Measure different flows correctly
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In order to determine the correct measurement procedure for the flow velocity measurement, the following parameters and ambient conditions must be taken into account preceding the measurement task:
- Flow measurement range
- Air temperature
- Level of contamination
- Measurement location
The most common measurement methods
- Thermal anemometers (hot-wire, hot-bulb)
- Vanes (large and small)
- Pitot tubes (straight and Prandtl)
- Funnel measurement
Thermal probes
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- Heat is removed from a heated element by a colder flow impacting onto it.
- The temperature is kept constant by means of a control circuit.
- In turbulent flows, the measurement result is influenced, i.e. increased, by flows from all directions.
- For exact measurements from 0 to 5 m/s
- For temperatures up to approx. +70 °C
Vane anemometers
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- The vane is set in motion by the air flow
- The rotational movement is then converted into electrical signals
- An inductive proximity switch "counts" the revolutions of the vane and supplies a sequence of pulses, which is displayed in the measuring instrument as a flow value
- For exact measurements from 5 to 40 m/s
- For temperatures up to approx. +350 °C
- Turbulent flow and low to medium velocity: large diameter (Ø 60 mm; Ø 100 mm)
- Duct: small diameters (Ø 16 mm)
Pitot tubes
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- The Pitot tube opening records the entire pressure and transmits this on to connection (a) of the pressure probe.
- The purely static pressure is recorded via lateral slots and transmitted to connection (b)
- The resulting differential pressure is the velocity-dependent dynamic pressure. This is then analyzed and displayed.
- For temperatures over +350 °C
- Depending on the differential pressure probe, measurements from 1 m/s are possible
- For measurements in dusty, dirty air