Visibility & Present Weather Sensor SWS-250


The SWS-250 is optimised for use in aviation applications where both visibility and extended present and past weather information is required.

The sensor measures: visibility (MOR, EXCO and TEXCO), fog, haze, drizzle, snow, hail and other non-frozen precipitation according to WMO table 4680. METAR coded outputs are also provided.

For ultimate visibility performance the visual range extends to 99.99km allowing use in meteorological observation networks and research applications.

The enhanced present weather information from the SWS-250 is due to the backscatter receiver which allows detailed precipitation analysis and the use of algorithms developed for Biral’s flagship VPF-750 present weather sensor.

Easy integration of the Biral ALS-2 ambient light sensor makes the SWS-250 perfect for use in aviation applications where both RVR and METAR data are needed. Calibration in the field can be accomplished quickly and simply by a single operator using the optional calibration kit

  • 10m to 99.99km measurement range (other ranges available)
  • Instantaneous and averaged visibility outputs
  • Transmissometer equivalent EXCO output (TEXCO)
  • 39 WMO 4680 present weather codes
  • Compact forward scatter design
  • Hood heating for use in extreme environments
  • Window heating and contamination monitoring
  • Serial data output (RS232, RS422 or RS485)
  • Comprehensive self-test capabilities
  • This product is certified for use in Russia by Rosstandart – the Federal Agency for Technical Regulation and Metrology.


  • Measures Visibility, Present and Past Weather
  • (MOR & EXCO)
  • Output Serial data
  • Range (visibility) Default 10m to 99.99km
  • Measurement Error:
  • ≤4.2% at 600m
  • ≤5.1% at 2km
  • ≤6.8% at 5km
  • ≤9.6% at 10km
  • ≤12.3% at 15km
  • ≤14.8% at 20km
  • ≤17.1% at 25km
  • ≤19.4% at 30km
  • Measurement Resolution 1m or 10m (default)
  • Measurement principle angle, centred at 45°
  • Forward scatter meter with 39° to 51°
  • Precipitation detection threshold Snow: 0.0015mm/hr (0.00006 in/hr)
  • Rain: 0.015mm/hr (0.0006 in/hr)
  • Maximum rain rate ~500 mm/hr (20 in/hr)
  • Rain intensity accuracy ≤5%


  • Output rate (seconds) 10 to 300 (selectable)
  • Serial outputs RS232, RS422 and RS485
  • WMO Codes 42 Table 4680 codes
  • METAR Codes 36 present and past weather


  • Sensor Power 9-36Vdc
  • Hood heating power 24Vac or dc
  • Basic sensor 2.5W
  • Window heaters3.5W
  • Hood heaters 36W


  • Hood heaters Fitted as standard
  • Window heaters Fitted as standard
  • Window contamination monitoring Fitted as standard to all sensor head windows


  • Operating temperature -40°C to +60°C
  • Operating humidity 0 – 100% RH
  • Protection rating IP66/IP67


  • CE Certified
  • EMC compliance with EN61326-1997, 1998, 2001
  • RoHS and WEEE compliant


  • Material Aluminium. Powder paint finish, with optional hard anodize base layer.
  • (incl. mounting kit)
  • Weight 4.5kg
  • Length 811mm
  • Warranty 3 years
  • Lifetime >10 years


  • Self-test capability As standard
  • User confidence check 6 months recommended
  • Window Cleaning Automatic compensation and warnings
  • Field calibration With optional calibration kit


The sensor is delivered in sturdy recyclable foam filled packaging with:

  • User manual and calibration certificates
  • Pole mounting kit (2 x U-bolt)


  • 00.SWS.CABLE-D SWS Series Data Cable per metre
  • 00.SWS.CABLE-P SWS Series Power Cable per metre
  • SWS.CAL SWS Series Calibration Kit
  • SWS.CASE SWS Series Transit Case
  • SWS.SK200 SWS 200 Spares Kit
  • SWS.WTY250 1 Year extended warranty
  • PW.CODE User defined precipitation definitions.
  • Per definition set
  • PW.MAINS Mains Power Adaptor