Campbell OBS-5+ User manual

OBS-5+
Turbidity and Temperature
Monitoring System
Operator’s Manual
Issued 7.12.09
Copyright ©2007-2009 Campbell Scientific Inc.
Printed under licence by Campbell Scientific Ltd.
CSL 729

Guarantee
This equipment is guaranteed against defects in materials and
workmanship. This guarantee applies for twelve months from date of
delivery. We will repair or replace products which prove to be defective
during the guarantee period 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.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package.
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,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
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.
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, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. Introduction...............................................................1-1
1.1 Features ................................................................................................... 1-1
1.2 Optics ...................................................................................................... 1-2
1.3 SSC-Measurement Principle................................................................... 1-2
2. Instrument Setup......................................................2-1
2.1 Mounting Suggestions............................................................................ 2-1
2.2 Surveys ................................................................................................... 2-1
2.3 Logging Data .......................................................................................... 2-2
2.4 Battery Installation ................................................................................. 2-2
3. Operations.................................................................3-1
3.1 Software Installation............................................................................... 3-1
3.2 Running OFW5+ For Windows............................................................. 3-1
3.3 Pull-Down Menus................................................................................... 3-2
3.4 Communication Settings ........................................................................ 3-3
3.5 Testing Sensors....................................................................................... 3-3
3.6 Monitoring Turbidity (NTU).................................................................. 3-4
3.7 Water Density and Barometric Corrections........................................... 3-5
3.8 Sample Statistics..................................................................................... 3-5
3.9 Sampling Modes and Terms................................................................... 3-5
3.10 Surveying.............................................................................................. 3-6
3.11 Cyclic Sampling ................................................................................... 3-8
3.12 Data Retrieval....................................................................................... 3-9
3.13 Shutdown .............................................................................................. 3-9
3.14 Graphing and Printing .......................................................................... 3-9
3.15 Excel Spreadsheets ............................................................................. 3-10
4. Troubleshooting........................................................4-1
5. Maintenance ..............................................................5-1
5.1 OBS-5+ Sensor....................................................................................... 5-1
5.2 Pressure Sensor....................................................................................... 5-1
5.3 Batteries .................................................................................................. 5-1
5.4 Pressure Housing .................................................................................... 5-2
5.5 User-Serviceable Parts ........................................................................... 5-2
6. Sediment and NTU Calibration ................................6-1
6.1 General Guidance ................................................................................... 6-1
6.2 Equipment and Materials ....................................................................... 6-4
6.3 Procedure for Sediment.......................................................................... 6-5
7. Turbidity (NTU) Calibration......................................7-1
7.1 Equipment and Materials ....................................................................... 7-1
7.2 Procedure for Turbidity.......................................................................... 7-1

ii
8. Interfering Factors ....................................................8-1
8.1 Particle Size ............................................................................................ 8-1
8.2 NIR Reflectivity ..................................................................................... 8-2
8.3 Particle Shape, Flocculation, and Disaggregation ................................. 8-3
9. References.................................................................9-1
10. Specifications........................................................10-1
Appendix
A. Turbidity Standards................................................ A-1
Figures
1-1. Dimensions (top), Sensor Endcap with Copper Antifoulant (Cu a.f.)
Collars (left) and Connector Endcap (right) .................................. 1-1
1-2. Schematic of optical system.................................................................. 1-2
1-3. Sample calibration curves (fine and bold lines), lookup tables I, II,
and III (bold curves), and sediment concentrations pf ND
(open arrow) and FD (solid arrow) peaks. ..................................... 1-3
1-4. Calibration curves for four different sediments and SSC values for
near-detector peaks (coloured arrowheads). .................................. 1-4
2-1. Electrical Connections........................................................................... 2-2
2-2. Battery Installation: A) Endcap Removal, B) Wiping, C) Cable
Disconnect, and D) Battery Contact .............................................. 2-3
4-1. Internal Components ............................................................................. 4-2
6-1. Manual (top and Automatic (bottom) Sediment Suspenders ............... 6-1
6-2. Lookup Tables and Table Limits (a, b, and c) ...................................... 6-2
6-3. OBS-5+ in Big Black Tub of Clean Water ........................................... 6-5
6-4. OBS-5+ in Suspender Tub .................................................................... 6-6
7-1. OBS-5+ in 100 mm Cup........................................................................ 7-2
8-1. Effects of Sediment Size ....................................................................... 8-2
8-2. Near-infrared Reflectivity of Minerals ................................................. 8-3
8-3. Effects of Disaggregation Methods....................................................... 8-4
Tables
2-1. Working and Maximum Depths............................................................ 2-1
5-1. Battery Life in Hours with 100% Power............................................... 5-2
6-1. Schedule of Concentrations for Sediment Calibrations........................ 6-3
6-2. SSC-Calculation Spreadsheet................................................................ 6-4
8-1. Relative magnitude of the effects of sediment characteristics on
OBS-5+ sensitivity ......................................................................... 8-1

1-1
Section 1. Introduction
The manual describes the features of the OBS-5+® as well as its use for surveys
and battery-powered, internal-logging operations. Using backscatter from a
780 nm laser diode and a patented dual-detection system (U.S. Patent Number
5,796,481), a calibrated OBS-5+ measures suspended sediment concentrations,
SSC, as large as 200 g l-1, which is about 10 times higher than standard OBS
technology. This manual covers the following topics: 1) OBS-5+ features, 2)
OBS-5+ for Windows (OFW5+) software, 3) instrument calibration, 4) survey
and logging operations, 5) troubleshooting, 6) maintenance, 7) interferences,
and 8) specifications.
1.1 Features
Figure 1-1 shows the dimensions of the OBS-5+, the sensors in the sensor endcap,
and underwater connection. Detailed specifications are provided in Section 10.
The OBS-5+ can be operated in Survey or Cyclic Modes. In Survey Mode, the
unit sends data via RS-232 or RS-485 to a PC at two Hz, and in Cyclic Mode, it
logs as many as 200,000 scans of time, date, depth, and g l-1 in FLASH memory
(one sample per hour for 23 years). When sampling continuously, the unit will
run about 125 hours on three C-size alkaline batteries in 20ºC water (about two
weeks of eight-hour survey days). When using the instrument for surveys, the
data are captured by a PC running OFW5+. Pressure is measured with a silicon
strain-gauge pressure sensor and the depth of the instrument is calculated from
water density and barometric pressure entered by the operator.
Figure 1-1. Dimensions (top), Sensor Endcap with
Copper Antifoulant (Cu a.f.) Collars (left) and Connector Endcap (right)

OBS-5A Turbidity and Temperature Monitoring System
1-2
1.2 Optics
The heart of the OBS-5+ is an optical system comprised of a near infrared (NIR)
laser diode and a photodetector positioned 10 mm from the laser, called the near
detector (ND), and one mounted 25 mm from the laser, called the far detector
(FD), see Figure 1-2. The detector acceptance-cone angle is 55º, which means
that photons must enter the detector sapphire windows at angles less than 27.5º to
be detected. The laser light is collimated to a 3 mm by 1 mm elliptical beam with
convergence < 2.5 mrad. The angle between the NIR beam and detector
acceptance-cone axes is 45º. The OBS-5+ can detect light scattered by particles
illuminated by the NIR beam at angles between 105º to 165º. With its automatic-
power-control circuit, the laser diode provides stable optical power over time and
the 0-30ºC operating temperature range.
Figure 1-2. Schematic of optical system
1.3 SSC-Measurement Principle
In Figure 1-2 suspended particles scatter light from the NIR beam onto the near
and far detectors, and SSC is estimated with signals in counts from these detectors
by a microcontroller, using a set of logic rules and lookup tables derived from
calibration data. Counts are the digital equivalents of the ND and FD signals and
are proportional to backscatter intensity. Sample calibration curves relating ND
and FD counts to sediment concentration in g l-1 are shown on Figure 1-3. As
particle concentration increases from 0, the ND and FD signals rise to maxima at
peak concentrations, shown by the red (open) and blue (solid) arrowheads above
the x axis. Beyond the peak sediment concentrations, light attenuation is the
dominant factor controlling the light level at the detectors, and so the ND and FD
counts decline. The scattered NIR must travel farther to be detected by the FD
than by the ND, and therefore the peak of the FD curve occurs at a lower sediment
concentration than the peak of the ND curve. The instrument exploits these peak
offsets to estimate sediment concentration. Using either the ND or FD counts,
whichever is indicated by the logic rules, the microcontroller does a spline
interpolation between calibration values to derive an SSC value. It then combines
this value with time and pressure data, and sends the results to a PC.

Section 1. Introduction
1-3
Figure 1-3. Sample calibration curves (fine and bold lines), lookup tables I,
II, and III (bold curves), and sediment concentrations pf ND (open arrow)
and FD (solid arrow) peaks.
The concentrations associated with the ND and FD peaks depend on sediment
characteristics as shown by the variety of response curves and the coloured
arrowheads on Figure 1-4. Other sediment characteristics being equal, such as
shape and NIR reflectivity (see Section 8), larger particles produce higher peak
concentrations and greater OBS-5+ measurement ranges than smaller particles.

OBS-5A Turbidity and Temperature Monitoring System
1-4
Figure 1-4. Calibration curves for four different sediments and SSC values
for near-detector peaks (coloured arrowheads).

2-1
Section 2. Instrument Setup
2.1 Mounting Suggestions
Maximum depth for the OBS-5+ is limited by the installed
pressure sensor. If the maximum depths are exceeded, the
pressure sensor will rupture and the housing will flood.
The depth limits are listed in Table 2-1.
Table 2-1. Working and Maximum Depths
Pressure Sensor Working Depth Maximum Depth
5 Bar 0 – 50 metres 75 metres
10 Bar 0– 100 metres 150 metres
20 Bar 0 – 200 metres 300 metres
(1 Bar = 10 dBar ≅10 metres of fresh water)
The following precautions should be followed to ensure the unit can function
properly and is not lost or damaged.
•Always orient the unit so that the OBS-5+ sensor “looks” into water clear of
reflective surfaces.
•Pad the endcaps that contact metal with electrical tape, neoprene, or expanded
polyethylene tubes.
•Never mount the instrument by its endcaps or attach anything to them. This
could cause a leak.
2.2 Surveys
The OBS-5+ will usually be towed with a cable harness for surveys. The serial
cable can tow the OBS-5+ without a depressor weight or vane as long as the
connector is strain relieved. Strain relief can be provided by attaching the cable to
the stainless steel housing (Figure 1-1) with a cable grip and a length of 1/8" (3
mm) wire rope. Install a cable clamp with a 0.5 metre wire rope to the serial
cable, and clamp the wire rope to the pressure housing with two stainless steel
hose clamps, providing a small loop of slack cable to absorb towing forces. The
unit can be powered with an external battery, as shown on Figure 2-1, and the
serial output can be transmitted by either RS-232 or RS-485 protocols. The latter
protocol is recommended for cable lengths greater than 25 m. An RS-485/232
serial converter is provided with each unit. An RS-232 to USB converter is an
available option.
CAUTION

OBS-5A Turbidity and Temperature Monitoring System
2-2
Figure 2-1. Electrical Connections
2.3 Logging Data
In applications where a survey cable is impractical or when the OBS-5+ must be
attached to an instrument frame, it can be powered by the internal batteries and the
data can be logged by the data FLASH memory.See instructions for Cyclic Mode
sampling in Section 3.
2.4 Battery Installation
Remove the set screws from the endcap with the handle and connector. If the unit
was submerged during the previous day, turn the sensor end up, so water around
the O-rings can drain out when the endcap is removed, Figure 2-2 (A). Pull
endcap out and disconnect the inline connector (B). Wipe water from the inside
wall of the housing tube with a paper towel (C). Turn the connector end up and
push the ridge on the battery sliding contact until the spent batteries pop out (D).
Insert new batteries with the positive terminal (+) toward the sliding contact. Push
the batteries down and slide the contact over the top of them and against the
housing wall. Inspect the O-ring in the cap, clean and grease or replace it if
necessary, and replace the cap and set screws.

Section 2. Instrument Setup
2-3
Figure 2-2. Battery Installation: A) Endcap Removal, B) Wiping,
C) Cable Disconnect, and D) Battery Contact

OBS-5A Turbidity and Temperature Monitoring System
2-4

3-1
Section 3. Operations
3.1 Software Installation
Copy all of the files on the supplied CD to a directory called OBS on your PC
hard drive. The program OFW5+.exe is the GUI interface with the OBS-5+.
Make a shortcut to this program on the PC desktop. The other files on the CD
include the OBS-5+ firmware, a system-maintenance program called HOST5.exe,
communication drivers, and an SSC-calibration spreadsheet.
This section explains how to program and operate the unit with OFW5+. It
covers: 1) turning the OBS-5+ ON and OFF and testing the sensors, 2) selecting
sensors and data statistics, 3) scheduling data logging, 4) recording data with a PC
or uploading data from the OBS-5+, 5) importing data into a spreadsheet, and 6)
plotting data with OFW5+.
3.2 Running OFW5+ For Windows
1) Set PC to the time standard for your project.
2) Double-click the icon to start OFW5+ and open the Data Window and
Toolbar with the View pull-down menu.
3) OFW5+ will create a new data log file and prompt you to accept the name.
Files are automatically named with Greenwich Date and Time as follows:
OBS5+_20010808_172433.log. Or you can create your own file name and
destination by choosing No. Data received from the OBS-5+ while it is
connected to the PC will be stored in this file.

OBS-5A Turbidity and Temperature Monitoring System
3-2
4) Connect the OBS-5+ to a PC with the test cable (Figure 2-1).
5) Click Connect/Disconnect to get a green light and synchronize the OBS-
5+ clock with your PC by clicking .
3.3 Pull-Down Menus
OFW5+ has four pull-down menus for File, OBS-5+, View, and Help.
The File menu allows you to select the location and formatting for OBS-5+ files.
Files can be opened as plots or ASCII text that can be brought into spreadsheet
programs or text editors. Plot files display OBS-5+ data graphically in the main
GUI window.
The OBS-5 menu is used to: 1) put the instrument into a low-power Sleep, 2)
wake it up if it is sleeping (Wakeup), 3) make a Barometric Correction (see

Section 3. Operations
3-3
Section 3.7), 4) view a list of calibration tables, 5) switch to RS485 serial
communication, or 6) set detector gains (Set Gains).
The View menu controls the display on your PC. Switches are provided for:
•Toolbar toggles the icons ON and OFF.
•Status Bar toggles the status bar at the bottom of the screen ON or OFF.
•Data Window pops the data window into view.
3.4 Communication Settings
The Plot and Port Settings button has a serial port tab for configuring the
communication settings. The OFW5+ default settings are: 115 kbs, 8 data bits, no
parity, no flow control. These settings will work for most applications and with
most PCs. In order to pick a slower baud rate and avoid data-transfer errors, select
the desired rate from the dialog box and click Apply. The rate adjustment takes
two seconds. If your PC is set to the wrong rate for some reason, use the check
box to select ONLY change host computer port. Then click Apply and the
OBS Settings button.
If you get the OBS-5+ information box, the baud rate of the unit is synchronized
with your PC. If you don’t get an information box, repeat the above procedure
until communication is established.
3.5 Testing Sensors
1) Before daily operations and deployments, verify that the instrument works by
clicking Open Plot, and then clicking Survey. Select all sensors
and click Start Survey. An example plot of data is shown below.

OBS-5A Turbidity and Temperature Monitoring System
3-4
2) Wave your hand in front of the OBS-5+ sensor; the turbidity and SSC levels
on the top plot will fluctuate as data scrolls across the plot.
3) Blow into the pressure sensor or press your thumb on it to compress air on the
diaphragm (Figure 1-1). A small elevation in the pressure signal will occur
(bottom plot).
4) Click Stop and then OBS Settings to view time, serial numbers,
depth corrections, and software versions.
3.6 Monitoring Turbidity (NTU)
Important: The OBS-5+ was calibrated and factory-certified using AMCO Clear,
U.S. EPA-approved turbidity standards (www.gfschemicals.com). In order to