SWT4 Tensiometer User Manual v3.1
Contents
1. 2 Connect the SWT4R to the measuring device and keep an eye on the pressure signal all the time In a downwards tilting installation the marked tube is the refilling tube In an upwards installation the unmarked tube is the refilling tube Pull off the rubber tube from the refilling tube Degas the water inside the syringe as described above Connect the syringe to the refilling tube and close the valve Connect vacuum bottle and de airing tube Using the vacuum pump evacuate the bottle to the maximum possible vacuum This will enlarge the remaining bubble inside the cup SWT4 User Manual v3 1 Service and maintenance 9 31 5 Now briefly open and close the valve at the syringe a few times water is drawn into the Tensiometer while at the same time the air bubble is sucked into the vacuum bottle Repeat this 2 or 3 times until no more bubbles come out 6 Close the valve of the vacuum bottle and remove the bottle Inject 5 ml of water from the syringe into the refilling tube Remove the syringe Put a drop of water on the end of both the rubber and steel tubes and connect them together 32 Service and maintenance SWT4 User Manual v3 1 4 2 Testing 4 2 1 Calibration When delivered Tensiometers are calibrated with an offset of 0 hPa when lying horizontally and a linear response The offset of the pressure transducer has a minimal drift over the years Therefore we recommend you check sensors once a year and re calibr2. If the soil is dryer than 1500 kPa air can enter the negative pressure inside the cup decreases and the readings go down to 0 kPa With these characteristics this material has outstanding suitability to work as the semi permeable diaphragm for Tensiometers Y The cup has a lifetime guarantee against breakage Y Ceramic cup Do not touch the cup with your fingers Grease sweat or soap residues will influence the ceramic s hydrophilic performance 2 2 External refilling SWT4R only I The SWTAR is equipped with 2 stainless steel capillary tubes which are led through the cable gland and the shaft Each one has an opening that ends inside the ceramic cup This allows easy refilling of the SWT4R while it remains installed in the ground Tube 1 ends at the very tip of the cup tube 2 ends next to the pressure transducer opening Outside both tubes are connected together with a short rubber tube Any air bubbles will ascend and accumulate either in the ceramic s tip around tube 1 upwards installation angle or next to opening 2 downwards installation angle Accordingly the air is removed either through tube 1 or 2 please see chapter 3 2 SWT4 User Manual v3 1 Sensor Description 13 Rubber tube Black mark on tube Filling tube marked blue or green Mork on shaft must be on upside a 7 Deairing tube SOs Sey not marked 2 3 Analog output signals The pressure transducer offers
3. Tensiometers are not usually damaged when the cup is installed in a frost free soil horizon Excess pressure The maximum non destructive pressure Is 300 kPa 3 bar 3000 hPa Higher pressures which might occur for example during insertion in wet clayey soils whilst measuring shear force or during refilling and reassembly will destroy the pressure sensor Electronic installation Any electrical installations must be executed by qualified personnel Ceramic cup Do not touch the cup with your fingers Grease sweat or soap residues will influence the ceramic s hydrophilic performance SWT4 User Manual v3 1 Introduction 5 1 2 Unpacking The SWT4 or SWTAR includes e Tensiometer calibrated and filled with 4 pin plug M12 IP67 with plug cap e This manual e Plastic bottle protecting the ceramic cup must be half filled with water to keep the cup wet e Rubber shaft water protection disk e Calibration certificate with each order for conversion of electrical to physical values e With type SWT4R a refill syringe Y SWT4 and SWTAR are filled and ready for installation when supplied See also Accessories on page 43 1 3 Foreword Measuring systems must be reliable and durable and should require a minimum of maintenance to achieve target oriented results and keep the servicing low Moreover the success of any technical system directly depends on it being used correctly
4. User Manual for the Tensiometer tyoes SWT4 amp SWT4R SWT4 UM 3 1 Delta T Devices Ltd Notices Copyright All rights reserved Under the copyright laws this manual may not be copied in whole or in part without the written consent of Delta T Devices Ltd and UMS GmbH Under the law copying includes translation into another language Copyright 2009 Delta T Devices Limited 2009 UMS GmbH CE conformity The sensors described in this document are CE marked by the manufacturer Design changes Delta T Devices Ltd reserves the right to change the designs and specifications of its products at any time without prior notice SWT4 User Manual Version 3 1 Oct 2009 Strictly observe rules for disposal of equipment containing electronics Within the EU disposal through municipal me es waste prohibited return electronic parts to your local distributor Delta T Devices Ltd Tel 44 1638 742922 130 Low Road Burwell Fax 44 1638 743155 CAMBRIDGE CB25 OEJ e mail sales delta t co uk U K tech support delta t co uk web hito www delta t co uk 2 52 Table of contents User Manual for the Tensiometer Notices 2 1 Introduction 1 Safety instructions and warnings 2 Unpacking 3 Foreword 4 Guarantee 5 Durability 6 SWT4 and SWT4R 6 Soils and soil water 6 Intended use 6 Types 7 Quick Start w N gt Sensor Description 1 Parts 1 1 Body and shaft 1 2 Pressure senso
5. At the beginning of a measuring task or research project the target all effective values and the surrounding conditions should be defined This then leads to the requirements for the scientific and technical project management which describes all quality related processes and decides the methods to be used the technical and measurement tools the verification of the results and the modeling The continuously optimized correlation of all segments and its quality assurance are decisive for the final success of a project We wish you good success with your projects Please do not hesitate to contact us for further support and information 1 4 Guarantee See Terms and Conditions of Sale on page 49 1 5 Durability The nominal lifespan for outdoor usage is 10 years but protection against UV radiation and frost as well as proper and careful usage substantially extends the lifespan 6 Introduction SWT4 User Manual v3 1 1 6 SWT4 and SWT4R 1 6 1 Soils and soil water All water movement in soil is directly dependant on the soil water tension because water both in the soil and on the surface will always move from a point of higher potential to a point of lower potential The majority of soil water flow take place in response to small water tensions Only Tensiometers allow the direct and precise measurement of these small tensions Natural soils in the ground are heterogeneous It is not just precipitation and evaporation that ma
6. loggers 45 SWT4 User Manual v3 1 51 M maintenance 26 measuring range 37 O Offset 33 Offset correction 21 Osmotic effect 39 output 14 P piezometer 40 pressure 12 problems 38 Protection 16 Q Quick start 8 R range 37 4 refill kit 30 Refill Kit SWT4 RK2 18 Refill kits 46 refilling 13 Refilling 26 S Service 26 50 soil sample 17 soils 7 Spares 50 specifications 4 SWT MR 44 T Technical Support 49 50 Temperature 39 Terms 49 Testing 33 Thermal effect 16 Troubleshooting 40 tubes insulation 43 protection 43 U Units 48 Unpacking 6 USB converter 44 V Vapor pressure 39 Voltage regulator 25 Voltage regulators 46 voltage Vin 41 W warnings 5 Wiring 42 Z zero ffset How to check 33 zero offset 22 52 Index SWT4 User Manual v3 1
7. 6 3 Vapor pressure influence 6 4 Osmotic effect 6 5 Using Tensiometers as a piezometer 7 Troubleshooting 8 Appendix 8 1 Technical specifications 8 2 Wiring configuration 8 3 Accessories 8 3 1 Connecting and extension cables 8 3 2 Handheld measuring device 9 Tensiometer loggers 9 1 1 Voltage regulators 9 1 2 Refill kits 9 1 3 Tensiometer augers 9 2 Units for soil water and matrix potentials 10 Technical Support Terms and Conditions of sale Service and Spares Technical Support Contact Details 11 Index 49 SWT4 User Manual v3 1 1 Introduction 1 1 Safety instructions and warnings Electrical installations must comply with the safety and EMC requirements of the country in which the system is to be used Please note that any damage caused by handling errors are out of our control and therefore are not covered by guarantee Tensiometers are instruments for measuring the soil water tension and soil water pressure and are designed for this purpose only Please pay attention to the following possible causes of risk Lightning Long cables act as antennas and might conduct surge voltage in case of lightning stroke this might damage sensors and instruments Frost Tensiometers are filled with water and therefore are sensitive to frost Protect Tensiometers from frost at any time Never leave Tensiometers over night inside a cabin or car when freezing temperatures might occur
8. Plug Male 4 pin thread M12 IP67 Pressure transducer Water tension Water level 100 kPa 85 kPa 85 kPa 0 kPa 100 kPa electronically 100 kPa physically 0 kPa Tensiometer 100 kPa Piezometer Output signal Pressure 85 mV 85 kPa OmV 0 kPa 100 mV 100 kPa Tensiometer Piezometer Pressure transducer 0 5 kPa Power supply Supply voltage Vin typ 10 6 VDC 5 15 VDC stabilized Current consumption 1 3mA at 10 6 VDC SWT4 User Manual v3 1 Appendix 9 41 8 2 Wiring configuration brown PIN 1 Supply teen atthe PIN 2 Signal mR blue PIN3 Supply SN black PIN 4 Signal Male plug on Female on sensor cable connecting cable AS thick black Pin and wire configuration for connecting cables SWTCC Ce ee Va brown 1 Supply pus Supply minus Sgnaipus A OUT white 22 Signal plus A OUT black 4 Signalminus 42 9 Appendix SWT4 User Manual v3 1 8 3 Accessories 8 3 1 Connecting and extension cables Cables must be ordered additionally for each Tensiometer 4 wire connecting cables SWTCC xx are fitted with a female plug M12 IP67 and 12 cm wire end sleeves Extension cables SWT EXT xx have one each male and female plug M12 IP67 Plugs are supplied with protective covers Delta T no 4 pin connection cables Clip on cable markers Please contact Delta T Plastic protection tubes Please contact Delta T Thermal insulation
9. T shall not be liable to the buyer by reason of any delay or failure to perform their obligations in relation to the goods and or services if the delay or failure was due to any cause beyond the Delta T s reasonable control SWT4 User Manual v3 1 Technical Support 49 Service and Spares Users in countries that have a Delta T distributor or technical representative should contact them in the first instance Spare parts for our own instruments can be supplied and can normally be despatched within a few working days of receiving an order Spare parts and accessories for products not manufactured by Delta T may have to be obtained from our supplier and a certain amount of additional delay is inevitable No goods or equipment should be returned to Delta T without first obtaining the return authorisation from Delta T or our distributor On receipt of the goods at Delta T you will be given a reference number Always refer to this reference number in any subsequent correspondence The goods will be inspected and you will be informed of the likely cost and delay We normally expect to complete repairs within one or two weeks of receiving the equipment However if the equipment has to be forwarded to our original supplier for specialist repairs or recalibration additional delays of a few weeks may be expected For contact details see below Technical Support Users in countries that have a Delta T distributor or technical represen
10. an linear output signal As the output signal directly depends on the supply voltage the supply voltage needs to be constant and stabilized As the pressure transducer is a Wheatstone full bridge it has to be connected in a certain way See also Connecting SWT4 and SWTAR on page 23 and the user manual for your display unit or data logger before connection 14 9 Sensor Description OWT4 User Manual v3 1 3 Installation 3 1 Advance planning 3 1 1 Selecting the measuring site The installation spot should be representative of the soil horizon Therefore in heterogeneous soils soil samples should be taken and classified before or during installation On farmed sites with vegetation root spreading and root growth during the measuring period must be considered Fine roots will grow around the Tensiometer cup as this is a poor but still secure source of water Therefore avoid the root zone or move the Tensiometer from time to time depending on the root growth Disturbing effects like the edge of a field slopes or hollows must be avoided or taken into account when interpreting the data 3 1 2 Number of Tensiometers per level The deeper the level the less the variation is in water potential In lower sandy or pebbly horizons just one Tensiometer per depth is sufficient Close to the surface about 3 Tensiometers per level are recommended Guiding principle More heterogeneous sites and soil structures require a higher number
11. tension to be negative 0 85 kPa 3 4 1 How to measure the zero offset of a tilted tensiometer As an alternative to using the table above if the tensiometer is to be installed pointing downwards submerge it up to one half the height of the ceramic cup in a beaker of water tilting the tensiometer to the desired angle The data logger reading in mV now represents OkPa water tension at that angle giving you the zero offset correction directly 22 9 Installation SWT4 User Manual v3 1 3 5 Connecting SWT4 and SWT4R 3 5 1 Spot reading with the SWT MR Infield7 SWT4 and SWTAR are fitted with a 4 pin plug The plug can be connected directly to an SWT MR handheld measuring device for taking spot readings of the soil water tension This displays and stores the soil water tension 3 5 2 Connecting cables Connecting and extension cables are required for connecting SWT4 and SWTAR to a data logger or other data acquisition device Find cables in the chapter Accessories on page 43 3 5 3 Connection to a data logger Delta T Logger users see Connection to Delta T Loggers on page 24 The pressure transducer is a non amplified full Wheatstone bridge circuit which is calibrated at 10 6 VDC It requires a stabilized power supply Some logger types can measure bridge circuits directly other loggers require additional measures because the signal minus and the supply minus do not have the same ground If supplied with ex
12. trapped inside the ceramic Insert the saturated but empty cup to the adapter and connect it to the degassing device Place the cup in water in an upright position with the external water level reaching up to 2 3 of the cup Half fill the second adapter capsule with water and insert the sensor body Connect the adapter to the degassing device as well Now start the vacuum pump With well saturated cups the procedure will take 1 to 2 hours From time to time knock on cup and sensor body to loosen bubbles Degassing is complete when no air bubbles ascend from ceramic and body and the cup is completely filled with water Before screwing together cup and sensor body connect the sensor to a measuring device to observe the pressure signal Warning Do not exceed 2 bar as 3 bar will destroy the sensor Hold the cup in an upright position fill it completely and with an overlapping meniscus of water Carefully and slowly screw the cup on the sensor body Allow the excess water to escape Make sure that no bubbles are enclosed Fix the Tensiometer at an angle so the cup is pointing downwards and the black mark on the shaft is on top Degas the water in the syringe as described above and connect it to the refilling tube it has a black mark Do not bend the rubber tube Carefully inject water into the refilling tube until no bubbles come out of the de airing tube Inject at least 25 ml Check the pressure all the time 10 Remove the syringe an
13. tubes Please contact Delta T SWT4 User Manual v3 1 Appendix 9 43 8 3 2 Handheld measuring device The SWT MR Infield7 manual readout unit for taking and storing spot readings of soil water tension soil temperature and filling status Includes an automatic offset correction for water column height and installation angle Suitable for all SWT Tensiometers The unit comes with a small carrying case Delta T no A USB converter is available for data collection from the SWT MR to a PC via PC or laptop It includes Windows PC software TensioVIEW Item Delta T no USB PC adapter for SWT MR SWT MR USB 44 Appendix SWT4 User Manual v3 1 9 Tensiometer loggers All SWT Tensiometers can be connected directly and without further power supply to the special Tensiometer logger DL6 tens Accessories are available for converting GP1 and DL2e loggers to take Tensiometer readings DL6 tens Logger The DL6 tens can take six SWT Tensiometers TEA This is a factory modified Delta T DL6 6 i RR channel logger modified with six 4 pin M12 sockets pt Each Tensiometer needs a SWTEC 20 extension cable GP1 Logger A GP1 logger can take two SWT Tensiometers Each tensiometer requires a GP1 PBA1 adapter and connection cables type SWTCC XX In addition 2 SM200 soil moisture sensors or 10K thermistors and a WET sensor may also be connected at the same time along with two digital s
14. GP1 Logger users LS2Win Software online help for DL2e Logger users SWT4 User Manual v3 1 Introduction 9 Please note Y Especially in loamy clayey soils a high pressure can occur just by inserting the SWT4 or SWTAR into the borehole Thus the pressure values should be continuously observed during installation with an SWT MR Infield7 Manual Readout Unit or a data logger Keep it less than 200 kPa i e 2000 hPa The less air left inside the cup and the better the soil s conductivity is the faster the Tensiometer will respond to tension changes If the soil is dryer than 90 kPa 900 hPa it does not make sense to refill the Tensiometer immediately Wait until any Tensiometer that is installed in the next lower level again reaches the reading it had when the upper Tensiometer dried out 10 Introduction SWT4 User Manual v3 1 External syringe refilling SWT4R only Installed SWTAR can be refilled or ventilated through the two capillary tubes stainless steel without being removed from the soil The tubes can be extended With the supplied refilling syringe a measuring range of at least 80 kPa can be assured With the special Refilling Kit SWT4 RK2 a range of 85 kPa can be assured Reference air pressure The reference atmospheric air pressure is conducted to the pressure transducer via the water impermeable white Teflon membrane and through the cable The membrane must always have contact to t
15. actly 10 6 V i e supply minus 0 V and supply plus 10 6 V the Tensiometer output signal range is between 3 2 V min and 6 8 V max relative to the power supply minus This may be outside the common mode range of some loggers Other supply voltage ranges are permissable but the output signal range has to be recalculated Y The supply voltage must be constant and stabilized If the Tensiometer is not permanently powered the warm up period before a measurement is normally 1 second It should be no greater than 10 seconds Y The Tensiometer plug should be covered with the protective cover as Supplied when not connected to a cable The supply voltage must not exceed 18 VDC SWT4 User Manual v3 1 Installation 9 23 3 5 4 Connection to Delta T Loggers All SWT Tensiometers can be connected directly and without further power supply to the special Tensiometer logger DL6 tens Accessories are available for converting GP1 and DL2e loggers to take Tensiometer readings DL6 tens Logger The DL6 tens can take six SWT Tensiometers This is a standard Delta T DL6 6 channel logger modified with six 4 pin M12 sockets Each Tensiometer needs a SWTEC 20 extension cable GP1 Logger A GP1 logger can take two SWT Tensiometers Each tensiometer requires a GP1 PBA1 adapter and connection cables type SWTCC XX In addition 2 SM200 soil moisture sensors or 10K thermistors and a WET sensor may also be connected at the same ti
16. ate them every two years Return the Tensiometers to Delta T for recalibration or contact us for details about available calibration accessories 4 2 2 Check the Offset There are two ways to check the offset 1 Connect the Tensiometer to a readout device Fill the beaker with distilled or de ionized water and immerse the ceramic cup to a depth of 7 5 cm Wait until the reading is stable If there are bubbles inside the cup this might take a while The reading now should be 0 kPa 2 To check the zero point more precisely unscrew the cup Shake the pressure sensor to remove water from the pressure transducer hole The offset is acceptable when the reading is between 0 5 and 0 5 kPa Y The pressure sensor diaphragm is inside the small hole on the pressure sensor body It is very sensitive and must never be touched It can be destroyed even by slightest contact No contamination should get on the sealing and gasket Before reassembling cup and sensor body carry out the degassing procedure see chapter 4 1 2 Refilling in the lab on page 27 For testing the gain a calibration kit is required Contact Delta T for details SWT4 User Manual v3 1 Service and maintenance 9 33 5 Protecting the measuring site 5 1 Theft and vandalism The site should be protected against theft and vandalism as well as against any farming or field work Therefore the site should be fenced and signposts could give information about the
17. atmospheric pressure of 950 hPa the Tensiometer cannot measure a tension below 927 hPa even if the soils gets drier than that The readings remain at a constant value Fig 6 1 between day 10 and 16 Typical behaviour of tensiometer readings when tension exceeds 15 000 hPa close to the surface 100000 Q O O A gt 0 C 0 See 0 z o Fig 6 1 Tensiometer readings with tensions beyond 15 000 hPa If the soil dries to 15 000 hPa the ceramic s bubble point is reached The water in the ceramic cup will run out quickly and the reading of the air filled cup will go to zero Fig 6 1 day 16 to 19 SWT4 User Manual v3 1 Useful notes 37 If it rains before the soils reaches 15 000 hPa the Tensiometer cup will suck up the soil water However the soil water includes dissolved gasses which will degas as soon as the soil dries again increasing the tension This will result in a poor response the signal curve will get flatter and readings will only slowly adapt to the actual soil water tension Depending on the size of the developed bubble readings will get less close to the maximum Fig 6 2 after day 20 Interpretation of readings below 10 000 hPa a 2 0 gt Se z 0 Fig 6 2 Tensiometer readings with tensions to 10 000 hPa Other problems that can be recognized by checking the data Soil water tension
18. d re connect the rubber tube to the open refilling tube 28 9 Service and maintenance SWT4 User Manual v3 1 4 1 3 Refilling in the field SWT4R only SWTAR Tensiometers can be refilled with the 50 ml syringe Supplied through the stainless steel tubes without removing them from the soil If the refilling tubes have a total length of 5 meters or more use the hand operated vacuum pump see section 4 1 4 With this method a range of at least 80 kPa can be measured Syringe De airing tube Fig 4 2 Downward tilted installation the marked tube is the refilling tube the unmarked tube the de airing tube De airing tube De airing tube with black mark Fig 4 3 Upwards tilted installation the marked tube is the de airing tube the unmarked tube the refilling tube SWT4 User Manual v3 1 Service and maintenance 9 29 Procedure see fig 4 2 amp 4 3 1 2 Connect the SWTAR to the measuring device and keep an eye on the pressure signal all the time Two steel capillary tubes come out from the SWT4R shaft the refilling tube and the de airing tube In a downwards tilting installations the marked tube is the refilling tube in an upwards installation the unmarked tube is the refilling tube Pull off the rubber tube from the refilling tube Degas the water inside the syringe as described above Connect the syringe to the refilling tube Carefully inject water into the refillin
19. e under permanent solar exposure the tubes get sticky Thermal inuslation and brownish tube Y Slide the supplied thermal insulation tube over the shaft end and the refilling tubes as shown in above photo 3 1 5 Use of Tube Jackets and Conduit Tube Jackets These are useful with shafts longer than 2 m in pebbly soils or gravel and for horizontal installations from inside a well or pit hole The tube jacket should end 30 to 50 cm away from the cup so that no leakage or condensation is conducted to the cup The inner diameter of the jacket should be at least 35 mm Tube Jackets 16 Installation SWT4 User Manual v3 1 Conduit This pictures shows an example of the use of flexible cable conduit trunking to protect the tensiometer cables 3 1 6 Ideal conditions for installation For the installation of Tensiometers the ideal conditions are e Frost free soil e Wet coarse clay or loess wind deposited soil e Low gravel content The more gravel in a soil the more often the drilling has to be repeated to reach the required depth 3 1 7 Documentation For every measuring spot you should e Measure out the position where the pressure sensor will be placed A must for installations below the ground surface Take documentary photos before during and after installation Save a soil sample Write down installation depth and angle with each sensor identification serial number e Mark all connecting cables w
20. e refilling tube is the longer stainless steel tube without the black mark Water is injected into this tube for refilling Before inserting the Tensiometer turn the shaft so the black mark near the shaft end points downwards Y Do not turn the shaft after it is inserted into the ground as this might loosen the cup Note that with a horizontal installation the optional filling indicator will not react until the cup is almost empty 18 9 Installation SWT4 User Manual v3 1 3 3 Installation procedure For the installation of the Tensiometer in the field the following tools are required e Tensiometer auger with diameter 25 mm ideally the SWT4 AUG Gouge Auger with shaped blade tip Rule spirit level angle gauge marker pen Notebook camera for documentation of site and soil profile Perhaps PE plastic bags for taking soil samples from the site Thermal insulation tubes for installations from soil surface Cable protection conduit Tube Jackets if required inner diameter gt 35 mm Please observe the following notes Do not touch the cup with your fingers The ceramic should not have contact with grease or soap as this will influence the hydrophilic performance Do not leave the cup in air for more than 5 minutes as Tensiometer water will evaporate and the Tensiometer will need to be refilled Procedure 1 Mark the required drilling depth on auger and Tensiometer shaft The reference point is the center o
21. eed 200 kPa 2000 hPa because gt 300 kPa is fatal Note for SWT4R Tensiometers Important Pay attention to the engraved black spot on the shaft s top end that marks the position of the exit opening of the external filling inside the cup a Downward tilting installations If the position of the cup will be lower than the end of the shaft the black mark must exactly face up b Upward tilting installations If the position of the cup will be higher than the end of the shaft the black mark must exactly face down Fig 3a Downwards installation Fig 3b Upwards installation 20 9 Installation SWT4 User Manual v3 1 5 Press the soil surface with your boots gently to the shaft to close the gap 6 Push the shaft water protection disk down to cover the soil surface This prevents water from running down into the borehole along the shaft 7 Leave the protective plastic cover on the plug whenever the plug is not connected 8 Connect the signal cables as described in the chapter Connecting the SWT4 or SWTAR on page 23 9 The Tensiometer will respond to changes in the soil water tension faster if there is no air inside the system and the soil water conductivity is high 10 Write down the serial number position installation angle and depth 11 Slide the supplied thermal insulation tube over the shaft end and the refilling tubes Bend the signal cable and lead it back through the thermal tube 12 Protec
22. ensors such as rain gauges When fitting 5 or more sensors use the GP1 LID2 expansion lid which has additional cable glands DL2e Logger Up to 60 SWT tensiometers may be connected to a single DL2e Each group of 15 Tensiometers require one LAC1 input cardand one TVB1 voltage regulator 60 channel DL2e logger Contact Delta T SWT4 User Manual v3 1 Tensiometer loggers 45 9 1 1 Voltage regulators Tensiometer power supply unit for SWT3 SWT4 SWT5 fitted to a DL2e logger extension frame left or as an open module right The regulated power supply itself can power up to 60 tensiometer Each TVB1 logger frame has supply terminals for 15 Tensiometers Contact Delta T if you wish to fit more than 15 Tensiometers to one DL2e logger Delta T no TV batt for DL2e logger TV batt module only 9 1 2 Refill kits A ae a SWT4 FRK2 Refill kit for SWT4 LRK2 Laboratory refill kit for externally refillable Tensiometers SWT4 amp SWTTAR incl Tensiometers SWTAR incl stand clamps adapter for SWT4 hand operated vacuum pump sensor body 500 ml bottle pressure 250 ml bottle refill syringe gauge tubes beaker refilling syringe tubes valves and pliers Delta T no Refill kit for field use SWT4 FRK2 Laboratory refill kit SWT4 LRK2 46 9 Tensiometer loggers SWT4 User Manual v3 1 All vacuum glass bottles are coated and implosion proof 9 1 3 Tensiometer augers Tensio
23. est of the user manual It is only a summary Please read the complete manual carefully before using the instrument particularly Chapter 3 and 5 1 Drilling the borehole Mark the required drilling depth both on auger and on Tensiometer shaft Note Installation depth drilling depth cos a For SWTA4R For installation from the soil surface an installation angle of 25 to 65 from the vertical line is ideal for the optimal removal of air from the cup Fig 1a For horizontal installation from a manhole the borehole should point upwards in an angle of 5 Fig 1b 2 Slurrying the cup is only reasonable in clayey soils and only if the bore hole is larger than the ceramic cup 24 mm In coarse sand or pebbly soils a fine pored slurry might create a water reservoir which slows down the response With the special Tensiometer gouge auger type SWT4 AUG slurrying is unnecessary because of the accurate fit of the Tensiometer into the hole 3 Take off the protective plastic bottle from the Tensiometer cup Tilt and pull the bottle off carefully If necessary carefully turn it counter clockwise only as marked on the bottle Y Turn the bottle counter clockwise only when you remove the bottle but also when you reassemble the bottle See arrow on bottle label 4 Insert the SWT4 or SWTA4R into the hole to the depth mark with constant gentle pressure and without using force In clayey soils a dangerous overpressure might devel
24. f the cup Drill a hole with the desired depth on the chosen measuring spot Auger in steps Take care when drilling the last 20 cm remove and save this soil Water will not run along the shaft if the Tensiometer is installed in an angle because the water will drain into the soil before it reaches the cup Read the chapter Selecting the installation angle for the best installation angle on page 18 2 When using augers with a diameter of over 25 mm mix a paste of water and crumbled soil material taken out of the borehole Fill the paste into the bottom area of the borehole by using a simple pipe with outer diameter 2 cm SWT4 User Manual v3 1 Installation 19 o9 Now remove the protective plastic bottle from the Tensiometer cup Important Only turn the bottle counter clockwise when taking the bottle off and also when putting it back on again Save the plastic bottles Do not store the Tensiometer without the protective plastic bottle since the cup empties quickly The bottle must be filled with some water for storage 4 Connect the Tensiometer to a readout unit Carefully insert the SWT4 SWTA4R into the borehole up to the stop while continuously observing the pressure signal Do not use any force Do not hit the Tensiometer this may damage cup and pressure sensor Especially in clayey soils the pressure reading must be monitored as high pressures might build up The pressure should not exc
25. filling tube is the unmarked tube 2 Connect the empty syringe to the refilling tube and completely suck out the Tensiometer water 3 Re connect rubber tubes and filling tube Y SWT4 Tensiometer if installed within the depth of frost penetration must be removed and stored in a frost free place 5 4 Lightning protection and grounding In the field measuring equipment is always susceptible to electrical surge Our equipment is protected against over voltage and wrong polarity as far as this is technically achievable There never can be total lightning protection Lighting strikes are unpredictable and vary significantly with region voltage and destructiveness Proper lightning protection has to be considered whenever a system with several sensors and loggers is installed Passive lightning protection measures would comprise one or more grounding rods preferably with ground water contact but without an electrical connection to the measuring system With an active lightning protection each sensor and the logger are equipped with an individual grounded surge protection module Unfortunately these are very expensive Please contact Delta T or your distributor for assistance about integrating SWT4 or SWTAR into your measurement system SWT4 User Manual v3 1 Protecting the measuring site 9 35 General recommendations for lightning protection and grounding for stations with battery power Measure the distances between sensor
26. for a period of twelve months from the date of delivery Delta T shall be under no liability in respect of any defect arising from fair wear and tear and the warranty does not cover damage through misuse or inexpert servicing or other circumstances beyond their control If the buyer experiences problems with the goods they shall notify Delta T or Delta T s local distributor as soon as they become aware of such problem Delta T may rectify the problem by replacing faulty parts free of charge or by repairing the goods free of charge at Delta T s premises in the UK during the warranty period If Delta T requires that goods under warranty be returned to them from overseas for repair Delta T shall not be liable for the cost of carriage or for customs clearance in respect of such goods However Delta T requires that such returns are discussed with them in advance and may at their discretion waive these charges Delta T shall not be liable to supply products free of charge or repair any goods where the products or goods in question have been discontinued or have become obsolete although Delta T will endeavour to remedy the buyer s problem Delta T shall not be liable to the buyer for any consequential loss damage or compensation whatsoever whether caused by the negligence of the Delta T their employees or distributors or otherwise which arise from the supply of the goods and or services or their use or resale by the buyer Delta
27. g tube until no bubbles come out of the de airing tube Inject at least 25 ml Check the pressure all the time Remove the syringe Put a drop of water on the ends of both the rubber and steel tubes and then connect them together 4 1 4 Refilling with a vacuum pump SWTAR only To achieve the maximum possible measuring range Tensiometers can be completely degassed using a vacuum pump This method can be applied for installed Tensiometers at any installation angle as well as for Tensiometers not yet installed For refilling tubes longer than 5 meter this method should always be used The refill kit SWT4 FRK2 includes all required tools hand operated vacuum pump vacuum bottle with tube and syringe with valve a Sal Asst Fig 4 4 External refill kit SWT4 FRK2 for the SWT4R 30 9 Service and maintenance SWT4 User Manual v3 1 Syringe AN Se Refilling tube with black mark gt ta Ie Mark on shaft Manual or other vacuum pump Vacuum bottle Fig 4 5 Downwards installation the marked tube is the refilling tube the unmarked tube the de airing tube fi Syringe 78 De airing tube Refillingtube __ 4 AE Mark on shaft Manual or other vacuum pump Vacuum bottle De airing tube with black mark Fig 4 6 Upwards installation the marked tube is the de airing tube the unmarked tube the refilling tube Procedure see Fig 5 4 amp 5 5 li
28. gligible because ion concentration differences are equalized quickly If the SWT4 cup is dipped into a saturated NaCl solution the reading will be 1 kPa for a short moment then it will drop to 0 kPa again SWT4 User Manual v3 1 Useful notes 39 6 5 Using Tensiometers as a piezometer SWT4 or SWTA4R can be used as a piezometer for measuring water overpressure Calculate the height of the water level with P 5 hPa Px20 Density of water at 20 C 0 998205 kg dm at 4 C 1 0 kg dm Pa N m N kg m s Pa kg s m A water column of 100 cm causes the following pressure p Pa N m 998 205 kg m x 9 81 m s x 1m 0 9792 39 kg m x m s x m 9 792 kPa Accordingly 10 kPa at 20 C indicate a water column of 102 15 cm 7 Troubleshooting Please refer to the Delta T website where you will find a regularly up dated list of FAQs http www delta t co uk product fag table html product2005092818915 40 Troubleshooting SWT4 User Manual v3 1 8 Appendix 8 1 Technical specifications Material and dimensions Ceramic material Ceramic dimensions Shaft material Sensor cable For shaft lengths lt 120 cm For shaft lengths gt 121 cm AlzO3 sinter bubble point gt 15 bar Length 60 mm 24 mm Impact proof PMMA 2 25 mm Length 1 5 m from sensor body effective length 1 5 m minus shaft length Length 2 3 m from sensor body effective length 2 3 m minus shaft length
29. he air and should never be submersed into water Cable gland P67 SWT4 and SWT4R can be completely buried if required If buried cables and tubes should be protected Special cable glands are available for making tight seal to with plastic protection tube for the cable see Accessories on page 43 Transparent acrylic shaft One piece shafts from 10 cm to 200 cm are available Shafts over 200 cm are divided with threaded adapter and are available up to nearly any length Sensor body with electronic The incorporated piezoelectric pressure sensor measures the soil water tension against atmospheric pressure Direct connection to any power supply e g battery TVB1 or TVB M power supply unit Pressure transducer Position of the pressure sensor opening position of the temperature sensor and the ventilation tube High grade porous ceramic cup Filled with degassed water with refilling tube SWT4 User Manual v3 1 Introduction 11 2 Sensor Description 2 1 Parts 2 1 1 Body and shaft The pressure transducer is integrated in the sensor body The electronics are completely sealed and thus well protected against moisture The shaft is made of transparent blue acrylic plastic and has a very high durability and impact resistance 2 1 2 Pressure sensor The piezoelectric pressure sensor measures the soil water tension against the atmospheric pressure Atmospheric pressure is conducted via a white air permeable membrane on t
30. he cable through the cable to the reference side of the pressure sensor Y The maximum permissible i e non destructive pressure is 3 bar 300 kPa 3000 hPa Higher pressure will damage the sensor and absolutely must be avoided High pressures can appear for example when cup and sensor are reassembled when inserted in wet clayey soils or in tri axial vessels used for measuring shear forces 2 1 3 Reference air pressure The reference atmospheric air pressure is conducted to the pressure transducer via the air permeable white Teflon membrane in line in the cable The membrane does not absorb water Water will not pass through the membrane into the cable but condenation inside the cable can leave the cable through the membrane Y The white membrane on the cable must always have contact to air and should never be submersed under water 12 9 Sensor Description SWT4 User Manual v3 1 2 1 4 The ceramic cup To transfer the soil water tension as a negative pressure into the Tensiometer a semi permeable barrier is required This must have good mechanical stability be permeable to water and impermeable to gas when wet The Tensiometer cup consists of ceramic Al2O3 sintered aluminium A special manufacturing process guarantees homogeneous porosity with good water conductivity and very high hardness Compared to conventional porous ceramic the cup is much more durable The bubble point is at least 1500 kPa 15 bar 15 000 hPa
31. hods e Syringe with valve one supplied with each order e Degassed de ionized or distilled water e Measuring device for checking the pressure signal Simple method to degas water The best way to degas water is by using a syringe e Draw up water into the syringe until it is 2 3 filled Close the valve or block the syringe with your finger e Now draw up the syringe as far as possible to create a vacuum inside Rotate the syringe to create one big bubble e Remove your finger or open the valve and squeeze out the bubble Repeat this procedure a few times 4 1 1 When do Tensiometers need to be refilled Tensiometers need to be refilled if e the curve of the readings apparently gets flatter for example a rain event has no sharp peak but is round e the maximum of 85 kPa is not reached anymore Refilling is only reasonable if the soil is moister than 90 kPa or as soon as a Tensiometer installed in a lower level shows wetter readings than the reading at which the upper Tensiometer stopped working If the soil gets dryer than 85 kPa the readings will remain constant at the vapor pressure of water for example the reading will be 92 7 kPa at 20 C and atmospheric pressure of 95 kPa By diffusion and slight leakage the reading will slowly drop within months 26 Service and maintenance SWT4 User Manual v3 1 If the soil dries out more than 1500 kPa 15 bar the negative pressure will drop much fas
32. ith the corresponding sensor identification serial number or logger channel on each end Clip on numbered rings are available as an accessory Contact Delta T for more information SWT4 User Manual v3 1 Installation 17 3 2 Selecting the installation angle Ideally a Tensiometer installation should not disturb the flow of water To prevent the preferential flow of water along the shaft Tensiometers should be installed at an angle 3 2 1 Vertical tilting downwards SWT4R only When installed from the surface an angle of 25 to 65 from the vertical is optimal for refilling In an absolutely vertical position air bubbles might hide inside the edges of the cup adapter Still they could be removed completely with a hand vacuum pump contact Delta T for details In this position the refilling tube is the shorter stainless steel tube with the black mark Water is injected Into this tube for refilling Before inserting the Tensiometer orient the shaft so the black mark near the shaft end points upwards Do not rotate the shaft after it is inserted into the ground as this might loosen the cup 3 2 2 Horizontal tilting upwards SWT4R only When installed horizontally from inside a well or pit hole the Tensiometer must point upwards This means the cup is in a higher position than the end of the shaft An upward angle of approx 5 is ideal for refilling Note that now de airing and refilling tube are switched th
33. me along with two digital sensors such as rain gauges When fitting 5 or more sensors use the GP1 LID2 expansion lid which has additional cable glands DL2e Logger Up to 60 SWT tensiometers may be connected to a single DL2e Each group of 15 Tensiometers require one LAC1 input card In addition each group of 15 require one TVB1 voltage regulator which itself requires a 12V supply from a 12V battery or mains powered power supply 24 Installation SWT4 User Manual v3 1 TVB M Voltage regulator for the DL2e Logger This regulated power supply is specially designed for powering Tensiometers SWT3 SWT4 SWT4R and SWT5 when connected to a DL2e logger It provides a stabilised 10 6 V power supply but with the supply minus at 5 V and supply plus at 5 6 V This arrangement ensures the Tensiometer signals are less than 1 V The TV Baitt itself requires power from a 12V battery or a mains to 12 V power converter Each TVB M module has screw terminals to power up to 15 Tensiometers See also Voltage regulators on page 46 SWT4 User Manual v3 1 Installation 9 25 4 Service and maintenance 4 1 Refilling To assure a rapid and reliable measurement of the soil water tension the cup must be filled possibly bubble free with degassed water After dry periods or periods with a large number of wet and drying out successions the SWT4 or SWT4R must be refilled The following items are required for all refilling met
34. meter gouge auger with specially shaped blade The tip of the blade has the same shape and diameter as the Tensiometer cup so the Tensiometer fits tightly into the borehole Thus no slurrying of the cup is necessary Set includes gouge auger and handle with hammering head Delta T no SWT4 AUG Please ask Extension rod length 100 cm SWT4 User Manual v3 1 Tensiometer loggers 47 000 000 000 0 9 908 6 000 000 0 Aap U AO uepu d p 00 000 00 9699 086 000 000 Ayipiuiny 1e Alp OL 000 0L 6990 86 000 00 _ yurod G L 00S L 6 602 000 0 1 8 0 000 L 9 9086 000 0 psepuels cor 00 67 gt 269 Lv YOSH 000 L 8900 860 0000 0218 06 OSH 2268 86 c9 6le 8690 66 1097 906 66 VOGHI re YT l l 9 2 Units for soil water and matrix potentials I SWT4 User Manual v3 1 48 9 Tensiometer loggers 10 Technical Support Terms and Conditions of sale Our Conditions of Sale ref COND 1 07 set out Delta T s legal obligations on these matters The following paragraphs summarise Delta T s position but reference should always be made to the exact terms of our Conditions of Sale which will prevail over the following explanation Delta T warrants that the goods will be free from defects arising out of the materials used or poor workmanship
35. normally change only slowly An erratic signal curve with many discontinuities could indicate for example loose contacts moisture in defective cables or plugs poor power supply or a data logger malfunction With SWT4R Tensiometers unsteady signals can also be caused by solar radiation on the refilling tubes To prevent this fit thermal insulation see page 16 38 Useful notes SWT4 User Manual v3 1 6 2 Temperature influences If the sensor is not powered continuously the voltage should be switched on for no longer than 10 seconds before a measurement In this case the self heating is negligible The correlation of water tension to water content is temperature dependent The influence is low at tensions of 0 to 10 kPa gt 0 0 6 kPa K but high for tensions over 100 kPa 1 bar 1000 hPa R T Y In M Po Water tension R Gas constant 8 31J mol K M Molecular weight p Vapor pressure Po Saturation vapor pressure at soil temperature from Scheffler Straub Grigull 6 3 Vapor pressure influence If the temperature of a soil with a constant water content rises from 20 C to 25 C the soil water tension is reduced for about 0 85 kPa due to the increased vapor pressure which opposes the water tension Pressure change per Kelvin in 7 porodom 6 4 Osmotic effect The ceramic has a pore size of r 0 3 um and therefore cannot block ions Thus an influence of osmosis on the measurements is ne
36. of Tensiometers 3 1 3 Extent of the site A large number of well spaced samples will help reduce sampling errors in heterogeneous soils To obtain a differential description of the soil water situation at least 2 Tensiometers are recommended per horizon one in the upper and one in the lower level The maximum recommended cable length for SWT4 and SWTAR is 40 meters Accuracy long cables reduce the accuracy Lightning cables act as antennas and should always be as short as possible SWT4 User Manual v3 1 Installation 9 15 3 1 4 Protection of refilling tubes SWT4R only A recent study by Prof Wolfgang Durner showed that refilling tubes must be protected from heating up and solar radiation If a bubble grows inside a refilling tube temperature changes will lead to an expansion of the air resulting in a variation of the reading Therefore refilling tubes should be as short as possible and should be thermally protected either by providing an insulating protection or by burying the tubes Thermal effect As long as the Tensiometer and its tubes are freshly and completely filled it will work perfectly Any air trapped inside the upper parts of the tube will expand when heated up by solar energy This causes a drop of the water tension and some water will flow from the cup into the ground Thus readings will fluctuate around the actual reading during solar radiation specially with low water potentials Furthermor
37. op So monitor the Tensiometers pressure with a type SWT MR INFIELD7 Manual Readout Unit or a data logger Y Do not exceed 2 bar 200 kPa 2000 hPa during insertion Y Do not turn the Tensiometer after it is inserted into the ground this might loosen the cup 8 9 Introduction SWT4 User Manual v3 1 Note for SWT4R Tensiometers Y Pay attention to the engraved black spot on the shaft s top end that marks the position of the exit opening of the external filling inside the cup a Downwards installation If the position of the cup will be lower than the end of the shaft the black mark must exactly face up The optimal installation angle is between 25 and 65 b Upwards installation If the position of the cup will be higher than the end of the shaft the black mark must exactly face down The optimal installation angle is about 5 Fig 1a Downwards installation Fig 1b Upwards installation 5 Push down the shaft water retaining disk to a position directly on the soil surface 6 For SWTAR Slide a thermal insulation tube over the capillary filling tubes 7 If the plug is not connected right away leave the protective cover on the plug Dirt will influence the impermeability and water tightness is only assured when the plug is kept clean 8 Connect the Tensiometer signal wires to either a data logger or the SWT MR Infield7 See also Wiring Configuration on page 42 GP1 PGA1 Quick Start Guide for
38. positions data acquisition etc to get to know the potential levels Recommendations for 2 or 3 meter masts can be equipped with a lightning protection on lightning rod which is installed on top of the masts mast and a grounding rod which is clamped to the foot of the mast This creates a zone of protection in a 45 degree angle cone around the tip Recommendations for Install surge protection devices in one lightning protection of corner of the measuring enclosure All lines enclosures to and from the surge protection devices should not run parallel System protection of Install a separate earth grid 50 cm below stations with enclosure the soil surface to equalize variations in the and mast ground potential between the sensors and the mast grounding rod Lightning protection According to the standards the ground rod with grounding rods diam 25 mm must be inserted into the ground for a minimum of 2 5 meters below the frost level i e in general 3 meters Cross shaped rods are less advisable for such low depths but this depends on soil type moisture or clay content and distance between soil surface and ground water level 36 9 Protecting the measuring site SWT4 User Manual v3 1 6 Useful notes 6 1 Maximum measuring range and data interpretation The measuring range of Tensiometers is limited by the boiling point of water At a temperature of 20 C the boiling point is at 23 hPa over vacuum So with 20 C and an
39. purpose of the site 5 2 Cable protection Cables should be protected against rodents with plastic protection tubes Contact Delta T for further information 5 3 Frost 5 3 1 Protection against frost Y Tensiometers are filled with water and can be damaged by frost Y Do not store filled Tensiometer at temperatures below 5 C Do not leave filled Tensiometers overnight in your car ina measuring hut etc Y Do not fill the Tensiometers with Ethanol as this is corrosive to some materials i e PMMA and will destroy these Also it is not recommended to fill the Tensiometers with Decalin mono ethylene glycol di ethylene glycol etc These could harm any of the materials destroy the ceramic cup or leak into the soil SWT4 and SWT4R Tensiometers may remain installed during the winter if the cup is below 20 cm Then the frost will enter the cup slowly without damaging the pressure sensor The reading will jump to a constant value After unfreezing the Tensiometer will continue to work But as this depends on the climate of your region please contact Delta T if you intend to install Tensiometers in extreme temperature zones 34 Protecting the measuring site SWT4 User Manual v3 1 5 3 2 Emptying SWT4 or SWT4R Also read chapter 4 1 SWTAR Tensiometers 1 Remove the connecting rubber tube from the refilling tube In a downwards installation the refilling tube is the marked tube in an upwards installation the re
40. r 1 3 Reference air pressure 1 4 The ceramic cup 2 External refilling SWT4R only 2 3 Analog output signals 3 Installation Advance planning 1 Selecting the measuring site 2 Number of Tensiometers per level 3 Extent of the site 4 Protection of refilling tubes SWT4R only 5 Use of Tube Jackets and Conduit 6 Ideal conditions for installation 7 Documentation 3 2 Selecting the installation angle 3 2 1 Vertical tilting downwards SWTAR only 3 2 2 Horizontal tilting upwards SWT4R only 3 3 Installation procedure 3 4 Offset correction for non horizontal installations 3 4 1 How to measure the zero offset of a tilted tensiometer 3 5 Connecting SWT4 and SWT4R 3 5 1 Spot reading with the SWT MR Infield7 3 5 2 Connecting cables 3 5 3 Connection to a data logger 3 5 4 Connection to Delta T Loggers 4 Service and maintenance ol CONNNNOOOOu SWT4 User Manual v3 1 9 3 4 1 Refilling 4 1 1 When do Tensiometers need to be refilled 4 1 2 Refilling in the lab 4 1 3 Refilling in the field SWT4R only 4 1 4 Refilling with a vacuum pump SWTAR only 4 2 Testing 4 2 1 Calibration 4 2 2 Check the Offset 5 Protecting the measuring site 5 1 Theft and vandalism 5 2 Cable protection 5 3 Frost 5 3 1 Protection against frost 5 3 2 Emptying SWT4 or SWT4R 5 4 Lightning protection and grounding 6 Useful notes 6 1 Maximum measuring range and data interpretation 6 2 Temperature influences
41. t the cables against rodent bites Lead the cables through plastic pipes or use the plastic protection tubes conduit or trunking Contact Delta T for details 3 4 Offset correction for non horizontal installations The pressure transducer is calibrated without a cup Thus no compensation is required for horizontal installations Ifa SWT4 or SWTAR is installed in a non horizontal position the vertical water column draws on the pressure sensor and causes an offset shift Compensate the offset e by calculation e by entering the installation angle in the Infield7 SWT MR for spot readings e inthe configuration of a data logger by setting an offset Transducer Middle of cup The middle of the cup is regarded to be the measuring level The correction is largest for a vertical water column at 0 and varies as the cosine of the installation angle as shown on the table below In an absolutely horizontal position the offset is zero SWT4 User Manual v3 1 Installation 21 Example 1 Using A 5 cm vertical column of water below the pressure sensor will create an 0 5 kPa offset This means that when the soil water tension is 0 kPa the sensor will indicate 0 5 kPa Table showing the offset correction when a 5 cm column of water is tilted at various angles Offset correction in KPa Offset correction in kPa 035 025 17 13 109 fo The offset is entered as in your logger if you regard the soil water
42. tative should contact them in the first instance Technical Support is available on Delta T products and systems Your initial enquiry will be acknowledged immediately with a reference 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 Tech Support Team Tel 44 0 1638 742922 Delta T Devices Ltd Fax 44 0 1638 743155 130 Low Road Burwell email tech support delta t co uk Cambridge CB25 0 U K email repairs delta t co uk web www delta t co uk 50 Technical Support SWT4 User Manual v3 1 11 Index A Accessories 43 Accuracy 41 atmospheric pressure 12 augers 47 C cable 41 extension 43 markers 43 Cable protection 34 cables 23 Calibration 33 CE conformity 2 ceramic 13 Ceramic 41 clay 17 Conditions of sale 49 Conduit 16 connection cables 43 Contact Details 50 Copyright 2 Current consumption 41 D data logger 23 Description 12 DL2e Logger 24 DL6 tens 24 45 Durability 6 E Emptying 35 F Frost 34 G GP1 Logger 24 gravel 17 grounding 35 I Infield7 44 Installation 15 procedure 19 installation angle 18 J Jacket Tubes 16 L Lightning protectio 35 loess 17
43. ter as air will enter the cup 4 1 2 Refilling in the lab To reach the optimal measuring range of 90 kPa Tensiometers should be refilled in the laboratory using the refill kit 1 Set up the refilling kit and connect the vacuum pump as shown in fig 4 1 The pump should achieve at least 0 8 kPa against vacuum Use distilled or de ionized water which does not necessarily have to be degassed when a pump is used 9 Vacuum gauge Adaptor for sensor body Adaptor for gt ceramic cup Connect to pump Fig 4 1 Laboratory refill kit SWT4 RK2 2 Unscrew the cup in clockwise direction and empty it Do not touch the ceramic cup with your fingers Wrap a clean towel or paper towels around the cup Y The pressure sensor diaphragm is inside the small hole on the pressure sensor body It is very sensitive and must never be touched It can be destroyed even by the slightest contact Nocontamination should get on to the sealing and gasket 3 Ifthe cup is dry it should be placed in a beaker filled with distilled water for several hours or overnight Initially there should be no water inside the cup Place the empty cup into the beaker in an upright position with the external water level reaching no higher than 2 3 of the cup SWT4 User Manual v3 1 Service and maintenance 9 27 Warning If the cup is filled with water and water intrudes from both inside and outside cavities of air will be
44. tter but also the soil texture particle size distribution cracks compaction roots and cavities All these heterogeneities cause the soil water tension to vary It is prudent therefore to have multiple measuring points particularly in soil horizons close to the surface 1 6 2 Intended use Tensiometers measure soil water tension a measure of the soll matrix potential which is the work the plant needs to do in order to extract water from a unit volume of the soil These Tensiometers work from 100 kPa water pressure to 85 kPa suction or soil water tension If the soil gets drier than 85 kPa the Tensiometer runs dry and must be refilled as soon as the soil is sufficiently moist again see Fig 6 1 Soil water and Tensiometer water have contact through the ceramic which is porous and permeable to water A wetted porous ceramic creates an ideal pore water interface The soil water tension is directly conducted to the pressure transducer which offers a continuous signal The atmospheric reference pressure is provided through a membrane on the cable a unique patented method 1 6 3 Types The SWT4 is available in 2 versions the standard SWT4 without refilling tubes and the SWT4R with refilling tubes for refilling the Tensiometer in the field with a syringe Separate refilling instructions for the SWT4R are provided in section 4 SWT4 User Manual v3 1 Introduction 7 1 7 Quick Start This section does not replace the r
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