SDI-12 Sensor User Manual
Contents
1. 0 16 mm in water 30 cm Modified Dielectric Mixing Model gt 2 GHz SDI 12 Revision 1 3 60 meters 50 4 15 VDC 12 uA typical 15 uA max 2 5 mA typical 4 mA max 425 ms total for each read cycle 30 mA at 12 VDC input 55 mA at 6 VDC input 75 mA at 4 VDC input 450 ms each sensing operation Notes 14 15 yO Acclima Acclima Inc 1763 W Marcon Ln Ste 175 Meridian Idaho USA 83642 www acclima com toll free 866 887 1470 fax 208 887 6368 User Manual SDI 12 Moisture Sensor 6 10 09 Rev 2 162. right to change any specification s without notice You can learn more about Acclima s products at www acclima com or email questions to sales acclima com Product Introduction The Series SDI 12 moisture sensor is a Digital Time Domain Transmissometer that measures the permittivity of soils by determining the propagation time of an electromagnetic wave transmitted along a waveguide through the soil The absolute moisture content of the soil is calculated from the permittivity using the Topp equation The sensor can be commanded to produce both the bulk permittivity and the moisture content of the soil The accuracy and stability of the SDI 12 moisture sensor is obtained through a patented hardware and firmware system that digitizes the return waveform and them uses proprietary digital signal analysis algorithms to extract the real propagation time and distortion parameters of the returned wave High accuracy is achieved over a wide range of soil temperatures and electrical conductivity In the SDI 12 series the resolution of the digitized waveform is 5 picoseconds permitting a small transducer to report very high resolution data From the extracted distortion parameters the transducer calculates and reports the electrical conductivity of the soil The permittivity and soil moisture measurements are compensated for temperature The transducer also reports soil temperature Installation and Connection The three wires from the sensor are th
3. 13 ch aM Start Non a0014 Concurrent Measurement takes 1 second and returns Measurement 4 values aMC Start Non a Concurrent Sensor returns a Service Request after Measurement measurement is made The data can be Request CRC retrieved using a aDO command aM Additional a0000 i Measurements The SDI 12 sensor does not require the aM9 use of this command If the command is aMC1 Additional received the sensor reports no data to be A Measurements returned aMcg Request CRC aRO Continuous a 5 Measurement The SDI 12 sensor does not use this aR9 command and responds with no data Command Function Sensor Response av Start a0031 Verification One data item will be returned after 3 seconds The data item will be the verification code requested by this command a The sensor returns a service request after the measurement is made The data can be retrieved using a aDO Command Setting the Address If more than one device is wired to the SDI 12 port you will need to assure that they all are set up with unique addresses If you are not sure you can connect them one at a time and use the Address Query command to read the addresses Only one device can be connected to the SDI 12 port when using this command The device will respond with its address To change the address of a device use the Change Address command The syntax is aAn where a is the present addre
4. A Accl ma User Manual SDI 12 Soil Moisture Digital TDT Sensor with SDI 12 Interface Part Number ACC SEN SDI Acclima Inc 1763 W Marcon Ln Ste 175 Meridian Idaho USA 83642 www acclima com Table of Contents Introduction Firmware and Manual Disclaimer Product Introduction Installation and Connection Operation Command Summary Command Reference Setting the Address Making Measurements with the SDI 12 Sensor Non Concurrent Measurement Concurrent Measurement Examples of Using the Sensor Troubleshooting Specifications Notes 0909 0 12 12 14 Introduction NOTE The Acclima Series SDI 12 Soil Moisture Sensor uses the industry standard SDI 12 interface for communicating with a Data Recorder or other SDI 12 equipped controller device The SDI 12 communications standard is digital serial data communications hardware and protocol standard based on 1200 baud ASCII character communications over the three wire BUS The SDI 12 Series is compliant with Version 1 3 of the SDI 12 standard Version 1 3 is the latest standard at the time of this printing March 2015 Firmware and Manual Disclaimer This manual was prepared for the current sensor firmware release at the time of the manual publication The manual has been thoroughly edited and is believed to be reliable Acclima assumes no liability for inaccuracies Errata may be published on our website or when deemed necessary by Acclima Acclima reserves the
5. arriage return and line feed characters After the sensor has finished its measurements it transmits a service request to the recorder 5 lt CR gt lt LF gt The service request is just the address of the sensor The recorder then sends a command to get the first set of data items 5DO The items requested are volumetric water content soil temperature soil permittivity and soil electrical conductivity Upon receiving this command the sensor responds with 5 25 03 32 16 32 13 1 6 lt CR gt lt LF gt The first 5 is the sensor address The remaining string contains the requested data items each preceded by a or sign Example 2 Reading sensor using concurrent commands This second example shows how a data recorder would obtain the same 4 data items from a sensor using concurrent commands In this example the data recorder will operate in the concurrent mode that is it will be free to service other sensors while the sensor with address 5 is making its measurements Concurrent measurement commands use C instead of M in the command Thus the command to start concurrent measurement is 5C The sensor immediately responds with 500104 10 With concurrent commands the sensor does not provide a service request after the measurements have been made The recorder relies on the timing information provided by the sensor and will not request data until the time interval has expired in this case 1 second The rec
6. e Request or after the indicated time has expired whichever occurs first The 8 a Service Request code is simply the address of the sensor a followed by carriage return and line feed characters Concurrent Measurement When using the concurrent measurement command the sensor does not return a service request when the data is ready for retrieval The recorder is allowed to perform other communications to other devices while the sensor is making the measurement and preparing the data Then when the recorder is available and the indicated measurement time has elapsed the recorder retrieves the data Data Retrieval To retrieve the requested measurement data the recorder sends a DO command to the sensor The DO command returns the basic 4 measurement items Volumetric Water Content Soil Temperature Soil Relative Permittivity and Soil Electrical Conductivity The syntax for the command is aDO where a is the sensor address Below is a table showing the data available from the SDI 12 sensor and the commands used to retrieve them Data Item Request Command Response Units Example Volumetric Water Content aDO 25 03 Soil Temperature aDO 32 16 C Bulk Relative Permittivity aDO 32 13 Soil Electric Conductivity aDO 1 6 dS m The format ofthe returned data is a 25 03 32 16 32 13 1 6 lt CR gt lt LF gt Note that the returned data is always preceded by th
7. e SDI 12 connections to the data recorder The white wire is the common return or ground terminal on the data recorder SDI 12 connector block The red wire is the power line and must attach to the power supply line on the data recorder SDI 12 connector block or to the positive side of an external power source The blue wire is the bidirectional half duplex data line that attaches to the serial data line 4 on the data recorder SDI 12 connector block If a power supply is used that is external to the data recorder then the negative side of the power supply must be attached to the ground terminal on the data recorder SDI 12 connector block Diagram for RS232 Serial Port to PC Connection SDI 12 Data Recorder providing 12 volts to SDI 12 port 12 volts as required by V D G COMM the SDI 12 spec The RED sensor can be powered by less in low power BLUE setups situations WHITE Diagram for a data logger providing power to the SDI 12 port 6 to 12 volt SDI 12 Data Recorder that does not Battery supply power to SDI 12 port D G COMM WHITE E RED BU Diagram for the data recorder using an external battery Operation The SDI 12 protocol allows multiple devices to be attached to one SDI 12 port In order for the data recorder and devices to facilitate unambiguous communications each device on the SDI 12 port is given a unique address The default address of the transduce
8. e device address a Each data value is preceded by a sign No units are returned but are assumed known by the user The units are as shown in the table above Each return data string is terminated by carriage return and line feed characters Examples of Using the Sensor Example 1 Reading sensors using non concurrent commands This first example shows how a data recorder would obtain 4 data items from a sensor that has address 5 1 Volumetric Water Content 2 Soil Temperature 3 Soil Permittivity or Dielectric Constant and 4 Soil Electric Conductivity In this example the data recorder will operate in the non concurrent mode that is it will not spend any time with other sensors until this sensor has completed its measurements and has reported them The first command from the data recorder is 5M This command is called the Start Measurement command The 5 in this command is the address of the sensor you wish to respond to the command It will cause the SDI 12 sensor to begin the process of taking a set of measurements The sensor will immediately respond to this command as follows 50014 lt CR gt lt LF gt This response starts with the address of the sensor 5 then continues with the number of seconds that are required to take the readings 001 1 second then finished with the number of data items that will be returned with each measurement request 4 Every response from the sensor is terminated with a c
9. her devices and try to read again Insure that the cable length to the sensor does not exceed 200 feet Specifications Physical Characteristics Dimensions without cable 20 cm x 5 33 cm x 1 5 cm Weight with 3 meter cable 220g Composition Type 304 stainless steel crystalline epoxy Cable polyethylene insulation 3 conductor 18 Ga PE sheath 3 meter Environmental Characteristics 12 a Operating Temp Range Storage Temp Range Lightning amp Surge Protection Operating Characteristics Volumetric Water Content Resolution Absolute VWC Accuracy VWC Temp Stability VWC Soil EC Stability Temp Reporting Accuracy EC Reporting Accuracy Architectural Characteristics Technology Effective Acquisition Bandwidth Propagation Time Resolution Waveform Propagation Resolution Waveguide Length Permittivity to VWC Calculation Propagation Waveform Bandwidth Communications Characteristics Communication Protocol Maximum Cable Length Maximum Devices per Cable Power Characteristics Operating Voltage Range Listening Sleep Mode Current Communications Current Read Moisture Comm Time Moisture Sense Current Moisture Sense Time 1Cto50C 20 Cto 75C 6kV 3kA 8 50us O to 100 0 06 VWC 2 typical 1 of full scale 1 C 50 C 1 of full scale O to 5 dS m BEC 2C Oto 50C 0 2 dS m 0 to 50 dS m BEC Waveform Digitizing Time Domain Transmissometer 200 Giga sample sec 5 ps 1 5 mm in air
10. no response to them Additional Extended Commands that are not innumerate here are incorporated by Acclima for digitized waveform dumps and factory calibration settings and readings Command Reference The table below documents all commands supported by the SDI 12 sensor in alphabetical order Command Function Sensor Response Address Query a Note only one device can be connected to the SDI 12 port when this command is used al Acknowledge a Active aAb Change Address b aC Start Concurrent a00104 Measurement Measurement takes 1 second 4 values are returned acc Start Concurrent Measurement Request CRC Command Function Sensor Response act Start Additional a00000 Concurrent No data to be provided aco Measurement aCC11 Start Additional a00000 Concurrent No data to be provided acc9 Measurement Request CRC aDO Get First 4 Data Asppp ppsTT skk kksee e Items in ppp pp is the water content TT TT is the response to a soil temp C kk kk is the soil relative Measurement permittivity ee e is the soil EC dS m command VWC Soil Temp Soil nta Permittivity Soil n is the verifying results EC Get the response from a Verify command al Send aSSVVVVVVPPPPPPCCCXX XX Identification a13Acclima0030316 2xx xX ss SDI 12 version 1 3 2 ch v Vendor ID Acclima 8 ch p Product ID 6 ch c Product Version 3 ch Xx Xx Serial Number
11. order then requests the four data items exactly in the same manner as with non concurrent readings Data Communication Error Checking So far all Start Measurement commands that we have discussed have requested data wherein no error checking is done to verify the correct reception of the data by the recorder The SDI 12 specification provides for error checking by using an additional command character C with the Start Measurement command Thus when the commands aMC Or acc are transmitted to the sensor the sensor appends a CRC code to the end of the returned data This code is generated from the data in such a manner that if the data changes in the transmission the change can be detected in the recorder If the recorder experiences such corruption in the data it will repeat the data request automatically 3 3 6 Verify Command The SDI 12 specification requires a special command for the purpose of verifying that the sensor is working properly Acclima s implementation of that command is as follows 1 The recorder sends out the verify command aV 2 Upon receiving the verify command the sensor will respond with atttn an where a is the sensor address ttt is the time required to make verification readings and n is the number of data items that will be returned For this command ttt 003 and n 1 3 The sensor takes 3 full sets of readings The corrected propagation times from the three readings a
12. r as shipped from the factory is O zero If this is the only device on the SDI 12 port on the recorder then you may leave the address as O If other devices are connected then you will need to insure that they each have unique addresses Setting the address will be discussed later SDI 12 commands are a concatenation of three fields The first is the device address This is a single character typically in the range of O to 9 but can also use the characters a to z and A to Z The second is the command which may consist of several characters The command characters are always upper case The last is the command terminator which is always an exclamation point Command Summary The SDI 12 sensor implements commands that comply with versions 1 0 1 1 1 2 and 1 3 of the SDI 12 specifications All commands require for full compliance of the version 1 3 specifications are implemented in the SDI 12 sensor However the additional measurements commands in the SDI 12 specification are meaningless to the Acclima SDI 12 sensors since the permittivity moisture conductivity and temperature measurements are all required and all made with every single measurement Hence the response for all of these additional measurements commands is a lt CR gt lt LF gt as required by the SDI 12 specification The sensor ignores unimplemented commands outside those require by the SDI 12 specification There is
13. re saved and compared If any of these propagation times are out range or if they differ by an unacceptable amount an error is acknowledged The sensor then sends out a service request a 4 The recorder issue a read data command DO 11 aDO The sensor responds with verification code Verification Codes Codes lt y Z D Sensor is good VCC or internal voltage test Test temperature sensor to see if too low Test temperature sensor to see if too high TPD Error Span Error Amp Error NI O J A WIN eO Variance Test Troubleshooting Problem Possible Resolution No Data Return Check the sensor connections to the data recorder by the SDI 12 The white wire connects to the SDI 12 port Ground sensor terminal The blue wire connects to the SDI 12 port Data terminal The red wire connects to the SDI 12 port V terminal or to the positive terminal of an external battery If an external battery is used the negative terminal of the battery connects to the ground terminal of the SDI 12 port Unreadable data Insure that there are no address conflicts Disconnect all other devices connected to the recorder Insure that the sensor address is used in the commands you are using Sensor not Check connections communicating Check Voltage Check address Review syntax Unreadable data parity errors Insure that there are no address conflicts Disconnect all ot
14. ss A is the Set Sensor Address command and n is the new address The device will return the new address For example if OA4 Is transmitted the sensor address will be re programmed to 4 and the sensor will return 4 To verify that the SDI 12 sensor is responding to its address use the Send Identification command all The SDI 12 sensor will respond with a13Acclima In the response the a is the device address 13 represents Version 1 3 the SDI 12 standard and the Acclima is the vendor ID Making Measurements with the SDI 12 Sensor There are two commands that cause the SDI 12 sensor to take measurements and store them for subsequent retrieval The first is the Non Concurrent Measurement Command M The second is the Concurrent Measurement Command C The sensor responds to both of an the commands with atttn where a is the sensor address ttt is the number of seconds before the data will be ready and n is the number of data items that will have been prepared For the Acclima SDI 12 sensor the number of data items is 9 Non Concurrent Measurement When using the non concurrent command the recorder waits for the sensor to complete its measurement and then retrieves the result The sensor sends a Service Report code to the recorder after preparing the data so that the recorder will retrieve the data at the appearance of the Servic
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