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afa-g-analyse.png: Humidity Measuring Instrument with Analoque Output AFA-G

Humidity Measuring Instrument with Analoque Output AFA-G

Capacitive method of measurement

Operating range: 0 ... 100% rH
pmax: pressureless
Temperature range: 0 ... 60°C
Accuracy: ± 2% rH (5 ... 95% rH)
Output: 4 ... 20 mA
Plug-on display: 3.5-digit LED
Option: limit switch


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Type KOBOLD AFA-G humidity sensors are suited for measuring relative humidity in air or in other non-aggressive gases. The sensors are based on capacitive metrology which is reasonably-priced, maintenance-free and highly accurate. Capacitive humidity sensor elements form the basis of these sensors. An electrode system, a moisture-sensitive polymer  layer and a gold layer that is permeable to vapour are situated on a small thin glass or ceramic substrate.

Since the hygroscopic polymer layer can absorb water molecules that alter its dielectric constant, this layered system acts as a moisture-dependant capacitor, whose capacitance is a measure of the surrounding relative humidity. The change in capacitance is converted to an electrical output signal by electronics normally mounted on the humidity sensor element. Both parts form a capacitive humidity sensor that can be adjusted using humidity references. Accuracy is approximately ±2%.

Besides providing the output signal of 4... 20 mA, the measuring instrument allows the measured value to be read off a red LED display at the measuring point. The display is supplied from the 4... 20 mA signal current and thus requires no additional power supply. The measuring instruments are also available with a programmable switching output. Sensors from the range are delivered with an aluminium sensor unit and a gauze filter. The connection is made with a right-angle plug according to DIN 43650.


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