Measure different flows correctly
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
- 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
- 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)
- 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