D-FL 200 / Rev. 6
12
______________________________________________________________________________________________________
Industrie Elektronik GmbH & Co KG
4. Choosing the Measuring Point
The technical conditions found in different stacks, boilers or filtering systems vary greatly. In principle, it
is advisable to have a qualified independent agency (e.g., TÜV) make the determination. One must
observe, however, that the most symmetrical flow profile possible is present at the measuring point.
There must also be enough space available to install the purge air system and evaluation unit.
The flow paths (length of stack) ahead of and after the measuring point should be at least 3D (D =
interior diameter of the stack). If using four transducers, the flow paths may, if necessary, be less than
3D. This should only be done, however, in consultation with the independent agency mentioned above.
The measuring point should not only be safely accessible for start-up and calibration procedures, but
also for any necessary future maintenance.
The measuring path should, if possible, be set up at an angle of 45
°
. If the interior diameter of the
stack is very great, the equipment may be installed at a flatter angle. According to the flow direction
the angle should be at the very most 60
°
. Also, the maximum measuring path length for the acoustic
signals may not be exceeded:
Maximum measuring path length, standard flue gas
Temperature
Measuring head 1
(50 kHz)
Measuring head 2
(41 kHz)
Measuring head 3
(30 kHz)
up to 80°C / 176°F
5m / 197 in
8m / 315 in
11m / 433 in
up to 120°C / 248°F
4m / 157 in
6,5m / 256 in
8,0m / 315 in
up to 160°C / 320°F
3m / 118 in
5m / 197 in
6m / 236 in
more than
160°C / 320°F
2m / 79 in
3,5m / 138 in
4,5m / 177 in
For stacks with a small interior diameter, it is recommended that the measuring heads be installed at a
smaller angle (min. 30
°
) concerning to the gas flow, since this increases the resolution. The minimum
measuring path length is 2 m/ 6.6ft. The angle is flexible enough that one can consider a working
platform, etc.
As already discussed in the section
2. Function, page 1 several installations are possible:
(Fig. 14) Measurement in a plane through the pipe axis, standard
