This product is no longer available and has been replaced by: CS120A. Some accessories, replacement parts, or services may still be available.
CS120 Atmospheric Visibility Sensor
Services Available
Repair Yes
Calibration Yes
Free Support Yes


The CS120 uses tried-and-tested, infrared forward-scatter technology, and uses the proven 42° scatter angle to report meteorological observable range (MOR) for fog and snow in the range 10 to 30,000 m. It combines a high specification with a very competitive price. The CS120 is ideal for stand-alone applications or in combination with automatic weather stations in road, aviation, solar-energy, and wind-energy environments.

Note: Campbell Scientific does not recommend using the CS120 for marine applications.

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Benefits and Features

  • High-performance sensor at a competitive price
  • Incorporates automatic dew and hood heaters for all-weather operation
  • Simple field calibration using optional calibration kit
  • Low power - suitable for remote applications
  • Automatic status check for faults or window contamination
  • Sensor design minimizes airflow disruption at measurement volume


Detailed Description

Compared to many such sensors the CS120 design means that visibility is being measured in a relatively clean space because the position of the heads and body minimize disturbance of the airflow at the measurement volume.

The CS120 uses continuous high-speed sampling, which improves the accuracy of the measurements taken during mixed weather such as rain and hail, while providing reliable readings during more stable events such as fog and mist. High speed sampling also allows the sensor to better respond to suddenly changing conditions.

The CS120 has several design features that keep its optics clean. Downward facing optics minimizes dirt and snow build up. Low powered heaters prevent the formation of dew, and a higher-powered heater prevents the formation of ice.

The sensor is very power efficient, drawing just 3 W during normal operation including the dew heaters; power can be reduced further by reducing the sample rate and manual control of the heaters.


Measurement Description Meteorological Observable Range (MOR)
Signal Type/Output RS-232, RS-485
Maximum Reported Visibility 32 km (~20 mi)
Minimum Reported Visibility 12 m (~39 ft)
Accuracy (0 to 10,000 m) ±10%
Accuracy (10,000 to 20,000 m) ±20%
Operating Temperature -25° to +60°C
Operating Humidity 0 to 100%
Wind Speed Up to 60 m/s
Sensor Sealing Rated to IP66
Mounting Stainless-steel V-bolt mounting to pole with OD of 32 to 52.5 mm (1.25 to 2 in.)
Dimensions 447 x 640 x 246 mm (17.6 x 25.2 x 9.7 in.)
Weight ~3 kg (6.6 lb) depending upon mounting system used


  • A low-voltage shutdown level can be set to prevent back-up batteries being damaged.
  • Lower power states can be achieved by less frequent sampling and remote control of heaters.
Electronic Supply Voltage 8 to 30 Vdc
Hood Heater Supply Voltage 24 Vdc or Vac
Hood Heater Power 2 x 30 W (total of 60 W)
Total Unit Power < 3 W while sampling continuously (including dew heaters)


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)


Emitter Light Frequency 850 nm
Lens Contamination Circuitry Monitors both the source and detector lenses for contamination/blockage at 1 s intervals. Sensor adjusts its 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.


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

Data Loggers

Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR23X (retired)
CR295X (retired)
CR3000 (retired)
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR800 (retired)
CR850 (retired)
CR9000 (retired)
CR9000X (retired)

Related Documents


CS120 Firmware v.6 (1.51 MB) 10-08-2012

Includes the current CS120 firmware and the CS120 support files for the Device Configuration Utility.

View Revision History

Articles and Press Releases

FAQs for

Number of FAQs related to CS120: 3

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  1. Most Campbell Scientific sensors are available as an –L, which indicates a user-specified cable length. If a sensor is listed as an –LX model (where “X” is some other character), that sensor’s cable has a user-specified length, but it terminates with a specific connector for a unique system:

    • An –LC model has a user-specified cable length for connection to an ET107, CS110, or retired Metdata1.
    • An –LQ model has a user-specified cable length for connection to a RAWS-P weather station.

    If a sensor does not have an –L or other –LX designation after the main model number, the sensor has a set cable length. The cable length is listed at the end of the Description field in the product’s Ordering information. For example, the 034B-ET model has a description of “Met One Wind Set for ET Station, 67 inch Cable.” Products with a set cable length terminate, as a default, with pigtails.

    If a cable terminates with a special connector for a unique system, the end of the model number designates which system. For example, the 034B-ET model designates the sensor as a 034B for an ET107 system.

    • –ET models terminate with the connector for an ET107 weather station.
    • –ETM models terminate with the connector for an ET107 weather station, but they also include a special system mounting, which is often convenient when purchasing a replacement part.
    • –QD models terminate with the connector for a RAWS-F Quick Deployment Station.
    • –PW models terminate with the connector for a PWENC or pre-wired system.
  2. Not every sensor has different cable termination options. The options available for a particular sensor can be checked by looking in two places in the Ordering information area of the sensor product page:

    • Model number
    • Cable Termination Options list

    If a sensor is offered in an –ET, –ETM, –LC, –LQ, or –QD version, that option’s availability is reflected in the sensor model number. For example, the 034B is offered as the 034B-ET, 034B-ETM, 034B-LC, 034B-LQ, and 034B-QD.

    All of the other cable termination options, if available, are listed on the Ordering information area of the sensor product page under “Cable Termination Options.” For example, the 034B-L Wind Set is offered with the –CWS, –PT, and –PW options, as shown in the Ordering information area of the 034B-L product page.

    Note: As newer products are added to our inventory, typically, we will list multiple cable termination options under a single sensor model rather than creating multiple model numbers. For example, the HC2S3-L has a –C cable termination option for connecting it to a CS110 instead of offering an HC2S3-LC model. 

  3. Many Campbell Scientific sensors are available with different cable termination options. These options include the following:

    • The –PT (–PT w/Tinned Wires) option is the default option and does not display on the product line as the other options do. The cable terminates in pigtails that connect directly to a data logger.
    • In the –C (–C w/ET/CS110 Connector) option, the cable terminates in a connector that attaches to a CS110 Electric Field Meter or an ET-series weather station.
    • In the –CWS (–CWS w/CWS900 Connector) option, the cable terminates in a connector that attaches to a CWS900-series interface. Connection to a CWS900-series interface allows the sensor to be used in a wireless sensor network.
    • In the –PW (–PW w/Pre-Wire Connector) option, the cable terminates in a connector that attaches to a prewired enclosure.
    • In the –RQ (–RQ w/RAWS Connector) option, the cable terminates in a connector that attaches to a RAWS-P Permanent Remote Automated Weather Station.

    Note: The availability of cable termination options varies by sensor. For example, sensors may have none, two, or several options to choose from. If a desired option is not listed for a specific sensor, contact Campbell Scientific for assistance.