Accurate, Rugged
Compact, low-power probe is field-proven
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The OBS-3+ is a submersible, turbidity probe that has sideways-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 OBS-3+ probe's output and calculate turbidity.

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Benefits and Features

  • Sideways facing optics avoid obstructions above and below the probe
  • Measures suspended solids and turbidity for up to 4000 NTUs
  • Provides a compact, low-power probe that is field proven
  • Accurate and rugged
  • Compatible with all Campbell Scientific dataloggers (including the CR200(X) series)
  • Stainless-steel body allows use down to 500 m in fresh water
  • Titanium body allows use down to 1500 m in fresh or salt water
  • 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 OBS-3+ uses its sideways-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 sideways-facing optics avoids obstructions above and below the probe. The OBS300 is available for locations that have obstructions around the sides of the probe.

OBS® is a registered trademark of Campbell Scientific.


Operating Temperature Range 0° to 40°C
Drift < 2% per year
Maximum Data Rate 10 Hz
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 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 14.1 cm (5.56 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

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X

Frequently Asked Questions

Number of FAQs related to OBS-3+: 17

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  1. 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.

  2. Possibly. Remember that the accuracy of the sensor is 0.5 NTU. If the drinking water standard is near 1, this sensor may not be a good match.

  3. This sensor is available with two types of wipers.

    • The Hydro-Wiper-C is a battery powered mechanical wiper with a scheduled wiping frequency.
    • The Hydro-Wiper-D is a mechanical wiper that is controlled and powered by the datalogger.
  4. 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.

  5. Generally, no, as this presents some hazards. For example, this sensor’s field of view in very clear water may extend 20 in., so a pipe less than 20 in. in diameter may distort the readings. Except for very turbid water, Campbell Scientific does not recommend placing this sensor in a pipe.

  6. 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.

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

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