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No other soil moisture probe system enables you to monitor your soil water profiles with such ease and flexibility. Install an access tube into the soil, insert the PR2 Profile Probe and press the HH2 [Read] button to display an instantaneous reading, or connect the PR2 to a data logger (DL6 or DL2e) and leave the system to record soil moisture changes over time.
The PR2 Profile Probe is built around patented sensing technology which provides unprecedented performance in all soil types, with minimal influence from either salinity or temperature. The PR2/4 model measures soil moisture at 4 depths down to 40cm or the PR2/6 measures at 6 depths down to 100cm.
The PR2 Profile Probe access tube requires an installation hole 27mm in diameter, allowing easy installation and minimal soil disturbance. Access tubes are manufactured to strict tolerances and are exceptionally strong and durable in the soil. Correct installation is essential and we recommend the use of our specially designed augering equipment.
The PR2 Profile Probe is available in two sizes to measure to a depth of 40cm or 100cm. The PR2/4 has sensing elements at 10/20/30/40cm
The PR2/6 has sensing elements at 10/20/30/40/60 and 100cm
Complete Auger KitAccess tube installation is vital. Click here for information about our augering equipment
IntroductionThis note explains some slight but important differences in the design evolution of Access Tubes for Profile Probes, and describes a simple bevelling operation recommended for tubes of older construction.Access Tube Design ChangesSome minor design changes were made to access tubes at the time of the introduction of the PR2 Profile Probe. This advice applies equally to long and short access tubes (types ATL1 and ATS1). The basic dimensions of the access tube have not changed, and Profile Probes type PR1 and PR2 can be used in any access tube. You can distinguish access tubes made for Profile Probes by the shape of the bottom plug. For the PR1 it was conical with a rounded end. For the PR2 it is pointed, as shown in the picture. Installation Warnings!The PR1 access tubes were designed for installation using a hitting block placed in the open end (the mouth) of the access tube. The PR2 access tubes are designed for installation using the Insertion Rod (type AT-ROD1) which applies the driving force to the bottom plug of the access tube. Do not use the PR2 Insertion Rod installation method with tubes of the older PR1 design! You will probably dislodge the bottom plug and destroy the tube. Use only the original hitting block to install this type of access tube.
If you are extracting older access tubes for re-installation in different locations, confirm the type of construction, and use only the insertion method appropriate to that type of tube. Some of the earliest PR2 access tubes were incorrectly manufactured. They were supplied around January to March 2005, and do not have enough adhesion between the bottom plug and the fibre material of the tube. If you cannot see a whitish area of internal grinding in the 2 cm above the bottom plug (see the location in the picture above) then the tube is suspect and should not be used. Delta-T can supply free replacement tubes. Please contact your distributor.
Access Tube Bevel UpgradeA further feature of access tubes introduced since mid 2005 is an internal bevel in the entry to the tube. This significantly improves the ease with which the Profile Probe is inserted into the tube and helps to avoid damage to the rings on the Profile Probe, especially if it is not correctly aligned when inserted into the access tube.The internal bevel is worth applying retrospectively to any access tube that does not already have it. Delta-T can provide a de-burring tool suitable for this operation. It can be used on access tubes whether or not they are already installed in the soil. Please contact your distributor.
Use of the Bevelling ToolIf your access tube does not already have this feature you can quickly create it with the bevelling tool. The desired effect is illustrated in the diagram.In any of the processes mentioned below, avoid fibre composite dust by mopping it up with a damp cloth at all stages. If there is any possibility of inhalation of dust, use a filter face mask before you start the process.First of all inspect the open end of the access tube. The top edge of the tube should be flat and in good condition. If it has been abraded or damaged by use, then use a fine toothed flat file to make it flat and smooth. Apply the bevelling tool (use the pointed end of the tool) to the open end of the access tube. Rotate it carefully by hand for a few rotations to create the desired amount of bevelling. Aim to produce a bevel of not more than half the wall thickness of the tube. Do not overdo this process! This is particularly important on the older PR1 tubes, because the whole of the installation force is transmitted through only the remaining flat area of the tube wall. Remember to clean and dry the inside of the access tube before using the Profile Probe.
The Profile Probe User Manual recommends that you use a Theta Probe (ML2x or ML2) to do a two-point soil-specific calibration.
You need to measure the moisture content of a wet sample of your soil, using the Theta Probe, and then oven-dry the sample and measure its water content once again.
The process is fully described in the Theta Probe User Manual and is also available in a detailed application note available from Delta-T. This should enable you to decide if the possible gain in accuracy is worth the additional effort of the calibration.
If you do not possess a Theta Probe, please contact your distributor or Delta-T for advice. The User Manual is available by email in electronic Acrobat pdf file format (and may be available for download from the Delta-T website).
0 to 0.4 m3.m-3 
± 0.04 m3.m-3
PR2/6: 6 x 0 to 1.0V PR2/4: 4 x 0 to 1.0V
5.5 to 15V PR2/6: ~120mA for 1sPR24: ~80mA for 1s
PR2/6: 10, 20, 30, 40, 60, 100 cmPR2/4: 10, 20, 30, 40 cm (nominal)
Vertically: ~95% sensitivity within ± 50mm of upper rings.Horizontally: ~95% sensitivity within 200mm dia.
PR2/4: 750 x 25.4mm dia.PR2/6: 1350 x 25.4mm dia.
ATL1: 1154mm x 28mm dia ATS1: 554mm x 28mm dia
 Measures full range up to 1.0 m3.m-3 with reduced accuracy Corresponding to 0 to 0.6 m3.m-3 5.5V DC with 2m cable, 7.5V with 100m
Delta-T Profile Probes have been installed at four sites across the U.K. to provide soil moisture data as part of FutMon, an EU Life+ project. The aim of FutMon is to create a Europe-wide long term forest monitoring system. The FutMon partner organisation in the UK is Forest Research (Centre for Forestry and Climate Change). The data required for FutMon are being collected at existing UK long term forest monitoring plots, established by Forest Research in 1994.
At each site, a single Delta-T Profile Probe (connected to a Delta-T Data Logger) is used to carry out continuous monitoring of soil moisture down to a depth of 40 cms. Once a month, when the site is visited to collect data, the Profile Probe is removed from its access tube and connected to a handheld readout meter. In this mode it is used to make instant readings at four nearby measurement points, each with its own access tube installed. After the measurements have been made, the Profile Probe is simply repositioned in its original access tube and reconnected to the DL6 Logger, ready for another month of unattended recording. The advantage for Forest Research is being able to use a single Profile Probe for continuous monitoring as well as for checking spatial variability. It minimises the cost of equipping each site, it means fewer cables and it reduces security risks. Forest Research use short Profile Probes (40 cm) for their shallow soils, but long Probes (100 cm) are also available.
Forest Research uses a DL6 Data Logger to log the PR2/4 Profile Probe at each site. The PR2 measures moisture content at depths of 10, 20, 30 and 40 cm which the DL6 logs every 12 hours. The DL6 has a dedicated IP67 socket for the PR2 cable which makes connection and disconnection very easy. The DL6 is waterproof (IP67) but to improve security at the monitoring plots, Forest Research conceal the logger in a camouflaged container buried just below ground level.
FutMon is an important EU Life+ project that brings together 38 research institutes spread across 24 European countries and has a total budget of 34 million Euros. The overall aim is to create a pan-European long term forest monitoring system to:
The Centre is based at Alice Holt, Farnham, Surrey and carries out research into the effects of environmental and climate change on forestry, and how the sector can play its part in adaptation and mitigation of climate change. The Head of Centre is Dr Andy Moffat.
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