RETIRED ›
This product is no longer available and has been replaced by: CLARIVUE10. Some accessories, replacement parts, or services may still be available.
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.

Dataloggers

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)
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+: 19

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  1. What is the difference between the backscatter measurement of the OBS-3+ and the side-scatter measurement of the ClariVue™10 sensor?

    The most significant difference between backscatter and side-scatter measurements is the sample volume. A backscatter sensor has a much larger sample volume that helps measure higher turbidity values. The smaller sample volume of side-scatter sensors works better at lower turbidities.

  2. What are the differences between the different turbidity units used, such as NTU, FBU, FTU, and FNU?

    It used to be that NTUs were the unit for all turbidity sensors. In 2007, an ASTM committee formed and established different units for each category of turbidity sensor technology, and there are many. Backscatter sensors such as the OBS-3+ and the OBS501 have units of FBU (Formazin Backscatter Units), whereas ISO 7027 side-scatter sensors have units of FNU (Formazin Nephelometric Units). The side-scatter OBS501 and the ClariVue™ sensors are part of this category. While sensors of different technical designs can be calibrated and measure Formazin the same, they will not make the same measurement in natural waters where size, shape, color, reflectivity, etc., of the particles vary. The ClariVue™ sensor measurements will not match the OBS-3+ measurements in natural waters.

  3. 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.

  4. 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.

  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. 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.

  7. What is the difference between the OBS-3+ and the OBS300?

    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.

  8. 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.

  9. What type of maintenance is needed for the OBS-3+ or OBS300?

    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.
  10. Can the OBS-3+ withstand dry weather conditions and work properly if it is not submerged in water all the time?

    Yes. However, contaminants may colonize the optics, which could distort the readings when water returns. Periodic cleaning may be required.

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