E+E Elektronik OMNIPORT 20 Manuel page 57

Manual
velocity
page 58
Information for using velocity probes:
Directional dependency:
Velocity probes have a minimal directional dependency. The measurement
error resulting from wrong installation with an angle of +15° (α) is less than
3% of the measurement value.
Pressure dependence
Correction factor
For precise determination at different altitudes h, the measurement value
can be corrected using the barometric height formula.
The usual method is to multiply the flow rate by a corresponding
correction factor (quotient of average air pressure / actual air pressure).
The calculated correction factor can be applied using the Pabs extra
function in the measurement device.
Note: If the actual air pressure is not known, average values for altitudes
can be used for minimizing the influence of pressure (see table).
Tips for selecting the correct measurement position:
- Provide long straight sections downstream of cross sectional changes,
- Measure upstream of pipeline diffusers and reducers
- Measure downstream of filters and straighteners (no turbulences!)
- Place the measurement head as close to the channel centre as
elbows or other disturbances (turbulences!)
possible
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