Campbell Scientific OBS-5+ User Manual
OBS-5+ System
Revision: 11/13
Copyright © 2008-2013
Campbell Scientific, Inc.
Warranty
“PRODUCTS MANUFACTURED BY CAMPBELL SCIENTIFIC, INC. are
warranted by Campbell Scientific, Inc. (“Campbell”) to be free from defects in
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consumables have no warranty. Campbell’s obligation under this warranty is
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which shall be the sole and exclusive remedy under this warranty. The
customer shall assume all costs of removing, reinstalling, and shipping
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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. Cautionary Statements............................................... 1
3. Initial Inspection .........................................................1
3.1 Ships With............................................................................................1
4. Overview......................................................................2
4.1 Optics ...................................................................................................2
4.2 SSC-Measurement Principle ................................................................3
5. Specifications .............................................................5
5.1 Measurement Range.............................................................................5
5.2 Accuracy ..............................................................................................6
5.3 OBS-5+ Sensor ....................................................................................6
5.4 Other Data............................................................................................6
5.5 Dimensions...........................................................................................6
6. Operation.....................................................................7
6.1 Instrument Setup ..................................................................................7
6.1.1 Mounting Suggestions...................................................................7
6.1.2 Surveys..........................................................................................7
6.1.3 Logging Data ................................................................................8
6.1.4 Battery Installation........................................................................8
6.2 OBS-5+Utility Software.......................................................................9
6.2.1 Software Installation .....................................................................9
6.2.2 Running the OBS-5+ Utility .......................................................10
6.2.3 Pull-Down Menus .......................................................................11
6.2.4 Communication Settings .............................................................11
6.2.5 Testing Sensors ...........................................................................12
6.2.6 Monitoring Turbidity (NTU).......................................................13
6.2.7 Water Density and Barometric Corrections ................................13
6.2.8 Sample Statistics .........................................................................13
6.2.9 Sampling Modes and Terms........................................................14
6.2.10 Surveying ....................................................................................15
6.2.11 Cyclic Sampling ..........................................................................17
6.2.12 Data Retrieval .............................................................................18
6.2.13 Shutdown ....................................................................................18
6.2.14 Graphing and Printing.................................................................18
6.2.15 Excel Spreadsheets......................................................................19
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Table of Contents
7. Calibration .................................................................20
7.1 Sediment and NTU Calibration......................................................... 20
7.1.1 General Guidance....................................................................... 21
7.1.2 Equipment and Materials............................................................ 24
7.1.3 Procedure for Sediment.............................................................. 24
7.2 Turbidity (NTU) Calibration ............................................................. 28
7.2.1 Equipment and Materials............................................................ 28
7.2.2 Procedure for Turbidity .............................................................. 28
8. Troubleshooting........................................................29
9. Maintenance ..............................................................32
9.1 OBS-5+ Sensor.................................................................................. 32
9.2 Pressure Sensor.................................................................................. 32
9.3 Batteries............................................................................................. 33
9.4 Pressure Housing............................................................................... 33
9.5 User-Serviceable Parts....................................................................... 33
10. Interfering Factors ....................................................34
10.1 Particle Size ....................................................................................... 34
10.2 NIR Reflectivity ................................................................................ 35
10.3 Particle Shape, Flocculation, and Disaggregation ............................. 36
11. References.................................................................38
Appendix
A.
Turbidity Standards ................................................A-1
Figures
4-1. Dimensions (top), sensor endcap with copper antifoulant (Cu a.f.)
collars (left) and connector endcap (right)....................................... 2
4-2. Schematic of optical system................................................................ 3
4-3. 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. ................................................. 4
4-4. Calibration curves for four different sediments and SSC values for
near-detector peaks (colored arrowheads). ...................................... 5
6-1. Electrical connections.......................................................................... 8
6-2. Battery installation: A) endcap removal, B) wiping, C) cable
disconnect, and D) battery contact................................................... 9
6-3. New data log prompt......................................................................... 10
6-4. Designating your own file name and destination............................... 10
7-1. Manual (left) and automatic (right) sediment suspenders.................. 21
7-2. Lookup tables and table limits (a, b, and c)....................................... 22
7-3. OBS-5+ in big black tub of clean water ............................................ 25
7-4. OBS-5+ in suspender tub................................................................... 26
7-5. OBS-5+ in 100 mm cup..................................................................... 29
ii
Tables
Table of Contents
8-1. Internal components...........................................................................31
10-1. Effects of sediment size .....................................................................35
10-2. Near-infrared reflectivity of minerals.................................................36
10-3. Effects of disaggregation methods.....................................................37
6-1. Working and Maximum Depths...........................................................7
7-1. Schedule of Concentrations for Sediment Calibrations......................23
7-2. SSC-Calculation Spreadsheet.............................................................23
9-1. Battery Life in Hours with 100% Power............................................33
10-1. Relative magnitude of the effects of sediment characteristics on
OBS-5+ sensitivity .........................................................................34
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Table of Contents
iv
OBS-5+ System
1. Introduction
The manual describes the features of the OBS-5+®, as well as its use for
surveys and battery-powered, internal-storage 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, suspended solids concentration (SSC), as large as 200 g L
which is about 10 times higher than standard OBS technology.
Before installing the OBS-5+, please study:
• Section 2, Cautionary Statements
• Section 3, Initial Inspection
2. Cautionary Statements
• Although the OBS-5+ is rugged, it should be handled as a precision
scientific instrument.
–1
,
• 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. See Section 6.1, Instrument Setup, for
more information.
• Always orient the unit so that the OBS-5+ sensor “looks” into water clear
of reflective surfaces.
• Pad the end caps that contact metal with electrical tape, neoprene, or
expanded polyethylene tubes.
• Never mount the instrument by its end caps or attach anything to them.
This could a cause a leak.
• Always put the OBS-5+ in sleep mode when it will not be used for a while
to conserve battery capacity (see Section 6.2.13, Shutdown).
3. Initial Inspection
• Upon receipt of the OBS-5+, inspect the packaging and contents for
damage. File damage claims with the shipping company.
• Check this information against the shipping documents to ensure the
correct product is received (see Section 3.1, Ships With).
3.1 Ships With
21304 Accessory Kit
20919 Software Support CD
ResourceDVD
1
OBS-5+ System
4. Overview
FIGURE 4-1 shows the dimensions of the OBS-5+, the sensors in the sensor
endcap, and underwater connection. Detailed specifications are provided in
Section 5, Specifications. 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 hertz, and in Cyclic Mode, it logs as many as 200,000 scans of time, date,
depth, and g L
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
the OBS-5+ software. 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.
–1
in flash memory (one sample per hour for 23 years). When
2
FIGURE 4-1. Dimensions (top), sensor endcap with copper antifoulant
(Cu a.f.) collars (left) and connector endcap (right)
4.1 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 4-2. 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 to 30ºC operating temperature range.
FIGURE 4-2. Schematic of optical system
OBS-5+ System
4.2 SSC-Measurement Principle
In FIGURE 4-2, suspended particles scatter light from the NIR beam onto the
near and far detectors, and suspended solids concentration (SSC) is estimated
with signals 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
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.
–1
are shown on FIGURE 4-3. As particle
3
OBS-5+ System
FIGURE 4-3. 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 colored
arrowheads on FIGURE 4-4. Other sediment characteristics being equal, such
as shape and NIR reflectivity (see Section 10, Interfering Factors), larger
particles produce higher peak concentrations and greater OBS-5+ measurement
ranges than smaller particles.
4
OBS-5+ System
FIGURE 4-4. Calibration curves for four different sediments and SSC
5. Specifications
Features:
5.1 Measurement Range
Mud (D50=20μm): 0 to 50,000 mg/l
values for near-detector peaks (colored arrowheads).
• Connects directly to a PC—no datalogger needed
• Operates up to six months on three C-cell batteries
• Monitors high sediment concentrations (up to 200g/L)
• Logs depth, wave height, wave period, temperature, and salinity
• Records 200,000 scans of data in the OBS-5+ flash memory
Sand (D
Pressure
Turbidity: 0.4 to 1,000 NTU
=250μm): 0 to 200,000 mg/l
50
1
: 0 to 10, 20, 50, 100, or 200 m
5
OBS-5+ System
5.2 Accuracy
5.3 OBS-5+ Sensor
5.4 Other Data
Mud: 2.0% of reading
Sand: 4.0% of reading
Pressure: 0.5% of full scale
Turbidity: 1.5% of full scale
Laser wavelength: 780 nm
Scattering angles (clean water): 105º to 165º
Drift over time: <30 ppm per month
Drift over temperature: <200 ppm per ºC
Maximum sampling rate: 25 Hz
Maximum data rate: 2 Hz
Data capacity: 8 MB/200,000 lines
Battery capacity: 8 A h
Maximum battery life
External supply voltage: 6 to 18 Vdc
External supply current: 55 mA
Serial-data protocols: RS-232 & RS-485
Maximum housing depth: 300 m (984 ft)
Operating temperature range: 0º to 40ºC
Storage temperature range: –20º to 70ºC
5.5 Dimensions
Length / diameter: 380 mm (15 in) / 60 mm (2.4 in)
2
: 3,000 hrs
6
Weight: 2.04 kg (4.5 lb)
Weight (submerged): 1.02 kg (2.3 lb)
1
Range depends on pressure sensor option chosen.
2
Sampling interval is two hours and duration is two minutes.
6. Operation
6.1 Instrument Setup
6.1.1 Mounting Suggestions
OBS-5+ System
CAUTION
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 6-1.
TABLE 6-1. Working and Maximum Depths
Pressure Sensor Working Depth Maximum Depth
5 Bar 0 to 50 meters 75 meters
10 Bar 0 to 100 meters 150 meters
20 Bar 0 to 200 meters 300 meters
(1 Bar = 10 dBar ≅ 10 meters 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.
6.1.2 Surveys
• Never mount the instrument by its endcaps or attach anything to them.
This could a cause a leak.
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 4-1) with a cable grip and a
length of 3 mm (1/8 in) wire rope. Install a cable clamp with a 0.5 m 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 6-1, 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.
7
OBS-5+ System
FIGURE 6-1. Electrical connections
6.1.3 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
Cyclic Mode sampling in Section 6.2.11, Cyclic Sampling.
6.1.4 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 6-2
(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.
8
6
7
5
4
3
2
6
6 – 18 V d.c. (Red)
Power GND (Black)
DB-9
3
8
4, 1, 5, 6, 9
DB-9
2
3
5
(RS485)
(A)
(B)
(GND)
(RS232)
(RD)
(TD)
(GND)
. See instructions for
8
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