Campbell OBS-3+ User manual

OBS-3+ and
OBS300
Suspended Solids and
Turbidity Monitors
Revision: 7/19
Copyright © 2008 – 2019
Campbell Scientific

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
We will repair or replace products which prove to be defective during the
guarantee period as detailed on your invoice, provided they are returned to us
prepaid. The guarantee will not apply to:

Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific

Batteries

Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
in removing and/or reinstalling equipment. This guarantee and the Company’s
obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
Scientific is not liable for consequential damage.
Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
request. It is the policy of Campbell Scientific to protect the health of its
employees and provide a safe working environment, in support of this policy a
“Declaration of Hazardous Material and Decontamination” form will be
issued for completion.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package. Complete the “Declaration of
Hazardous Material and Decontamination” form and ensure a completed copy
is returned with your goods. Please note your Repair may not be processed if
you do not include a copy of this form and Campbell Scientific Ltd reserves
the right to return goods at the customers’ expense.
Note that goods sent air freight are subject to Customs clearance fees which
Campbell Scientific will charge to customers. In many cases, these charges are
greater than the cost of the repair.
Campbell Scientific Ltd,
80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [e-mail]
www.campbellsci.co.uk

PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the North
American market. Some spellings, weights and measures may reflect this origin.
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
In addition, while most of the information in the manual is correct for all countries, certain information
is specific to the North American market and so may not be applicable to European users.
Differences include the U.S standard external power supply details where some information (for
example the AC transformer input voltage) will not be applicable for British/European use. Please note,
however, that when a power supply adapter is ordered it will be suitable for use in your country.
Reference to some radio transmitters, digital cell phones and aerials may also not be applicable
according to your locality.
Some brackets, shields and enclosure options, including wiring, are not sold as standard items in the
European market; in some cases alternatives are offered. Details of the alternatives will be covered in
separate manuals.
Part numbers prefixed with a “#” symbol are special order parts for use with non-EU variants or for
special installations. Please quote the full part number with the # when ordering.
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse but
sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX,
UK Tel: [phone] Fax: [phone]
Email: [e-mail]
www.campbellsci.co.uk

Safety
DANGER —MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON
OR AROUND TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS,
CROSSARMS, ENCLOSURES, ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE,
INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS, TOWERS, AND ATTACHMENTS, AND FAILURE TO HEED
WARNINGS, INCREASES THE RISK OF DEATH, ACCIDENT, SERIOUS INJURY, PROPERTY DAMAGE, AND
PRODUCT FAILURE. TAKE ALL REASONABLE PRECAUTIONS TO AVOID THESE HAZARDS. CHECK WITH YOUR
ORGANIZATION'S SAFETY COORDINATOR (OR POLICY) FOR PROCEDURES AND REQUIRED PROTECTIVE
EQUIPMENT PRIOR TO PERFORMING ANY WORK.
Use tripods, towers, and attachments to tripods and towers only for purposes for which they are designed. Do not
exceed design limits. Be familiar and comply with all instructions provided in product manuals. Manuals are
available at www.campbellsci.eu or by telephoning [phone] (UK). You are responsible for conformance
with governing codes and regulations, including safety regulations, and the integrity and location of structures or land
to which towers, tripods, and any attachments are attached. Installation sites should be evaluated and approved by a
qualified engineer. If questions or concerns arise regarding installation, use, or maintenance of tripods, towers,
attachments, or electrical connections, consult with a licensed and qualified engineer or electrician.
General
•Prior to performing site or installation work, obtain required approvals and permits. Comply with all
governing structure-height regulations, such as those of the FAA in the USA.
•Use only qualified personnel for installation, use, and maintenance of tripods and towers, and any
attachments to tripods and towers. The use of licensed and qualified contractors is highly recommended.
•Read all applicable instructions carefully and understand procedures thoroughly before beginning work.
•Wear a hardhat and eye protection, and take other appropriate safety precautions while working on or
around tripods and towers.
•Do not climb tripods or towers at any time, and prohibit climbing by other persons. Take reasonable
precautions to secure tripod and tower sites from trespassers.
•Use only manufacturer recommended parts, materials, and tools.
Utility and Electrical
•You can be killed or sustain serious bodily injury if the tripod, tower, or attachments you are installing,
constructing, using, or maintaining, or a tool, stake, or anchor, come in contact with overhead or
underground utility lines.
•Maintain a distance of at least one-and-one-half times structure height, or 20 feet, or the distance
required by applicable law, whichever is greater, between overhead utility lines and the structure (tripod,
tower, attachments, or tools).
•Prior to performing site or installation work, inform all utility companies and have all underground utilities
marked.
•Comply with all electrical codes. Electrical equipment and related grounding devices should be installed
by a licensed and qualified electrician.
Elevated Work and Weather
•Exercise extreme caution when performing elevated work.
•Use appropriate equipment and safety practices.
•During installation and maintenance, keep tower and tripod sites clear of un-trained or non-essential
personnel. Take precautions to prevent elevated tools and objects from dropping.
•Do not perform any work in inclement weather, including wind, rain, snow, lightning, etc.
Maintenance
•Periodically (at least yearly) check for wear and damage, including corrosion, stress cracks, frayed cables,
loose cable clamps, cable tightness, etc. and take necessary corrective actions.
•Periodically (at least yearly) check electrical ground connections.
WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL
SCIENTIFIC PRODUCTS, THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER
INSTALLATION, USE, OR MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS
SUCH AS SENSORS, CROSSARMS, ENCLOSURES, ANTENNAS, ETC.

i
Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.
1. Introduction................................................................ 1
2. Precautions ................................................................ 1
3. Initial Inspection ........................................................ 2
4. QuickStart .................................................................. 2
4.1 Preparation for Use ..............................................................................2
4.2 Use SCWin to Program Data Logger and Generate Wiring Diagram..2
5. Overview .................................................................... 4
5.1 Applications .........................................................................................5
5.2 Turbidity...............................................................................................5
5.3 Design Details ......................................................................................5
5.4 Measurement Details............................................................................6
6. Specifications ............................................................ 7
7. Installation ................................................................. 9
7.1 Pre-Deployment Tests ..........................................................................9
7.2 Mounting Considerations .....................................................................9
7.2.1 Siting .............................................................................................9
7.2.2 Mounting Options .........................................................................9
7.2.2.1 PVC Pipe............................................................................9
7.2.2.2 Cable Ties or Hose Clamps ..............................................10
7.3 Wiring to Data Logger .......................................................................10
7.4 Data Logger Programming.................................................................11
7.5 Calibration Certificate ........................................................................12
8. Calibration................................................................ 14
8.1 Turbidity.............................................................................................14
8.1.1 Materials and Equipment ............................................................16
8.1.2 Setup ...........................................................................................17
8.1.3 Procedure ....................................................................................17
8.2 Sediment.............................................................................................18
8.2.1 Dry-sediment Calibration............................................................18
8.2.2 Wet-sediment Calibration ...........................................................18
8.2.3 In situ Calibration........................................................................19
8.2.3.1 Materials and Equipment..................................................19
8.2.3.2 Setup.................................................................................19
8.2.3.3 Procedure..........................................................................20
9. Troubleshooting ...................................................... 21

Table of Contents
ii
10. Maintenance............................................................. 22
11. Factors that Affect Turbidity and Suspended-
Sediment Measurements ...................................... 23
11.1 Particle Size........................................................................................23
11.2 Suspensions with Mud and Sand........................................................24
11.3 Particle-Shape Effects ........................................................................24
11.4 High Sediment Concentrations...........................................................25
11.5 IR Reflectivity—Sediment Colour.....................................................26
11.6 Water Colour......................................................................................27
11.7 Bubbles and Plankton.........................................................................27
11.8 Biological and Chemical Fouling.......................................................28
12. References ............................................................... 28
13. Terminology............................................................. 29
Appendices
A. Importing Short Cut Code Into CRBasic Editor... A-1
B. Example Programs ................................................ B-1
B.1 CR1000X Example Program............................................................B-1
B.2 CR200(X) Example Program ...........................................................B-2
C. Electrical Connections Details ............................. C-1
D. Data Logger Connection to a Relay ..................... D-1
Figures
5-1. Components of the OBS-3+ (left) and orientation source beam and
detector acceptance cone of the OBS-3+ (top right) and OBS300
(bottom right)....................................................................................6
7-1. OBS-3+ connected to a CR1000 data logger (OBS300 has the
same wiring) ...................................................................................11
7-2. Calibration certificate showing millivolt coefficients ........................13
7-3. Calibration certificate showing volts coefficients ..............................14
8-1. Normalized response of OBS-3+ to AMCO Clear®turbidity. The
inset shows the response function of an OBS sensor to high
sediment concentrations..................................................................15
8-2. Position of OBS-3+ (left) and OBS300 (right) in clean tap water
in big black tub ...............................................................................17
8-3. OBS-3+ (left) and OBS300 (right) in 500-NTU AMCO Clear®
turbidity standard in 100-mm black polyethylene calibration cup..18
8-4. Portable sediment suspender (left) and OBS beam orientation in
suspender tub (right) .......................................................................20
11-1. Normalized OBS sensitivity as a function of grain diameter .............23
11-2. The apparent change in turbidity resulting from disaggregation
methods...........................................................................................24

Table of Contents
iii
11-3. Relative scattering intensities of grain shapes....................................25
11-4. Response of an OBS sensor to a wide range of SSC..........................26
11-5. Infrared reflectivity of minerals as a function of 10-Munzell value..27
C-1. Pin assignments for MCBH and MCIL wet-pluggable connectors ..C-1
D-1. Wiring diagram for connecting an OBS sensor to an external
relay and a data logger ................................................................. D-1
Tables
7-1. Wire Colour, Function, and Data Logger Connection........................10
8-1. SDVB NTU values for turbidity calibrations in standard low
ranges..............................................................................................15
8-2. Change in NTU value resulting from one hour of evaporation1of
SDVB standard; in other words, loss of water but not particles. ....16
9-1. Troubleshooting Chart .......................................................................22
C-1. Pin numbers, electrical functions and wire colourcodes for OBS
sensor bulkhead connectors. .........................................................C-2
CRBasic Examples
B-1. CR1000X Program Measuring the Turbidity Sensor .......................B-1
B-2. CR200X Program Measuring the Turbidity Sensor .........................B-2

1
OBS-3+ and OBS300 Suspended Solids
and Turbidity Monitors
1. Introduction
The OBS-3+ and OBS300 are submersible, turbidity sensors that use 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. The OBS-3+ and OBS300 are identical except for the
orientation of their optics. The OBS-3+ “looks” perpendicular to the length of
the sensor, whereas the OBS300 “looks” out the end of the sensor. Throughout
this manual any time OBS sensor is mentioned, it is valid for both the OBS-3+
and OBS300.
This manual provides information only for CRBasic data loggers.
It is also compatible with most of our retired Edlog data loggers.
For Edlog data logger support, see an older manual at
www.campbellsci.com/old-manuals.
2. Precautions
•READ AND UNDERSTAND the Safety section at the front of this
manual.
•Although the OBS-3+ and OBS300 are rugged, they should be handled as
precision scientific instruments.
•The titanium body option (option -TB) must be used if submersing the
probe in seawater. Using an OBS sensor with a stainless steel housing
(option -SB) in seawater voids the warranty and causes corrosion and
leakage.
•There are no user-serviceable parts inside the sensor housing. Do not
remove the sensor or connector from the pressure housing. This will void
the warranty and could cause leakage.
•Do not use solvents such as MEK, toluene, acetone, or trichloroethylene to
clean the sensor.
•The sensor may be damaged if it is encased in ice.
•Damages caused by freezing conditions will not be covered by our
warranty.
•Campbell Scientific recommends removing the sensor from the water for
the time period that the water is likely to freeze.
NOTE

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
2
3. Initial Inspection
•Upon receipt of the OBS-3+ or OBS300, inspect the packaging and
contents for damage. File damage claims with the shipping company.
•The sensor is shipped with a calibration sheet and an instruction manual.
4. QuickStart
4.1 Preparation for Use
1. Bench test the sensor to ensure that it functions properly prior to making
field installations (see Section 7.1, Pre-Deployment Tests (p. 9)).
2. Calibrate the sensor using suspended solids from the waters that will be
monitored (see Section 8, Calibration (p. 14)).
3. Refer to Section 7.2, Mounting Considerations (p. 9), for siting and
mounting options.
4.2 Use SCWin to Program Data Logger and Generate Wiring
Diagram
Avideo that describes data logger programming using Short Cut is available
at: www.campbellsci.eu/videos/cr1000x-datalogger-getting-started-program-
part-3. Short Cut is an easy way toprogram your data logger to measure the
sensor and assign data logger wiring terminals. Short Cut is available as a
download on www.campbellsci.eu.It is included in installations ofLoggerNet,
PC200W, PC400, or RTDAQ.
The following procedure also shows using Short Cut to program the OBS-
3+/OBS300.
1. Open Short Cut and click Create New Program.
2. Double-click the data logger model.

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
3
3. In the Available Sensors and Devices box, type OBS-3+ or find the
sensor in the Sensors > Water > Quality folder. Double-click OBS-
3+/OBS300 Turbidity Sensor. Select your sensor Low and High NTU
Range and Maximum Voltage Output. You can use the default value (V)
forthe Coefficients based on signal voltage in units of. Enter the Low
Range Coefficients and High Range Coefficients according to your
calibration sheet (see Section 7.5, Calibration Certificate (p. 12)).
4. Click the Wiring tab. Click OK after wiring the sensor.
5. Repeat steps three and four for other sensors you want to measure. Click
Next.

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
4
6. In Output Setup, type the scan rate, a meaningful Table Name, and Data
Output Storage Interval. Click Next.
7. Select the output options.
8. Click Finish and save the program. Send the program to the data logger if
the data logger is connected to the computer.
9. If the sensor is connected to the data logger, check the output of the sensor
in LoggerNet, PC400, RTDAQ, or PC200W to make sure it is making
reasonable measurements.
5. Overview
The heart ofan OBS®sensor isa near infrared (NIR) laser and photodiode for
detecting the intensity oflight scattered from suspended particles in water.
Electrical connections are made with a moulded-cable assembly terminated
with an MCIL wet-pluggable underwater connector. With its unique optical
design (U.S. Patent No. 4,841,157), OBS sensors perform better than most in
situ turbidity monitors inthe following ways:
•Small size and low power
•Highly linear response

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
5
•Insensitivity to bubbles and organic matter
•Ambient-light rejection and low temperature coefficient
5.1 Applications
OBS sensors are used for a wide variety of monitoring tasks in riverine,
oceanic, laboratory, and industrial settings. They can be integrated in water-
quality monitoring systems, CTDs, laboratory instrumentation, and sediment-
transport monitors. The applications include:
•Compliance with permits, water-quality guidelines, and regulations
•Determination of transport and fate of particles and associated
contaminants in aquatic systems
•Conservation, protection and restoration of surface waters
•Assess performance of water and land-use management
•Monitor waterside construction, mining, and dredging operations
•Characterization of wastewater and energy-production effluents
•Tracking water-well completion including development and use
5.2 Turbidity
Conceptually, turbidity isa numerical expression inturbidity units (NTU) of
the optical properties that cause water toappear hazy orcloudy asa result of
light scattering and absorption by suspended matter. Operationally, a NTU
value isinterpolated from neighbouring light-scattering measurements made
on calibration standards such as Formazin,StablCal, or SDVB.
Turbidity iscaused by suspended and dissolved matter such as sediment,
plankton, bacteria, viruses, and organic and inorganic dyes. In general, asthe
concentration ofsuspended matter in water increases, sowill its turbidity, and
as theconcentration ofdissolved light-absorbing matterincreases, turbidity
will decrease. Descriptions ofthe factors that affect turbidity are given in
Section 11, Factors that Affect Turbidity and Suspended-Sediment
Measurements (p. 23).
Like all other optical turbidity monitors, the OBS response
depends on the size, composition, and shape of suspended
particles, and for this reason, the sensor must be calibrated
with suspended solids from the waters to be monitored.
There is no ‘standard’ turbidimeter design or universal formula for converting
NTU values to physical units such as mg L–1 or ppm. NTU values have no
intrinsic physical, chemical, or biological significance. Empirical correlations
between turbidity and environmental conditions, established through field
calibration, can be useful in water-quality investigations.
5.3 Design Details
OBS sensors detect suspended matter in water and turbidity from the relative
intensity of light backscattered at angles ranging from 90oto 165o, in clean
water. A 3D schematic of the main components of the OBS-3+ is shown in
CAUTION

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
6
FIGURE 5-1. The OBS300 has the same components but they are arranged
differently.
The OBS light source is a Vertical-Cavity Surface-Emitting Laser diode
(VCSEL), which converts 5 mA of electrical current to 2000 µW of optical
power. The detector is a low-drift silicon photodiode with enhanced NIR
responsivity, the ratio of electrical current produced per unit of light power in
A W–1. A light baffle prevents direct illumination of the detector by the light
source and in-phase coupling that would otherwise produce large signal biases.
A daylight-rejection filter blocks visible light in the solar spectrum and reduces
ambient-light interference. In addition to the filter, a synchronous detection
circuit is used to eliminate the bias caused by ambient light. The VCSEL is
driven by a temperature-compensated voltage-controlled current source
(VCCS).
The interface between the optics and the water sample is a window made of
cast optical epoxy.
Window transmittance must remain constant in order to
prevent calibration drift, so keeping the OBS window clean
is the most important maintenance item; see Section 10,
Maintenance (p. 22).
FIGURE 5-1. Components of the OBS-3+ (left) and orientation source
beam and detector acceptance cone of the OBS-3+ (top right) and
OBS300 (bottom right)
The beam divergence angle of the VCSEL source is 42o(95% of the beam
power is contained within a 42ocone). The sensor can see to a distance of
approximately 50 cm (20 in) in very clean water.
5.4 Measurement Details
The OBS-3+ and OBS300 are dual range sensors having both a low- and a
high-range output. The standard low ranges are 250, 500, 1000, or 4000 NTU,
and the corresponding high ranges are 1000, 2000, and 4000 NTU. OBS
CAUTION

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
7
sensors can be purchased with a 4 to 20 mA current output on the low range
and a 0 to5 V output on the high range. Voltage outputs can be 0 to 2.5 or 0 to
5V;see Section 6, Specifications (p. 7). It is also possible topurchase sensors
configured to operate from 5-Vpower, however, theoutput span is limited to
2.5 V.
The sensor needs tobe connected toa data logger, current meter, orCTD
instrument. The data logger (or other device) powers the sensor, digitizes its
analogue signals, computes NTU and Suspended Solids Concentration (SSC)
values, andrecords the statistical result inflash memory. To make the
conversion from digitized signals toengineering units (for example, NTU, mg
L–1,and ppm), the data logger must have the calibration equations inits
operating program or the conversion must be doneinpostprocessing.
When using some current meters or CTD instruments, the OBS
sensor should be calibrated while it is connected to the device
exactly as it will be used. The reason for this is that the factory
calibration is performed with a NIST-traceable digital multimeter
and the numerical values reported by some host devices not NIST-
certified will be different.
6. Specifications
Features:
•Measures suspended solids and turbidity for up to 4000 NTU
•Provides a compact, low-power probe that is field proven
•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
•Accurate and rugged
•Compatible with Campbell Scientific CRBasic data loggers:
CR200(X) series, CR300 series, CR6 series, CR800 series, CR1000,
CR1000X, CR3000, CR5000, and CR9000(X)
Operating Temperature: 0° to 40°C
Sensor may be damaged if it is encased in frozen liquid.
Ranges
Turbidity (low/high): 250/1000 NTU; 500/2000 NTU; 1000/4000 NTU
Mud1:5000 to 10,000 mg L–1
Sand1:50,000 to 100,000 mg L–1
1Range depends on sediment size, particle shape, and reflectivity.
Accuracy
Turbidity2:2% of reading or 0.5 NTU
Mud2:2% of reading or 1 mg L–1
Sand2:4% of reading or 10 mg L–1
2Whichever is larger.
NOTE
CAUTION

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
8
Power
Voltage output: 5 to 15 VDC/15 mA (Volts outputs)
4-20 mA transmitter: 9 to 15 VDC/45 mA max. (4 to 20 mA output)
Operating wave length: 850 ± 5 nm
Optical power: 2000 µW
Drift: <2% per year
Daylight rejection: –28 dB (re:48 mW cm–2)
Maximum data rate: 10 Hz
Minimum warm-up time: 2 s
Maximum depth
Stainless steel body: 500 m (1640.5 ft)
Titanium body: 1500 m (4921.5 ft)
Weight:
Dimensions:
181.4 g (0.4 lb)
The following OBS-3+ length is for SN 11000 or
later. The length of older OBS-3+ sensors are
141 mm (5.56 in).
131 mm
(5.15 in)
25 mm
(0.98 in)
147 mm
(5.79 in)
25 mm
(0.98 in)