Campbell OBS500 Operator's Manual

OPERATOR’S MANUAL

OBS500 Smart Turbidity Meter

Copyright © 2008- 2016

Campbell Scientific, Inc.

with ClearSensor® Technology

Revision: 1/16

Limited Warranty

“Products manufactured by CSI are warranted by CSI to be free from defects in
materials and workmanship under normal use and service for twelve months
from the date of shipment unless otherwise specified in the corresponding
product manual. (Product manuals are available for review online at

www.campbellsci.com.) Products not manufactured by CSI, but that are resold

by CSI, are warranted only to the limits extended by the original manufacturer.
Batteries, fine-wire thermocouples, desiccant, and other consumables have no
warranty. CSI’s obligation under this warranty is limited to repairing or
replacing (at CSI’s option) defective Products, which shall be the sole and
exclusive remedy under this warranty. The Customer assumes all costs of
removing, reinstalling, and shipping defective Products to CSI. CSI will return
such Products by surface carrier prepaid within the continental United States of
America. To all other locations, CSI will return such Products best way CIP
(port of entry) per Incoterms ® 2010. This warranty shall not apply to any
Products which have been subjected to modification, misuse, neglect, improper
service, accidents of nature, or shipping damage. This warranty is in lieu of all
other warranties, expressed or implied. The warranty for installation services
performed by CSI such as programming to customer specifications, electrical
connections to Products manufactured by CSI, and Product specific training, is
part of CSI's product warranty. CSI EXPRESSLY DISCLAIMS AND

EXCLUDES ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE. CSI hereby disclaims,
to the fullest extent allowed by applicable law, any and all warranties and
conditions with respect to the Products, whether express, implied or
statutory, other than those expressly provided herein.”

Assistance

Products may not be returned without prior authorization. The following
contact information is for US and international customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit

www.campbellsci.com to determine which Campbell Scientific company serves

your country.

To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an application engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container. Campbell
Scientific’s shipping address is:

CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784

For all returns, the customer must fill out a “Statement of Product Cleanliness
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
[phone]. Campbell Scientific is unable to process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer’s expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

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.com or
by telephoning [phone] (USA). 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, 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.

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

3.1 Ships With ............................................................................................ 2

4. QuickStart ................................................................... 2

4.1 Mounting Suggestions .......................................................................... 2

4.2 Datalogger Programming and Wiring .................................................. 6

5. Overview ..................................................................... 8

5.1 Applications ......................................................................................... 8

5.2 Turbidity Units ..................................................................................... 9

5.3 Measurement Details .......................................................................... 10

5.4 Vertical-Cavity Surface-Emitting Laser Diode .................................. 10

6. Specifications ........................................................... 11

7. Installation ................................................................ 12

7.1 Default Settings .................................................................................. 12

7.2 Device Configuration Utility .............................................................. 13

7.3 Datalogger/RTU Connection ............................................................. 16

7.3.1 SDI-12 Wiring ............................................................................ 17

7.3.2 RS-232 Wiring ............................................................................ 17

7.3.3 Analog 0 to 5 Volt Wiring .......................................................... 18

7.4 Communication Modes ...................................................................... 18

7.4.1 SDI-12 ......................................................................................... 18

7.4.1.1 SDI-12 Addresses ............................................................. 20

7.4.1.2 SDI-12 Transparent Mode ................................................ 20

7.4.2 RS-232 ........................................................................................ 21

7.5 Calibration.......................................................................................... 22

7.5.1 Turbidity ..................................................................................... 22

7.5.2 Sediment ..................................................................................... 26

7.5.2.1 Dry-Sediment Calibration ................................................ 26

7.5.2.2 Wet-Sediment Calibration ................................................ 26

7.5.2.3 In situ Calibration ............................................................. 27

7.5.2.4 Performing a Dry-Sediment Calibration........................... 27

7.6 Programming ...................................................................................... 28

7.6.1 SDI-12 Programming .................................................................. 29

7.6.2 RS-232 Programming ................................................................. 29

7.6.3 Analog Programming .................................................................. 29

7.7 Operation in High Sediment Loads and Sandy Sediments ................. 29

7.7.1 Wiper Removal Procedure .......................................................... 30

i

Table of Contents

8. Factors that Affect Turbidity and Suspended-

Sediment Measurements ....................................... 32

8.1 Particle Size ....................................................................................... 32

8.2 Suspensions with Mud and Sand ....................................................... 34

8.3 Particle-Shape Effects ....................................................................... 34

8.4 High Sediment Concentrations .......................................................... 35

8.5 IR Reflectivity—Sediment Color ...................................................... 35

8.6 Water Color ....................................................................................... 36

8.7 Bubbles and Plankton ........................................................................ 36

9. Maintenance ............................................................. 37

10. Troubleshooting ....................................................... 38

11. References ................................................................ 40

Appendices

A. Importing Short Cut Code Into CRBasic Editor ... A-1

B. Example Programs ................................................. B-1

B.1 CR1000 SDI-12 Program ................................................................ B-1

B.2 CR1000 RS-232 Program ................................................................ B-2

B.3 CR1000 Analog Program ................................................................ B-3

B.4 Examples for High Sediment Loads ................................................ B-4

B.4.1 Normally Open CR1000 Example ........................................... B-4

B.4.2 Cycle Shutter/Wiper for Each Measurement CR1000 Program B-5

C. OBS500 Copper Sleeve Kit Installation ................ C-1

D. SDI-12 and RS-232 Measurement Commands

for OS Version 1 ................................................... D-1

Figures

4-1. Use strain relief to keep stress off the cable and provide extra

security ............................................................................................. 3

4-2. Apply tape to protect sensor ................................................................ 4

4-3. Secure with hose clamps. Do not overtighten. .................................... 4

4-4. Place and secure mounting fixture ...................................................... 5

5-1. Drawing of the OBS500 sensor ......................................................... 10

5-2. Orientation of emitter cone (source beam) and OBS and

sidescatter detector (acceptance) cones .......................................... 11

7-1. Device Configuration Utility ............................................................. 13

7-2. Terminal Mode using 1 and H commands......................................... 14

7-3. Settings Editor screen ........................................................................ 15

7-4. Terminal Emulator ............................................................................ 21

7-5. Normalized response of OBS500 to AMCO Clear® turbidity.

The inset shows the response function of a turbidity sensor to

high-sediment concentrations. ....................................................... 23

ii

Table of Contents

Tables

7-6. Position of OBS500 in clean tap water in big black tub..................... 25

7-7. OBS500 in 500-TU AMCO Clear® turbidity standard in 100-mm

black polyethylene calibration cup ................................................. 26

7-8. Portable Sediment Suspender (left) and OBS beam orientation in

suspender tub (right) ....................................................................... 27

7-9. Remove the screw .............................................................................. 31

7-10. Insert screwdriver and rotate clockwise ............................................. 31

7-11. Shutter disassembled .......................................................................... 31

7-12. Shutter components ............................................................................ 32

8-1. Normalized sensitivity as a function of grain diameter ...................... 33

8-2. The apparent change in turbidity resulting from disaggregation

methods........................................................................................... 33

8-3. Relative scattering intensities of grain shapes .................................... 34

8-4. Response of an OBS sensor to a wide range of SSC .......................... 35

8-5. Infrared reflectivity of minerals as a function of 10-Munzell

Value .............................................................................................. 36

9-1. DevConfig, Send OS .......................................................................... 38

7-1. Factory Settings ................................................................................. 13

7-2. RS-232 Terminal Commands ............................................................. 15

7-3. OBS500 Connector Pin-Out ............................................................... 16

7-4. SDI-12 Wiring ................................................................................... 17

7-5. RS-232 Wiring ................................................................................... 17

7-6. Analog 0-5 Volt Wiring ..................................................................... 18

7-7. SDI-12 and RS-232 Measurement Commands for OS Version 2

or Higher ......................................................................................... 19

7-8. RS-232 Settings ................................................................................. 22

7-9. Calibration Materials and Volumes ................................................... 23

7-10. Change in TU value resulting from one hour of evaporation of

SDVB standard, i.e., loss of water but not particles. ...................... 24

10-1. Troubleshooting Chart. ...................................................................... 39

D-1. SDI-12 and RS-232 Measurement Commands ............................... D-1

CRBasic Examples

B-1. CR1000 SDI-12 Program ................................................................. B-1

B-2. CR1000 RS-232 Program ................................................................ B-2

B-3. CR1000 Analog Program ................................................................. B-3

B-4. Normally Open CR1000 Example ................................................... B-4

B-5. Cycle Shutter/Wiper for Each Measurement CR1000 Program ....... B-5

iii

Table of Contents

iv

NOTE

OBS500 Smart Turbidity Meter
with ClearSensor® Technology

1. Introduction

2. Precautions

The OBS500 submersible turbidity meter is designed for general pressure
measurements. The OBS500 uses ClearSensor
an anti-fouling scheme that uses a shutter/wiper mechanism to protect and
clean the optics and a refillable biocide chamber to allow biocide to leach out
over the optics continually while in the closed position. It uses the SDI-12 or
RS-232 communication protocol to communicate with an SDI-12 or RS-232
recorder simplifying installation and programming. It can also be used as an
analog sensor with 0 to 5 V output.

This manual provides information only for CRBasic dataloggers.
It is also compatible with most of our retired Edlog dataloggers.
For Edlog datalogger support, see an older manual at

www.campbellsci.com/old-manuals or contact a Campbell

Scientific application engineer for assistance.

• READ AND UNDERSTAND the Safety section at the front of this

manual.

• The OBS500 needs to be sent in after two years or 70,000 cycles for drive

shaft seal replacement. (See m8! command in TABLE 7-7.)

• The sensor may be damaged if it is encased in ice.

®

(U.S. Patent No. 8,429,952),

• 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.

• Sand grains between moving surfaces can jam the shutter/wiper. For high

sediment load and large grain size installations, operate the OBS500
normally open to minimize the chance of sand grains jamming the
shutter/wiper, and orient the sensor vertically facing downstream (see
Section 7.7, Operation in High Sediment Loads and Sandy Sediments

• Minimize temperature shock. For example, do not take sensor from sunny

dashboard and immediately drop it in frigid water.

• Ensure that obstructions are not in the backscatter sensor’s large field of

view. See Section 4, QuickStart

• Maximum depth for the OBS500 is 100 meters.

(p. 2), for more information.

(p. 29)).

1

OBS500 Smart Turbidity Meter with ClearSensor® Technology

• If possible orient the unit vertically and facing downstream.

• The probe must be calibrated with sediments from the waters to be

monitored. The procedure for calibrating the probe is provided in Section

7.5, Calibration

• Sites with high sediment loads or large sand grains can be problematic for

the shutter and its motor. Refer to Section 7.7, Operation in High Sediment
Loads and Sandy Sediments

• The OBS500 will be damaged if it is encased in frozen liquid.

• Use electrical tape or neoprene to pad the parts of the OBS500 housing

that will contact metal or other hard surfaces.

• Remember that although the OBS500 is designed to be a rugged and

reliable device for field use, it is also a highly precise scientific instrument
and should be handled as such.

(p. 22).

3. Initial Inspection

• Upon receipt of the OBS500, inspect the packaging for any signs of

shipping damage, and, if found, report the damage to the carrier in
accordance with policy. The contents of the package should also be
inspected and a claim filed if any shipping-related damage is discovered.

(p. 29), for more information.

3.1 Ships With

4. QuickStart

4.1 Mounting Suggestions

• When opening the package, care should be taken not to damage or cut the

cable jacket. If there is any question about damage having been caused to
the cable jacket, a thorough inspection is prudent.

• The model number is engraved on the housing. Check this information

against the shipping documentation to ensure that the expected model
number was received.

• Refer to the Ships With list to ensure that all parts are included (see

Section 3.1, Ships With

(1) Calibration Certificate
(1) 27752 OBS500 Spare Parts Kit
(1) ResourceDVD

Maximum depth for the OBS500 housing is 100 meters.

Schemes for mounting the OBS500 will vary with applications; however, the
same basic precautions should be followed to ensure the unit is able to make a
good measurement and that it is not lost or damaged.

(p. 2)).

2

OBS500 Smart Turbidity Meter with ClearSensor® Technology

CAUTION

• The most important general precaution is to orient the unit so that the

OBS sensor looks into clear water without reflective surfaces. This

includes any object such as a mounting structure, a streambed, or
sidewalls. The backscatter sensor in the OBS500 can see to a distance of
about 50 cm (20 in) in very clean water at angles ranging from 125° to
170°. The sidescatter (SS) sensor can only “see” to about 5 cm (2 in) at
90°.

• The sensor has ambient-light rejection features, but it is still best to orient

it away from the influence of direct sunlight. Shading may be required in
some installations to totally protect from sunlight interference.

• Nearly all exposed parts of the instrument are made of Delrin, a strong but

soft plastic.

Always pad the parts of the OBS500 housing that will
contact metal or other hard objects with electrical tape or
neoprene.

• Mounting inside the end of a PVC pipe is a convenient way to provide

structure and protection for deployments. The OBS500 will fit inside a
2-in. schedule 40 PVC pipe.

The most convenient means for mounting the unit to a frame or wire is to use
large, high-strength nylon cable ties (7.6 mm (0.3 in) width) or stainless steel
hose clamps. First cover the area(s) to be clamped with tape or 2 mm (1/16 in)
neoprene sheet. Clamp the unit to the mounting frame or wire using the padded
area. Do not tighten the hose clamps more than is necessary to produce a firm
grip. Overtightening may crack the pressure housing and cause a leak. Use
spacer blocks when necessary to prevent chafing the unit with the frame or
wire.

Mounting Example:

FIGURE 4-1. Use strain relief to keep stress off the cable and provide

extra security

3

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 4-2. Apply tape to protect sensor

FIGURE 4-3. Secure with hose clamps. Do not overtighten.

4

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 4-4. Place and secure mounting fixture

5

OBS500 Smart Turbidity Meter with ClearSensor® Technology

4.2 Datalogger Programming and Wiring

Short Cut is an easy way to program your datalogger to measure the sensor and
assign datalogger wiring terminals. Short Cut is available as a download on

www.campbellsci.com and the ResourceDVD. It is included in installations of

LoggerNet, PC200W, PC400, or RTDAQ.

The following procedure shows using Short Cut to program the OBS500.

1. Open Short Cut and select New Program.

2. Select Datalogger Model and Scan Interval (default of 5 seconds is OK

for most applications). Click Next.

6

OBS500 Smart Turbidity Meter with ClearSensor® Technology

3. Under the Available Sensors and Devices list, select the Sensors |

Water | Quality folder. Select OBS500 Smart Turbidity Meter. Click

to move the selection to the Selected device window. Temperature
defaults to degrees Celsius and the sensor is measured every scan. These
can be changed by clicking the Temperature or Measure Sensor box and
selecting a different option. Typically, the default SDI-12 address of 0 is
used.

4. After selecting the sensor, click Wiring Diagram to see how the sensor is

to be wired to the datalogger. The wiring diagram can be printed now or
after more sensors are added.

5. Select any other sensors you have, then finish the remaining Short Cut

steps to complete the program. The remaining steps are outlined in Short

Cut Help, which is accessed by clicking on Help | Contents |
Programming Steps.

7

OBS500 Smart Turbidity Meter with ClearSensor® Technology

6. If LoggerNet, PC400, or PC200W is running on your PC, and the PC to

datalogger connection is active, you can click Finish in Short Cut and you
will be prompted to send the program just created to the datalogger.

7. If the sensor is connected to the datalogger, as shown in the wiring

diagram in step 4, check the output of the sensor in the datalogger support
software data display to make sure it is making reasonable measurements.

5. Overview

The heart of the OBS500 sensor is a near-infrared (NIR) laser and two
photodiodes for detecting the intensity of light scattered from suspended
particles in water. One detector measures the backscatter energy, and the
second is positioned at 90 degrees to the emitter to measure the sidescatter
energy.

Backscatter and sidescatter sensors have unique strengths and weaknesses.
Generally speaking, backscatter provides high-range (HR) measurements, and
sidescatter provides low-range (LR) measurements. The OBS500 combines
both in one sensor to provide unequalled performance in a field turbidity
sensor. With their unique optical design (U.S. Patent No. 4,841,157),
backscatter sensors perform better than most in situ turbidity monitors in the
following ways:

Sidescatter sensors have the following advantages:

5.1 Applications

Turbidity sensors are used for a wide variety of monitoring tasks in riverine,
oceanic, laboratory, and industrial settings. They can be integrated in water­quality monitoring systems, CTDs, laboratory instrumentation, and sediment­transport monitors. The electronics of the OBS500 are housed in a Delrin
package, which is ideal for salt water or other harsh environments.
Applications include:

• Measure turbidity to 4000 TU (compared to 1200 TU typically for

sidescatter sensors)

• Insensitivity to bubbles and organic matter

• Ambient-light rejection

• Low temperature coefficient

• More accurate in very clean water

• Fixed measurement volume

• 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 the effect of land-use management on water quality

• Monitor waterside construction, mining, and dredging operations

• Characterization of wastewater and energy-production effluents

• Tracking water-well completion including development and use

8

5.2 Turbidity Units

Conceptually, turbidity is a numerical expression in turbidity units (TU) of the
optical properties that cause water to appear hazy or cloudy as a result of light
scattering and absorption by suspended matter. Operationally, a TU value is
interpolated from neighboring light-scattering measurements made on
calibration standards such as Formazin, StablCal, or SDVB beads. Turbidity is
caused by suspended and dissolved matter such as sediment, plankton, bacteria,
viruses, and organic and inorganic dyes. In general, as the concentration of
suspended matter in water increases, so will its turbidity; as the concentration
of dissolved, light-absorbing matter increases, turbidity will decrease.

Descriptions of the factors that affect turbidity are given in Section 8, Factors
that Affect Turbidity and Suspended-Sediment Measurements
other optical turbidity monitors, the response depends on the size, composition,
and shape of suspended particles. For this reason, for monitoring
concentrations, the sensor must be calibrated with suspended sediments from
the waters to be monitored. There is no “standard” turbidimeter design or
universal formula for converting TU values to physical units such as mg/l
ppm. TU values have no intrinsic physical, chemical, or biological
significance. However, empirical correlations between turbidity and
environmental conditions, established through field calibration, can be useful
in water-quality investigations.

OBS500 Smart Turbidity Meter with ClearSensor® Technology

(p. 32). Like all

or

The USGS has an excellent chapter (6) on turbidity measurements in their
“National Field Manual for the Collection of Water-Quality Data”:

http://water.usgs.gov/owq/FieldManual/Chapter6/Section6.7_v2.1.pdf

Historically, most turbidity sensor manufacturers and sensor users labeled the
units NTUs, for Nephelometric Turbidity Units. ASTM and the USGS have
come up with the following unit classifications that are applicable to the
OBS500:

Optical Backscatter FBU Formazin Backscatter Unit

Sidescatter FNU Formazin Nephelometric Unit

Ratio Back and Sidescatter FNRU

Formazin Nephelometric Ratio Unit

The document “U.S. Geological Survey Implements New Turbidity Data­Reporting Procedures” details the units:

http://water.usgs.gov/owq/turbidity/TurbidityInfoSheet.pdf

Throughout this manual, the measurements will simply be referred to as
Turbidity Units (TU).

9

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 5-1. Drawing of the OBS500 sensor

5.3 Measurement Details

The OBS500 design combines the sensor, analog measurement, and signal
processing within a single housing resulting in the integration of state-of-the­art sensor and measurement technology. The 24-bit A/D has simultaneous
50/60 Hz rejection and automatic calibration for each measurement. A number
of additional advanced measurement techniques are employed to harness the
best possible performance available from today’s state-of-the-art sensor
technology. The sensor reverts to a low-power sleep state between
measurements. A series of measurements is performed, yielding two turbidity
and one temperature value. This measurement cycle takes about 20 seconds.
The measurement cycle is activated by commands via SDI-12, RS-232
terminal commands, or a control line(s) going high (analog measurements).

The OBS500 has three communication modes: SDI-12, RS-232, or 0 to 5 V.
The mode defaults to SDI-12/RS-232 but can be set in our Device
Configuration Utility (DevConfig) to analog. As an SDI-12/RS-232 sensor, the
OBS500 is shipped with an address of 0.

With SDI-12 and RS-232, the basic values output by the OBS500 are
backscatter turbidity, sidescatter turbidity, and temperature. The OBS500 can
also output a ratiometric measurement that combines the backscatter and
sidescatter measurements. Other diagnostic information is available (see
TABLE 7-7) including the raw voltage output from the backscatter and
sidescatter sensors, the current to open and close the shutter, an open and close
position count, total open and close cycles, and a moisture alarm. The OBS500
is shipped from the factory to output turbidity in TU and temperature in
degrees Celsius. The analog output supports backscatter and/or sidescatter
according to the status of a control line.

10

5.4 Vertical-Cavity Surface-Emitting Laser Diode

OBS500 sensors detect suspended matter in water and turbidity from the
relative intensity of light backscattered at angles ranging from 125°

to 170°,

OBS500 Smart Turbidity Meter with ClearSensor® Technology

Emitter Cone

OBS Detector
Cone

90° Sidescatter
Detector Cone

and at 90° for the sidescatter measurement. A 3D schematic of the main
components of the sensor is shown in FIGURE 5-2. The OBS500 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 detectors are low­drift silicon photodiodes with enhanced NIR responsivity. NIR responsivity is
the ratio of electrical current produced per unit of light power in A/W. A light
baffle prevents direct illumination of the detector by the light source and in­phase coupling that would otherwise produce large signal biases. A daylight­rejection filter blocks visible light in the solar spectrum and reduces ambient­light 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).

FIGURE 5-2. Orientation of emitter cone (source beam) and OBS and

The beam divergence angle of the VCSEL source is 4° worst case and 2°
typical

6. Specifications

Features:

Dual Probe: Backscatter and 90-degree sidescatter

sidescatter detector (acceptance) cones

(95% of the beam power is contained within a 5° cone).

• Dual backscatter and sidescatter sensors used to measure turbidity

• ClearSensor

biologically active water

• Shutter/wiper mechanism keeps lenses clean

• Refillable biocide chamber prevents fouling

• Disposable plastic sleeve facilitates cleanup

• Optional copper sleeve for additional protection (especially for sea

water) or disposable plastic sleeve facilitates easy cleanup

• Compatible with Campbell Scientific CRBasic dataloggers: CR6,

CR200(X) series, CR800 series, CR1000, CR3000, and CR5000.

®

antifouling method for better measurements in

TU Range: 0 to 4000 TU

Active and Passive Antifouling: Shutter, wiper, biocide, copper, optional

removable sleeve

11

OBS500 Smart Turbidity Meter with ClearSensor® Technology

Accuracy: 0.5 TU or ±2% of reading, whichever is

Temperature Accuracy: ±0.3 °C, 0 to 40 °C

Temperature Range: 0 to 40 °C, non-freezing, ice may destroy

Storage Temperature: 0 to 45 °C

Emitter Wavelength: 850 nm

Power Requirements: 9.6 to 18 Vdc

Power Consumption
Quiescent Current: < 200 μA
Measurement/
Communication Current: < 40 mA
Shutter Motor Active Current: < 120 mA
Maximum Peak Current: 200 mA for 50 ms when shutter motor

Cycle Time: Open, measure, close, < 25 s

greater

the sensor

starts

7. Installation

Measurement Time: < 2 s

Outputs: SDI-12 (version 1.3) 1200 bps

RS-232 9600 bps, 8 data bits, 1 stop bit,

no parity, no flow control

Analog 0 to 5 Volts

Submersion Depth: 100 m (328 ft)

Diameter: 4.76 cm (1.875 in)

Length: 27 cm (10.625 in)

Weight: 0.52 kg (1.15 lb)

Maximum Cable Length: 460 m (1500 ft) (1 channel SDI-12 or

Analog); 15 m (50 ft) (RS-232)

If you are programming your datalogger with Short Cut, skip Section 7.3,

Datalogger/RTU Connection
Cut does this work for you. See Section 4, QuickStart

tutorial.

(p. 16), and Section 7.6, Programming (p. 28). Short

(p. 2), for a Short Cut

12

7.1 Default Settings

The OBS500 is configured at the factory with the default settings shown in
TABLE 7-1. For most applications, the default settings are used.

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-1. Factory Settings

NOTE

SDI-12/Analog SDI-12

SDI-12 Address 0

RS-232 Baud Rate 9600

Turbidity units TU

Temperature units Celsius

7.2 Device Configuration Utility

The Device Configuration Utility (DevConfig) is used to change settings, set up
the analog sensor, enter RS-232 commands, and update the operating system.

Use the OBS500 test cable to connect the OBS500 to a computer running
DevConfig. The red wire is connected to a 12 Vdc power supply and the black
to ground. The datalogger power supply is a good choice to use for the power
supply. DevConfig software is shipped on the Campbell Scientific
ResourceDVD included with the OBS500.

The OBS500 is supported in DevConfig version 1.16 or higher.

FIGURE 7-1. Device Configuration Utility

13

OBS500 Smart Turbidity Meter with ClearSensor® Technology

After installing DevConfig, select the OBS500 in the Device Type selection.
Select the correct PC Serial Port and then click Connect (see FIGURE 7-1).

The Terminal tab can be used to verify the setup of the OBS500. Select the
Terminal tab. Click in the Terminal window and push the Enter key several
times. This will wake up the RS-232 mode of the sensor. Once successfully
connected, you will see an OBS-500> prompt. FIGURE 7-2 shows DevConfig
after pressing ‘l’ (one) to identify the OBS500. By default, the OBS500 is in
the SDI-12 mode for communication. Once in the RS-232 mode, if there is no
communication for 20 seconds, the sensor will return to the SDI-12 mode.

14

FIGURE 7-2. Terminal Mode using 1 and H commands

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-2. RS-232 Terminal Commands

Terminal Commands Values Returned

1 Identify Serial Number, SDI-12 address, etc.

2 Open Wiper Command to open wiper started – please wait

Wiper now open – average current was xxx mA

3 Close Wiper Command to close wiper started – please wait

Wiper now closed – average current was xxx mA

H or h Help menu

DevConfig allows you to change the configuration of the OBS500.

Select the Settings Editor tab.

FIGURE 7-3. Settings Editor screen

15

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-3. OBS500 Connector Pin-Out

NOTE

NOTE

There are three settings that can be changed: SDI-12 address, measurement
mode, and sidescatter ratio top. Select the desired values and press the Apply
button.

The SDI-12 address is not used while in analog mode.

7.3 Datalogger/RTU Connection

The OBS500 field cable is typically used to connect to a datalogger or RTU.
The field cable is a molded-cable assembly that terminates with an MCIL wet
pluggable underwater terminator. TABLE 7-3 shows the contact numbers for
the MCIL/MCBH-8 connectors and the electrical functions and wire colors.

MCIL-8-MP/MCBH-8-FS

Contact Number

1 Power Ground Black

2 SDI-12/RS232 TX/Analog

3 Power (9.6 to 15 V) Red

4 Analog Signal Green

5 RS-232 RX/Shutter Open Blue

6 NC

7 Analog Ground Brown

8 NC

No Connection Clear/Braid

This document provides the recommended wiring configuration for connecting
the OBS500 field cable to a Campbell Scientific datalogger. Wiring to
dataloggers or RTUs manufactured by other companies is similar.

Campbell Scientific recommends powering down the system
before wiring the OBS500. The shield wire plays an important role
in noise emissions and susceptibility as well as transient
protection.

Electrical Function

SS-BS Control

Wire Color

White

16

7.3.1 SDI-12 Wiring

TABLE 7-4. SDI-12 Wiring

TABLE 7-5. RS-232 Wiring

OBS500 Smart Turbidity Meter with ClearSensor® Technology

1

C1, C3...)

7.3.2 RS-232 Wiring

Our CR800, CR850, CR1000, and CR3000 dataloggers have COM ports
(control port Tx/Rx pairs) that can be used to measure RS-232 sensors. Both
the C and U terminals can be configured as Tx/Rx pairs for measuring RS-232
sensors.

Color

Description

CR800
CR5000
CR3000
CR1000

CR200X

Series

CR6

Red Power 12V Battery+ 12V

Black

Power

Ground

G G G

Control

White

SDI-12

Signal

Control

1

Port

C1/

SDI-12

1

or

Port

Universal

Channel

Brown not used not used not used not used

Blue not used not used not used not used

Green not used not used not used not used

Clear Shield G G G

Only odd control ports or universal channels can be used for SDI-12 (for example,

1

Color OBS500 Function Connection

RS-232 9-pin /

Datalogger Control Port

Red +12VDC Power Source

Black Power Ground Power Ground

White RS-232 Tx (Output) Transmit

Blue RS-232 Rx (Input) Receive

Pin 2 Rx (Input)/

Control Port Rx

Pin 3 Tx (Output)/

Control Port Tx

Brown

Green

Clear Shield GND Ground

17

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-6. Analog 0-5 Volt Wiring

NOTE

7.3.3 Analog 0 to 5 Volt Wiring

Color

Blue Shutter Open - Control High Control Port

White

Green Signal

Brown Analog Ground

Black Power Ground G

Red Power SW12V

Clear Shield G

The measurement sequence is to raise the blue wire from ground to 5 volts to
open the shutter, delay 6 seconds, and then measure the backscatter analog
output on the green wire. If sidescatter is desired, then raise the white wire
from ground to 5 volts, delay 3 seconds, and then measure the sidescatter
analog output on the green wire. In either case, lower the blue wire to ground
to close the shutter. Note that measurements can be differential or single­ended. Differential measurements are recommended.

Backscatter (Low) or

Sidescatter (High) Control

Description

CR6, CR800, CR850,

CR1000, CR3000, CR5000

Control Port

Differential High or

Single-Ended Input

Differential Low or

Analog Ground

The output is scaled as 1 mV per TU. For example, 100 mV = 100 TU, 4000 mV =
4000 TU.

7.4 Communication Modes

7.4.1 SDI-12

The OBS500 uses an SDI-12-compatible hardware interface and supports a
subset of the SDI-12 commands. The most commonly used command is the
aM! command, issued by the datalogger. Here, a represents the sensor address
(0 to 9). The communication sequence begins with the datalogger waking the
sensor and issuing the aM! command. The sensor responds to the datalogger
indicating that two measurements will be ready within two (2) seconds.
Subsequent communications handle data reporting from the sensor to the
datalogger.

The SDI-12 protocol has the ability to support various measurement
commands. TABLE 7-7 provides the commands available for the OBS500
operating system (OS) version 2 or higher.

If you have OS version 1, see Appendix D,
Measurement Commands for OS Version 1 (p. D-1). Use the aI! SDI-
12 command or use DevConfig to see the OS version downloaded
to your OBS500. The OS version can be updated by using

DevConfig.

SDI-12 and RS-232

18

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-7. SDI-12 and RS-232 Measurement Commands

Commands

Process

Values Returned

aM!

a = address

Open Wiper

Send Data

obs (tu)

wet dry (0=dry 1=wet)

aC1!

Burst Data

bs median

ss maximum.

aM2!

Open Wiper

obs (tu)

wet dry (0=dry 1=wet)

aM3!

Open Wiper

open wiper position count

total open/close count

aM4!

Measure

obs (tu)

wet dry (0=dry 1=wet)

aC5!

Burst Data

bs median

ss maximum.

aM6!

Measure

obs (tu)

wet dry (0=dry 1=wet)

for OS Version 2 or Higher

aC!

aC2!

aC3!

Measure
Close

Open Wiper
Measure 100 Times
Close
Send Data

Measure
Close
Send Data

Send Data

ss (tu)
temperature (ºC)

bs mean
bs standard deviation
bs minimum
bs maximum
ss median
ss mean
ss standard deviation
ss minimum

ss (tu )
ratio (tu)
temperature (ºC)
raw obs (V)
raw ss (V)
open current (mA)
close current (mA)

open max current count
open timeout count
open current (mA)

aC4!

aC6!

Send Data

Measure 100 Times
Send Data

Send Data

ss (tu)
temperature (ºC)

bs mean
bs standard deviation
bs minimum
bs maximum
ss median
ss mean
ss standard deviation
ss minimum

ss (tu )
ratio (tu)
temperature (ºC)
raw obs (V)
raw ss (V)
open current (mA)
close current (mA)

19

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-7. SDI-12 and RS-232 Measurement Commands

Commands

Process

Values Returned

aM7!

Close Wiper

close wiper position count

aC8!

Raw Burst Data in Volts

bs median

aM9!

Wiper

total open/close count

for OS Version 2 or Higher

aC7!

7.4.1.1 SDI-12 Addresses

The OBS500 SDI-12 address can be set to 0 to 9, A to Z, or a to z which allows
multiple sensors to be connected to a single digital I/O channel (control port) of
an SDI-12 datalogger. (Most Campbell Scientific dataloggers support SDI-12.)

Send Data

Open
Measure 100 Times
Close
Send Data

Leave Open

close max current count
close timeout count
close current (mA)
total open/close count

bs mean
bs Standard deviation
bs minimum
bs maximum
ss median
ss mean
ss standard deviation
ss minimum
ss maximum.

open wiper position count
open max current count
open timeout count
close wiper position count
close max current count
close timeout count

7.4.1.2 SDI-12 Transparent Mode

20

The OBS500 is shipped from the factory with the address set to 0. When it is
necessary to measure more than one OBS500, it is easiest to use a different
control port for each OBS500 instead of changing the address. If additional
control ports are not available, the address will need to be changed.

The address on the OBS500 can be changed by sending the SDI-12 change
address command aAb!. The change address command can be issued from
most SDI-12 recorders. For example, to change the address of a sensor that has
a default address of 0 to the address of 1 the following command can be sent:

0A1!

The address may also be changed by connecting to the probe in DevConfig.
Once connected, in the Settings Editor tab click in the address box and enter
the new address. Press Apply to save the changes.

The transparent mode allows direct communication with the OBS500. This
may require waiting for programmed datalogger commands to finish before
sending responses. While in the transparent mode, datalogger programs may
not execute. Datalogger security may need to be unlocked before the
transparent mode can be activated.

OBS500 Smart Turbidity Meter with ClearSensor® Technology

The transparent mode is entered while the PC is in telecommunications with
the datalogger through a terminal emulator program. It is most easily accessed
through Campbell Scientific datalogger support software, but it is also
accessible with terminal emulator programs such as Windows Hyperterminal.

To enter the SDI-12 transparent mode, enter the terminal emulator from
LoggerNet, PC400, or PC200W datalogger support software. A terminal
emulator screen is displayed. Click the Open Terminal button.

For CR800 series, CR1000, and CR3000 dataloggers, press <Enter> until the
datalogger responds with the prompt (e.g., “CR1000>” for the CR1000). Type

SDI12 at the prompt and press <Enter>. In response, the query Enter Cx Port
1,3,5 or 7 will appear. Enter an integer value indicating the control port to

which the OBS500 is connected. A response of Entering SDI12 Terminal
indicates that SDI-12 Transparent Mode is active. Any of the SDI-12
commands may be entered (e.g., aM1! where a refers to the address). After
entering a command, the results may be viewed by entering aD!.

7.4.2 RS-232

FIGURE 7-4. Terminal Emulator

Only one sensor of the same address can be connected when using the change
address command.

RS-232 measurements of the OBS500 are typically made by a CR800, CR850,
CR1000, or CR3000 datalogger or an RTU device. The OBS500 field cable is

21

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-8. RS-232 Settings

used and wired appropriately for the measurement device. See TABLE 7-8 for
settings.

Bits per second 9600

Data bits 8

Parity None

Stop bits 1

Flow control None

Measurement commands are the same for RS-232 and SDI-12 as shown in
TABLE 7-7.

7.5 Calibration

7.5.1 Turbidity

Field recalibration is not recommended and usually not needed until the
OBS500 is sent back to Campbell Scientific for the two year service. We
recommend checking the calibration in the field as described below. If a
9-point calibration is needed, the OBS500 should be sent to Campbell
Scientific to perform the calibration.

The normalized response of an OBS500 sensor to SDVB turbidity over the
range from 0 to 4,000 TU is shown in FIGURE 7-5. As shown on the inset, the
response function is contained within region A, the linear region, of the
universal response curve. However, there is residual nonlinearity that is
removed by calibration and by computation of a TU value with a 2nd-order
polynomial. This section explains how to do a turbidity calibration.

22

OBS500 Smart Turbidity Meter with ClearSensor® Technology

0 1000 2000 3000 4000

Turbidity (TU)

0.0

0.2

0.4

0.6

0.8

1.0

Normalized OBS-3+ Response (OPV330 VCSEL)

TABLE 7-9. Calibration Materials and Volumes

0 20000 40000 60000

SSC (mg/l)

0

1000

2000

3000

4000

Turbidity (NTU)

A

B C

FIGURE 7-5. Normalized response of OBS500 to AMCO Clear

AMCO Clear
sensor. SDVB standards are made for individual instruments. Standards made
for one model of turbidity meter cannot be used to calibrate a different model.

Sidescatter 90-Degree Materials

®

turbidity. The inset shows the response function of a turbidity
sensor to high-sediment concentrations.

®

SDVB turbidity standards are used to calibrate an OBS500

Calibration Cup Diameter

(mm/inches)

8594 - 20TU 100 (~4)

8595 - 40TU 100 (~4)

8596 - 125TU 100 (~4)

8597 - 250TU 100 (~4)

8598 - 500TU 100 (~4)

8599 - 1000TU 100 (~4)

OBS Sensor Material

8600 - 125TU 200 (~7.9)

8601 - 250TU 200 (~7.9)

8602 - 500TU 200 (~7.9)

8603 - 1000TU 100 (~4)

8604 - 2000TU 100 (~4)

8605 - 4000TU 100 (~4)

23

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 7-10. Change in TU value resulting from one hour of

The GFS item numbers, standard values, and volumes required for the standard
low ranges are given in TABLE 7-9. SDVB standards have a shelf life of two
years provided that they are stored in tightly sealed containers and evaporation
is minimized.

The TU values of the standards will remain the same as long as the ratio of
particle mass (number of particles) to water mass (volume) does not change.
Evaporation causes this ratio to increase, and dust, bacteria growth, and dirty
glassware can also cause it to increase. Therefore, take the following
precautions. 1) Always use clean glassware and calibration containers.

2) Don’t leave standards on the bench in open containers or leave the standard
bottles uncapped. Perform the calibration as quickly as possible and return the
AMCO solutions to their bottles. 3) Clean dirty sensors with a clean, alcohol­soaked cloth to sterilize them before dipping them into the standards.

4) Transfer entire bottles between containers. To avoid aeration, do not shake
excess fluid off the glassware.

Because of the intrinsic errors in the TU value of formazin used by the SDVB
manufacturer (GFS Chemicals) and the dilution procedures, the uncertainty in
the TU value of an SDVB standard is ± 1% of the value indicated on the
standard bottle. Consequently, the TU value of one liter of standard in an
uncovered 100-mm calibration cup will increase ~1% in 10 hours on a typical
summer day (R.H. = 90% and air temp. = 18 °C). For example, the TU value of
a 2000-TU standard in a 100-mm cup will increase by about 2 TU (0.1%) per
hour. TABLE 7-10 gives the increases for some other commonly used
standards.

evaporation of SDVB standard, i.e., loss of water but not particles.

Calibration-cup Size φ mm (φ in)

100 (4) +0.26 +0.52 +2.10 +4.20

150 (6) +0.60 +1.20 +4.80 +9.70

Materials and equipment: OBS500 with cable, datalogger, large black
polyethylene plastic tub (0.5 M I.D. X 0.25 M deep) for measuring the clear­water points, and 100-mm and 200-mm black PE (polyethylene) calibration
cups.

Procedure

1. Swab sensor with an alcohol-soaked towel to sterilize it. Position the OBS

sensor in a large, black tub of fresh tap water as shown in FIGURE 7-6 and
record a 10-second average of the low-range output. Record the average
output on the calibration log sheet.

250 TU 500 TU 2000 TU 4000 TU

24

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 7-6. Position of OBS500 in clean tap water in big black tub

2. Pour the first SDVB standard into the appropriately sized cup (see TABLE

7-9).

3. Position the OBS sensor in the cup as shown in FIGURE 7-7 and record

10-second averages of the low- and high-range outputs. Record the
average outputs on the calibration log sheet.

4. Pour the standard back into its container.

5. Wipe sensor with a clean, dry towel to remove residual standard.

6. Repeat steps 2, 3, 4, and 5 for the other standards.

7. Perform 2

nd

-order polynomial regressions on the calibration data to get the

coefficients for converting OBS signals to TU values.

25

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 7-7. OBS500 in 500-TU AMCO Clear

100-mm black polyethylene calibration cup

7.5.2 Sediment

There are three basic ways to calibrate an OBS sensor with sediment. These are
described in the following sections. However, only the procedures for dry­sediment are explained in this manual. Typically, the sensor will record in
turbidity units and the relationship to suspended sediment is calculated in a
spread sheet or database after the data is retrieved to a computer.

7.5.2.1 Dry-Sediment Calibration

Dry-sediment calibration is a calibration performed with sediment that has
been dried, crushed, and turned to powder. This is the easiest calibration to do
because the amount of sediment can be determined accurately with an
electronic balance and the volume of water in which it is suspended can be
accurately measured with volumetric glassware. Of the three methods, dry­sediment calibration causes the greatest physical and chemical alteration of the
sediment. Alteration of the sediment size as a result of processing can
significantly affect the calibration slope. FIGURE 7-5 shows, for example, that
reducing the grain size by a factor of two during grinding can increase OBS
sensitivity by a factor of two.

®

turbidity standard in

26

7.5.2.2 Wet-Sediment Calibration

Wet-sediment calibration is performed with sediment obtained from water
samples or from the bed of a river that has not been dried and pulverized.
Consolidation and biochemical changes during storage and processing cause
some alteration of wet sediment, and for this reason, sediment and water
samples should be stored at about 4 °C prior to use. The wet sediment is
introduced into the sediment suspender as it comes from the field. This kind of

OBS500 Smart Turbidity Meter with ClearSensor® Technology

calibration requires that water samples be withdrawn from the suspender after
each addition of sediment for the determination of SSC (suspended sediment
concentration) by filtration and gravimetric analysis.

7.5.2.3 In situ Calibration

In situ calibration is performed with water samples taken from the immediate
vicinity of an OBS sensor in the field over sufficient time to sample the full
range of SSC values to which a sensor will be exposed. SSC values obtained
for these samples with concurrent recorded OBS500 signals and regression
analysis establishes the mathematical relation for future SSC conversions by an
instrument. This is the best sediment-calibration method because the particles
are not altered from their natural form in the river (see Lewis, 1996). It is also
the most tedious, expensive, and time-consuming method. It can take several
years of water sampling with concurrent OBS measurements to record the full
range of SSC values on a large river.

7.5.2.4 Performing a Dry-Sediment Calibration

Materials and equipment: OBS500 with test cable; dry, disaggregated
sediment from the location where the OBS500 will be used (sediment should
be in a state where grinding, sieving, or pulverization does not change its
particle-size distribution); datalogger with 12 V power supply; sediment
suspender (if a suspender is not available, use a 200 mm I.D. dark plastic
container and a drill motor with paint-mixing propeller); electronic balance
calibrated with 10 mg accuracy; 20 ml weigh boats; large, black polyethylene
plastic tub for measuring the clear-water points; 1 liter, class A, volumetric
flask; tea cup with round bottom; and teaspoon.

1. Check the balance with calibration weights; recalibrate if necessary.

2. Connect the OBS500 to a computer or datalogger so that the measured

values can be observed.

3. Add three liters of tap water to the suspender tub with the volumetric flash.

4. After measuring the clear-water signal (Step 1, Section 7.5.1, Turbidity

(p. 22)), mount the OBS500 so that the sensor end is 50 mm above the

bottom of the suspender tub and secure it in the position that minimizes
reflections from the wall; see FIGURE 7-8.

FIGURE 7-8. Portable Sediment Suspender (left) and OBS beam

orientation in suspender tub (right)

27

OBS500 Smart Turbidity Meter with ClearSensor® Technology

SSC = Wt

w = volume of water in liters, ρ = density of water (ρ = 1.0 kg L

V

and ρ

s [Vw + Wts/ρs]

s = sediment density (assume 2.65 10

–1

, where Wts = total sediment weight in tub in mg,

3

mg L–1)

–1

at 10 ° C),

Procedure

1. Record and log the clean-water signal as in Step 1, Section 7.5.1, Turbidity

(p. 22); see FIGURE 7-6. Use the same value, such as, sidescatter,

backscatter, or ratio throughout the calibration.

2. Move the OBS500 to the suspender as described in setup.

3. Weigh 500 ± 10 mg of sediment in a weigh boat and transfer it to the

teacup. Record the weight on the calibration log sheet and add about 10 cc
of water from the suspender tub to the teacup and mix the water and
sediment into a smooth slurry with the teaspoon.

4. Add the sediment slurry to the tub and rinse the teacup and spoon with tub

water to get all the material into the suspender.

5. Turn the suspender on and let it run for 10 minutes or until the OBS signal

stabilizes.

6. Take averages of signals with the computer or datalogger and enter them

on the calibration log sheet.

7. Calculate the sediment-weight increment as follows: W

8. Add enough additional sediment to get one full increment of sediment, W

9. Repeat step 8 until five full increments of sediment have been added or

10. Perform 3

7.6 Programming

Short Cut is the best source for up-to-date datalogger programming code.
Programming code is needed when:

If your data acquisition requirements are simple, you can probably create and
maintain a datalogger program exclusively with Short Cut. If your data
acquisition needs are more complex, the files that Short Cut creates are a great
source for programming code to start a new program or add to an existing
custom program.

i = 2500 mg

(4000/V

x), where Wi = the incremental weigh of sediment and Vx = the

average output signal from step 6. The resulting weight gives the amount
of sediment to add in order to have evenly spaced calibration points.

± 5%. Repeat steps 4, 5, and 6.

until the OBS signals exceed the output range.

rd

order polynomial regressions on the data to get the coefficients

for converting OBS output to SSC.

• Creating a program for a new datalogger installation

• Adding sensors to an existing datalogger program

i

28

OBS500 Smart Turbidity Meter with ClearSensor® Technology

NOTE

NOTE

Short Cut cannot edit programs after they are imported and edited
in CRBasic Editor.

A Short Cut tutorial is available in Section 4, QuickStart (p. 2). If you wish to
import Short Cut code into CRBasic Editor to create or add to a customized
program, follow the procedure in Appendix A, Importing Short Cut Code Into
CRBasic Editor

Programming basics for CRBasic dataloggers are provided in the following
sections. Complete program examples for select CRBasic dataloggers can be
found in Appendix B, Example Programs
programming examples for Edlog dataloggers are provided at

www.campbellsci.com/old-manuals.

7.6.1 SDI-12 Programming

The SDI12Recorder instruction is used to read the OBS500 in SDI-12 mode.
A multiplier of 1.0 and an offset of 0.0 yield water level in psig and
temperature in degrees C.

The SDI12Recorder instruction has the following form:

(p. A-1).

(p. B-1). Programming basics and

SDI12Recorder(Destination, Output String, Multiplier, Offset)

Refer to Appendix B.1, CR1000 SDI-12 Program (p. B-1), for an example of
using this CRBasic instruction.

7.6.2 RS-232 Programming

The SerialOut() instruction sends strings over the Tx COM port and the
SerialIn() instruction receives strings from the Rx COM port.

Refer to Appendix B.2, CR1000 RS-232 Program

(p. B-2), for an example of

using these CRBasic instructions.

7.6.3 Analog Programming

The PortSet instruction is used to open the shutter. Either the VoltDiff
(recommended) or VoltSe instruction is used to measure the analog voltage
output.

Refer to Appendix B.2, CR1000 RS-232 Program

(p. B-2), for an example of

using these CRBasic instructions.

7.7 Operation in High Sediment Loads and Sandy Sediments

Sites with high sediment loads and large sand grains can be problematic for the
shutter and its motor. The recommendations provided in this section should
help reduce these problems.

Typically sites with high biological growth have relatively low
sediment loads.

29

OBS500 Smart Turbidity Meter with ClearSensor® Technology

CAUTION

1. Run the OBS500 in a normally open mode. For example, close then open

the wiper once every four hours. This reduces the wear on the motor
significantly, and save power. The interval can be adjusted over time.
Increase the interval if experiencing fouling. If the windows are staying
clean, slow it down even more. Example CRBasic programs are provided
at Appendix B.4, Examples for High Sediment Loads

a. M3! opens the wiper

b. M4!, M5!, or M6! perform measurements when the wiper is open

c. M7! closes the wiper

2. Clean the shutter assembly. The frequency that the shutter should be

cleaned depends on the sediment load and can vary from weeks to months
(step 3 can help you determine the required frequency for cleaning). Two
levels of cleaning should be done;

a. flush the wiper as it opens and closes with a stream of clean water, or

b. remove the wiper from the OBS500 by removing one screw and

follow the directions provided in Section 7.7.1, Wiper Removal
Procedure

(p. 30). Flush and clean.

(p. B-4).

3. Store the current used to open and close the slider. The open and close

SDI-12 instructions (M3! and M7!) output the current. Normally the
current is around 100 mA. As sand grits lodge in the groves, the resistance
to movement increases and the motor has to work harder. This increases
the current usage. Therefore, increased current usage indicates that the
wiper needs to be cleaned (see step 2).

4. Mount the sensor between 45 degrees pointing down to vertical hanging

down.

7.7.1 Wiper Removal Procedure

1. Remove the stop screw in the OBS500 housing at the end of the

shutter/wiper slot.

2. Remove the 4-40 flat head screw and copper plate to expose the drive shaft

access port (FIGURE 7-9).

3. Insert a slot screw driver (2.5 mm (0.1 in.) wide blade) into the access port

(FIGURE 7-10).

4. Engage the end of the drive shaft and then rotate clockwise until the

shutter is free (FIGURE 7-10 and FIGURE 7-11).

Keep track of all of the components (FIGURE 7-12

).

30

5. Reassemble by reversing the steps.

OBS500 Smart Turbidity Meter with ClearSensor® Technology

Remove 4-40

flat head screw

Copper plate

Drive shaft

FIGURE 7-9. Remove the screw

access port

FIGURE 7-10. Insert screwdriver and rotate clockwise

FIGURE 7-11. Shutter disassembled

31

OBS500 Smart Turbidity Meter with ClearSensor® Technology

Shutter

Floating nut

Floating

copper plate

spacer

nut

FIGURE 7-12. Shutter components

8. Factors that Affect Turbidity and Suspended­Sediment Measurements

This section summarizes some of the factors that affect OBS measurements
and shows how ignoring them can lead to erroneous data. If you are certain that
the characteristics of suspended matter will not change during your survey and
that your OBS was factory-calibrated with sediment from your survey site, you
only need to skim this section to confirm that no problems have been
overlooked.

8.1 Particle Size

The size of suspended sediment particles typically ranges from about 0.2 to
500 μm in surface water (streams, estuaries, and the ocean). With size, shape,
and color remaining constant, particle area normal to a light beam will
determine the intensity of light scattered by a volume of suspended matter.
Results of tests with sediment shown in FIGURE 8-1 indicate a wide range of
sensitivity is associated with fine mud and coarse sand (about two orders of
magnitude). The significance of these results is that size variations between the
field and laboratory and within a survey area during monitoring will produce
shifts in apparent TU and SSC values that are unrelated to real changes in
sediment concentration. FIGURE 8-2 shows the difference in apparent
turbidity that can result from different ways of disaggregating sediment.

32

OBS500 Smart Turbidity Meter with ClearSensor® Technology

10.0 100.0 1000.0
Median Particle Size (D

50

)

0.01

0.10

1.00

OBS Sensitivty, S (mV per mg l

-1

)

S ~ 1/D

50

Sonic Probe

Hand Shaking

Aggressive)

Sonic Bath

FIGURE 8-1. Normalized sensitivity as a function of grain diameter

(Most Aggressive)

(Least

FIGURE 8-2. The apparent change in turbidity resulting from

disaggregation methods

33

OBS500 Smart Turbidity Meter with ClearSensor® Technology

0 20 40 60 80 100 120 140 160 180

Scatt ering Angle

0.01

0.1

1

Relative Scattering Intensity

Cubes

Plates

Spheres

OBS-3+

8.2 Suspensions with Mud and Sand

As mentioned in Section 8.1, Particle Size (p. 32), light scattering from particles
is inversely related to particle size on a mass concentration basis. This can lead
to serious difficulties in flow regimes where particle size varies with time. For
example, when sandy mud goes through a cycle of suspension and deposition
during a storm, the ratio of sand to mud in suspension will change. A turbidity
sensor calibrated for a fixed ratio of sand to mud will, therefore, indicate the
correct concentration only part of the time. There are no simple remedies for
this problem. One solution is to take a lot of water samples and analyze them in
the laboratory. This is not always practical during storms when the errors are
likely to be largest. Do not rely solely on turbidity sensors to monitor
suspended sediments when particle size or composition is expected to change
with time at a monitoring site.

8.3 Particle-Shape Effects

In addition to size and flocculation/aggregation, particle shape has a significant
effect on the scattering intensity from a sample and calibration slope of a
turbidity sensor. As the graph in FIGURE 8-3 shows, plate-shaped particle
(clay-mineral particles, for example) backscatter light about ten times more
efficiently than spherical particles, and angular shapes have intermediate
scattering efficiency. Turbidity sensors are very sensitive to shape effects and
this makes it very important to calibrate with material from the monitoring site.
It is also essential that particle shape remains constant during the monitoring
period.

FIGURE 8-3. Relative scattering intensities of grain shapes

34

OBS500 Smart Turbidity Meter with ClearSensor® Technology

8.4 High Sediment Concentrations

At high sediment concentrations, particularly in suspensions of clay and silt,
the infrared radiation from the emitter can be so strongly attenuated along the
path connecting the emitter, the particle, and the detector, that backscatter
decreases exponentially with increasing sediment concentration. For mud, this
occurs at concentrations greater than about 5,000 mg/l. FIGURE 8-4 shows a
calibration in which sediment concentrations exceeding 6,000 mg/l
output signal to decrease. It is recommended not to exceed the specified
turbidity or suspended sediment ranges, otherwise the interpretation of the
signal can be ambiguous. For example, a signal level of 2,000 mV (FIGURE

8-4) could be interpreted to indicate SSC values of either 3,000 or 33,000 mg/l.

Factory calibrations are performed in the linear region designated ‘A’ on the
graph.

cause the

FIGURE 8-4. Response of an OBS sensor to a wide range of SSC

8.5 IR Reflectivity—Sediment Color

Infrared reflectivity, indicated by sediment color, has a major effect on
sensitivity because with other factors remaining constant, it changes the
intensity of light scattering. Although turbidity sensors are color blind, tests
have shown that “whiteness”, color, and IR reflectivity are correlated. Calcite,
which is highly reflective and white in color, will produce a much stronger
turbidity signal on a mass-concentration basis than magnetite, which is black
and IR-absorbing. Sensitivity to colored silt particles varies from a low of
about one for dark sediment to a high of about ten for light gray sediment; see
FIGURE 8-5. In areas where sediment color is changing with time, a single
calibration curve may not work. Resulting errors will depend on the relative
concentrations of colored sediments.

35

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 8-5. Infrared reflectivity of minerals as a function of

10-Munzell Value

8.6 Water Color

Some OBS users have been concerned that color from dissolved substances in
water samples, not colored particles as discussed in Section 8.5, IR
Reflectivity—Sediment Color
measurements. Although organic and inorganic IR-absorbing, dissolved matter
has visible color, its effect on turbidity measurements is small unless the
colored compounds are strongly absorbing at the sensor wavelength (850 nm)
and are present in high concentrations. Only effluents from mine-tailings
produce enough color to absorb measurable IR. In river, estuary, and ocean
environments, concentrations of colored materials are too low by at least a
factor of ten to produce significant errors.

8.7 Bubbles and Plankton

Although bubbles efficiently scatter light, monitoring in most natural
environments shows that OBS signals are not strongly affected by bubbles. The
sidescatter measurement may be more affected. Bubbles and quartz particles
backscatter nearly the same amount of light to within a factor of approximately
four, but most of the time bubble concentrations are at least two orders of
magnitude less than sand concentrations. This means that sand will produce
much more backscatter than bubbles in most situations, and bubble interference
will not be significant. Prop wash from ships and small, clear, mountain
streams where aeration produces high bubble concentrations are exceptions to
this generality and can produce erroneous turbidity values resulting from
bubbles.

(p. 35), produces erroneously low turbidity

36

OBS sensors detect IR backscattered between 90°
scattering intensities are nearly constant with the scattering angle. Particle
concentration has the most significant effect in this region. OBS sensors are

and 165° where the

more sensitive, by factors of four to six, to mineral particles than particulate

WARNING

WARNING

organic matter, and interference from these materials can, therefore, be ignored
most of the time. One notable exception is where biological productivity is
high and sediment production from rivers and re-suspension is low. In such an
environment, OBS signals can come predominately from plankton.

9. Maintenance

There is a biocide chamber in the slider that is refillable. The default biocide
from the factory is copper braid. The braid will last for many years, but it can
be replaced as desired. Other solid biocides can be placed in the chamber. To
be effective over time, the biocide should be slow to dissolve.

The OBS500 should be sent in for service (seal, shaft, and nut replacement)
after 2 years or 70,000 cycles of the shutter, whichever occurs first. The sensor
has a cycle count and a moisture alarm in the data string (SDI-12 and RS-232
only). If the seals are not replaced, the sensor will eventually leak and
potentially be destroyed. It is recommended that the cycles and moisture alarm
be recorded regularly. If a moisture alarm is recorded, the sensor shutter should
be parked and the sensor taken out of the water and returned for repair as soon
as possible.

OBS500 Smart Turbidity Meter with ClearSensor® Technology

Other than the sleeve and the biocide chamber on the
sensor tip, 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 a leak.

Plastic (pn 27473) and copper (pn 27803) sleeves are available for the OBS500
to reduce required cleaning. The plastic sleeve is intended to be disposable.
The copper sleeve should slow fouling growth, but it may need to be cleaned.
If the sleeve becomes encrusted with organisms, such as barnacles or tube
worms, remove the sleeve. The sleeve can be soaked in weak acids or other
cleaning products that are compatible with copper. The sleeve may have to be
gently scraped with a flexible knife blade followed by a SkotchBrite scouring
pad.

Do not use solvents such as MEK, Toluene, Acetone, or
trichloroethylene on OBS sensors.

Downloading a New Operating System

DevConfig is used to download a new operating system to the OBS500. Select
the Send OS tab and follow the directions on the screen.

37

OBS500 Smart Turbidity Meter with ClearSensor® Technology

FIGURE 9-1. DevConfig, Send OS

10. Troubleshooting

A common cause for erroneous, turbidity-sensor data is poor sensor
connections to the datalogger.

Problem:

Unit will not respond when attempting serial communications.

Suggestion:

Check the power (Red is +V and Black is Ground) and signal (White is SDI-12
Data) lines to ensure proper connection to the datalogger. Check the datalogger
program to ensure that the same port the SDI-12 data line is connected to is
specified in the measurement instruction.

38

OBS500 Smart Turbidity Meter with ClearSensor® Technology

TABLE 10-1. Troubleshooting Chart.

The following three tests are used to diagnose malfunctions of an OBS500.

1. The Finger-Wave Test is used to determine if an OBS sensor is ‘alive’.

Power the OBS sensor and connect datalogger (see Section 7.2, Device
Configuration Utility

(p. 13)). Wave your finger across the sensor window

about 20 mm away from it. The datalogger should show the output
fluctuating from a few TU to the full-scale signal. If there are no signal
fluctuations of this order, there is a problem that requires attention.

2. The Shake Test is done to determine if water has leaked inside the

pressure housing. Unplug the cable and gently shake the sensor next to
your ear and listen for sloshing water. This test gives a false negative
result when the amount of water in the housing is large enough to destroy
the circuit but too small to be audible.

3. A Calibration Check is done to verify if a working OBS sensor needs to

be recalibrated. In order to be meaningful, the user must have a criterion
for this test. For example, this criterion might be 5%. The sensor is placed
in calibration standards with the 1

st

and 2nd TU values listed in FIGURE

7-5 and the datalogger readings are logged. If either reading differs by

more than 5% from ones reported on the factory calibration certificate, or
the user’s own calibration data, the sensor should be recalibrated. If the
first two calibration points fall within the acceptance criterion, then the
third value can be tested. The recommended frequency for calibration
checks is quarterly when an OBS sensor is in regular use. Otherwise it
should be performed prior to use. Calibration checks can be done in the
field.

Fault Cause of Fault Remedy

Fails finger­wave test

No power, dead battery Replace battery and reconnect

wires.

Plug not fully seated Disconnect and reinsert plug.

Sensor broken Visually inspect for cracks.

Return OBS500 to
manufacturer if cracks are
found.

Electronic failure. Unit

draws less than 11 mA or

Return OBS500 to
manufacturer.

more than 40 mA.

Fails shake
test

Fails
calibration
check

Sensor leaked Return OBS500 to

manufacturer.

Aging of light source
causes it to become

Recalibrate (see Section 7.5,
Calibration

(p. 22)).

dimmer with time

39

OBS500 Smart Turbidity Meter with ClearSensor® Technology

11. References

Anderson, C.W., 2005, Turbidity (ver. 2.1): U.S. Geological Survey Techniques of
Water-Resources Investigations, book 9, chap. A6., sec. 6.7, Sept 2005, accessed
December 8, 2011, from http://pubs.water.usgs.gov/twri9A6/.

Boyd Bringhurst and Jeff Adams. “Innovative Sensor Design for Prevention of
Bio-fouling.” Oceans 2011, September 2011.

Lewis, Jack. 1996. Turbidity-controlled Suspended Sediment Sampling for
Runoff-event Load Estimation. Water Resources Research, 32(7), pp. 2299-

2310.

“U.S. Geological Survey Implements New Turbidity Data-Reporting Procedures.” U.S.
Geological Survey. http://water.usgs.gov/owq/turbidity/TurbidityInfoSheet.pdf.

40

NOTE

Appendix A. Importing Short Cut Code Into CRBasic Editor

This tutorial shows:

• How to import a Short Cut program into a program editor for

additional refinement

• How to import a wiring diagram from Short Cut into the comments of

a custom program

Short Cut creates files, which can be imported into CRBasic Editor. Assuming
defaults were used when Short Cut was installed, these files reside in the
C:\campbellsci\SCWin folder:

• .DEF (wiring and memory usage information)

• .CR6 (CR6 datalogger code)

• .CR2 (CR200(X) datalogger code)

• .CR1 (CR1000 datalogger code)

• .CR8 (CR800 datalogger code)

• .CR3 (CR3000 datalogger code)

• .CR5 (CR5000 datalogger code)

Use the following procedure to import Short Cut code and wiring diagram into
CRBasic Editor.

1. Create the Short Cut program following the procedure in Section 4,
QuickStart

file name used when saving the Short Cut program.

2. Open CRBasic Editor.

3. Click File | Open. Assuming the default paths were used when Short Cut
was installed, navigate to C:\CampbellSci\SCWin folder. The file of
interest has the .CR6, .CR2, .CR1, .CR8, .CR3, or .CR5 extension. Select
the file and click Open.

4. Immediately save the file in a folder different from
C:\Campbellsci\SCWin, or save the file with a different file name.

Once the file is edited with CRBasic Editor, Short Cut can no
longer be used to edit the datalogger program. Change the name
of the program file or move it, or Short Cut may overwrite it next
time it is used.

5. The program can now be edited, saved, and sent to the datalogger.

(p. 2). Finish the program and exit Short Cut. Make note of the

6. Import wiring information to the program by opening the associated .DEF
file. Copy and paste the section beginning with heading “-Wiring for
CRXXX–” into the CRBasic program, usually at the head of the file. After
pasting, edit the information such that an apostrophe (') begins each line.

A-1

Appendix A. Importing Short Cut Code Into CRBasic Editor

This character instructs the datalogger compiler to ignore the line when
compiling.

A-2

Appendix B. Example Programs

CRBasic Example B-1. CR1000 SDI-12 Program

'CR1000 Series Datalogger

B.1 CR1000 SDI-12 Program

'Declare Public Variables

Public SDI (4)

'Declare Other Variables

Alias SDI(1) = OBS
Alias SDI(2) = SS
Alias SDI(3) = Temp
Alias SDI(4) = WetDry

'Define Data Tables

DataTable (Test,1,1000)

DataInterval (0,15,Min,10)
Sample (1,OBS,FP2)
Sample (1,SS,FP2)
Sample (1,Temp,FP2)
Sample (1,WetDry,FP2)

EndTable

'Main Program

BeginProg

Scan (30,Sec,0,0)

SDI12Recorder (SDI(),1,0,"M!",1.0,0)

'Call Output Tables

CallTable Test
NextScan

EndProg

Although this is a CR1000 program, other CRBasic dataloggers are
programmed similarly.

B-1

Appendix B. Example Programs

CRBasic Example B-2. CR1000 RS-232 Program

'CR1000 Series Datalogger

EndProg

B.2 CR1000 RS-232 Program

'Declare Public Variables

Public RS232 (5)
Public Counter
Public OutString As String * 20
Public OutString2 As String * 10
Public InString As String * 100

'Declare Other Variables
'RS232(1) is the address

Alias RS232(2) = OBS
Alias RS232(3) = SS
Alias RS232(4) = Temp
Alias RS232(5) = WetDry

'Define Data Tables

DataTable (Test,1,1000)
DataInterval (0,60,Min,10)
Sample (1,OBS,FP2)
Sample (1,SS,FP2)
Sample (1,Temp,FP2)
Sample (1,WetDry,FP2)
EndTable

'Main Program

BeginProg

SerialOpen (Com1,9600,0,0,150)

Scan (30,Sec,0,0)

OutString2 = CHR (13) 'a series of carriage returns will put OBS500 into RS-232 mode

OutString = "0M!" + CHR (13) 'address and then use commands M to M8

'Send String over communication port C1 (COM1 TX).
SerialOut (Com1,OutString2,"OBS_500",15,100) 'put OBS500 into RS232 mode
delay (1,1,Sec)
SerialOut (Com1,OutString,"",0,1000) 'send command,

'Receive String over communication port C1 (COM1 RX).

SerialIn (InString,Com1,5,33,150) 'The sensor echoes back the command ending with an "!" (CHR 33)
SerialIn (InString,Com1,2500,62,150) 'The sensor will open, close and after about 20 seconds
'send "OBS_500>" and then the data. CHR 62 is ">"
SerialIn (InString,Com1,100,13,200) 'Now the data comes ending with a carriage return, CHR 13
SplitStr (RS232(),InString,"",5,0) 'Split the ASCII string into numeric variables

'Call Output Tables
'Example:

CallTable Test
NextScan

Although this is a CR1000 program, other CRBasic dataloggers are
programmed similarly.

B-2

B.3 CR1000 Analog Program

CRBasic Example B-3. CR1000 Analog Program

'CR1000 Series Datalogger

EndProg

'OBS500_analog_O&M.CR1 for the CR1000
'wiring: Green to 1H; Brown to 1L; Red to SW12; Black to Grnd; Blue to C1; and White to C2

'Declare Public Variables

Public PTemp, batt_volt
Public Results (2)
Alias Results(1)=obs
Alias Results(2)=ss

Units obs=NTU
Units ss=NTU

DataTable (OBS500_analog,1,-1)

DataInterval (0,3,min,10)
Minimum (1,batt_volt,FP2,0,False)
Sample (1,PTemp,FP2)
Sample(1,obs,FP2)
Sample(1,ss,FP2)

EndTable

'Main Program

BeginProg

Scan (30,sec,3,0)
PanelTemp (PTemp,250)
Battery (batt_volt)
PortSet (1 ,1 ) 'blue wire -- drive high to open shutter
PortSet (2,0) 'white wire selects obs (0) or ss (1)
Delay (0,9500,msec) '6 secs (shutter open) + 3.5 secs
VoltDiff (obs,1,0,1,1,0,_60Hz,1,0) '1 mV = 1 TU
PortSet (2 ,1 ) 'white wire to +5 volts for ss meas
Delay (0,800,msec) 'wait until meas is done
VoltDiff (ss,1,0,1,1,0,_60Hz,1,0)
PortSet (1,0) 'blue wire -- drive low to close shutter
CallTable(OBS500_analog)
NextScan

Appendix B. Example Programs

Although this is a CR1000 program, other CRBasic dataloggers are
programmed similarly.

B-3

Appendix B. Example Programs

CRBasic Example B-4. Normally Open CR1000 Example

EndProg

B.4 Examples for High Sediment Loads

B.4.1 Normally Open CR1000 Example

'CR1000 Series Datalogger
'OBS500 normally open

'In normally open mode the OBS500 can make measurement multiple times per minute but the wiper interval could be set
'to as low as a time or two a day. This mode is also beneficial where the power budget is critical since opening and
'closing the wiper consumes considerably more power than making the turbidity measurement.

'Declare Public Variables

Public OBS500(4)
Public TimeCounter
Public obsDatOpen(4),obsDatClose(4)

'Declare Other Variables

Alias OBS500(1) = turb_bs
Alias OBS500(2) = turb_ss
Alias OBS500(3) = tempC_obs500
Alias OBS500(4) = wet_dry
Alias obsDatOpen(1) = Open_counts 'Full movement of slider is about 20,000 counts. If it jams this # will be smaller
Alias obsDatOpen(2) = Open_Max_mA_cnts 'Number of times the shutter stops while opening because of max current
Alias obsDatOpen(3) = Open_slip 'Open timeout count. If the threads are stripped the slide will not move and this count will increase
Alias obsDatOpen(4) = Open_mA 'mA current of the motor
Alias obsDatClose(1) = Close_counts 'Full movement of slider is about 20,000 counts. If it jams this # will be smaller
Alias obsDatClose(2) = Close_Max_mA_cnts 'Number of times the shutter stops while opening because of max current
Alias obsDatClose(3) = Close_slip 'Open timeout count. If the threads are stripped the slide will not move and this count will increase
Alias obsDatClose(4) = Close_mA 'mA current of the motor

Units turb_bs = fbu
Units turb_ss = fnu
Units tempC_obs500 = degC
Units wet_dry = YesNo

'Define Data Tables

DataTable (Test,1,1000)

DataInterval (0,5,Min,10)
Sample (1,turb_bs,FP2)
Sample (1,turb_ss,FP2)

EndTable

'Main Program

BeginProg

SDI12Recorder (obsDatOpen(),1,0,"M3!",1,0) 'Start with shutter open

Scan (1,Min,0,0)

TimeCounter = TimeCounter + 1

'Wipe at a slower interval than the scan interval

If TimeCounter >= 60 Then 'This value, 60, will wipe once every 60 scan intervals. 60 minutes in this case
SDI12Recorder (obsDatClose(),1,0,"M7!",1,0)
SDI12Recorder (obsDatOpen(),1,0,"M3!",1,0)
TimeCounter = 0
EndIf

'Read OBS500 each scan interval

SDI12Recorder(OBS500(),1,0,"M4!",1,0) 'Measure without moving the wiper

'Call Output Tables

CallTable Test
NextScan

B-4

CRBasic Example B-5. Cycle Shutter/Wiper for Each Measurement CR1000 Program

'CR1000 Series Datalogger

'OBS500 cycle shutter each measurement

EndProg

'Declare Public Variables

Public OBS500(4)
Public obsDatOpen(4),obsDatClose(4)
Public Open

'Declare Other Variables

Alias OBS500(1) = turb_bs
Alias OBS500(2) = turb_ss
Alias OBS500(3) = tempC_obs500
Alias OBS500(4) = wet_dry
Alias obsDatOpen(1) = Open_counts 'Full movement of slider is about 20,000 counts. If it jams this # will be smaller
Alias obsDatOpen(2) = Open_Max_mA_cnts ' Number of times the shutter stops while opening because of max current
Alias obsDatOpen(3) = Open_slip 'Open timeout count. If the threads are stripped the slide will not move and this count will increase
Alias obsDatOpen(4) = Open_mA 'mA current of the motor
Alias obsDatClose(1) = Close_counts 'Full movement of slider is about 20,000 counts. If it jams this # will be smaller
Alias obsDatClose(2) = Close_Max_mA_cnts 'Number of times the shutter stops while opening because of max current
Alias obsDatClose(3) = Close_slip 'Open timeout count. If the threads are stripped the slide will not move and this count will increase
Alias obsDatClose(4) = Close_mA 'mA current of the motor

Units turb_bs = fbu
Units turb_ss = fnu
Units tempC_obs500 = degC
Units wet_dry = YesNo

'Define Data Tables

DataTable (Test,1,1000)

DataInterval (0,5,Min,10)
Sample (1,turb_bs,FP2)
Sample (1,turb_ss,FP2)

EndTable

'Main Program

BeginProg

Scan (60,Sec,0,0)

'If open make measurement and close. If closed, open then make measurement.

If Open = 1 Then 'If open the make measurement, then close
SDI12Recorder(OBS500(),1,0,"M4!",1,0) 'Measure without moving the wiper
SDI12Recorder (obsDatClose(),1,0,"M7!",1,0) 'Close wiper
Open = 0
Else 'if closed
SDI12Recorder (obsDatOpen(),1,0,"M3!",1,0) 'Open wiper
Delay (0,11,Sec)
SDI12Recorder(OBS500(),1,0,"M4!",1,0) 'Measure without moving the wiper
Open = 1
EndIf

'Call Output Tables

CallTable Test
NextScan

Appendix B. Example Programs

B.4.2 Cycle Shutter/Wiper for Each Measurement CR1000

Program

The following CRBasic program will:

• Open the shutter if closed, then make a measurement

• Make a measurement if open, then close

Shutter/wiper cycles will be cut by 50%. This will reduce wear and power
consumption 50% but still leave the optics shuttered 50% of the time.

B-5

Appendix B. Example Programs

B-6

Appendix C. OBS500 Copper Sleeve Kit Installation

1. Remove the Button Head Hex Screw as shown.

2. Slide the Copper Sleeve over the OBS500 and snap it into place.

3. Install the 4-40 x ¼ SS Slot Head Screw.

C-1

Appendix C. OBS500 Copper Sleeve Kit Installation

C-2

TABLE D-1. SDI-12 and RS-232 Measurement Commands

Appendix D. SDI-12 and RS-232 Measurement Commands for OS Version 1

OBS500 OS version 1 supports different commands than newer operation
systems. TABLE D-1 shows the commands available for OS version 1. Use the
aI! SDI-12 command or use DevConfig to see the OS version downloaded to
your OBS500. The OS version can be updated by using DevConfig.

Commands Process Values Returned

aM!
aC!

a = address

aM1!
aC1!

aM2!
aC2!

aM3!
aC3!

aM4!
aC4!

Open Wiper
Measure
Close
Send Data

Open Wiper
Measure
Close
Send Data

Open Wiper
Measure
Close
Send Data

Open Wiper
Send Data

Measure
Send Data

obs (tu)
ss (tu )
temperature (degc)
wet dry (0=dry 1=wet)

ratio (tu)
temperature (degc)
wet dry (0=dry 1=wet)

obs (tu)
ss (tu )
ratio (tu)
temperature (degc)
raw obs (volts)
raw ss (volts)
open current (ma)
close current (ma)
wet dry (0=dry 1=wet)

open wiper position count
open max current count
open timeout count
open current (ma)

obs (tu)
ss (tu )
temperature (degc)
wet dry (0=dry 1=wet)

aM5!
aC5!

Measure
Send Data

ratio (tu)
temperature (degc)
wet dry (0=dry 1=wet)

D-1

Appendix D. SDI-12 and RS-232 Measurement Commands for OS Version 1

TABLE D-1. SDI-12 and RS-232 Measurement Commands

NOTE

Commands Process Values Returned

aM6!
aC6!

aM7!
aC7!

aM8!
aC8!

aC9! Open Wiper

Measure
Send Data

Close Wiper
Send Data

Send Wiper Data Open close total count

Measure 100 Times
Close
Send Data

obs (tu)
ss (tu )
ratio (tu)
temperature (degc)
raw obs (volts)
raw ss (volts)
open current (ma)
close current (ma)
wet dry (0=dry 1=wet)

Close wiper position count
Close max current count
Close timeout count
Close current (ma)

Open wiper position count
Open max current count
Open timeout count
Close wiper position count
Close max current count
Close timeout count

obs median
obs mean
obs standard deviation
obs min
obs max
ss median
ss mean
ss standard deviation
ss min
ss max

With the SDI-12 concurrent measurements (aCx!), the datalogger
does not request the data until the next interval hits. For example,
if you have a 30-minute interval, you will not see the data for 30
minutes. There is not an equivalent M command to the aC9!
command since the M command is limited to nine returned values.

As the measurement data is transferred between the probe and datalogger
digitally, there are no offset errors incurred with increasing cable length as seen
with analog sensors. However, with increasing cable length, there is still a
point when the digital communications will break down, resulting in either no
response or excessive SDI-12 retries and incorrect data due to noise problems.
Using SDI-12 commands which add a CRC check (e.g., aMC!), can
significantly improve incorrect data issues.

D-2

Campbell Scientific Companies

Campbell Scientific, Inc.

815 West 1800 North

Logan, Utah 84321

UNITED STATES

www.campbellsci.com • [e-mail]

Campbell Scientific Africa Pty. Ltd.

PO Box 2450

Somerset West 7129

SOUTH AFRICA

www.campbellsci.co.za • [e-mail]

Campbell Scientific Southeast Asia Co., Ltd.

877/22 Nirvana@Work, Rama 9 Road

Suan Luang Subdistrict, Suan Luang District

Bangkok 10250

THAILAND

www.campbellsci.asia • [e-mail]

Campbell Scientific Australia Pty. Ltd.

PO Box 8108

Garbutt Post Shop QLD 4814

AUSTRALIA

www.campbellsci.com.au • [e-mail]

Campbell Scientific (Beijing) Co., Ltd.

8B16, Floor 8 Tower B, Hanwei Plaza

7 Guanghua Road

Chaoyang, Beijing 100004

P.R. CHINA

www.campbellsci.com • [e-mail]

Campbell Scientific do Brasil Ltda.

Rua Apinagés, nbr. 2018 ─ Perdizes

CEP: 01258-00 ─ São Paulo ─ SP

BRASIL

www.campbellsci.com.br • [e-mail]

Please visit www.campbellsci.com to obtain contact information for your local US or international representative.

Campbell Scientific Canada Corp.

14532 – 131 Avenue NW

Edmonton AB T5L 4X4

CANADA

www.campbellsci.ca • [e-mail]

Campbell Scientific Centro Caribe S.A.

300 N Cementerio, Edificio Breller

Santo Domingo, Heredia 40305

COSTA RICA

www.campbellsci.cc • [e-mail]

Campbell Scientific Ltd.

Campbell Park

80 Hathern Road

Shepshed, Loughborough LE12 9GX

UNITED KINGDOM

www.campbellsci.co.uk • [e-mail]

Campbell Scientific Ltd.

3 Avenue de la Division Leclerc

92160 ANTONY

FRANCE

www.campbellsci.fr • [e-mail]

Campbell Scientific Ltd.

Fahrenheitstraße 13

28359 Bremen

GERMANY

www.campbellsci.de • [e-mail]

Campbell Scientific Spain, S. L.

Avda. Pompeu Fabra 7-9, local 1

08024 Barcelona

SPAIN

www.campbellsci.es • [e-mail]