OBS300 Turbidity Sensor
Accurate, Rugged
Optics avoid obstructions on sides of probe
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


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 dataloggers
  • 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)


Detailed 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.)


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
Maximum Submersion Depth
  • 500 m (1640.5 ft) for stainless-steel body
  • 1500 m (4921.5 ft ) for titanium body
Maximum Concentration Range
  • 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
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


Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X CR300 Series CR6 Series

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X

Frequently Asked Questions

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 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 datalogger to record and store data from each output, or choose which output to use automatically depending on the turbidity.

  4. These devices employ optical backscatter to measure light absorption and should produce comparable data, but variation is likely between sensors.

  5. This has not been tested; however, it is likely that, as the sensor moves through the water, disturbances or bubbles are created that could distort the turbidity measurements.

  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. Campbell Scientific does not offer a display that can be attached directly to the sensor; however, the datalogger used to capture and record the data may have a display.

  8. The beam divergence angle of the sensor is 42°. (Within this 42° cone, 95% of the beam power is contained.)

  9. Short Cut does not allow mV readings. To record the raw mV data before it is converted to NTU, open the Short Cut file in the CRBasic Editor, and alter the program manually.

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