CS125 Present Weather and Visibility Sensor
Unrivalled Performance
Ideal for transportation applications
weather applications supported water applications supported energy applications supported gas flux and turbulence applications supported infrastructure applications supported soil applications supported


The CS125 is an infrared forward-scatter visibility and present weather sensor for stand-alone use or with automatic weather stations including those for road, marine, and airport applications. The CS125 has an attached 5 m (16.4 ft) cable and DB9 connector. 

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Benefits and Features

  • High performance sensor at a competitive price
  • Three year extended warranty available on this product
  • Sensor design minimises airflow disruption at measurement volume
  • Simple field calibration using optional calibration kit
  • Low power - suitable for remote application
  • Automatic status check for faults or window contamination
  • Incorporates automatic dew and hood heaters for all-weather operation
  • Made in UK
  • Type certified for Aviation use by the German Meteorological Service, Deutscher Wetterdienst (DWD)


Technical Description

The CS125 uses the well-established forward scatter system for visibility measurement, using a 42° scatter angle, which gives accurate estimates of Meteorological Observable Range (M.O.R.) for fog and snow.

It identifies precipitation particles from their scattering properties and fall speeds, and combines this with a temperature measurement to identify the weather type. It has downward-pointing optics that reduce the risk of contamination of the optics and blockage with snow. Interference to the sample volume from the sensor by flow distortion or heat is minimized.

It also provides reliable present weather information in the form of SYNOP codes, including information on the intensity of precipitation. Accumulation can also be reported.

The CS125 uses continuous high-speed sampling to reduce errors during mixed-weather events and events that return intermittent signals, such as rain and hail, while still providing reliable readings during more stable events, such as fog and mist. The CS125 has high immunity to interference from the visible and infrared warning lights used to mark obstructions, such as wind turbines.

The sensor can be set to a lower sampling frequency to save power, if required.

The CS125 incorporates low-power dew prevention heaters, as well as higher-power anti-icing heaters for the hoods as standard. These heaters are automatically controlled to ensure operation in all weather, or they can be disabled individually to save power.

The CS125 continuously monitors its own status and will report internal faults and contamination or blockage of the sensor lenses. It also has two user-configurable alarm outputs that can be used to drive audio or visual alarms using solid-state relays.

The CS125 is certified by Deutscher Wetterdienst as suitable for use to control wind turbine obstruction light systems as specified by 506/04, General Administrative Rules for the Identification of Aircraft Obstructions.



Maximum Reported Visibility 100 km (62.1 mi)
Minimum Reported Visibility 5 m (16.4 ft)
Resolution 1 m (3.28 ft)
Outputs Present and past weather: identifies as standard mist, fog, drizzle, freezing drizzle, drizzle and snow, rain, freezing rain, rain and drizzle, rain and snow, and snow. 57 SYNOP present weather codes and associated METAR and NWS present weather codes - hail detection; past weather codes.
  • ±8% (up to 600 m [1968.5 ft])
  • ±10% (600 to 10,000 m [1968.5 to 32,808.4 ft])
  • ±15% (10,000 to 15,000 m [32,808.4 to 49,212.6 ft])
  • ±20% (above 15,000 m [49,212.6 ft])
Precipitation Detection Sensitivity 0.05 mm/h
Accumulation Reporting Range 0 to 999.9 mm (0 to 39.37 in.)
Accumulation Accuracy ±15% (against factory calibration standards in the laboratory, for liquid precipitation)
Accumulation Resolution 0.1 mm (0.0039 in.)
Rain Intensity Range 0 to 999.9 mm/h (0 to 39.37 in./h)
(The maximum intensity reported is dependent on the mixture of precipitation falling.)
Intensity Accuracy ±15% (against factory calibration standards in the laboratory, for liquid precipitation)
Intensity Resolution 0.01 mm/h (0.00039 in./h)
Operating Temperature Range -25° to +60°C (standard)
Extended Operating Temperature Range -40° to +70°C (This extended version is available as a special. Contact Campbell Scientific for more information.)
Operating Humidity 0 . . . 100%
Operating Wind Speed Up to 60 m/s
Sensor Sealing Rated to IP66
Total Unit Power Less than 3 W while sampling continuously (including dew heaters)


Material Stainless steel and hard-anodized aluminum powder-coated
Mountings Stainless-steel clip on V-bolt mounting to pole with diameter of 32 to 52.5 mm (1.26 to 2.07 in.)
Mounting Pole An optical mounting pole is available to place the sample volume at 1.5 m (4.9 ft), as recommended by the WMO.
Frangible Mast Frangible masts are available to customer requirements to meet ICAO recommendations (typically placing the sample volume at 2.5 m [8.2 ft]).
Visibility Sensor Dimensions 540 x 640 x 246 mm (21.26 x 25.2 x 9.7 in.) including mount
Cable Length 5 m (16.4 ft)
Sensor Weight ~3 kg (6.61 lb) dependent upon mounting system


-NOTE- Lower power states can be achieved by less frequent sampling and remote control of heaters.

Optional power supplies with battery backup available.

Connectors in place of flying leads are available.

A low-voltage shutdown level can be set to prevent backup batteries from being damaged.
Electronics Supply Voltage 7 to 30 Vdc
Hood Heater Supply Voltage 24 V (dc or ac)
Hood Heater Power 2 x 30 W (total of 60 W)
Dew Heater Power 2 x 0.6 W (total of 1.2 W)


Serial Interface RS-232 or RS-485
Serial Data Rates 1200 to 115,200 bps (38,400 bps default rate)
Alarm Outputs 2 x 0 to 5 V outputs, 32 mA (max)


-NOTE- Lens contamination circuity monitors both the source and detector lenses for contamination/blockage at 1 s intervals.

The sensor can be configured to adjust calibration for low to moderate window contamination.

Light source stability control ensures stable operation through variations in temperature and with sensor aging.

Corrected at 1 s intervals.
Emitter Light Frequency 850 nm


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR800 (retired)
CR850 (retired)


CR1000X CS125 example programs v.1 (10 KB) 18-03-2020

CR1000X programs that read continuous data and polled data and use the SET, SETNC, and GET commands. The program that uses the SETNC command powers the CS125 hood heaters when needed according to the dew point. A HygroVUE5 Air Temperature and Relative Humidity Sensor provides the measurements used in the dew point calculation.

CS125 and CS120A OS v.17 (555 KB) 08-06-2023

Campbell Scientific has introduced a new operating system, OS 17, for the CS120A visibility sensor and CS125 present weather sensor. It is backwards compatible and is easily installed on all CS120A and CS125 sensors (but not older CS120 sensors). OS 17 is available free of charge and can be downloaded here or supplied by email on request.

Upgrade to OS 17 is recommended.

View Revision History

Campbell Viewpoint v. (86 MB) 09-10-2019

Campbell Viewpoint is viewing software designed to accompany the Campbell Scientific optical sensor range, including the CS135 ceilometer, SkyVue PRO, SkyVue 8, SkyVue 8M, CS120A visibility and CS125 present weather sensors. It is free to download (or via email on request) and use for 100 hours, after which you will need to purchase a key to continue using it.


Viewpoint version has introduced our new ceilometer sensors to the list of instruments that can be monitored.  This includes the SkyVue PRO, SkyVue 8 and SkyVue 8M.  

Previous sensors are still available.

Version also includes some minor bug fixes and improvements to the help menu.

Case Studies

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