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Flow Measurement – The Almemo Way
When measuring flows using ALMEMO® sensors, the ALMEMO® instruments provide important data functions for averaging (over time or over single measurements) and for volume flow measurement (width, length, diameter, cross sectional area of the ventilating channel). For Pitot tube measurements the temperature influence can be automatically compensated. Please ask for our detailed ALMEMO® Manual. It will provide you with valuable tips and a detailed description regarding flow measurements using ALMEMO® equipment.
SENSOR TYPE | FLOW VELOCITIES | OPERATING TEMPERATURES |
|---|---|---|
| Thermoanemometer | ||
| Rotating Vane | ||
| Pitot tubes |
Selecting the Right Flow Sensor
| SENSOR TYPE | ADVANTAGES | DISADVANTAGES |
|---|---|---|
| Thermoanemometer | Very small air flows can be measured, e.g. draft measurements. Non-directional measurement is possible | Sensitive sensor electronics, sensitive with regards to mechanical stress and contamination, sensitive with regard to turbulent flow, high current consumption, limited ambient temperature |
| Rotating Vane | High accuracy at medium flow velocities and medium ambient temperatures, insensitive to turbulent flow | Sensitive sensor electronics, sensitive to mechanical stress and dependant on direction |
| Pitot tubes | Copes with high flow velocities and rough operating conditions, high operating temperatures possible, easy to clean | Highly dependant on direction, low flow velocities cannot be measured, depending on temperature, limited accuracy, sensitive to turbulent flow |
Pitot Tubes
The air velocity is determined by the dynamic pressure and the static pressure.
Pitot tubes are robust and available in special steel or nickel-plated brass. They connect to ALMEMO® devices by silicone hoses and a differential pressure module.
Advantages
Suitable for high flow velocities and harsh operating conditions, high ambient temperatures possible, easy to clean.
Disadvantages
Strongly directional, low flow velocities are not measureable, temperature dependent, limited accuracy, sensitive to turbulent flows.
Rotating Vanes
The flow velocity is determined through a frequency measurement.
Our rotating vanes are sensitive transducers with diamond bearings that are very precisely adjusted. This ensures high accuracy.
Advantages
High accuracy at medium flow velocities and medium ambient temperatures, insensitive to turbulent flows.
Disadvantages
Sensitive sensor technology, sensitive to mechanical stress, directional
Thermo-Anemometers
Thermistors and hot wire anemometers are highly sensitive sensors.
The measuring element is continuously heated up. A control circuit keeps the temperature of the element, which has cooled down by the air flow, on a constant value. The control current is proportional to the flow velocity.
Advantages
Even very small air speeds can be measured (e.g. draught measurements), direction-independent measurements are also possible.
Disadvantages
Sensitive sensor technology, sensitive to mechanical stress and contamination, sensitive to turbulent flows, high current consumption, limited ambient temperature.