the hotspot can
already be searched during this time.
The CO protection pump protects the CO sensor. If a preset CO threshold value is ex-
ceeded during the flue gas measurement, the pump will be activated automatically, so
that the flue gas cannot reach the CO sensor any more. The sample pump will continue
to work, and the measurement can continue without damaging the sensitive CO sen-
sor. (Only the Wöhler A 550 is equipped with a protection pump).
The sensors are protected against condensate by a four-step-filter conditioning:
The first step is the coarse filter in the probe handle. Most of the particles will be re-
moved from the sample. After that the gas passes the condensate trap, where the gas
is cooled by a spiral and the condensate is collected.
The second step is an exchangeable cotton filter. Fine particles and rests of water will
be removed from the sample.
The last step is the Water Stop Filter. This filter will not allow any kind of moisture to
pass. The filter will clog automatically in contact with water, so that the sensors are
protected against moisture.
The sample passes all sensors. O
2
is always the first sensor and CO (4.000 ppm) is
always the last sensor.
The fourth step is the LT-filter. This chemical filter removes all harmful gas compo-
nents. It is situated immediately in front of the CO sensor.
