CTDElectrical Conductivity,

Temperature & Depth Sensor

Operator’s ManualVersion 3

Decagon Devices, Inc.2365 NE Hopkins Court

Pullman WA 99163www.decagon.comsoils@decagon.com

©2012 Decagon Devices, Inc.All rights reserved

CTD SensorTable of Contents

Contents

1. Introduction . . . . . . . . . . . . . . . . . .1Customer Support . . . . . . . . . . . . . . . . . . . . . . . 1Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Warranty Information . . . . . . . . . . . . . . . . . . . . 3Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Measurements . . . . . . . . . . . . . . . 5Water Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Electrical Conductivity . . . . . . . . . . . . . . . . . . . 5

3. Calibration . . . . . . . . . . . . . . . . . . 7

4. Connecting Sensors . . . . . . . . . . . 8Connecting to an Em50 Series logger . . . . . . . 8

3.5mm Stereo Plug Wiring . . . . . . . . . . . . . . . . 9Connecting to a Non-Decagon Logger . . . . . . 9

Pigtail End Wiring . . . . . . . . . . . . . . . . . . . . . . 10

5. Communication . . . . . . . . . . . . . .12Decagon Serial String . . . . . . . . . . . . . . . . . . . 12SDI-12 communication . . . . . . . . . . . . . . . . . . 13

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CTD SensorTable of Contents

SDI-12 commands . . . . . . . . . . . . . . . . . . . . . 13SDI-12 sensor bus . . . . . . . . . . . . . . . . . . . . . . 13SDI-12 address . . . . . . . . . . . . . . . . . . . . . . . . 14Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Installation . . . . . . . . . . . . . . . . .16Proper well installation . . . . . . . . . . . . . . . . . . 16Down-well Sensor Installation . . . . . . . . . . . . 16Refilling the Decagon CTD Sensor . . . . . . . . 17EC Sensor Cleaning . . . . . . . . . . . . . . . . . . . . 18

Cleaning Method . . . . . . . . . . . . . . . . . . . . . . . 18Literature cited . . . . . . . . . . . . . . . . . . . . . . . . . 18

7. Troubleshooting . . . . . . . . . . . . .19

Declaration of Conformity . . . . . . 20

ii

CTD Sensor1. Introduction

1. IntroductionThe Decagon CTD sensor is designed to measure waterdepth, electrical conductivity, and temperature of groundwateror surface water. Using a vented differential pressure trans-ducer, it measures the pressure being applied by the water col-umn to determine water depth. A thermistor in thermalcontact with the probe provides water temperature, while thescrews on the surface of the sensor form a four-electrodearray to measure electrical conductivity. This manual isdesigned to help you understand the sensor’s features and howto use this device successfully.

Customer SupportIf you ever need assistance with your CTD, or if you just havequestions or feedback, there are several ways to contact us.Customer service representatives are available to speak withyou Monday thru Friday, between 7am and 5pm Pacific time.

NOTE: If you purchased your CTD through a distributor,please contact them for assistance.

E-mail: support@decagon.com or sales@decagon.com

Phone:1-509-332-5600

Fax: 1-509-332-5158

If contacting us by email or fax, please include as part of yourmessage your instrument’s serial number, your name, address,and phone.

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CTD Sensor1. Introduction

SpecificationsWater Depth

Accuracy: 0.2 % of f.s.Resolution: 1 mmRange: 0 to 3500 mm

TemperatureAccuracy: ±1°CResolution: 0.1°CRange: -40°C to +50°C*

*If water freezes in the CTD sensor pressure transducer cavity, the pres-sure transducer will be permanently and catastrophically damaged by theice formation. If the sensor is in water, it must not be allowed to experi-ence temperatures below 0° C.

Bulk Electrical ConductivityAccuracy: ±0.01 dS/m or ±10% (whichever is greater)Resolution: 0.001 dS/mRange: 0 to 120 dS/m (bulk)

GeneralDimensions: 9 cm (1) x 3.4 cm (w) Measurement Time: 300 ms (milliseconds)Power Requirements: 3.6 - 15 VDC, 0.03 mA quiescent, 0.5 mA during 300 ms measurementOutput: Serial (TTL), 3.6 voltage levels or SDI-12Operating Temperature: -40 to 50 °C

Connector types: 3.5 mm (stereo) plug or stripped & tinned lead wires (Pigtail)Cable Length: 10m standard; custom cable length available upon request

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CTD Sensor1. Introduction

Datalogger Compatibility (not exclusive): Decagon: Em50, Em50R, Em50G Campbell Scientific: Loggers with serial I/O including CR10X, CR23X, any CRBasic type logger (CR850, 1000, 3000, etc.) Other: Any data acquisition system capable of 3.6 - 15V excitation and serial or SDI-12 communication.Handheld Reader Compatibility: ProCheck (rev 1.34+)Software Compatibility: ECH2O Utility (rev 1.64+ ), DataTrac 3 (rev 3.4+)

Warranty InformationAll Decagon products have a 30-day satisfaction guaranteeand a one-year warranty.

Seller’s LiabilitySeller warrants new equipment of its own manufacture againstdefective workmanship and materials for a period of one year fromdate of receipt of equipment (the results of ordinary wear and tear,neglect, misuse, accident and excessive deterioration due to corro-sion from any cause are not to be considered a defect); but Seller’sliability for defective parts shall in no event exceed the furnishingof replacement parts F.O.B. the factory where originally manufac-tured. Material and equipment covered hereby which is not manu-factured by Seller shall be covered only by the warranty of itsmanufacturer. Seller shall not be liable to Buyer for loss, damage orinjuries to persons (including death), or to property or things ofwhatsoever kind (including, but not without limitation, loss ofanticipated profits), occasioned by or arising out of the installation,operation, use, misuse, nonuse, repair, or replacement of said mate-rial and equipment, or out of the use of any method or process forwhich the same may be employed. The use of this equipment con-stitutes Buyer’s acceptance of the terms set forth in this warranty.

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CTD Sensor1. Introduction

There are no understandings, representations, or warranties of anykind, express, implied, statutory or otherwise (including, but with-out limitation, the implied warranties of merchantability and fitnessfor a particular purpose), not expressly set forth herein.

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CTD Sensor2. Measurements

2. Measurements

Water DepthThe CTD sensor uses a differential pressure transducer tomeasure the pressure being applied by the water columnabove the sensor. A direct relationship between pressure andwater depth is used by the sensor to output water depth. Thereference port of the pressure transducer is vented throughthe cable to atmospheric pressure, so no reference barometricpressure is required. A porous Teflon vent near the datalog-ger end of the cable provides the reference. The Teflon keepsliquid water out of the cable, but allows air to enter and leave.This vent must be kept open to the same atmospheric pres-sure that is applied to the water whose depth is being mea-sured. Since the cable is conducting reference air between thesensor and the atmosphere, it is extremely important that thecable be protected from any damage that would allow water toenter.

TemperatureA thermistor near the electrical conductivity sensor senses thetemperature of the water. This temperature is used to adjustthe EC measurements to their 25°C value, and provides thetemperature output for the data stream.

Electrical ConductivityElectrical conductivity (EC) is used to measure the concentra-tion of salts in the water and also gives information about dis-solved solids. EC is measured by applying an alternating

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CTD Sensor2. Measurements

electrical current to two electrodes, measuring the currentflow through those electrodes, and measuring voltage dropwith a separate set of electrodes. The conductance is the ratioof current to voltage. Conductivity is conductance multipliedby a cell constant which is obtained using conductivity stan-dards. It is important to realize that a 4 electrode sensor willgive unpredictable readings in air because there will be no con-nection between the voltage and current electrodes.

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CTD Sensor3. Calibration

3. Calibration

The water depth and EC sensors are calibrated at the factory,and calibration values are stored internally in flash memory.The depth sensor is calibrated in known depths of water. TheEC sensor is calibrated using KCl solutions of known concen-tration.

The following table relates electrical conductivity at 25°C toconcentration for various concentrations of KCl. Perfor-mance of the CTD EC sensor can be verified using these solu-tions. The values output from the CTD Sensor are internallycorrected to 25°C.

Electrical conductivity of KCl solutions for testing CTD cali-brations.

Electrical Conductivity (S/cm)

g KCl per kg of distilled water

100 0.0446

200 0.0930

500 0.2456

1000 0.5120

2000 1.0673

5000 2.8186

10,000 5.8758

20,000 12.2490

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CTD Sensor4. Connecting Sensors

4. Connecting Sensors

The Decagon CTD Sensor was designed to work most effi-ciently with Decagon's Em50, Em50R, Em50G dataloggers,or our ProCheck handheld reader. The standard sensor (with3.5 mm stereo connector) quickly connects to and is easilyconfigured within a Decagon logger or ProCheck.

The Decagon CTD Sensor incorporates several features thatalso make it an excellent sensor for use with third party log-gers. The sensor may be purchased with stripped and tinnedwires (pigtail) for terminal connections. Visit www.deca-gon.com/support/literature to get extensive directions onhow to integrate the CTD Sensor into third party loggers.

Decagon CTD Sensor comes standard with a 10 meter cable.Sensors may be purchased with custom cable lengths for anadditional fee (on a per-meter basis). Decagon has tested itsdigital sensors successfully up to 1000 meters (3200 ft). Thisoption eliminates the need for splicing the cable (a possiblefailure point).

Connecting to an Em50 Series loggerThe Decagon CTD Sensor has been designed to work specifi-cally with Em50 series data loggers. Simply plug the 3.5mm"stereo" connector directly into one of the five sensor ports.

The next step is to configure your logger port for the Deca-gon CTD Sensor and set the measurement interval. This maybe done using either ECH2O Utility or ECH2O Utility Mobile

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CTD Sensor4. Connecting Sensors

(see respective manuals). Please check your software versionto ensure it will support the Decagon CTD Sensor. To updateyour software to the latest version, please visit Decagon's soft-ware and firmware download site: www.decagon.com/sup-port/downloads.

The following firmware and software supports the DecagonCTD Sensor:Em50 Firmware version 2.09 or greaterECH2O Utility 1.64 or greaterECH2O DataTrac 3.4 or greater

To download data from the logger to your computer, you willneed to use the ECH2O Utility, ECH2O DataTrac or a termi-nal program on your computer.

3.5mm Stereo Plug Wiring

Connecting to a Non-Decagon LoggerThe Decagon CTD Sensor may be purchased for use withnon-Decagon dataloggers. These sensors typically come pre-configured with stripped and tinned (pigtail) lead wires for usewith screw terminals. Refer to your logger manual for details

Digital out

Ground Excitation

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CTD Sensor4. Connecting Sensors

on wiring. Our integrator's guide gives detailed instructions onconnecting the CTD Sensor to non-Decagon loggers. Pleasevisit www.decagon.com/support/literature for the completeintegrator's guide.

Pigtail End Wiring

Connect the wires to the data logger as shown, with the sup-ply wire (white) connected to the excitation (3.6 - 15 volts), thedigital out wire (red) to a digital input, the black ground wireto analog ground and the bare ground wire to shield or earthground.

Analog out (Red)

Ground (Bare)

Excitation (White)Sensor cable

Ground (Black)

Switched3-15V DC

G

Supply Digitalout Ground

Datalogger

Digital In

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CTD Sensor4. Connecting Sensors

If your Decagon CTD Sensor is equipped with the standard3.5mm plug, and you wish to connect it to a non-Decagondatalogger, you have two options. First, you can clip off theplug on the sensor cable, strip and tin the wires, and wire itdirectly into the datalogger. This has the advantage of creatinga direct connection with no chance of the sensor becomingun-plugged; however, it then cannot be easily used in thefuture with a Decagon readout unit or datalogger.

The other option is to obtain an adapter cable from Decagon.The 3-wire sensor adapter cable has a connector for the sen-sor jack on one end, and three wires on the other end for con-nection to a datalogger (this type of wire is often referred to asa "pigtail adapter"). Both the stripped and tinned adapter cablewires have the same termination as seen above; the white wireis excitation, red is output, and the bare and black wires areground.

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CTD Sensor5. Communication

5. Communication

The Decagon CTD sensor can communicate using two differ-ent methods, Decagon serial stream or SDI-12 communica-tion protocol. In this chapter we will briefly discuss thespecifics of each of these communication methods. Pleasevisit www.decagon.com/support/literature for the completeintegrator's guide, which gives more detailed explanations andinstructions.

Decagon Serial StringWhen excitation voltage is applied, the Decagon CTD sensormakes a measurement. Within about 140 ms of excitationthree measurement values are transmitted to the data logger asa serial stream of ASCII characters. The serial out is 1200baud asynchronous with 8 data bits, no parity, and one stopbit. The voltage levels are 0-3.6V and the logic levels are TTL(active low). The power must be removed and reapplied for anew set of values to be transmitted. The ASCII stream con-tains 3 numbers separated by spaces. The first number iswater depth in mm, the second number is temperature in °Cwith a resolution of 0.1 °C, and the third number is EC in dS/m, with a resolution of 1 dS/m. A carriage return follows thethree numbers, then the character 't', indicating that this is aCTD sensor, then a checksum character, and finally a carriagereturn and line feed.

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CTD Sensor5. Communication

SDI-12 communicationThe CTD Sensor can also communicate using SDI-12 proto-col, a three-wire interface where all sensors are powered(white wire), grounded (bare wire and black wire), and com-municate (red wire) on shared nodes (for more informationon the SDI-12 protocol, visit www.sdi-12.org). Below is abrief description of SDI-12 for communication. If you planon using SDI-12 for communication with the CTD Sensor,please see our integrator's guide at www.decagon.com/sup-port/literature for detailed instructions.

SDI-12 commandsFollowing are SDI-12 commands that the CTD Sensorresponds to. The sensor address is shown as 'a'. If a '?' is sub-stituted for 'a' all addresses respond.

SDI-12 sensor busUp to 62 sensors can be connected to the same 12 V supplyand communication port on a datalogger. This simplifies wir-ing because no multiplexer is necessary. However, one sensorproblem can bring down the entire array (through a short cir-

Send Identification aI! a13DECAGON CTD 316<CR><LF>

Change Address aAb! b<CR><LF> (b is new address)

Address Query ?! a<CR><LF>

Start Measurement aM! 00013<CR><LF>

Send Data aD0! a+9+22.2+0<CR><LF> (3 values)

Measure & Send Data

aR0! a 0+9+22.2+77<CR><LF> (3 values)

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CTD Sensor5. Communication

cuit or incorrect address settings). If you use an SDI-12 sen-sor bus we recommend that you make an independentjunction box with wire harnesses where all sensor wires attachto lugs so sensors can be disconnected individually if a prob-lem arises. A single three-wire cable can be run from the junc-tion box to the datalogger.

SDI-12 addressThe SDI-12 protocol requires that all sensors have a uniqueaddress. CTD Sensors come from the factory with an SDI-12address of 0. To add more than one SDI-12 sensor to a sys-tem, the sensor address must be changed. Address optionsinclude {0…9, A…Z, a…z}. The best and easiest way tochange an address is to use Decagon's ProCheck (if the optionis not available on your ProCheck, please upgrade to the latestversion of firmware). SDI-12 addressing can be accessed inthe "CONFIG" menu by selecting "SDI-12 Address."Addresses may then be changed by simply pressing the up ordown arrows until you see the desired address and pushing"Enter."

The SDI-12 communication protocol is supported by Camp-bell Scientific dataloggers like the CR10X, CR200, CR1000,CR3000, etc. Direct SDI-12 communication is supported inthe "Terminal Emulator" mode under the "Tools" menu onthe "Connect" screen. Detailed information on setting theaddress using CSI dataloggers can be found on our website athttp://www.decagon.com/support/downloads.

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CTD Sensor5. Communication

PowerThe sensor can be powered using any voltage from 3.6 to 15VDC, but 12 V is optimal. The CTD sensor is an extremelylow power sensor. When continuously powered, but notmaking a measurement or communicating, it uses 30A.When using the sensor as part of an SDI-12 bus, it is recom-mended that the sensors be excited continuously to avoidissues with initial sensor startup interfering with the SDI-12communications.

ReadingAn example program from Edlog and CRBasic can be foundin our software section online at http://www.decagon.com/support/downloads. As with the Decagon Serial String, thewater depth is the first number output by the sensor, in mm.The second number is temperature in Celsius. The third num-ber is electrical conductivity, in S/cm.

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CTD Sensor6. Installation

6. Installation

The Decagon CTD Sensor is designed to be installed in wells3.5 cm diameter or larger. It is designed for use in groundwa-ter monitoring wells or piezometers, surface water monitoring,and wetland monitoring. It is important that properlydesigned wells are used in order to obtain accurate data as wellas for proper sensor operation.

Proper well installation Hydrology studies using monitoring wells or piezometers areonly as good as the wells that are installed no matter what typeof sensor is used. Well design depends on the desired mea-surement, whether it is groundwater flow, quality, level, orpressure head. To learn about how to properly install a moni-toring well or piezometer it is recommended that you read"Installing Monitoring Wells in Soils" published by the USDA-NRCS (Sprecher, S.W. 2008). This publication can be found atthe following link: www.decagon.com/wellinstallation.

Down-well Sensor InstallationThe Decagon CTD sensor can be installed down a well bysuspending the sensor at the desired depth in the well. Whendeciding on how deep to install the CTD sensor several thingsneed to be considered. It is best to keep the sensor underwater at all times in order to ensure measurements are contin-uous as well as to prevent air from entering the measurementtube. Air in the tube can result in reduced accuracy of the sen-sor. If this does occur, refill the tube following the refill

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CTD Sensor6. Installation

instructions. The range of the sensor also needs to be consid-ered. The maximum measurement depth of the CTD sensoris 3.5 m. If the water level rises above this level you will notget accurate water depth readings and run the risk of poten-tially damaging the sensor.

If water freezes in the CTD sensor pressure transducer cavity,the pressure transducer will be permanently and catastrophi-cally damaged by the ice formation. If the sensor is in water, itmust not be allowed to experience temperatures below 0° C.This will generally not be a problem in deep underground wellinstallations, but might be an issue in surface water wells andunderground installations above the frost depth. Exposingthe CTD sensor to freezing temperatures with water in thepressure transducer cavity will void the sensor warranty.

Refilling the Decagon CTD SensorThe CTD Sensor pressure transducer is connected to thewater column through a small tube extending from the bot-tom of the CTD sensor assembly. In order to maintain thebest possible accuracy the tube must be filled with water andfree of air. The tube must be filled with water before insertioninto a well. Warning: If this tube drains it will need to berefilled in order to maintain accuracy. A syringe and ahypodermic needle are included with the sensor for refilling.Below are the instructions for refilling the CTD sensor:

1. Fill syringe with water and remove air.2. Attach needle to tip of syringe.3. Insert needle into the tube. Ensure that the needle is com-

pletely inserted into the tube. There is a lip that the needle can get caught on. Work the needle around until you feel

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CTD Sensor6. Installation

it move past the lip. You will not damage the pressure transducer by inserting the needle.

4. Orient the sensor with the end of the tube facing upwards.5. Begin filling the tube with water until you no longer see air

coming out of the end of the tube.6. Continue filling the tube with water as you remove the nee-

dle to make sure no air is introduced. This illustration on the next page shows how to properly refill the Decagon CTD Sensor. When inserting the hypodermic needle into the tube it is important to insure you get it past the lip of the pressure transducer.

EC Sensor CleaningA four electrode conductivity measurement is less sensitive tosensor fouling than a two electrode sensor, but contaminationof the electrodes can still affect the measurement. The elec-trodes are stainless steel.

Cleaning Method1. Insert swab into slot on side of sensor housing. Rub the

screws vigorously with Swab. 2. Rinse the sensor and screws thoroughly with tap or DI

water.Be sure not to touch the screws with an ungloved hand or tocontact them with any source of oil or other non-conductingresidue.

Literature citedSprecher, S.W. 2008. Installing monitoring wells in soils (Version1.0). National Soil Survey Center, Natural Resources Conserva-tion Service, USDA, Lincoln, NE.

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CTD Sensor7. Troubleshooting

7. Troubleshooting

If you encounter problems with the CTD sensor, they mostlikely will manifest themselves in the form of incorrect orerroneous readings. Before contacting Decagon about thesensor, do the following:

Data Logger 1. Check to make sure the connections to the data logger are

both correct and secure. 2. Ensure that your data logger's batteries are not dead or

weakened. 3. Check the configuration of your data logger in ECH2O

Utility or DataTrac to make sure you have selected CTD Sensor.

4. Ensure that you are using the most up to date software and firmware. You can find the most up to date version of the software and firmware at www.decagon.com/support.

Sensors 1. Ensure that your sensors are installed according to the

"Installation" section of this manual. 2. Check sensor cables for nicks or cuts that could cause a

malfunction. 3. Check the pressure transducer tube to ensure that it is not

clogged or damaged.

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CTD SensorDeclaration of Conformity

Declaration of Conformity

Application of Council Directive:89/336/EE6

Standards to Which Conformity EN61326 : 1998is Declared: EN51022 : 1998

Manufacturer’s Name: Decagon Devices, Inc. 2365 NE Hopkins Court Pullman, WA 99163 USA

Type of Equipment: Water Depth Sensor

Model Number: CTD

Year of First Manufacture: 2012

This is to certify that the CTD, manufactured by DecagonDevices, Inc., a corporation based in Pullman, Washington,USA meet or exceed the standards for CE compliance as perthe Council Directives noted above. All instruments are builtat the factory at Decagon and pertinent testing documentationis freely available for verification.

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CTD SensorIndex

Index

CCalibration 7Cleaning Method 18Customer support 1

DDeclaration of conformity 20

EElectrical conductivity (EC) 5E-mail 1

FFax 1

IInstallation 16

LLiability 3

PPower requirements 2

RRefill sensor 17

SSDI-12 communication 13Seller’s liability 3Sensor cleaning 18

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CTD SensorIndex

Serial String 12Specifications 2

TTelephone 1Temperature 5

WWarranty 3Water depth 5

22