Campbell 229 User manual

229 Heat Dissipation
Matric Water
Potential Sensor
User Manual
Issued 21.2.12
Copyright ©2006-2009 Campbell Scientific Inc.
Printed under licence by Campbell Scientific Ltd.
CSL 678

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
This guarantee applies for twelve months from date of delivery. We will
repair or replace products which prove to be defective during the guarantee
period provided they are returned to us prepaid. The guarantee will not apply
to:
•Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific
•Batteries
•Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
in removing and/or reinstalling equipment. This guarantee and the Company’s
obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
Scientific is not liable for consequential damage.
Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
request. It is the policy of Campbell Scientific to protect the health of its
employees and provide a safe working environment, in support of this policy a
“Declaration of Hazardous Material and Decontamination” form will be
issued for completion.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package. Complete the “Declaration of
Hazardous Material and Decontamination” form and ensure a completed copy
is returned with your goods. Please note your Repair may not be processed if
you do not include a copy of this form and Campbell Scientific Ltd reserves
the right to return goods at the customers’ expense.
Note that goods sent air freight are subject to Customs clearance fees which
Campbell Scientific will charge to customers. In many cases, these charges are
greater than the cost of the repair.
Campbell Scientific Ltd,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the
North American market. Some spellings, weights and measures may reflect this origin.
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
In addition, while most of the information in the manual is correct for all countries, certain information
is specific to the North American market and so may not be applicable to European users.
Differences include the U.S standard external power supply details where some information (for
example the AC transformer input voltage) will not be applicable for British/European use. Please
note, however, that when a power supply adapter is ordered it will be suitable for use in your country.
Reference to some radio transmitters, digital cell phones and aerials may also not be applicable
according to your locality.
Some brackets, shields and enclosure options, including wiring, are not sold as standard items in the
European market; in some cases alternatives are offered. Details of the alternatives will be covered in
separate manuals.
Part numbers prefixed with a “#” symbol are special order parts for use with non-EU variants or for
special installations. Please quote the full part number with the # when ordering.
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. General Description.....................................................1
1.1 Compatibility............................................................................................2
1.2 Measurement Principle.............................................................................2
2. Specifications ..............................................................3
3. Installation....................................................................4
3.1 Orientation................................................................................................4
3.2 Contact......................................................................................................4
3.3 Equilibration and Saturation of the Sensor Before Installation................4
4. Wiring............................................................................4
5. Example Programs......................................................5
5.1 Choosing a Reference for the Thermocouple Readings ...........................5
5.2 Adjusting for Thermal Properties of Sensor During Early Heating Times6
5.3 Datalogger Program Structure and Multiplexers......................................6
5.4 Temperature Correction............................................................................7
5.5 Example #1 — CR1000 with CE4 and Four 229s....................................8
5.6 Example #2 — CR1000 with AM16/32-series Multiplexer,
CE4 and Sixteen 229 Sensors with Temperature Correction.............10
5.7 Example #3 — CR10X with 229 Sensor................................................12
5.8 Example #4 — CR10X with AM16/32-series, CE4, and
Sixteen 229 Sensors...........................................................................15
6. Calibration..................................................................18
6.1 General....................................................................................................18
6.2 Normalized Temperature Change and Correction for Soil Temperature......19
6.2.1 Normalized Temperature Change.................................................19
6.2.2 Correction for Soil Temperature...................................................20
6.3 Using Pressurized Extraction Methods...................................................23
6.4 General Description of Calibration/Measurement Process using
Pressure Plate Extractor .....................................................................23
6.4.1 Wiring for Calibration using Pressure Plate Extractor..................24
7. Maintenance...............................................................25
8. Troubleshooting ........................................................25

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9. References..................................................................26
List of Figures
1-1. 229 Heat Dissipation Matric Water Potential Sensor and Hypodermic
Assembly............................................................................................. 1
1-2. CE4 and CE8 Current Excitation Modules............................................. 2
1-3. Typical Temperature Response of 229 Sensor in Silt Loam Soil........... 3
4-1. Schematic of Connections for Measurement of a 229 Sensor................ 5
6-1. Data Points and Regression for Typical Calibration ............................ 19
6-2. Measurement error for range of soil temperatures and wide range of
matric potential.................................................................................. 21
6-3. Measurement error for range of soil temperatures and wetter range of
matric potential.................................................................................. 22
6-4. Datalogger and Peripheral Connections for 229 Calibration................ 24
List of Tables
4-1. 229 Sensor and CE4/CE8 Wiring........................................................... 5
5-1. Wiring for Four 229s with CR1000 and CE4......................................... 8
5-2. 229 Sensor and CE4 Wiring with CR1000 and AM16/32-series......... 10
5-3. 229 Sensor and CE4/CE8 Wiring with CR10XTCR............................ 12
5-4. 229 Sensor and CE4/CE8 Wiring with AM16/32 Multiplexer............. 15

1
229 Heat Dissipation Matric Water
Potential Sensor
1. General Description
The 229 Heat Dissipation Matric Water Potential Sensor uses a heat dissipation
method to indirectly measure soil water matric potential. The active part of the
229 Soil Water Potential Sensor is a cylindrically-shaped porous ceramic body. A
heating element which has the same length as the ceramic body is positioned at the
centre of the cylinder. A thermocouple is located at mid-length of the ceramic and
heating element. The position of the heating element and the thermocouple is
maintained by placing both inside a hypodermic needle. This also protects the
delicate wires. The volume inside the needle which is not occupied by wiring is
filled with epoxy.
Figure 1-1. A 229 Heat Dissipation Matric Water Potential Sensor is shown at the top. The hypodermic
assembly (without epoxy and ceramic) is shown just below. Cutaway view shows longitudinal section of
the needle with heater and thermocouple junction.
The ceramic cylinder has a diameter of 1.5 cm and a length of 3.2 cm. Three
copper wires and one constantan wire, contained in a shielded, burial-grade sheath
provide a path for connection to measuring instrumentation. An epoxy section
which is the same diameter as the ceramic matrix gives strain relief to the cable.
The 229 is used to measure soil water matric potential in the range -10 kPa to
-2500 kPa. The method relies on hydraulic continuity between the soil and the
sensor ceramic for water exchange. The variability in heat transfer properties
among sensors makes individual calibration by the user a requirement. See
Section 6 for calibration information.
Use of the 229 sensor requires a constant current source. Campbell Scientific
offers the CE4 and CE8 current excitation modules (Figure 1-2), which have
respectively four and eight regulated outputs of 50 milliamp ±0.25 milliamp. All
of the outputs of the excitation module are switched on or off simultaneously by
setting a single datalogger control port to its high or low state.

229 Heat Dissipation Matric Water Potential Sensor
2
The –L option on the model 229 Heat Dissipation Matric Water Potential Sensor
(229-L) indicates that the cable length is user specified. This manual refers to the
sensor as the 229.
Figure 1-2. CE4 and CE8 Current Excitation Modules
1.1 Compatibility
Compatible dataloggers include our 21X, CR7, CR10(X), CR23X, CR800,
CR850, CR1000, and CR3000. The 229 is not compatible with our CR200-series,
CR500, or CR510 dataloggers. The 229 can be connected with a multiplexer.
Compatible multiplexers include our AM16/32, AM16/32A, and AM16/32B.
When using multiplexers, the user should be aware that switching
currents of greater than 30 mA will degrade the contact surfaces of
the mechanical relays. This degradation will adversely affect the
suitability of these relays to multiplex low voltage signals.
Although a relay used in this manner no longer qualifies for low
voltage measurements, it continues to be useful for switching
currents in excess of 30 mA. Therefore, the user is advised to
record which multiplexer channels are used to multiplex the 50 mA
excitation for the 229-L sensors in order to avoid using those
channels for low voltage measurements in future applications.
1.2 Measurement Principle
Movement of water between the 229 ceramic matrix and the surrounding soil
occurs when a water potential gradient exists. When the water potential of the soil
surrounding a 229 sensor changes, a water flux with the ceramic matrix will occur.
The time required for hydraulic equilibration of the water in the soil and ceramic
depends on both the magnitude of the water potential gradient and the hydraulic
conductivity. Typically this equilibration time is on the order of minutes or tens
of minutes.
A change in the water potential and water content of the ceramic matrix causes a
corresponding change in the thermal conductivity of the ceramic/water complex.
As the water content in the ceramic increases, the thermal conductivity of the
complex also increases. At very low water contents, the ceramic material controls
the thermal conductivity. As water content in the ceramic increases, water films
are established between the solid particles, resulting in a rapid increase in thermal
conductivity. As the pores in the ceramic continue to fill, the thermal conductivity
becomes increasingly controlled by the continuous water and the increase in
thermal conductivity of the ceramic/water complex approaches a constant value.
When a constant power is dissipated from the line heat source, the temperature
increase near the heat source will depend on the thermal conductivity of the
ceramic/water complex surrounding the heater. A temperature increase is caused
by heat that is not dissipated. As the water content and thermal conductivity of the
ceramic increases, the temperature increase as measured by the thermocouple will
NOTE