EQ2 user manual version 1.2
Contents
1. soils at the other There is no generalised method of converting from soil water content to matric potential though a number of expressions have been found which have been successfully applied to a restricted list of soil types see for example references 2 1 Gaskin G J and J D Miller 1996 Measurement of soil water content using a simplified impedance measuring technique J agric Engng Res 63 153 160 2 Campbell G S 1974 A simple method for determining unsaturated conductivity from moisture retention data Soil Sci 117 311 314 EQ2 UM 1 3 Guarantee repairs and service Our Conditions of Sale ref COND 91 11 set out Delta T s legal obligations on these matters For your information the following paragraphs summarise Delta T s position but reference should always be made to our Conditions of Sale which prevail over the following explanation Instruments supplied by Delta T are guaranteed for one year against defects in manufacture or materials used The guarantee does not cover damage through misuse or inexpert servicing or other circumstances beyond our control For the UK this means that no charges are made for labour materials or return carriage for guarantee repairs For other countries the guarantee covers free exchange of faulty parts during the guarantee period Alternatively if the equipment is returned to us for guarantee repair we make no charge for labour or materials but we do charge for carriage and UK2. 9 1 values in the mV column step size step size EA a Q used to calc Interpolated 50 tables original calibration table i E71 table as FULL range DEAE supplied Output Matric Potential i mV Matric mV kPa Potential kPa EMO 0 10 l 20 383 40 198 0 150 1320 600 100 150 200 300 400 1000 1298 900 Page 11 EQ2 UM 1 3 Wet range 0 4 es 0 0 50 0 100 0 150 0 200 0 250 0 300 0 350 0 400 0 450 0 Y Q u A 100 Q de ae m qun H 4 Matric Potential kPa ny polynomial curve fit Matric Potential kPa m e e e O 9 9 9 9 300 y 25 85E 12 x 46 55E 9x 34 52E 6x 13 50E 3x 2 94E 0x 338 57E 0x 16 28E 3 400 010 50 0 100 150 EQ2 output mV Full range 200 0 250 0 300 0 350 0 400 0 450 0 100 Matric Potential kPa 200 300 400 e 500 600 Matric Potential kPa 700 E 800 900 1000 EQ2 UM 1 3 EQ2 output mV Page 12
3. The soil matric potential within a region of soil will be affected by local variations in soil density and composition rates of percolation runoff evaporation and the uptake of water by nearby roots The resultant differences in pressure will equilibrate over time at a rate which is determined by the local hydraulic conductivity It is important to take the degree of variability of these various parameters into account when deciding on the number of probes to use at any particular location In particular if the soil is known to be very heterogeneous or the distribution of roots is very non uniform it will be necessary to take measurements from at least three closely spaced locations Extension tubes Optional extension tubes can be fitted to enable easier withdrawal and to protect the cable from damage by animals etc Two lengths are available ML EX50 is 50cms long and ML EX100 is 100cms long These can be screwed into each other to make longer lengths as required The outside diameter of the extension tubes is 4cms so an auger of approximately 5cms is recommended Instructions for adding extension tubes Carefully remove the black plastic thread protection cover from the Equitensiometer This cover protects the extension tube mating thread when extension tubes are not needed It can be removed by sliding it up the cable Pass the Equitensiometer cable through the hole in the extension tube ensuring that the female thread in the ext
4. be used or if the logger has to supply significant power to other sensors or accessories we recommend powering the logger and sensors from an external power supply Although the probe can be continuously powered significant power can be saved by using a warm up relay to energise the sensor just before and during a log The DL2e and DL3000 loggers include a minimum of two relay controlled outputs to provide and control sensor power Each relay is capable of switching 1A which means that each logger can power 60 Equitensiometers provided they are the sole warm up relay contact load DL2e connection and configuration This diagram shows the connections for an Equitensiometer connected to channel 1 of a DL2e in differential mode and powered through the loggers internal power supply Further details can be found in the SENSORS TXT file which is supplied with the DL2e sensor codes for the Equitensiometer and in the DL2e user manual in the Relay Channels section Two sensor configuration codes are supplied with the DL2e E2D is intended for linearising the full range of EQ2 output 0 to 1000kPa and E2W which provides more resolution at the wet end only 0 to 350kPa You will need to enter the individual linearisation table values attached to the calibration data that is supplied with each of your Equitensiometers DL3000 connection and configuration Full details including example connection diagrams are available in the online
5. help provided with Acquire The DL3000 can accept linearisation tables with unequal step SiZes so you can enter the calibration table exactly as supplied and the DL3000 will then linearise to full resolution over the full range Note each Equitensiometer needs its own linearisation table Operational considerations EQ2 UM 1 3 Hysteresis and response time effects The Equitensiometer only reads correctly once the equilibrium state within the probe is reached Normally there is a time lag between the change of matric potential of the surrounding soil and the response of the Equitensiometer This time lag is greatest when the matric potential is changing fast and at large negative matric potentials see Table 1 Under natural conditions changes in matric potential are normally less than 0 01 kPa min so the associated errors will therefore be much lower than the values in Table 1 As shown Page 6 in Fig 3 in both the wetting and drying phases the time lag is similar to that for transducer tensiometers Table 1 Hysteresis of the Equitensiometer in a rapid drying test The values are much higher than under natural conditions Matric potential absolute changes Errors in kPa after minutes EPA pa mim 120 180 300 360 10 sop epee i e CM A UM De NS ee E CER Maintenance Page 7 Soil properties and salinity The Equitensiometer is unaffected not damaged by physical soil properties organic matter stones bulk
6. Equitensiometer SOIL MATRIC POTENTIAL SENSOR TYPE EQ USER MANUAL EQ2 UM 1 3 Contents Patents The Equitensiometer is the result of a joint development between Dr Liu UP GmbH and Delta T Devices and uses novel measurement techniques Patent application 19629745 1 Copyright Copyright 1999 Delta T Devices Ltd 128 Low Road Burwell Cambridge CB5 OEJ England All rights reserved Under the copyright laws this book may not be copied in whole or in part without the written consent of Delta T Devices Ltd Under the law copying includes translation into another language Delta T Devices Ltd 128 Low Road Burwell Cambridge CB5 OEJ England Telephone 44 1638 742922 Fax 44 1638 743155 E mail sales delta t co uk EQ2 UM 1 3 Page 2 Introduction and description Page 3 Equilibrium body The Equitensiometer measures Soil matric potential that is the negative pressure or suction required to extract water from between the matrix of soil particles It is an important indication of plant water stress The value of soil matric potential measured depends mainly on the quantity of water present and the make up of the soil though it is also affected by temperature and salinity The Equitensiometer consists of a precision soil moisture sensor the ThetaProbe whose measuring rods are embedded in a porous material the equilibrium body This material has a known stable relationship between water con
7. customs clearance We strongly prefer to have such repairs discussed with us first and if we agree that the equipment does need to be returned we may at our discretion waive these charges SERVICE AND SPARES We recognise that some users of our instruments may not have easy access to technically specialised backup Spare parts for our own repairable instruments can be supplied from our works These can normally be despatched within 1 working day of receiving an order Spare parts and accessories for sensors not manufactured by Delta T but supplied by us individually or as part of the weather station or other system may be obtained from the original manufacturer We will endeavour to obtain parts if requested but a certain amount of additional delay is inevitable Should it prove necessary instruments may be returned to our works for servicing We normally expect to complete repairs of our own instruments within 2 days of receiving the equipment Other manufacturers sensors supplied by us and returned for servicing will take longer They will have to be returned to the original manufacture for servicing and may be subject to additional delays of two to four weeks Users in countries that have a Delta T Agent or Technical Representative should contact them in the first instance EQ2 UM 1 3 Page 10 Sample Calibration Data Sheet EQ2 interpolation of calibration values for DL2e sensor tables calibration values serial No EQ2
8. density and most chemical soil properties e g pH No tests have been carried out in saline soils so the performance of the Equitensiometer in saline soils is unknown Temperature The output of the Equitensiometer is slightly dependent on temperature The Calibration certificate gives values correct at 20 C For regions with strong temperature variations the following temperature correction should be applied temperature C 20 4 The Equitensiometer will not be damaged by frost but its sensitivity to ice is very much less than water so any measurements taken below freezing will be meaningless Corrected _ value mV measured _ value mV Large concentrations of Sodium ions may affect the calibration curves If the equilibrium body becomes contaminated the sodium may be washed out by repeatedly wetting it in de ionised water and then drying it out by inserting it into dry non saline soil Washing with water does not help because in that case no exchange of water or solute takes place The calibration should be stable for 2 years It can be checked by putting the probe into de ionised water and checking the reading against the 0 kPa value in its calibration table at 20 C the reading should be within 20 mV If re calibration is required the probe will need to be returned to Delta T Devices No other maintenance is required EQ2 UM 1 3 Specifications 40 Measurement parameter Matric soil water p
9. ension tube is towards Equitensiometer Screw the extension tube onto Equitensiometer and hand tighten only Repeat this process for additional extension tubes to make up the length required Finally thread the cable through the black plastic thread protection cover and slide the cover into place over the male thread on the end of the extension tube This will minimise water ingress into the extension tube Frost The Equitensiometer will withstand frosts but any readings taken when the water inside the probe is frozen will be meaningless Page 4 Connections Cable Connections The Equitensiometer is supplied with a four core screened cable which provides these connections Red Power V4 Blue Power 0V Yellow Signal HI load resistance 10KO minimum Green Signal LO Braid Cable screen Not connected within probe The Blue and Green leads are connected internally The braid screen should be connected to digital ground on the logger or other measuring unit If not using Delta T equipment please refer to the manufacturer s instructions If you simply want to log the probe voltage directly it can be treated as a differential voltage source of range 0 1 5V DC and the attached meter or logger should be configured accordingly Warning use as a single ended voltage source will introduce measurement errors due to the sensor power return current and is not recommended Some Equitensiometer variants have a connector fitted in orde
10. otential Accuracy 10 kPa from 0 to 100 kPa 5 of reading from 100 to 1000 kPa Hysteresis not detectable if the change of matric potential is slower than 0 1 kPa min Electronics sealed to IP68 to 5m all exposed parts suitable for long term burial 0 to 40 C Not damaged by use in frozen soils but readings will be incorrect approximately 150 to 550 mV non linear Calibration data and graph supplied with each sensor Dimensions Diameribmm Length 2i0m EQ2 UM 1 3 Page 8 Definitions References Page 9 Soil Matric Potential Studies of plant growth need to characterise the availability of water to the plant and this is usually done using the water potential Y which measures the suction necessary to extract water from the soil and has units of pressure kPa Components of this water potential are contributed by gravity atmospheric pressure osmosis and the capillary action of the soil particles This last component called the Soil Matric Potential Y is highly dependent on the wetness of the soil and varies from 0 kPa at field capacity down to approximately 1500 kPa at the permanent wilting point Soil Water Content versus Soil Matric Potential The relationship between soil matric potential and soil water content is called the soil water release curve it seems to have about 5 other names as well It differs enormously form one soil to another particularly from clay soils at one extreme to sandy
11. r to mate to the appropriate Delta T instrumentation Connection details are given in the relevant instrumentation User Manual Electromagnetic Compatibility EMC The Equitensiometer has been assessed for compatibility under the European Union EMC Directive 89 336 EEC and conforms to the appropriate standards provided the moisture measuring rods and probe body are completely immersed in the soil or other material being measured The cable connecting the Equitensiometer to its associated instrumentation should also be routed along the surface of the soil If the probe is not installed in this way some interference may be experienced on nearby radio equipment Under most conditions moving the equipment further from Equitensiometer typically 1 2 metres will stop the interference Equitensiometers installed near to each other will not malfunction due to interference Power supply and warm ups The Equitensiometer requires a power supply of 5 to 15V DC at approximately 20mA For complete stability a warm up time of 5s is recommended although good repeatability can be achieved using a 1s warm up Battery power consumed by a probe for a single measurement taken with a 5 second warm up time is typically 20mA 5s 0 03mA h Page 5 EQ2 UM 1 3 Connection and configuration for Delta T loggers DL2 amp DL3000 Equitensiometers can be directly powered by Delta T loggers using their internal batteries However if several probes are to
12. tent and matric potential When the probe is inserted into the soil the matric potential within the equilibrium body rapidly equilibrates to that of the surrounding soils The water content of the matric material is measured directly by the ThetaProbe and this can be converted into the matric potential of the surrounding soil using the calibration curve supplied with each Equitensiometer Figure 1 EQ2 UM 1 3 Installation EQ2 UM 1 3 The Equitensiometer should be thoroughly wetted before use and installed at a horizontal or slanting angle Vertical installation may slow the response time and also lead to incorrect readings because rainfall running down the side of the probe housing may wet the soil around the probe excessively This is particularly important if the probe is being installed below the soil surface using a probe extension tube Any gaps between the Equitensiometer and soil should be filled with quartz powder suspension Small changes to the soil structure surrounding the probe will not affect readings It is important to protect the Equitensiometer from strong temperature fluctuations and in particular to avoid exposing the electronics and equilibrium body to different temperatures e g by installing it with the case in strong sunlight Avoid flexing the PVC cable at low temperatures It is advisable to protect the cable before burying it in conditions where it may be attacked by soil insects etc Soil sampling points
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