AMR ALMEMO Sensors-Humidity


		AMR - ALMEMO SENSORS Humidity, Temperature, Pressure, Air Velocity, Conductivity, Gas Concentration HUMIDITY THE RIGHT HUMIDITY SENSOR FOR EACH APPLICATION Different methods are customary for measurement of humidity, which differ essentially in their accuracy, their suitability for long-term measurements and the medium for the measurement. • Capacitive measurement of air humidity • Psychrometric measurement of air humidity • Hygrometric measurement of air humidity • Dielectric moisture measurement • Conductance moisture measurement CAPACITIVE MEASUREMENT OF AIR HUMIDITY With capacitive sensors, a moisture-sensitive polymer layer is applied on a glass substrate between two metal layers. As a result of water absorption, corresponding to the relative air humidity, the dielectric constant and thus the capacitance of the thin-film sensor alters. The measured signal is directly proportional to the relative humidity and is independent of the ambient pressure. Advantage: The sensor can be used flexibly and over long periods of time without maintenance, even at sub-zero temperatures. Disadvantage: Limited accuracy and long-term stability, sensitivity to moisture condensation and certain corrosive media. Go To Capacitive Humidity Sensors PSYCHROMETRIC MEASUREMENT OF AIR HUMIDITY Psychrometers are high-precision instruments with a dry and a wet temperature sensor. Evaporation cools down the wet sensor. To enable this, an air velocity of at least 2 m/s for cooling down is induced by means of a fan within the psychrometer. From the temperature difference (psychrometric difference) between the two sensor the humidity values are calculated. The calculation formulas for the Almemo instruments are equal to those of the German meteorological office related to nominal atmospheric pressure of 1013 mbar. For high-precision measurements, actual ambient atmospheric pressures can be programmed. Advantage: No aging of the sensor, with the exception of contamination of the wick. High degree of accuracy. Disadvantage: Long-term measurement limited by the supply of water necessary for the wet sensor. Can only be operated with difficulty at sub-zero temperatures. Go To Psychrometric Humidity Sensors
	HYGROMETER MEASUREMENT OF HUMIDITY Hygrometric sensors are equipped with a measuring strip, which expands and contracts corresponding to the humidity. The measuring strip consists of many single fibers (measuring harp) which are made of organic or synthetic material. Advantage: Simple and good measuring technique. Little maintenance required. Disadvantage: Limited accuracy and measuring range. Slow measurement. DIELECTRIC MOISTURE MEASUREMENT Measurement is carried out indirectly by determining the dielectric constant. This is done by means of a capacity measurement in a high-frequency electric field which passes through the material without damaging the same. Advantage: Simple and fast measurement. Disadvantage: Limited accuracy. Go To Dielectric Humidity Sensors Almemo Plug. At the heart of the AMR data logging system is the Almemo connection plug. By using the Almemo connection plug, almost any sensor can be connected directly to an AMR logger or indicator and will have measured values displayed with proper scaling and engineering units. Also, calibration corrections may be made to compensate for sensor error, maintaining the highest level of accuracy at all times.
Please use the following links to navigate through the Almemo Sensors section. Temperature, Pressure, Air Velocity, Conductivity, Gas Concentration For assistance call 978-568-3400

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