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OBS-3+ Turbidity Sensor
Services Available
Repair No
Free Support Yes

Overview

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 data loggers 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
  • Compatible with most Campbell Scientific data loggers
  • Accurate and rugged
  • 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)

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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.

Specifications

Range
  • 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
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
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)
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 14.7 cm (5.79 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

Compatibility

Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR300
CR3000 (retired)
CR310
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR6
CR800 (retired)
CR850 (retired)
CR9000 (retired)
CR9000X (retired)

Frequently Asked Questions

Number of FAQs related to OBS-3+: 17

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  1. Is a version of the OBS-3+ available that has a 1500 m rating with a biofouling control (wiper or shutter)?

    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 data logger.
  2. Using an OBS-3+ or OBS300, when would it be advantageous to use a 4X curve instead of a 1X curve?

    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.

  3. Is it possible to operate an OBS-3+ or OBS300 onboard a vessel while the vessel is in motion?

    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.

  4. Are data from the OBS-3A comparable with data from the OBS-3+ or OBS300?

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

  5. What size is the arc that the OBS-3+ or OBS300 measures?

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

  6. Is it possible to adjust an OBS-3+ or OBS300 for measurements up to 4,000 NTUs?

    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. What is the accuracy and deviation from actual NTU in the low range for the OBS-3+ or OBS300?

    The accuracy is 0.5 NTU or 2% of reading.

  8. Using either an OBS-3+ or OBS300 with Short Cut, how can both NTU and mV values be included as outputs?

    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.

  9. Can the OBS-3+ be installed on a pipe?

    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.

  10. Can an OBS-3+ or OBS300 be used in a drinking water plant where the NTU is expected to be on a very low range?

    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.

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