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Volume Flow Measurement

Procedure:

If the measurements are performed according to the guidelines VDI/VDE 2640

the following notes must be observed:

- Depending on the type of ventilation system there can already be turbu-

lences at low flow velocities.

- Perform the measurements in a quiet section of the ventilation system

where turbulences are minimal.

- Select the measuring point so that maximum safety distances are available

before and after the measuring point. The safety distance N is the distance

from a turbulence point to the measuring point. Turbulences can develop,

for example, at fans, pipe bends, reductions, control flaps, rectifiers, heating

units and filters etc.

- The following formulae can be used to calculate the safety distances N for

selecting the measuring point. L represents the free straight leg of a ventilat-

ing channel that is free from obstructions.

- Select the safety distance N

/D before the measuring point so that it is

equal or larger than 6 and select the safety distance N

/D after the meas-

uring point so that it is equal or larger than 2.

- If short, straight elements of a piping system are only available, a shorter

safety distance N can be chosen when a larger number of measuring points

is used for the averaging. However, N

/D must at least total 2.5.

3-5-24 ALMEMO

Sensors

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Ahlborn ALMEMO 2390-5 Wartungshandbuch Seite 24