This product is no longer available and has been replaced by: CLARIVUE10. Some accessories, replacement parts, or services may still be available.
OBS300 Turbidity Sensor
Services Available
Repair Yes
Free Support Yes


The OBS300 is a submersible turbidity probe that has downward-facing optics. It uses OBS® technology to measure suspended solids and turbidity for applications ranging from water quality in freshwater rivers and streams to sediment transport and dredge monitoring. Campbell Scientific dataloggers measure the OBS300 probe's output and calculate turbidity.

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Benefits and Features

  • Downward-facing optics avoid obstructions around the sides of the probe
  • Measures suspended solids and turbidity for up to 4000 NTUs
  • Provides a compact, low-power probe that is field proven
  • Stainless-steel body allows use down to 500 m in fresh water
  • Compatible with most Campbell Scientific data loggers
  • Titanium body allows use down to 1500 m in fresh or salt water
  • Accurate and rugged
  • Fitted with MCBH-5-FS, wet-pluggable connector—multiple mating cable length options available
  • Offers an optional five-point sedimentation calibration for better measurements (see Ordering Info on the web page)


Technical Description

The OBS300 uses its downward-facing optics to emit a near-infrared light into the water. It then measures the light that bounces back from the water’s suspended particles.

If an obstruction is in the emitted light’s range, the light will scatter back and the turbidity reading will be too high. This probe's downward-facing optics avoid obstructions around the sides of the probe. The OBS-3+ is available for locations that have obstructions above and below the probe. (OBS® is a registered trademark of Campbell Scientific.)


  • 0 to 250 NTU
  • 0 to 500 NTU
  • 0 to 1000 NTU
  • 0 to 3000 NTU
  • 0 to 4000 NTU
Maximum Submersion Depth
  • 500 m (1640.5 ft) for stainless-steel body
  • 1500 m (4921.5 ft ) for titanium body
Maximum Concentration Range
  • Maximum concentration depends on sediment size, particle shape, and reflectivity.
  • 5,000 to 10,000 mg/l (for mud)
  • 50,000 to 100,000 mg/l (for sand)
Concentration Accuracy
  • 2% of reading or 1 mg/l (whichever is larger) for mud
  • 4% of reading or 10 mg/l (whichever is larger) for sand
Operating Temperature Range 0° to 40°C
Drift over Time < 2% per year
Maximum Data Rate 10 Hz
Minimum Warm-up Time 2 s
Infrared Wavelength 850 nm ±5 nm
Daylight Rejection -28 dB (re: 48 mW/cm-2)
Optical Power 2000 µW
Turbidity Accuracy 2% of reading or 0.5 NTU (whichever is larger)
Housing Material 316 stainless steel or titanium
Connector MCBH-5-FS, wet-pluggable
Diameter 2.5 cm (0.98 in.)
Height 13.1 cm (5.15 in.)
Weight 181.4 g (0.4 lb)

-2.5 Output Option

Output Voltage 0 to 2.5 V (over selected NTU range)
Supply Voltage 5 to 15 Vdc
Current Drain 15 mA

-5 Output Option

Output Voltage 0 to 5 V (over selected NTU range)
Supply Voltage 5 to 15 Vdc
Current Drain 15 mA

-20 Output Option

Output Voltage 4 to 20 mA (over selected NTU range)
Supply Voltage 9 to 15 Vdc
Current Drain 45 mA


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


Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR216X (retired)
CR5000 (retired)
CR800 (retired)
CR850 (retired)
CR9000X (retired)

FAQs for

Number of FAQs related to OBS300: 16

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  1. Typically, users use a clamp (a hose clamp, for example) to fasten the sensor to a permanent structure in the water so that the optics are orientated toward the open water.

  2. Yes. The OBS300 is not harmed by being dry. The optics, however, need to be cleaned of any dust or contamination before the measurements are resumed.

  3. The following are some suggestions:

    • Keep the optics clean.
    • Site-specific field calibration may be necessary for the best performance. 
    • Prevent the sensor from freezing.
  4. Campbell Scientific does not offer a display that can be attached directly to the sensor; however, the data logger used to capture and record the data may have a display.

  5. The OBS-3+ or OBS300 provides two separate outputs to match the two turbidity ranges selected at the time of purchase. Use the curve that matches the turbidity range likely to be experienced during monitoring. Program the data logger to record and store data from each output, or choose which output to use automatically depending on the turbidity.

  6. Sensors are calibrated at the factory for measurements up to 4,000 NTUs, if requested at the time of order. Sensor ranges cannot be adjusted outside the factory.

  7. This depends on the turbidity of the water. In very clear water exposed to direct sunlight, up to 18 in. of water may be needed to prevent the sun from affecting the readings. Less sunlight penetrates more turbid water, which means the sensor would not need to be positioned as deeply. If the target water is clear and shallow, it may be necessary to construct a canopy above the water to shadow the monitoring site.

    In addition, the sensor must be positioned in the water so that nothing obstructs its field of view. In very clear water, this may require an 18 in. standoff.

  8. The OBS-3+ and the OBS300 are essentially the same sensor but with differing optic placement. The OBS-3+ has sideways-facing optics, whereas the OBS300 has downward-facing optics.

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