The Air Velocity Transducer MM0038 is based on the constant temperature difference anemometer principle. The transducer is designed to measure air velocities in indoor climates. Therefore, the transducer's measurement range concentrates on the lower velocities. Here, the transducer reacts very quickly to changes in the air velocities (fluctuations) and provides very stable and accurate results. Because of the nature of the air flow in indoor climates, the transducer measures omni-directional air velocities.
Measurement Principle
Air velocity is measured as a function of heat loss from a heated body, by measuring the power input required to maintain a constant temperature between two sensor elements. Heat loss is, however, also a function of the temperature and direction of air-flow and the radiative exchange with the surroundings. The errors associated with these effects are eliminated through the design and construction of this transducer.
Transducer Design
Two sensor elements, one of which is heated electrically, are housed in two plastic foam ellipsoids on a single shaft. The heated sensor contains three heated coils. Temperature and heat loss is measured on the middle one. This provides a better frequency response. The eccentricity of the ellipsoids and the length of the heating coils are optimized to give the smallest possible variation in directional sensitivity. The controlled electrical heating maintains a constant temperature difference of 15°C (27°F), independent of the ambient temperature, between the two sensors. The smallish sphere at the end of the shaft prevents errors occurring if the air-flow is parallel to the shaft.
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To be used with Thermal Comfort Datalogger 1221
Download MM0060 Product Data Sheet
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