SWS-050T Visibility Sensor

Model Number: SWS-050T
Manufacturer: Biral
Product Brochure: Download

The SWS-050T is designed for use in road and tunnel applications where accurate and reliable visibility measurements are required


SWS-050T Visibility Sensor

The SWS-050T is designed for use in road and tunnel 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 and will not be influenced by local light sources, even those that flash.

The standard 10m to 2km measurement range is optimal for use in road and tunnel applications however, other measurement ranges up to 40km are available.

Heating of the optical windows and sensor hoods is provided as standard allowing use in the harshest of conditions. Both optical windows are monitored for contamination and the visibility output is automatically compensated to reduce maintenance requirements.

In addition to the serial data interface the sensor provides voltage and current outputs of visibility (MOR) or extinction coefficient (EXCO). Optional relays provide threshold and selftest switching capability.

  • 10m to 2km measurement range
  • Compact forward scatter design
  • Hood heating for use in extreme environments
  • Window heating and contamination monitoring
  • 4-20 mA and relay outputs
  • Comprehensive self-test capabilities
  • Serial data output (RS232, RS422 or RS485)

Technical Description

The 45° forward scatter angle and 850nm infrared light source used by the SWS-050T 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 provide compatibility with the widest range of control systems.

In common with all Biral visibility and present weather sensors the SWS-050T uses 2kHz modulation of the light source combined with narrow pass band optical filters and synchronous detection at the receiver to ensure the measurement is not affected by bright or flashing lights. This 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 or 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 sensors analogue voltage and current outputs can be configured to report either MOR or EXCO. The sensor can be supplied with two user configurable threshold relays and one fault relay.

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-050T 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
0 - 10 V and 4-20mA
2 Threshold and 1 Fault Relay (optional)
Measurement Principle Forward scatter 45°
Measurement Error 5% at 2,000m
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

Sales & Support

Contact Biral for more information

To find out more about this instrument or to discuss your application requirements please do not hesitate to contact Biral.

  • email enquiries@biral.com (or use the Request More Information button below the product photograph)
  • Telephone to 01275 847787 (from the UK) or +44 1275 847787 (International)

After Sales Support

Biral offers free advice and technical support for the lifetime of the instruments we sell. Once you have purchased the unit you can always contact us for help using the links on our Technical Support page.


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