Sensors

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Sensors

Temperature

Temperature is measured by a PT100 VAISALA DTS12 which is a platinum resistance thermometer with a precision of ±0.13 °C at -50 °C. The standard range of measurement is -50 ÷ +30 °C , depending on an electronic preconditioner. The thermometer is calibrated with an electronic simulator, where the PT100 reading is compared with a certified thermometer.

Relative humidity

This sensor is made up of a HUMICAP® capacitive element, manufactured by VAISALA. This has a precision of ±2% and is protected by a filter. Variations in humidity change the HUMICAP® capacity value and are converted into volts. Sensor calibration is carried out in the laboratory with a LiCl saturated solution for low humidity values (approx 12 %) and a NaCl saturated solution for high humidity values (approx 75 %).

Atmospheric pressure

This sensor is a VAISALA DPA12 transducer, with an accuracy of ±0.5 hPa. Atmospheric pressure is measured by three independent aneroid capsules that change their capacity with pressure variations. This capacity value is then processed by a CPU that controls the responses of the three capsules, rejecting any incorrect data. Calibration is undertaken by comparing the instrument values with a digital barometer.

Wind direction

This sensor is a VAISALA optoelectronic counter WAV 15A model containing a pierced disk attached to the wind vane. Infrared light emitting diodes and phototransistors are mounted in six orbits on each side of the disk. The disk, turned by the wind vane, creates changes in a six bit Gray code and pulses are received by the phototransistors. Its precision is approx ± 2.8 degrees (± */64) with 0.3 m/s wind.

Wind speed

This sensor is a 3-cup optoelectronic anemometer (VAISALA WAA 15A model). It comprises a toothed disk attached to the shaft of the anemometer. When rotating, the disk interrupts the luminous beam of an emitting diode, generating pulses for a phototransistor. The pulse frequency is directly proportional to wind speed. The sensor accuracy is about ±2% with 0.4 m/s wind speed. The sensor does not need to be calibrated, but the ball bearings must be replaced every year.

Solar radiation

This instrument is a Kipp & Zonen piranometer model CM11. It measures the radiation (watt/m2) on a level surface, resulting from direct solar radiation and incident diffuse radiation. Spectrum widths range from 335 to 2200 nm , and sensitivity ranges from 4 to 6 microV/Wm-2. The electronics are calibrated by a simulator.

Snow depth

This sensor model SR50 is manufactured by Campbell Scientific. Being an acoustic sensor, it operates on the output and relevant backscattering of a series of ultrasonic frequency pulses toward the surface of which the distance has to be known. Furthermore, the variation of sound propagation at different air densities is corrected through an algorithm using the temperature measured by the meteorological station.

Wind speed and direction

Snow depth

Temperature