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| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | www.ahlborn.com | | | | | | | | | | AIR FLOW | | | | | | | | | | | | | | | | | | | | For measuring the flow velocity, typically, three methods are used, which are particularly different from each other with regard to their measuring range and the operating temperature: ► Rotating vanes ► Thermoanemometer probes | | | | | | | | | | Pitot Tubes | | | | | | | | | | | | | | | | | | | | | ^ Static Pressure | | | | | Total Pressure | | | | | r - | | | | | | | | | | | | | | | | | | | | | | The air velocity is determined by the dynamic pressure and the static pressure. Pitot tubes are robust and are available in special steel or nickel-plated brass. They connect to ALMEMO® devices by silicone hoses and a differential pressure module. Advantage: suitable for high flow velocities and harsh operating conditions, high ambient temperatures possible, easy to clean Disadvantage: strongly directional, low flow velocities are not measurable, 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. Advantage: high accuracy at medium flow velocities and medium ambient temperatures, insensitive to turbulent flows Disadvantage: sensitive sensor technology, sensitive to mechanical stress, directional | | | | | | | | | lo CU DO <-) "to _ Ç-j "cz cu cu TO E O .op cu cu > cu LT) CU CU o o | | | | | | Thermoanemometers | | | | | | | | | | 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. Advantage: even very small air speeds can be measured (e.g. draught measurements), direction-independent measurements are also possible Disadvantage: sensitive sensor technology, sensitive to mechanical stress and contamination, sensitive to turbulent flows, high current consumption, limited ambient temperature | | | | | | | | | | | | | | 10.02 | | | | | | o | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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