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MiniPWS Optisk-værsensor

MiniPWS Optisk-værsensor er en kompakt og kostnadseffektiv aktiv værsensor. Instrumentet måler kun 68 mm i diameter, og inkluderer tre viktige vær-parametere som sikt, regn, snø og temperatur.

  • Raskere respons og høyere nøyaktighet i små nedbørsmengder enn en tipping bucket
  • Enkel RS-232 utgang er kompatibel med mange dataloggere
  • Lett å montere og kun 68 mm i diameter

    Description

    Overview

    The MiniPWS is is a companct and cost-effective Present Weather Sensor (PWS). Measuring just 68 mm in diameter, it provides three important weather parameters:

    • Visibility
    • Rain – fast response and better accuracy at low amounts than a tipping bucket
    • Snow – same as rain (most tipping buckets do not detect snow at all)
    In addition, the sensor can also measure:

    • Ambient light – accuracy is limited but provides information such as whether it is day or night, cloudy or sunny, etc.
    • Temperature – limited accuracy as well (~±2°C) because it is located inside the sensor body but provides trend information
    RS-232 Output

    The output is presented in digital form as an ASCII string on the RS232 output, 2400 baud 8N1, that is transmitted "streaming" every 5 minutes. This string can be received by many loggers with RS232 inputs but also by a PC via the serial port and with a terminal program like Hyper Terminal (part of Windows).This is an example of an output string:

    09:24:16> 000196 01530 00000 00211 -6 02 72

    • Figures before ‘>’ character are a timestamp made by the terminal program
    • 2nd figure (00196): Extinction coefficient, often called alfa, multiplied with 100.000. The relation between the extinction and visibility, VIS, is alfa=3/VIS. The alfa parameter can be used for monitoring trends in visibility when the visibility is larger than 5000 meters. But note that the absolute accuracy in alfa is limited in such cases.
    • 3rd figure (01530): Visibility in meters. 05000 is displayed if the measured visibility is larger than 5000 meters.
    • 4th figure (00000): A measure of the rain precipitation in µm during the last 5 minutes data collecting period.
    • 5th figure (00211): A measure of the snow precipitation in µm during the last 5 minutes data collecting period.
    • 6th figure (-6): Ambient temperature.
    • 7th figure (02): An uncalibrated and rough measure of the ambient solar irradiance. The sensitivity depends strongly on how the sensor is aimed. It may vary considerably. Even if the measurement is not very accurate, it may be useful for instance for telling if it is day or night.
    • 8th figure (72): WMO-code for the weather state.
    Mounting

    The sensor is delivered with a PMMA plastic mounting bracket. An important advantage with this bracket is that it isolates the sensor electrically, which reduces the risk for surge currents during lightning, etc.

    The sensor is heated a little above ambient temperature in order to keep moisture away. It is delivered with a 6 meter, 5-wire cable connected. In order to keep the electronics dry a there is membrane ventilator that keeps the pressure inside at the same level as outside. This prevents liquid water from sucking into the sensor through micro cracks at falling temperature - a creative solution to a big problem....

    The sensor should be mounted so that it "looks" roughly north (on the southern hemisphere south). There must not be anything in the sightline closer than about 5 meters. Outside a cone of about 30° objects can be tolerated at down to about 1 meter.

    • Dimensions: 68 x 45 x 34 mm
    • Weight: 170 grams
    • Warm up time: 5 minutes
    • Current consumption: 20 mA mean at 12 VDC
    • Outputs: Digital, streaming RS-232
    • Update time: 5 minutes
    • Temperature range: -20 to +50°C
    • Optical power output: Max about 1,8 mW from an IR laser
    • Laser safety class: 3R
    • Wavelength: 980 nm
    • Housing: Anodized aluminum, openings sealed with O-rings
    • Visibility range: Visibilities from 5 km down to 20 m
    • Visibility reading accuracy: ±30%
    • Measured rain amount accuracy: ±40%

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