User Manual: True TDR-315
Contents
1. 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 21 Address Query a Note only one device can be connected to the SDI 12 port when this command is used a lt CR gt lt LF gt Acknowledge a a lt CR gt lt LF gt Active Change Address b b lt CR gt lt LF gt Command Function Sensor Response 21 Address Query a Note only one device can be connected to the SDI 12 port when this CO aia command is used a lt CR gt lt LF gt Acknowledge a a lt CR gt lt LF gt aC Start Concurrent a00305 lt CR gt lt LF gt Measurement Measurement takes 3 seconds 5 values are returned Start Concurrent Measurement Request CRC Start Additional a00000 lt CR gt lt LF gt Concurrent No data to be provided Measurement Start Additional a00000 lt CR gt lt LF gt Concurrent No data to be provided Measurement Request CRC Get First 4 Data a VW V TT T PP P EEEE CCCC lt CR gt lt LF gt Items in response where a device address to aMeasurement VW V volumetric water content command VWC TT T soil temperature degrees C Soil Temp Soil PP P soil permittivity Permittivity Soil EEEE soil bulk EC in uS cm EC CCCC temperature corrected bulk EC in US cm Get the response from a Verify command Data buffer Populated by Command Description Response to aDO No data2. generating command has been issued or a command was aborted Data buffer is none abort empty a lt CR gt lt LF gt a VVV V TT T PP P EEEE CCCC lt CR gt lt LF gt where VVV V Volumetric water TT T Temperature C PP P Permittivity no units aM Fill data buffer with standard measurement EEEE Bulk electrical conductivity uS cm CCCC Temperature corrected BEC uS cm Fill data buffer with standard measurement concurrently with other sensors aC Same as aM a VVV V TT T PP P EEEE CCCC lt CR gt lt LF gt where VVV V Volumetric water TT T Temperature C PP P Permittivity no units EEEE Bulk electrical conductivity uS cm Fill data buffer with standard measurement and CRC check in the data response CCCC Temperature corrected BEC uS cm Fill data buffer with standard measurement concurrently with other sensors and with a CRC check in the data response Same data as aMC AAA ee aM1 Same as aM zz Fill data buffer with standard measurements concurrently with other sensors a l aC1 Same as above Same as aMC except Bulk electrical Fill data buffer with standard measurement and CRC check in the data response conductivity EEEE is normalized to 25 C Fill data buffer with standard measurement concurrently with other sensors and with a CRC check in the data response Same as above av Verify Sensor operation This command produces the same result as the aM Command Sa
3. 8 887 6368 User Manual TDR 315 July 2015 Rev 1c 16
4. A Acclima User Manual True TDR 315 Volumetric Water Content Temperature Permittivity Bulk Electrical Conductivity Temperature Corrected BEC Part Number ACC TDR 315 TDR 315 Soil Water Content BECA Temperature u aa Table of Contents Product Introduction Installation and Connection Operation Command Summary Command Reference Setting the Address Making Measurements with the TDR Sensor Non Concurrent Measurement Concurrent Measurement Data Retrieval Examples of Using the TDR Sensor Accessing the TDR 315 Waveform Troubleshooting Specifications Notes PRR NNO0 0 0000 O1 0101 P W gt N Notices 2015 All rights reserved by Acclima Inc The Acclima True TDR 315 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 July 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 publish
5. Measurement Command M The second is the Concurrent Measurement Command C The sensor responds to both of 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 TDR 315 SDI 12 sensor the number of data items is 5 7 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 Service Request or after the indicated time has expired whichever occurs first The 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 ba
6. 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 True TDR 315 sensor implements commands that comply with versions 1 0 1 1 1 2 and 1 3 of the SDI 12 specifications All commands required for full compliance of the version 1 3 specifications are implemented in the TDR 315 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 required by the SDI 12 specification There is no response to them Additional Extended Commands that are not enumerated here are incorporated by Acclima for digitized waveform dumps
7. OT e 8 mn un ke LLJ ab Q Y lt a x L A Gan Ww a p lt oO r b p m O A o g lt b o 0 50 1000 2000 3000 4000 5000 6000 NaCl concentration ppm Troubleshooting 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 Insure that there are no address conflicts Disconnect data parity errors all other 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 9 cm Weight with 10 meter cable 440g Composition Type 304 stainless steel epoxy polyethylene insulation Cable 3 conductor 22 Ga Water proof and UV resistant PVC jacket 10 meters Enviro
8. as 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 50035 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 003 3 seconds then finished with the number of data items that will be returned with each measurement request 5 Every response from the sensor is terminated with a carriage return and line feed characters After the sensor has finished its measurements it transmits a service request to the recorder 8 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 1600 1700 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 record
9. ed on our website or when deemed necessary by Acclima Acclima reserves the right to change any specification s without notice You can learn more about Acclima s products at www acclima com or by emailing your questions to sales acclima com Product Introduction The Acclima TDR 315 is a genuine Time Domain Reflectometer complete with an integrated 150ps rise time step function generator a 15 cm waveguide a 5ps resolution waveform digitizer and a precision time base that measures waveform temporal features as short as 5ps and as long as 20ns The built in algorithms in its floating point micro processor search the digitized waveform and capture the incident and reflected wave time ordinates and from these the permittivity of the medium surrounding the waveguide is calculated using the first principals based EM propagation equation From that a proprietary dielectric mixing model calculates the water content of the medium The mixing model matches the Topp Equation very closely up to around 46 water content but behaves in a more representative fashion up to 100 water content providing the assurance that the TDR 315 can be used in all applications including slurries where water content may reach 100 A precision thermistor is thermally coupled to the waveguide and reports medium temperature with 0 2 degree C accuracy The waveguide electrodes are also used to measure the Electrical Conductivity of the medium This property is also repor
10. er 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 lt CR gt lt LF gt 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 recorder 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 exper
11. iences 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 lt CR gt lt LF gt 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 are 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 lt CR gt lt LF gt 4 The recorder issue a read data command DO aDO Accessing the TDR 315 Waveform The TDR 315 was developed as a Time Domain soil permittivity and moisture content measuring device but has application in many other research disciplines TDR waveforms contain much more data than soil moisture content Soil electrical conductivity can be accurately determined from them Also other properties of the soil such as porosity and particle size have an influence on the characteristics of the waveform hence it is appropriate to u
12. installed in the root zone without incurring root and compaction disturbances and can remain there indefinitely Soil tillage can be performed over the installation as long as the tillage depth does not reach within 2 inches of the sensor 3 Power consumption of each TDR sensor is reasonably low allowing for low cost alkaline battery operation or rechargeable batteries coupled with a solar panel 4 The cost of the TRD 315 is about 5 of the cost of a conventional TDR set capable of equivalent performance 3 All measurements are performed automatically without the need for setting up the console cable probe PC and software The first principles based calculations are also performed automatically and the multiple data points are delivered within 2 seconds in industry standard metrics The advantage of the TDR 315 over capacitive impedance and frequency domain sensors is one that is best explained by the fundamental physics behind the measurement True Time Domain based sensors are designed to derive medium permittivity based on TEMPORAL measurements only Voltages currents impedances thresholds etc are avoided in the gathering of the physical properties from which permittivity is calculated True Time Domain sensors are based in Ampere s and Faraday s Laws in a form known as the propagation equation This equation 3 states that if the propagation speed can be accurately measured then the permittivity can be accurately known e
13. me data as aM aD1 No data for this Command Function Sensor Response aM aM aM9 aMC1 aMC9 Acknowledge Active Send Identification Start Non Concurrent Measurement Start Non Concurrent Measurement Request CRC Additional Measurements Additional Measurements Request CRC Continuous Measurement Start Verification Address Query a Note only one device can be connected to the SDI 12 port when this command is used a lt CR gt lt LF gt a a lt CR gt lt LF gt aSSVVVVVVPPPPPPcccxx xx al3Acclima TDR315 1 3xx xx lt CR gt lt LF gt 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 13 ch a0035 lt CR gt lt LF gt Measurement takes 3 seconds and returns 5 values a lt CR gt lt LF gt Sensor returns a Service Request after measurement is made The data can be retrieved using a aDO command a0000 lt CR gt lt LF gt The SDI 12 sensor does not require the use of this command If the command is received the sensor reports no data to be returned a lt CR gt lt LF gt The SDI 12 sensor does not use this command and responds with no data a0031 lt CR gt lt LF gt One data item will be returned after 3 seconds The data item will be the verification code requested by this command a lt CR gt lt LF gt The sensor returns a service request after the measurement is made The data can be re
14. nmental Characteristics Operating Temp Range 20 C to 50 C 12 Storage Temp Range 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 20 Cto 75C O to 100 0 1 VWC 2 typical 1 of full scale 1 C 50C 2 of full scale O to 5 dS m BEC 0 2 COto 50C 2 5 100uS cm O to 10 000 uS cm BEC Waveform Digitizing Time Domain Reflectometer 200 Giga sample sec 5 ps 1 5 mm in air 0 16 mm in water 15 cm Modified Dielectric Mixing Model 3 5 GHz SDI 12 Revision 1 3 60 meters 50 6 15 VDC 31 uA typical 35 uA max 4 mA typical 5 mA max 425 ms total for each read cycle 180 mA at 12 VDC input 300 mA at 6 VDC input 2 2 seconds 13 Notes 15 ee Acclima Acclima Inc 1763 W Marcon Ln Ste 175 Meridian Idaho USA 83642 www acclima com toll free 866 887 1470 fax 20
15. quire successive points and thus get an entire waveform using this command The plot on the next page shows TDR waveforms gathered from several different media The text over the waveforms Shows the readings that were taken by the TDR 315 for each medium 10 r Tr lt SS SS eee ee ore Oe eee ees or A er oe eee ere oe eee eee oe a 7 nm 1 I I I I T I I I J im GER ER I I T I I 333 uS cm water VWC __ R E bE F E b b A A A ee 0 2000 4000 6000 3 000 10 000 12000 14000 16 000 18 000 20 0 The EC measuring capability of the TDR 315 is based on Giese and Tiemann method for measuring EC with conventional TDR equipment It provides high accuracy EC readings over a very wide range of conductivity The chart on the next page shows the composite response from 20 TDR 315s compared to carefully prepared NaCl EC solutions at 25C The tightness of the response among the 20 sensors at each measured point was less than 1 rms deviation from the mean The absolute accuracy of the mean reading at each point is shown on the plot with the X marks Note that the error of the mean reading relative to the standard is less than 1 5 from O to about 6000 uS cm At 9000 uS cm the error is 2 4 11 2 50 2 00 N N N N N ex 1 50 x N gt 1 00 Actual EC x e e EC READING Percent Error 0 50 x ERROR 0 00 P
16. se TDR waveforms in characterizing these additional properties The spectral content of the TDR 315 waveform is well preserved since there is no low pass filter between the waveguide and the digitizer This provides an opportunity for high quality frequency domain analysis of the waveform that can yield additional characteristics of the medium In order to Support research using these enabling tools we have provided an extended SDI12 command that allows you to gather TDR waveforms from your subject media The command is aXAtttt Where a is the device address XA is the extended command code tttt is a hexadecimal time ordinate in 5ps units and l is the command terminator This command returns a hexadecimal string which represents the waveform amplitude at the tttt time ordinate For Example If the amplitude of the waveform at 1100ps is desired it is necessary to convert the time ordinate to 5ps units or 220 This number is then converted to hexadecimal 220 decimal ODC hex If the device address is 1 then the following command is sent to the TDR 315 1XAODC The sensor returns the string 18E6 lt CR gt lt LF gt The first character 1 of the string is the device address The other characters are the waveform amplitude at 1100ps Note that the amplitude is normalized to a 12 bit binary number and must be divided by 4096 The return amplitude is then 8E6 hex 4096 or 2278 4096 0 556 You can write your own code to ac
17. sic 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 ie used to retrieve them Data Item Request Command Response Units Example Volumetric Water Content aDO 25 03 2503 03 a eg Bulk Relative Permittivty abor 3213 Soil Electric Conductivity aDor 1600 uS om Temperature Corrected BEC D0 1700 us em The format of the returned data is a t25 03 32 16 32 13 1600 lt CR gt lt LF gt Note that the returned data is always preceded by the 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 TDR 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 h
18. ted along with water content permittivity and temperature For researchers who wish to perform their own unique analyses and experiments the TDR 315 can export TDR waveforms in csv format The exported waveforms contain rich data relationships that can be used to determine other properties of the medium besides its permittivity and water content The device uses the standard SDI 12 interface Version 1 3 and can be used with any Data Recorder or readout device that supports that standard The integration of the Time Domain Reflectometer into a single package provides several advantages over conventional high performance TDR systems using a mainframe coaxial cable and waveguide probe 1 Conventional TDR systems use a TDR console coupled to a waveguide probe with a coaxial cable An expensive high performance coaxial cable is required to reduce the unwanted reflections from the impedance irregularities within the cable Further the cable acts as a low pass filter that removes information from both the incident and reflected waves The absence of the coaxial cable coupling the TDR electronics to the waveguide of the TDR 315 allows the full bandwidth of the step function generator to be applied to the waveguide and also facilitates an unfiltered capture of the reflected wave 2 Conventional TDR systems cannot be deployed for continuous season long field measurements without risking damage and a nuisance to crop managers The TDR 315 can be completely
19. trieved 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 aAb where a is the present address 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 TDR sensor is responding to its address use the Send Identification command al The SDI 12 sensor will respond with a13Acclima TDR315 1 3xx xx 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 TDR315 represents the sensor model the next three characters report the firmware version of the TDR sensor which is then followed by the serial number 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
20. ven under highly saline conditions That measured permittivity can then be converted to water content through the Topp equation or a suitable dielectric mixing model Using the propagation equation requires taking accurate time measurements on a waveform propagated through the soil This requires very sophisticated electronics and techniques since the time measurements may be only trillionths of a second In fact the TDR 315 can measure time intervals as short as the time it takes light to travel 1 5 mm in air Soil Electrical Conductivity is the killer of credibility in capacitive impedance and frequency domain sensors Although these sensors use widely differing architectures they are all based on deriving permittivity through measuring voltage and current relationships This works well in non conductive soils but when external ions such as salts or fertilizers are present those ions affect internal voltage and current magnitudes and relationships through Gauss Law Many of these sensors attempt to compensate for these EC effects but with marginal results EC is a very strong function of water content and hence compensation of water content requires knowing water content The TDR 315 by passes the effects of Gauss Law by avoiding any dependence upon the measurement of fields and fluxes Only precise time measurements are made Installation and Connection The three wires from the sensor are the SDI 12 connections to the data recorder The white
21. 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 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 SDI 12 Data Recorder Providing 7 15 volts dc to the SDI 12 port V Data G Common 7 Note 12 volts dc is required by the SDI 12 spec Blue wire White wire ll Diagram for a data recorder providing power to the SDI 12 port SDI 12 Data Recorder that does not provide power to the to the SDI 12 port Data G Common Rediwire Bluel wire White wire ll 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 transducer 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
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