Bristol Industrial & Research Associates Ltd (BIRAL)

- Model SWS-050 - Visibility Sensor



The SWS-050 Visibility Sensor is optimised for use in applications where accurate and reliable visibility measurements are required. The forward scatter measurement principle and unique design ensure the output is both accurate and reliable in all weather conditions.

With a measurement range of 10m to 40km the sensor is suitable for use in road and aviation applications as well as meteorological observation networks. The measurement accuracy easily exceeds that specified by the International Civil Aviation Organisation for visibility sensors used in METAR and RVR applications.

  • 10m to 40km measurement range
  • Compact forward scatter design
  • Hood heating for use in extreme environments
  • Window heating and contamination monitoring
  • Easy integration of Biral ALS-2 Ambient Light Sensor
  • Comprehensive self-test capabilities
  • Serial data output (RS232, RS422 or RS485)

The 45° forward scatter angle and 850nm infrared light source used by the SWS-050 provide the best possible visibility measurement accuracy in all weather conditions. Visibility is output as both Meteorological Optical Range (MOR) and Extinction Coefficient (EXCO) to simplify integration with monitoring systems.

In common with all Biral visibility and present weather sensors the SWS-050 uses 2kHz modulation of the light source combined with narrow pass band optical filter and synchronous detection at the receiver to ensure the measurement is not affected by bright or flashing lights. The design also ensures the sensor accurately reports visibility during precipitation. The horizontal hood design eliminates the problems caused by surface reflections that are a source of error in sensors employing look down hood geometries.

The sensor hoods are fitted with heaters to ensure blowing snow does not block the optical path. The hood heaters have their own supply connection allowing the use of unregulated supplies which can help to reduce installation costs. The hood heating only operates when the temperature drops below 4°C and can be disabled through the sensor interface if required.

The optical windows of the sensor are fitted with low power heaters to prevent the formation of condensation. Window contamination monitoring and compensation allows the visibility output to maintain its accuracy even as dirt builds up on the optical surfaces. The sensor reports the window contamination in the output message using two stages of warning flags allowing cleaning to take place in a convenient manner.

Communication with the sensor is over a serial data link that is user configurable for RS232, RS422 or RS485 signal levels. ASCII encoded data is used and the sensor can operate in either a polled broadcast modes. The data message can include a time stamp from the internal real time clock in addition to the standard visibility and basic self-test information.

The sensor operates from a low voltage DC supply and requires just 3.5W. The low power window heaters that can be set to only operate when condensation is detected take an additional 1.7W. The higher power hood heaters are supplied separately allowing the use of an unregulated heating supply.

The SWS-050 is a single lightweight unit that can be easily installed by one person. The sensor enclosure is constructed from aluminium which is surface passivated and finished with a white powder coat paint. It is designed for use in all types of weather and has a wide operating temperature.

  • Measurement : Visibility, MOR and EXCO
  • Output : RS232, RS422 or RS485
  • Measurement Principle : Forward scatter 45°
  • Measurement Error : 5% at 1,500m
  • Sensor Power : 9 – 36 V DC (5.2W)
  • Hood heating power : 24 V AC or DC (24W)
  • Window heating and contamination monitoring : Fitted
  • Operating Temperature : -40°C to 60°C
  • Operating Humidity : 0 – 100% RH
  • Protection rating : IP66/IP67
  • Weight : 4.2 kg

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