Delta-T Devices WET150 Скачать руководство пользователя страница 55

Страница: 55 / 72

Technical Reference

⚫

References

•

Topp, G. C., J. L. Davis, A. P Annan (1980).

Electromagnetic determination of

soil water content

Water Resour. Res

(3) 574-582

•

Whalley, W R (1993).

Considerations on the use of time-domain reflectometry

(TDR) for measuring soil moisture content

Journal of Soil Sci.

, 1-9

•

White, I, Knight, J H, Zegelin, S J, and Topp, G C (1994).

Comments on

‘Considerations on the use of time-domain reflectometry (TDR) for measuring
soil water content

’ by W R Whalley

Journal of Soil Sci

, 503-508

•

Roth, C H, Malicki, M A,and Plagge, R. (1992).

Empirical evaluation of the

relationship between soil dielectric constant and volumetric water content as
the basis for calibrating soil moisture measurements

. Journ

al of Soil Sci

1-13

•

Knight, J.H. (1992).

Sensitivity of Time Domain Reflectometry measurements

to lateral variations in soil water content

•

Gregory, A.P., Clark, R.N. (2012) Tables of the Complex Permittivity of
Dielectric Reference Liquids at Frequencies up to 5 GHz.

NPL REPORT

MAT 23.

•

Hilhorst, M.A. (1998)

Dielectric characterisation of soil

Doctoral Thesis

, ISBN

90-5485-810-9, Wageningen Agricultural University, Wageningen, The
Netherlands.

•

Hilhorst, M.A. (2000) A Pore Water Conductivity Sensor.

Soil Science Society

of America Journal. 64

, Issue 6, 1922-1925

•

Hübner,C., Kaatze, U. (2016) Electromagnetic Moisture Measurements.

Universitätsverlag Göttingen.

•

Kaatze, U., Uhlendorf, V. (1981)

The dielectric properties of water at

microwave frequencies.

Zeitschrift für Phys. Chem.,

Neue Folge, Bd. 126, 151-

165.

•

Mualem, Y., Friedman, S.P. (1991)

Theoretical prediction of electrical

conductivity in saturated and unsaturated soil.

Water Resources Research,

2771-2777

•

Malicki, M.A., Walczak, R.T., Koch, S., Flühler, H. (1994)

Determining soil

salinity from simultaneous readings of its electrical conductivity and permittivity
using TDR.

Proceedings:

Symposium on TDR in Environmental, Infrastructure

and Mining Applications

, September 1994, held at Northwestern University,

Evanston, Illinois, USA. Special Publication SP 19-94, US Department of
Interior Bureau of Mines, 328-336

•

Nyfors, E., Vainikainen, P. (1989)

Industrial microwave sensors

Artech Hous,

Norwood, USA.

•

Peyman, A., Gabrriel, C., Grant, E.H. (2007) Complex permittivity of sodium
chloride solutions at microwave frequencies.

Bioelectromagnetics

:264-274

•

Rhoades, J.D., Shouse, P.J., Alves, W.J., Manteghi, N.A., Lesch, S.M.
(1990)

Determining soil salinity from soil electrical conductivity using

different models and estimates

Soil Science Society of America Journal

, 46-54

Содержание WET150

Страница 1: ...User Manual for the WET150 Sensor type WET150 Delta T Devices Ltd WET150 UM 1 1 ...

Страница 2: ... the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residenti...

Страница 3: ...work Cabling 13 Maximum cable length and network size 14 Connecting to loggers or controllers 15 Wiring 15 Other loggers and systems wiring 15 GP2 wiring using internal power 16 GP2 wiring using external power 17 Give Each WET150 a Unique Address 18 Install DeltaLINK 18 1 Open DeltaLink Transparent Mode 19 2 Find out WET150 s current address 19 3 Change the address 20 Create GP2 Program 21 1 Add a...

Страница 4: ...ifications 40 Edge Effects 41 Trouble Shooting 42 Error Codes 42 How it works 43 Sensing soils and substrates 43 Permittivity and soil composition 43 Converting permittivity to water content 44 Generic soil calibrations 46 Soil specific calibrations 48 Technical Reference 49 Dielectric properties 49 Measuring Soil Moisture 50 Pore water conductivity 51 References 55 Definitions 56 Technical Suppor...

Страница 5: ...cted by sensitive circuits operating at 100MHz Sensing field Extends 100mm into the soil but field is strongest close to the rods install carefully to avoid air gaps SDI 12 Industry standard digital interface compliant to version 1 3 Outputs Sophisticated correction algorithms ensure accurate readings across the full range of water content EC and temperatures Temperature Thermistor is located with...

Страница 6: ...he electrical conductivity of the water within the pores of the soil ECp Temperature is measured by a miniature sensor built into the body of the sensor The WET150 Sensor works with the WET150 Meter and the GP2 logger controller It can also be used with other SDI 12 loggers and with SDI 12 fertigation and irrigation control systems Advantages of the WET150 Sensor Fast accurate adaptable and easy t...

Страница 7: ...trical conductivity and composition of the soil surrounding the pins determines its dielectric properties The WET150 sensor detects these dielectric properties from their influence on the electromagnetic field and calculates Soil Moisture and Pore Water Conductivity It also records Temperature and uses that to improve the accuracy of the other measurements and sends the results on demand to either...

Страница 8: ... directly or via SDI 12 network of EXT 5W xx cables EXT 5W 01 EXT 5W 05 EXT 5W 10 EXT 5W 25 1 m 5 m 10 m and 25 m extension cables with 5 way M12 connectors Connects WET150 to an SDI 12 sensor network GP2 NTP 3 way network T Piece for connection WET150 and EXT 5W xx cables ML EX50 ML EX100 Extension tubes 50 and 100 cm SM AUG 100 Spiral Auger 1 2 m ...

Страница 9: ...age when not in use Take care when attaching cables to ensure that the connectors are clean undamaged and properly aligned before pushing the parts together Do not pull the WET150 out of the soil by its cable If you feel strong resistance when inserting the WET150 into soil it is likely you have encountered a stone Stop pushing and re insert at a new location WET150 is unsuitable for use in hard s...

Страница 10: ...n C or F EC is displayed as the pore water conductivity ECp in mS m 1 or the soil bulk conductivity ECb when the RAW display option is selected Address can be a to z A to Z or 0 to 9 0 is not advised on a network WET150 Meter Buttons READ takes and displays a reading SET shows the settings menu You can scroll up or down through these options Soil type Units and Address and Contrast Press SET to se...

Страница 11: ...temperature Temperature can be displayed in C or F Pore Water EC ECp The EC Electrical Conductivity of the water in the soil pores is calculated by applying the Hilhorst equation This is a very useful approximation that works exceptionally well with the WET150 because the sensor measures permittivity and measured bulk electrical conductivity ECb in the same sample volume at the same frequency 100M...

Страница 12: ...readings from a WET150 sensor 1 Press SET Wakes the Meter and displays the first option in the settings menu 2 Press twice Scrolls down to the Address setting menu 3 Press SET Selects that menu and displays the current SDI 12 address 4 Press or as often as necessary Scrolls to the desired target address 5 Press SET Attempts to set that address Success is indicated by the brief appearance of the sy...

Страница 13: ...nd modify SDI 12 networks Later if a network fails due to a faulty sensor or damaged cable it is easy to isolate sections by temporarily disconnecting whole network branches or individual sensors to trace the fault M12 connectors on cables and the WET150 are waterproof to an IP rating of IP68 but must be screwed together tightly to form this waterproof seal Failure to sufficiently tighten the thum...

Страница 14: ... voltage cable type logger type and environmental factors such as whether the cable is buried and proximity to electrical noise sources like transmitters and power transformers While it is not possible to test every network configuration tests have been carried out on various configurations with different cable lengths and numbers of WET150s One such scenario was fifteen WET150 sensors daisy chain...

Страница 15: ...re is a lot of electrical noise in the environment connecting the green screen wire to ground in the logger or controller may help reduce data corruption For other connection details to third party loggers and controllers please consult the SDI 12 sections of those products manuals For SDI 12 screw terminal cable connector information see pages 12 32 and 33 of the SDI 12 for GP2 User Manual See Po...

Страница 16: ... extension cables and T pieces connect multiple sensors in a network Optional The green wire is connected to the cable screen The SDI 12 specification does not require the green wire cable screen to be connected If there is a lot of electrical noise in the environment connecting the green screen wire to the GND terminal with the blue ground wire in the GP2 may help reduce data corruption The figur...

Страница 17: ... cable type SMSC lw 05 to the external power source 12Vdc terminal Wiring connection diagram showing external SDI 12 power connections for the SDI 12 network along with the optional green screen wire Ensure there is a fuse or other protection in line with this external power source in case short circuit faults develop on the SDI 12 network The Ground or 0V terminal of the external power source sho...

Страница 18: ...d below Install DeltaLINK To operate the functions of the GP2 logger controller its companion computer software DeltaLINK needs to be downloaded and installed This PC software is available from the Delta T website at www delta t co uk software deltalink DeltaLINK version 3 9 or later is required for use with the WET150 If your existing install of DeltaLINK is older than this version please install...

Страница 19: ...arent Mode Terminal as shown below Once the SDI 12 Transparent Mode Terminal is open the GP2 behaves like a transparent serial link between SDI 12 sensors and the PC 2 Find out WET150 s current address Send a command to tell the sensor to reply with its address You type Reply a We usually expect the address of a new sensor is to be zero but it might not be If you already have another sensor with t...

Страница 20: ...program to create a WET150 sensor type measurement with the correct address and repeat this for each sensor to go on the network See also Create GP2 Program on page 21 You can change the default Measurement name to add useful metadata such as the address e g Theta becomes Theta Z and so see the address displayed in the results But the ECp calculation also uses the Permittivity and SoilTemp reading...

Страница 21: ...howing steps in the creation of a WET150 soil moisture sensor measurement type in a GP2 program 1 With DeltaLINK 3 9 or later running on your PC and connected to a GP2 select Program 2 Select Change Under Measurements click on click to add a new item 3 Select Soil Moisture 1 2 3 4 5 Change ...

Страница 22: ... that of the WET150 sensor as described on page18 You should now see the following Illustration showing three sensor measurement types added to take readings from a single WET150 for soil moisture pore water conductivity and temperature These all have the same SDI 12 address which in this example has been changed to 7 from the default 0 address The default measurement period of 1 hour for all read...

Страница 23: ...change a Measurement name then ensure it is updated in the Recording Rate The program will object and fail to Apply if you don t do this Also if changing the WET150 Theta or SoilTemp Measurement names you will need to use the same names used in the ECp Calculation section Example change the Measurement name to add useful metadata e g Theta becomes Theta Z to display the address in the results The ...

Страница 24: ...ufacturers which can t do maths as well as the GP2 6 Send data Command No action required Your GP2 logger knows which D command to send so this is not something you need to worry about Note for other logger users The Dn command is sent by the logger to retrieve the results when the sensor is ready n can be 0 to 8 In reply the sensor may send up to 76 characters to the logger The number of characte...

Страница 25: ...is about once every 5 seconds for one WET150 on a GP2 62 sensors may take 50 55 seconds in the standard sequential mode In a heavy clay you may wish to start recording once per hour and wait and see how quickly the soil responds to wetting and drying events 4 Next Steps Click on Apply to install the program in the logger Select the Sensors tab and click on Read now to see the WET150 readings Pleas...

Страница 26: ...to 90 mA dependent upon network and power supply impedances 4 Active computation 2mA over 200ms The GP2 logger controller provides a regulated 12 VDC output at 500 mA from its internal batteries This power rail meets the SDI 12 specification and can be switched on and off under program control It is ideal for powering multiple WET150s and other low power SDI 12 devices on a network If not using th...

Страница 27: ...a time All the others are either in SDI 12 network activity mode when the data line is active or idle mode when it is not Concurrent Measurements All WET150s in the network are individually instructed to take a measurement as soon as possible without waiting for any other WET150 They then hold their measurement results until the logger requests them from each sensor individually in sequence Due to...

Страница 28: ...nsors are variable in length and therefore transmission time As an indication a standard three parameter W E T reading on a WET150 has the following typical durations From start of SDI 12 measurement command to finish of SDI 12 data ready service request command including active sensing and results computation 360ms From start of SDI 12 data request command to finish of SDI 12 measurement data tra...

Страница 29: ...oisture units after logging or program your data logger to convert the output automatically before saving the data using the information supplied in the Conversion to Soil Moisture section Alternatively by using one of the available SDI 12 commands a WET150 can be instructed to output data in soil moisture units for a range of soils See WET150 SDI 12 Programmers Guide pdf ...

Страница 30: ...ting the pins to ensure good soil contact If you feel strong resistance when inserting the WET150 you have probably hit a stone Stop and re insert at a new location Note With surface installation air temperature and radiant heat on the sensor body can affect temperature readings Partial or full burial of the WET150 will improve temperature accuracy particularly where there is a large temperature d...

Страница 31: ...sion tube to the WET150 remember to pass the cable through the extension tube and fit the connector first Push the WET150 into the soil fully inserting the pins to ensure good soil contact Alternatively Dig a trench and install horizontally Note Extension tubes are available for installing the WET150 in an augered hole ...

Страница 32: ...devices Fortunately just two simple commands are required for changing sensor addresses Address Query find out the existing address of the single WET150 connected to the GP2 Address Assign change the existing address to a new address The following examples explain what you need to type in the command entry box and how to interpret responses in the terminal window Full details of these and all SDI ...

Страница 33: ...ode terminal window Type in command box Press the ENTER key or click on the Send button Terminal window shows 0 The visible terminal window character string 0 can be broken down and explained as Commands from the GP2 logger controller Character Meaning The SDI 12 command for Address Query The SDI 12 end of command character automatically added in transparent mode Reply from the WET150 sensor Chara...

Страница 34: ...sing the DeltaLINK transparent mode terminal window Type in command box 0Ad Press the ENTER key or click on the Send button Terminal window shows 0Ad d The visible terminal window character string 0Ad d can be broken down and explained as Commands from the GP2 logger controller Character Meaning 0 The SDI 12 address of the sensor you wish to communicate with A The SDI 12 command character for Addr...

Страница 35: ...Send button Terminal window shows dI d13Delta T WET150v01 D1234567 The visible terminal window character string dI d13Delta T WET150v01 D1234567 can be broken down and explained as Commands from the GP2 logger controller Character Meaning d The SDI 12 address of the sensor you wish to communicate with I The SDI 12 command character for Identify The SDI 12 end of command character automatically add...

Страница 36: ...t CRC error checking In summary these measurement commands are Measurement type Commands Standard sequential aM and aM1 aM9 Standard concurrent aC and aC1 aC9 Sequential with CRC error checking aMC and aMC1 aMC9 Concurrent with CRC error checking aCC and aCC1 aCC9 where a is the address of the sensor All measurements sets other than aM9 can be customised See the following sections for customisatio...

Страница 37: ...ter 4 1 T C Ɛr permittivity none ECb bulk EC mS m 1 aM2 Water content vol Using Organic soil type calibration ECp pore water EC mS m 1 Compensated to 25 C linearly at 2 C soil parameter 4 1 T C Ɛr permittivity none ECb bulk EC mS m 1 aM3 Water content vol Using PeatMix soil type calibration ECp pore water EC mS m 1 Compensated to 25 C linearly at 2 C soil parameter 4 1 T C Ɛr permittivity none ECb...

Страница 38: ... mS m 1 Compensated to 25 C linearly at 2 C soil parameter 4 1 T C Ɛr permittivity none ECb bulk EC mS m 1 aM7 Blank aM8 Blank aM9 Ɛr permittivity none ECb bulk EC mS m 1 T C Multi parameter measurement sets M and M1 to M8 in the table above can be customised to better suit your application particularly for use with third party non Delta T Devices loggers and controllers For information on how to ...

Страница 39: ...ly therefore an error code value of 8020 is returned instead Using the default soil parameter value of 4 1 and the generic soil type calibrations the lower soil moisture limit for ECp calculations are Generic soil type calibration Lower limit soil moisture content for ECp calculation Mineral 12 67 vol Organic 17 72 vol PeatMix 21 22 vol Coir 20 30 vol MinWool 21 43 vol Perlite 24 57 vol For furthe...

Страница 40: ...nge 0 to 2000 mS m Temperature WET150 must be fully buried to accurately measure soil temperature Accuracy 1 C Range Accurate range 20 to 50 C Full range 20 to 60 C Operating specifications Interface SDI 12 version 1 3 Maximum cable length1 600 m see page 14 Power requirement 6 to 20 V 22 mA over 12 ms see page 26 Operating range 20 to 60 C sensor does not detect ice Environmental IP68 Sample volu...

Страница 41: ...rom the edge of plant plots if possible to avoid the edge effect shown in the graph below 6 5 4 3 2 1 0 1 0 5 10 15 20 25 30 35 40 Error of reading Gap between WET150 body and wall of pot mm WET150 Error close to wall of plant pot live pin nearest to pot wall ...

Страница 42: ...ls in place of the expected Pore EC value This is not a sensor fault See Note about Pore EC ECp calculations on page 39 for more information All other error codes indicate a possible sensor fault condition Please contact Delta T devices support for assistance See also Technical Support on page 62 ...

Страница 43: ...lt units mS m 1 Along with temperature T default units C these three measurements form the native WET150 outputs which can be logged directly or used in further calculations It is possible to calculate the water content of any soil or substrate from its permittivity value provided that certain composition properties of the soil or substrate are known Permittivity and soil composition Soils are typ...

Страница 44: ...rmittivity contributions depending upon their relative quantity in the mix Converting permittivity to water content The relationship between soil permittivity Ɛ and its equivalent water content θ depends upon the mix proportions of its constituent materials sand organic matter water air etc This relationship between soil permittivity and water content is also non linear However for any given soil ...

Страница 45: ...rresponds approximately to Ɛ 𝑤𝑎𝑡𝑒𝑟 1 and usually takes a value about 8 0 Real soil 𝑎0 and 𝑎1 values can vary significantly from these guidelines when they are affected by other factors in particular bound water in clay may result in higher values of 𝑎1 0 0 2 0 4 0 6 0 8 0 0 0 0 2 0 4 0 6 0 8 Soil refractive index ε Soil moisture m3 m 3 Soil calibrations Offset a0 Slope a1 ...

Страница 46: ...h are predominantly made of sand silt and clay The organic generic soil type is for soils with a high organic matter content See also Definitions on page 56 In DeltaLINK the soil type for a WET150 logging program can be selected from a drop down in the properties panel on the right of the program editor window under the calculation section This auto populates the 𝑎0 and 𝑎1 values for the water con...

Страница 47: ... WET150 is also able to directly compute and output soil water content for the generic soil types on page 46 The pre configured WET150 measurement sets and SDI 12 commands assigned to these generic soil types are given in the tables following page 36 See the WET150 SDI 12 Programmer s Guide for more information on outputting water content measurements directly from the WET150 ...

Страница 48: ...50 logging program using custom 𝑎0 and 𝑎1 values from a soil specific calibration can be entered in the properties panel on the right of the program editor window under the calculation section These values will then be used for the water content theta calculation Note As the properties panel is context sensitive the Theta measurement must first be selected in the overview panel on the left of the ...

Страница 49: ...ted as a complex number j 1 where the real part of the permittivity represents the energy stored and the imaginary component represents the total energy absorption or loss Both values are frequency and temperature dependent For a static electric field the real part of the permittivity is often referred to as the dielectric constant The energy losses include dielectric loss d and loss by ionic cond...

Страница 50: ... and 10GHz The following graph shows composite data for a number of different agricultural soils You can see from this graph that the accuracy of the water content measurements would be improved by using a different calibration for each soil However the improvement would be small typically 2 or 3 so a generalised mineral calibration is appropriate for a good range of agricultural soils Warning Thi...

Страница 51: ...y and conductivity of the pore water will be denoted by the subscript p The imaginary part of the complex permittivity of the pore water is p In soil science it is more practical to use the conductivity of the pore water p which can be defined as 0 0 0 ip dp p p 4 where ip represents the ionic conductivity of the extracted pore water Dielectric losses are frequency dependent and have a maximum at ...

Страница 52: ... so the conductivity of the bulk soil b 0 Dry soil material is still polarisable so 0 b 0 and 0 b appear as an offset to b By assuming that g takes into account the proportionality constant it is reasonable to postulate the following form for the complex permittivity of the bulk soil g p b b 0 7 Note that 0 b is a complex value and includes dielectric and ionic loss However since b 0 we may approx...

Страница 53: ... to b Y may be written in terms of C and G as C j G Y 10 From Eq 9 and Eq 10 and with Eq 4 to Eq 8 in mind the real and imaginary parts of Y can be found p g G 11 and p 0 0 b g C 12 In terms of the measurable bulk quantities b and b p b g 13 and p 0 b b g 14 From Eq 13 and 14 the ionic conductivity of the pore water can be written as 0 b b p p b 15 The model of Eq 15 describes the relationship bet...

Страница 54: ...ather than free water The model of Eq 15 cannot be used for the conductivity due to ions moving through the lattice of ionic crystals in a dry or almost dry soil the model is only valid for the free water in the matrix Thus 0 b is not the value for b if 0 For sand the free water content corresponds to 0 01 but for clay it can be 0 12 Dirksen and Dasberg 1993 As a rule of thumb the model applies fo...

Страница 55: ...lands Hilhorst M A 2000 A Pore Water Conductivity Sensor Soil Science Society of America Journal 64 Issue 6 1922 1925 Hübner C Kaatze U 2016 Electromagnetic Moisture Measurements Universitätsverlag Göttingen Kaatze U Uhlendorf V 1981 The dielectric properties of water at microwave frequencies Zeitschrift für Phys Chem Neue Folge Bd 126 151 165 Mualem Y Friedman S P 1991 Theoretical prediction of e...

Страница 56: ...rox 0 02 m3 m 3 for sandy soils at the permanent wilting point through approx 0 4 m3 m 3 for clay soils at their field capacity up to values as high as 0 85 m3 m 3 in saturated peat soils Gravimetric Soil Moisture Content where Mw is the mass of water in the sample and MS is the total mass of the dry sample To convert from volumetric to gravimetric water content use the equation 𝜃𝐺 𝜃𝑉 𝜌𝑊 𝜌𝑆 where ...

Страница 57: ...ercentage Carbon and is a measure of organic content Salinity The preferred SI units for ionic conductivity are mS m 1 where S is Siemens the unit of electric conductance Dimensionally it is equivalent to the inverse of resistance i e Ohm 1 The following conversions apply 1 mS m 1 0 01 dS m 1 0 01 mS cm 1 10 µS cm 1 Soil salinity can be classified using the following descriptive categories 0 200 4...

Страница 58: ...ens per meter S m 1 We have used mS m 1 throughout this manual because it is an SI preferred unit The following conversions apply 1 mS m 1 0 01 mS cm 1 10 µS cm 1 Pore Water Conductivity ECp or p The electrical conductivity of the water within the soil pores It is determined by the concentration of different ions within the pore water and by the temperature Bulk Electrical Conductivity ECb or b Th...

Страница 59: ...y but may be more rigorously defined as the real part of the permittivity in a static electric field Saturation The moisture content at which all the air within the pores has been replaced by water It s not a stable situation because the water will immediately start to drain through It s a property of soil type only Field Water Capacity or Field Capacity The moisture content obtained when a satura...

Страница 60: ...ry between about 0 04 m3 m 3 for sandy soils to 0 22 m3 m 3 for clay soils Dry Zero moisture content Available Water Capacity The difference between Field Capacity and Wilting Point Water Deficit The amount of irrigation water or rainfall mm that has to be added to a soil profile in order to bring it back up to field capacity plant water use plant stressed waterlogged oven dry all water no soil Fi...

Страница 61: ...lta T Distributor or Technical Representative should contact them in the first instance Spare parts for our own instruments can be supplied from our works These can normally be despatched within a few working days of receiving an order Spare parts and accessories for sensors or other products not manufactured by Delta T may have to be obtained from our supplier and a certain amount of additional d...

Страница 62: ...ence number Make sure to quote the reference number subsequently so that we can easily trace any earlier correspondence In your enquiry always quote instrument serial numbers software version numbers and the approximate date and source of purchase where these are relevant Contact details Technical Support Delta T Devices Ltd 130 Low Road Burwell Cambridge CB25 0EJ England UK Tel 44 1638 742922 Fax...

Страница 63: ...ibration for clay soils We use the term substrate to refer to any artificial growing medium Underlying principle Soil moisture content θ is proportional to the refractive index of the soil as measured by the WET150 see How it works on page 43 The goal of calibration is to generate two coefficients a0 a1 which can be used in a linear equation to convert probe readings into soil moisture 1 0 a a ...

Страница 64: ... soil or substrate This sample needs to be unchanged from its in situ density to be 1 0 litre to have the correct dimensions to fit the beaker and to be generally uniform in water content For cohesive soils this is most easily done with a soil corer Sandy soils can be repacked into the beaker but if the sample is quite damp you should take the subsequent measurements quickly as the water may begin...

Страница 65: ...le to dry the sample at a lower temperature to avoid driving off volatile factions Weigh the dry sample in the beaker W0 1400g Re insert the WET150 into the dry sample and again record the permittivity reading ε0 2 56 I e ε0 1 60 Calculate a0 Since the water content of the dry soil θ0 0 this gives a0 directly ε0 a0 1 60 Calculate w The water content of the wet soil w can be calculated from the wei...

Страница 66: ...s in place of the default calibrations to convert WET150 readings into volumetric water content θ using 1 0 a a See the WET150 SDI 12 Programmer s Guide for details on how to configure the WET150 to output soil moisture readings directly using custom calibrations See also Underlying principle on page 63 ...

Страница 67: ...ance accurate to 1g Temperature controlled oven Process Notes and example Collect a wet sample of the clay soil 25 to 30 water content would be ideal This sample needs to be unchanged from its in situ density to be 1 0 litre to have the correct dimensions to fit the beaker and to be generally uniform in water content This is most easily done with soil corer Measure the volume occupied by the sampl...

Страница 68: ... sample thoroughly With clay soils this is usually achieved by keeping it in the oven at 105 C for several hours or days the time required depends on the sample size and porosity Weigh the dry sample in the beaker W0 1400g Calculate w The water content of the wet soil w can be calculated from the weight of water lost during the full drying process Ww W0 and its volume Ls 𝜃𝑤 𝑊 𝑤 𝑊0 𝐿𝑠 1693 1400 960...

Страница 69: ...soil is now calibrated you can now use these two numbers in place of the default calibrations to convert WET150 readings into volumetric water content θ using 1 0 a a See the WET150 SDI 12 Programmer s Guide for details on how to configure the WET150 to output soil moisture readings directly using custom calibrations See also Underlying principle on page 63 ...

Страница 70: ... water 6 7 51 58 Connecting wiring connecitons 15 Conversions 29 Current consumption 26 D Data send and receive 15 Data logger 29 DeltaLINK 18 Description 6 Dielectric refractive index 63 Dielectric constant 59 Dielectric properties 6 7 49 55 Dimensions 40 E ECp 11 Electrical conductance 58 conductivity 6 51 58 Electrical Conductivity 11 electrical noise 15 Environmental specification 40 EXT 5W 01...

Страница 71: ...ory Compliance 2 Rods 9 S Salinity 55 57 Sample volume 40 SDI12 Address 18 Duration of commands 28 high and low voltage requirements 28 wiring 15 SDI12 commands 32 SDI12 WET150 Measurement Commands 36 Send data Command SDI12 command 24 Sensor type Settings 23 Sequential SDI12 measurment mode 24 Sequential measurements 27 Servicing 61 Set field capacity 59 60 units 58 SM AUG 100 8 SMSC lw 05 8 Soil...

Страница 72: ...72 Index Warranty 61 Water content 6 7 50 51 53 54 55 59 Water deficit 60 WET150 Kit 8 WET150 Meter 10 Wilting Point 60 Wiring 15 Wiring connection external SDI12 power with GP2 17 ...

Результаты поиска

Содержание WET150

Отзывы:

Похожие инструкции для WET150

Бренды по названию

Популярные бренды

Delta-T Devices WET150, Руководство пользователя

Результаты поиска

Содержание WET150

Отзывы:

Похожие инструкции для WET150

Бренды по названию

Популярные бренды