METER TEROS 21 User Manual

TEROS 21

i

TABLE OF CONTENTS

1. Introduction ..............................................................................................1

2. Operation ...................................................................................................2

2.1 Installation ................................................................................................2

2.2 Connecting .................................................................................................3

3. System .........................................................................................................6

3.1 Specifications ............................................................................................6

3.2 Components ..............................................................................................9

3.3 Theory ........................................................................................................9

3.3.1 Water Potential Measurement .........................................................9

3.3.2 Measurement Range ...................................................................... 10

3.3.3 Measurement Accuracy .................................................................12

3.3.4 Temperature Measurement ............................................................13

3.4 Considerations.........................................................................................13

3.4.1 Measuring in Frozen Soils .............................................................. 13

3.4.2 Measuring in High Salinity ............................................................. 14

3.4.3 Temperature Sensitivity .................................................................14

4. Service ....................................................................................................... 15

4.1 Calibration ............................................................................................... 15

4.2 Maintenance ............................................................................................ 15

4.3 Troubleshooting ....................................................................................... 16

4.4 Customer Support....................................................................................16

4.5 Terms and Conditions .............................................................................. 17

References ....................................................................................................19

Index .................................................................................................................20

13755-03

11.10.2017

1

TEROS 21

1. INTRODUCTION

Thank you for purchasing the TEROS 21 Soil Water Potential Sensor from METER Group.

TEROS 21 was designed to be a maintenance-free matric potential sensor designed for long­term, continuous field measurements. The TEROS 21 measures the dielectric permittivity of
a solid matrix to determine the water content of the solid matrix. The relationship between
water content and matric potential, known as the soil moisture characteristic curve, is used
to calculate the soil matric potential. This measurement approach, along with the calibration
process used in production, allows for accurate measurements of water potential.

Prior to use, verify the TEROS 21 arrived in good condition.

2

OPERATION

2. OPERATION

Please read all instructions before operating the TEROS 21 to ensure it performs to its
full potential.

SAFETY PRECAUTIONS

METER sensors are built to the highest standards, but misuse, improper protection, or
improper installation may damage the sensor and possibly void the manufacturer’s warranty.
Before integrating TEROS 21 into a system, follow the recommended installation instructions

and have the proper protections in place to safeguard sensors fromdamage.

2.1 INSTALLATION

Follow the steps listed in Table 1 to set up the sensor. It is critical that the sensor has good
hydraulic contact with the soil to make accurate measurements.

Table 1 Installation

Tools Needed

Auger or shovel

Knife (if installing in shallow depth)

Water (for packing soil or making slurry)

Preparation

Check Sensor Functionality

Plug the sensor into the logger (Section 2.2) to make sure the sensor

isfunctional.

Field Installation

Create Hole

Auger or trench a hole to the desired sensor depth.

Pack Sensor

Moisten native soil and pack it rmly around the entire sensor discs. Ensure

the soil is in contact with all surfaces of the ceramic.

NOTE: Sandy soils may not adhere to the sensor even when wet. If so, place the sensor at
the bottom of the hole and carefully pack the soil around the sensor. Be sure to pack the
soil firmly around ceramic surfaces.

3

TEROS 21

Table 1 Installation (continued)

Field Installation
(continued)

Install Sensor

For shallow installation (less than ~30 cm), use a knife to remove a small sliver
of soil. Insert packed sensor into the channel.

For deep installation (greater than ~30 cm), use the native soil to make a slurry

with water. Lower sensor into the hole and ll with the slurry.

NOTE: Soils with high shrink-swell potential may pull away from the sensor as they dry
and disrupt measurements.

NOTE: Do not install the sensor with the body exposed above ground.

Connect to Logger

Leave at least 15 cm (6 in) of sensor cable beneath the soil before bringing the
cable to the surface. At least 10 cm (4 in) of cable should exit the sensor body
in a straight line before bending the cable.

Plug the sensor into the logger.

Use the data logger to make sure the sensor is reading properly.



Return soil to the hole, packing the soil back to its native bulk density.

2.2 CONNECTING

The TEROS 21 sensors work best with METER data loggers or ProCheck handheld readers.

1. Check data logger software and firmware versions to ensure they support

TEROS21 sensors (http://www.metergroup.com/teros21-support/).

Plug the stereo plug connector directly into one of the sensor ports.

2. Congure the logger port for TEROS 21 using the appropriate logger application.

The TEROS 21 sensors have a 5-m cable. Customers may purchase custom cable lengths
for an additional per-meter fee. If the cable needs to be extended, ensure to adequately
waterproof the cable splices to prevent a major failure point. Read Wire splicing and sealing

technique for soil moisture sensors for more information.

The sensor uses a 3.5-mm stereo plug connector (Figure1). Customers may purchase the
sensor with stripped and tinned wires (pigtail) for terminal connections for third-party data
loggers (Figure2). Refer to the individual third-party logger manual for details on wiring.

NOTE: The acceptable range of power voltages is from 3.9 to 15.0 VDC, with 12 VDC being the optimal voltage.

Ground
Data
Power

 3.5-mm stereo plug connector

4

OPERATION

Ground (bare)

Data (orange)

Power (brown)

 Pigtail wiring

NOTE: Sensors manufactured as MPS-6 use white wire for power and red wire for data output.

TEROS 21 sensors communicate using two different methods: serial (TTL) and SDI-12.
Please refer to the complete TEROS 21 Integrator Guide for more detailed explanations

andinstructions.

There are two options to connect a sensor with the standard stereo plug to a non-METER
data logger.

Option 1

1. Clip the plug off the sensor cable.

2. Strip and tin the wires.

3. Connect the wires directly into the data logger.

This will create a direct connection with no chance of the sensor becoming unplugged;
however, the sensor cannot be easily used in the future with a METER readout unit or

datalogger.

Option 2

Obtain an adapter cable from METER.

The adapter cable has a 3.5-mm stereo plug connector for connecting to the sensor on one
end and three wires for connecting to a data logger (a stereo-to-pigtail adapter) on the other
end. The stripped and tinned adapter cable wires have the same termination as seen in

Figure2; the brown wire is power, orange is output, and the bare wire is ground.

Because TEROS 21 sensors use digital communication, they require special considerations
when connecting to an SDI-12 data logger. Read SDI-12 example programs to view sample
Campbell Scientific programs.

5

TEROS 21

The SDI-12 protocol requires that all sensors have a unique address. TEROS 21 sensors
factory default is an SDI-12 address of 0. To add more than one SDI-12 sensor to a bus, the
sensor address must be changed as described below:

1. Using a ProCheck connected to the sensor, press the Menu button to bring up the

CONFIGmenu.

NOTE: If the ProCheck does not have this option, please upgrade its firmware to the latest version from the METER

Legacy Handheld Devices webpage.

2. Scroll down to SDI-12 Address. Press Enter.

3. Press the UP or DOWN arrows until the desired address is highlighted.

Address options include 0...9, A…Z, and a…z.

4. Press Enter.

Detailed information can also be found in the application note Setting SDI-12 addresses on

METER digital sensors using Campbell Scientific data loggers and LoggerNet.

When using the sensor as part of an SDI-12 bus, excite the sensors continuously to avoid
issues with initial sensor startup interfering with the SDI-12 communications.

SDI-12 communication can convey multiple parameters from a single function call. In the
data stream, TEROS 21 reports (1) the sensor address, (2) the water potential (in kilopascals),
and (3) the temperature (in Celsius).

6

SYSTEM

3. SYSTEM

This section reviews the components and functionality of the TEROS 21 sensor.

3.1 SPECIFICATIONS



Water Potential

Range: −9 to −100,000 kPa (1.96 to 6.01 pF)

Resolution: 0.1 kPa

Accuracy: ±(10% of reading + 2 kPa) from −9 to −100 kPa

Temperature

Range: −40 to 60 °C

Resolution: 0.1 °C

Accuracy: ±1 °C

Operating Temperature

−40 to 60 °C (0%–100% RH)
No water potential measurement <0 °C

NOTE: Sensors may be used at higher temperatures under certain conditions; contact Customer Support



Power Requirements

3.9 to 15.0 VDC, 0.03 mA quiescent, 10 mA max during 150-ms measurement



Dimensions

9.6 cm × 3.5 cm × 1.5 cm

Sensor Diameter

3.2 cm

Dielectric Measurement Frequency

70 MHz

Measurement Time

150 ms

7

TEROS 21

Output

RS232 (TTL) with 3.9-VDC levels or SDI-12 communication protocol

Connector Types

3.5-mm stereo plug connector or stripped and tinned wires

Cable Length

5 m (standard)
75 m (maximum custom cable length)

Data Logger Compatibility

Any data acquisition system capable of 3.9- to 15.0-VDC power and serial or
SDI-12 communication



Supply Voltage (VCC) to GND

Minimum 3.6 VDC

Typical

Maximum 15.0 VDC

Digital Input Voltage (logic high)

Minimum 2.8 V

Typical 3.6 V

Maximum 3.9 V

Digital Input Voltage (logic low)

Minimum –0.3 V

Typical 0.0 V

Maximum 0.8 V

Power Line Slew Rate

Minimum 1.0 V/ms

Typical

Maximum

8

SYSTEM

Current Drain (during measurement)

Minimum 3.0 mA

Typical 3.6 mA

Maximum 10.0 mA

Current Drain (while asleep)

Minimum

Typical 0.03 mA

Maximum

Operating Temperature Range

Minimum –40 °C

Typical

Maximum 50 °C

Power Up Time (DDI serial)

Minimum

Typical

Maximum 100 ms

Power Up Time (SDI-12)

Minimum 100 ms

Typical 150 ms

Maximum 200 ms

Measurement Duration

Minimum

Typical 150 ms

Maximum 200 ms

Compliance

Manufactured under ISO 9001:2015

EM ISO/IEC 17050:2010 (CE Mark)

9

3.2 COMPONENTS

The TEROS 21 sensor measures the water potential and temperature of soil with porous
ceramic discs (Figure3). TEROS 21 sensors measure moisture content changes of two
engineered ceramic discs sandwiched between stainless steel screens and the circuit
board. These sensors have a low power requirement, which makes them ideal for permanent
burial in the soil and continuous reading with a data logger or periodic reading with a

handheldreader.

Vinyl lled with

polurethane resin

Grounded stainless

steel screen

Ceramic disc

(static matrix)

Printed circuit

board

Sensor body

Sensor head

 TEROS 21 sensor

3.3 THEORY

TEROS 21 sensors measure water potential, so they are not as sensitive to soil disturbance
as water content sensors. TEROS 21 need good hydraulic contact with the surrounding soil
for accurate measurements.

3.3.1 WATER POTENTIAL MEASUREMENT

All soil water potential measurement techniques measure the potential energy of water in
equilibrium with water in the soil. The Second Law of Thermodynamics states that connected
systems with differing energy levels move toward an equilibrium energy level. When an
object comes into hydraulic contact with the soil, the water potential of the object comes
into equilibrium with the soil water potential.

TEROS 21 uses a solid matrix equilibration technique to measure the water potential of
the soil. This technique introduces a material with a known pore size distribution into
the soil and allows it to come into hydraulic equilibrium according to the Second Law of
Thermodynamics. Because the two are in equilibrium, measuring the water potential of the
solid matrix gives the water potential of the soil.

10

SYSTEM

TEROS 21 measures the dielectric permittivity of a solid matrix (porous ceramic discs)
to determine its water potential. The dielectric permittivity of air, the solid ceramic,
and water are 1, 5, and 80, respectively. So, the dielectric permittivity of the porous
ceramic discs is highly dependent on the amount of water present in the pore spaces.
Measuring the dielectric permittivity of the ceramic discs resolves a wide range of water

contentmeasurements.

Water content and water potential are related by a relationship unique to a given material,
called the moisture characteristic curve. The ceramic used with the TEROS 21 has a wide
pore size distribution and is consistent between discs, giving each disc the same moisture
characteristic curve. Thus, the water potential can be inferred from water content using the
moisture characteristic curve of the ceramic

Equation 1 gives the component variables for determining total soil water potential(Ψ

t   

):

Equation 1

pg mt

WWWWW

=+++

o

where Ψp is pressure, Ψg is gravitational, Ψo is osmotic, and Ψm is matric.

For TEROS 21 applications, Ψp and Ψg are generally insignificant. Ψo arises from dissolved
salts in the soil and only becomes important if a semipermeable barrier is present that
prevents ionic movement (e.g., plant roots or cell membranes). Ψm arises from the attraction
of water to the soil particles and is the most important component of water potential in most
soils. TEROS 21 responds to the matric potential of the soil (Ψm ). In highly salt-affected soils,
it may be necessary to quantify Ψo independently if the measurements of soil water potential
are related to biological activity (Section 3.4.2).

3.3.2 MEASUREMENT RANGE

TEROS 21 measures the water content of porous ceramic discs and converts the measured
water content to water potential using the moisture characteristic curve of the ceramic.
Therefore, it is important that the ceramic discs drain over a wide water potential range.
Pore size determines the water potential at which a pore drains (the air entry potential
or bubble pressure), so the ideal ceramic would have pores that range from very small to
relatively large. METER designed the ceramic discs to approach this ideal (Figure4). The
discs have a total pore volume that is weighted toward the larger pores, which drain at water
potentials within the plant-available range (approximately −33 to −1,500 kPa). However, the
TEROS21 measurement range extends all the way to air dry (−100,000 kPa).

11

TEROS 21

0.00 0

0.10 0

0.20 0

0.30 0

0.40 0

0.50 0

0.60 0

0.70 0

0.80 0

0.90 0

1.00 0

110100 1,00010,00

01

00,000

WATER POTENTIAL (-kPa)

GRAVIMETRIC WATER CONTENT

 Moisture characteristic curve of TEROS 21 ceramic derived from mercury porosimeter data



As the sensor dries past the plant-available range, the total pore volume that drains at
a given water potential decreases. At these low water potentials, the measured water
potential can become somewhat noisy because small changes in measured water content
of the ceramic translate into large changes in water potential. This phenomenon is most
pronounced when the sensor is air dry. It is expected that the measured water potential of an
open air and dry sensor can jump around throughout the range of −50,000 to −100,000 kPa.
The noise level is much lower when the sensor is installed in the soil, even at air-dry

waterpotential.



The air entry potential of the largest pores in the ceramic is about −9 kPa. However, the

ceramic disc must have access to air for the large pores to begin draining and the response
of the sensor to change. If the soil around the sensor has an air entry potential lower (drier)

than −9 kPa, the ceramic will not begin to lose water until reaching the air entry potential

of the soil. In this scenario, the air entry potential of the soil limits the wet-end range,
rather than the ceramic discs themselves. The sensor may not begin to respond until lower

water potentials (−10 kPa). This is generally only an issue when using the sensor in poorly

structured soils with high clay content.

12

SYSTEM

3.3.3 MEASUREMENT ACCURACY

TEROS 21 is calibrated at a saturated state (0 kPa), at an air-dry state (−100,000 kPa), and at
three calibration points between 0 and −100 kPa, resulting in accuracy of ±(10% of reading +
2 kPa) over the range of −9 to −100 kPa.

At water potentials drier than −100 kPa, TEROS 21 relies on the linear relationship between
the logarithm of water content and the logarithm of water potential. Laboratory evaluations
have shown good accuracy and low sensor-to-sensor variability to at least −1,500 kPa (plant
permanent wilting point). Field evaluations have shown low sensor-to-sensor variability to

−2,000 kPa (Figure5 and Figure6).

NOTE: METER strongly discourages dry-end calibrations in the pressure plate apparatus. Early attempts to improve
sensor dry-end performance in the pressure plate apparatus actually decreased accuracy, likely because of pressure
plate dry-end equilibrium issues pointed out in the literature (e.g., Campbell [1998], Gee et al. [2002], Bittelli and Flury
[2009], and Frydman and Baker [2009]).

−2,000.0

−1,500.0

−1,000.0

−500.0

0.0

SOIL WATER POTENTIAL (kPa)

TIME (DAYS)

0

20 40

60 80

Sensor 1
Sensor 2
Sensor 3

Permanant wilting point

 Time series TEROS 21 water potential data collected at 80 cm depth

under a beech forest in Switzerland (Walthert, 2013). Note the good sensor



13

TEROS 21

−2,000.0

−1,500.0

−1,000.0

−500.0

0.0

−2,500.0

−3,000.0

−3,500.0

−4,000.0

−4,500.0

0

20 40

60 80

TIME (DAYS)

SOIL WATER POTENTIAL (kPa)

Sensor 1
Sensor 2
Permanant wilting point

 Time series TEROS 21 water potential data collected at 20 cm under a dry oak forest in

Switzerland (Walthert 2013). Note the range extends well beyond permanent wilting point.

3.3.4 TEMPERATURE MEASUREMENT

TEROS 21 uses a surface-mounted thermistor to take temperature readings. The thermistor
is located underneath the sensor epoxy. The TEROS 21 output temperature readings in
degrees Celsius unless otherwise stated in preference settings in METER software programs.
If the black plastic body of the sensor is exposed to solar radiation, the temperature
measurement may read high. Exposure of the body also drastically decreases the life
expectancy of the sensor. Do not install the sensor with the body above ground.

3.4 CONSIDERATIONS

TEROS 21 sensors use similar technology to METER water content sensors and are
susceptible to the same constraints. Using TEROS 21 in certain environments will require
additional considerations.

3.4.1 MEASURING IN FROZEN SOILS

TEROS 21 measures the dielectric permittivity of two ceramic discs to measure their water
content and then derive their water potential. The dielectric permittivity of water in the
ceramic discs is 80 compared to a dielectric permittivity of ~5 for the ceramic material or
1 for air. When water freezes to ice, the dielectric permittivity drops to 5 at the frequency
of the sensor measurement, meaning that the sensor can no longer accurately measure
the water in the ceramic. TEROS 21 does not accurately measure water potential in frozen
soil conditions. However, the water potential of the soil under frozen soil conditions can be

14

SYSTEM

estimated by measuring the soil temperature accurately (Koopmans and Miller, 1966). For
each 1 °C decrease in temperature below 0 °C, the water potential in the soil decreases by
~1,200 kPa. Spaans and Baker (1996) showed that this relationship is valid in field soils for

water potentials below about −50 kPa.

Rigorous testing indicates that repeated freeze–thaw cycles do not affect the ceramic discs.
Several sensors were equilibrated in saturated soil and then subjected to numerous freeze–
thaw cycles in a temperature-controlled chamber. The freezing rate of the soil containers
was at least an order of magnitude faster than could be achieved in field soils under natural
conditions. At several points during the test, and at the end of the test, the ceramic discs
were evaluated for damage due to repeated rapid freezing of pore spaces full of water. None
of the ceramic discs showed any signs of physical damage, and none of the sensors showed
any significant change in output due to the freeze–thaw tests.

3.4.2 MEASURING IN HIGH SALINITY

A saturation extract electrical conductivity (EC) greater than 10 dS/m will confound the
capacitance measurement taken by the sensor resulting in erroneous matric potential
readings. It is recommend that the TEROS 21 only be used in environments where the
saturation extract EC does not exceed 10 dS/m.

3.4.3 TEMPERATURE SENSITIVITY

Fluctuations in temperature can affect the capacitance readings at matric potential less
than about −500 kPa (Figure7). Although temperature can affect the output of the reading,
the nature of the moisture retention curve of the ceramic results in an extremely small effect
on matric potential until the substrate dries out to about −500 kPa. A small change in water
content can result in a relatively large change in matric potential beyond −500 kPa.

−1,800.0

−1,600.0

−1,400.0

−1,200.0

−1,000.0

−800.0

−600.0

−400.0

−200.0

0.0

010203040506070

WATER POTENTIAL (kPa)

Sensor 1 (5-cm depth)
Sensor 2 (15-cm depth)

TIME (DAYS)

 Temperature sensitivity data for TEROS 21 sensors

15

TEROS 21

4. SERVICE

This section describes the calibration and maintenance of TEROS 21. Troubleshooting
solutions and customer service information are also provided.

4.1 CALIBRATION

TEROS 21 calibration is not affected by soil type because the sensors only measure the
water potential of the ceramic discs in equilibrium with the soil. TEROS 21 works in any
soil type or other porous media as long as it is installed correctly with adequate hydraulic
contact (to ensure timely water potential equilibrium between the sensor and the medium

ofinterest).

The amount of water that a soil holds at a given water potential is greater if the material
is dried to that water potential than if the material is wet up to that water potential; a
phenomenon known as hysteresis. Because TEROS 21 essentially makes a dielectric
measurement of water content and converts that to water potential, sensor measurements
have some hysteresis. In most situations, soil undergoes brief periods of wet up
(precipitation or irrigation events) followed by longer dry down periods, where water
potential measurements are most useful. METER performs TEROS 21 calibration on the
drying leg of the hysteresis loop, so the measurements are most accurate as the soil dries.
Measurements as the soil wets up are slightly drier (more negative water potential) than the
true water potential of the soil. METER wetting and drying tests show the magnitude of the

hysteresis error is <10 kPa in the −20 to −100 kPa range.

4.2 MAINTENANCE

TEROS 21 may be returned to METER for maintenance in the following areas: system
inspection, parts replacement, and instrument cleaning. Replacement parts can also be
ordered from METER. Contact Customer Support for more information.

The ceramic discs are brittle and can chip or crack if abused. The metal screens afford the
discs some amount of protection, but sharp trauma on the disc edges or massive impact
(such as dropping the sensor onto a hard surface) can cause the ceramic to break. One or two
small chips on the edge of the disc do not affect the sensor accuracy significantly. However,
a cracked ceramic disc results in a loss of accuracy.

For TEROS 21 to accurately measure water potential, the ceramic discs must readily take
up water. Exposure to oils or other hydrophobic substances compromises the ability of the
discs to take up water from the soil. This inability to take up water leads to slow equilibration
times and loss of accuracy. Minimize exposure of the ceramic material to skin oils, grease,
synthetic oils, or other hydrophobic compounds.

16

SERVICE

4.3 TROUBLESHOOTING

Table 2 lists common problems and their solutions. Most issues with the TEROS 21 sensor

will manifest themselves in the form of incorrect or erroneous readings. If the problem is not
listed or these solutions do not solve the issue, contact Customer Support.

Table 2 Troubleshooting TEROS 21

Problem Possible Solutions

Data logger is not
recognizing sensor

If using a METER logger, update logger rmware.

Data logger is not receiving
readings from the sensor

Check to make sure the connections to the data logger are both
correct and secure.

Ensure that your data logger batteries are not dead or weakened.

Check conguration of data logger through software to ensure
TEROS21 is selected.

Ensure the software and rmware is up to date.

Sensor does not appear to
be responding to changes
in soil water potential

Ensure that sensors are installed correctly.

Check sensor cables for damage that could cause a malfunction.

Check the ceramic disc for damage or contamination.

4.4 CUSTOMER SUPPORT

Customer service representatives are available for questions, problems, or feedback Monday
through Friday, 8 am–5 pm Pacific time.

Email: [e-mail]
[e-mail]

Phone: [phone]

Fax: [phone]

Website: www.metergroup.com

If contacting METER by email or fax, please include the following information:

Name
Address
Phone

Email address
Instrument serial number
Description of the problem

NOTE: For TEROS 21 Soil Water Potential sensors purchased through a distributor, please contact the
distributor directly for assistance.

17

TEROS 21

4.5 TERMS AND CONDITIONS

CONTRACT FORMATION. All requests for goods and/or services by METER Group, Inc. USA

(METER) are subject to the customer’s acceptance of these Terms and Conditions. The
Buyer will be deemed to have irrevocably accepted these Terms and Conditions of Sale
upon the first to occur of the Buyer’s issuance of a purchase order or request for goods or
services. Unless expressly assented to in writing by METER, terms and conditions different
are expressly rejected. No course of dealing between the parties hereto shall be deemed to
affect or to modify, amend, or discharge any provisions of this agreement.

PRICES AND PAYMENT. Invoice prices will be based upon METER prices as quoted or at
METER list price in effect at the time an order is received by the Seller. Prices do not include
any state or federal taxes, duties, fees, or charges now or hereafter enacted applicable to the
goods or to this transaction, all of which are the responsibility of the Buyer. Unless otherwise
specified on the invoice, all accounts are due and payable 30 days from the date of invoice.
Unpaid accounts extending beyond 30 days will be subject to a service charge of 2% per
month (24% per annum). Should Seller initiate any legal action or proceeding to collect on
any unpaid invoice, Seller shall be entitled to recover from Buyer all costs and expenses
incurred in connection therewith, including court costs and reasonable attorney’s fees.

RISK OF LOSS AND DELIVERY TITLE. Liability for loss or damage passes to the Buyer when
the Seller delivers the goods on the Seller’s dock or to the transporting agent, whichever
occurs first. The Seller has the right to deliver the goods in installments. Shipping and
delivery dates communicated by the Seller to the Buyer are approximate only.

SHIPMENT. In the absence of specific shipping instructions, the Seller, if and as requested
by the Buyer, will ship the goods by the method the Seller deems most advantageous. Where
the Seller ships the goods, the Buyer will pay all transportation charges that are payable on
delivery or, if transportation charges are prepaid by the Seller, the Buyer will reimburse the
Seller upon receipt of an invoice from the Seller. The Buyer is obligated to obtain insurance
against damage to the goods being shipped. Unless otherwise specified, the goods will be
shipped in the standard Seller commercial packaging. When special packing is required or, in
the opinion of the Seller, required under the circumstances, the cost of the special packaging
shall be the responsibility of the Buyer.

INSPECTION AND ACCEPTANCE. Goods will be conclusively deemed accepted by the Buyer
unless a written notice setting out the rejected goods and the reason for the rejection
is sent by the Buyer to the Seller within 10 days of delivery of the goods. The Buyer will
place rejected goods in safe storage at a reasonably accessible location for inspection by

theSeller.

CUSTOM GOODS. There is no refund or return for custom or nonstandard goods.

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WARRANTIES. The Seller warrants all equipment manufactured by it to be free from

defects in parts and labor for a period of one year from the date of shipment from factory.
The liability of the Seller applies solely to repairing, replacing, or issuing credit (at the
Seller’s sole discretion) for any equipment manufactured by the Seller and returned by the
Buyer during the warranty period. SELLER MAKES NO SEPARATE OR OTHER WARRANTY
OF ANY NATURE WHATSOEVER, EXPRESS OR IMPLIED, INCLUDING THE WARRANTY OF
MERCHANTABILITY OR FOR A PARTICULAR PURPOSE. There shall be no other obligations
either expressed or implied.

LIMITATION OF LIABILITY. Seller will not be liable to the Buyer or any other person or entity
for indirect special, incidental, consequential, punitive, or exemplary damages in connection
with this transaction or any acts or omissions associated therewith or relating to the sale
or use of any goods, whether such claim is based on breach of warranty, contract, tort, or
other legal theory and regardless of the causes of such loss or damages or whether any other
remedy provided herein fails. In no event will the Seller’s total liability under this contract
exceed an amount equal to the total amount paid for the goods purchased hereunder.

WAIVER. In the event of any default under or breach of the contract by the Buyer, the Seller
has the right to refuse to make further shipments. The Seller’s failure to enforce at any time
or for any period of time the provisions of this contract will not constitute a waiver of such
provisions or the right of the Seller to enforce each and every provision.

GOVERNING LAW. The validity, construction, and performance of the contract and the
transactions to which it relates will be governed by the laws of the United States of America.
All actions, claims, or legal proceedings in any way pertaining to this contract will be
commenced and maintained in the courts of Whitman County, State of Washington, and the
parties hereto each agree to submit themselves to the jurisdiction of such court.

SEVERABILITY. If any of the Terms and Conditions set out in this contact are declared
to be invalid by a court, agency, commission, or other entity having jurisdiction over the
interpretation and enforcement of this contract, the applications of such provisions to
parties or circumstances other than those as to which it is held invalid or unenforceable
will not be affected. Each term not so declared invalid or unenforceable will be valid and
enforced to the fullest extent permitted by law and the rights and obligations of the parties
will be construed and enforced as though a valid commercially reasonable term consistent
with the undertaking of the parties under the order has been substituted in place of the
invalid provision.

SET-OFF. The Buyer may not set-off any amount owing from the Seller to the Buyer against
any amount payable by the Buyer to the Seller whether or not related to this contract.

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TEROS 21

REFERENCES

Bittelli M and Flury M. 2009. Errors in water retention curves determined with pressure
plates. Soil Sci Soc Am J. 73:1453–1460.

Campbell GS. 1988. Soil water potential measurement: an overview. Irrigation Sci. 9:265–273.

Frydman S and Baker R. 2009. Theoretical soil–water characteristic curves based on
adsorption, cavitation, and a double porosity model. Int J Geomech. 9(6):250–257.

Gee GW, Ward AL, Zhang ZF, Campbell GS, and Mathison J. 2002. The influence of hydraulic
nonequilibrium on pressure plate data. Vadose Zone J. 1:172–178.

Koopmans RWR and Miller RD. 1966. Soil freezing and soil water characteristic curves1. Soil
Sci Soc Am J. 30:680–685.

Spaans EJA and Baker JM. 1996. The soil freezing characteristic: Its measurement and
similarity to the soil moisture characteristic. Soil Sci Soc Am J. 60:13–19.

Walthert L. 2013. Soil as a site factor in Swiss forests (project title). Swiss Federal Institute
for Forest, Snow, and Landscape WSL Research.

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S

specifications 6–7

cable length 7
dimensions 6

T

temperature 6, 9, 13
terms and conditions 17–18
theory

dielectric permittivity 10, 13–14
dry-end limitations 11
measurement accuracy 12–13
measurement range 10–11
measuring in frozen soil 13–14
measuring in high salinity 10, 14
moisture characteristic curve 10
temperature measurement 13
temperature sensitivity 14
water potential 9
wet-end limitations 11–12

troubleshooting 16

W

water content 9, 10, 15
water potential 12, 15

See alsomoisture characteristic curve;
ceramic pore size

measurement 6, 9, 16

wilting point 12–13

INDEX

C

cable colors 4
calibration 12, 15
ceramic pore size 13–14
cleaning. Seemaintenance
components

ceramic discs 9, 10, 10–11, 15, 16
circuit board 9
screens 9, 15

sensor body 3, 9, 13
connecting 3–5, 16
customer support 16

E

electrical conductivity 14

H

hydraulic equilibrium 9, 15
hysteresis 15

I

installation 2–3, 13

connecting 3–5

tools needed 2

L

limitations

dry-end limitations 11

measuring in high salinity 10, 14

temperature sensitivity 14

wet-end limitations 11–12

M

maintenance 15
matric potential 10, 14
moisture characteristic curve 10–11

R

references 19

14567-01

11.10.2017

METER Group

2365 NE Hopkins Court

Pullman, WA 99163

T: +1.509-332-2756 F: +1.509.332.5158

E: [e-mail]
W: www.metergroup.com

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