Campbell Scientific 253-L User Manual

253-L and 257-L

Soil Matric Potential Sensors

Revision: 9/13

Copyright © 1993-2013

Campbell Scientific, Inc.

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Table of Contents

PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.

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

2. Cautionary Statements...............................................1

3. Initial Inspection .........................................................1

4. Quickstart .................................................................... 2

4.1 Installation/Removal ............................................................................2

4.2 Use SCWin to Program Datalogger and Generate Wiring Diagram....3

4.2.1 257 SCWin Programming.............................................................3

4.2.2 253 SCWin Programming.............................................................7

5. Overview....................................................................12

6. Specifications ...........................................................13

7. Operation...................................................................14

7.1 Wiring ................................................................................................14

7.1.1 257 Wiring ..................................................................................14

7.1.2 253 Wiring ..................................................................................14

7.2 Programming......................................................................................15

7.2.1 CRBasic Dataloggers ..................................................................15

7.2.1.1 BRHalf Instruction ...........................................................15

7.2.1.2 Resistance Calculation .....................................................16

7.2.2 Edlog Dataloggers.......................................................................16

7.2.2.1 Program Instruction 5.......................................................16

7.2.2.2 Program Instruction 59.....................................................16

7.2.3 Calculate Soil Water Potential ....................................................17

7.2.3.1 Linear Relationship ..........................................................17

7.2.3.2 Non-Linear Relationship ..................................................18

7.2.3.3 Soil Water Matric Potential in Other Units ......................19

7.3 Example Programs .............................................................................19

7.3.1 257 Program Examples ...............................................................19

7.3.1.1 Program Example #1 — CR1000 with One 107 and

One 257.........................................................................19

7.3.1.2 Program Example #2 — CR10X with One 107 and

One 257.........................................................................20

7.3.2 253 Program Examples ...............................................................22

7.3.2.1 Program Example #3 — Five 107 Temperature Probes

and Five 253’s on AM16/32 and CR1000 ....................22

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Table of Contents

7.3.2.2

Program Example #4 — Five 107 Temperature Probes

and Five 253’s on AM16/32 and CR10X Using Non-

Linear Equation............................................................ 24

7.4 Interpreting Results ........................................................................... 27

8. Troubleshooting........................................................27

9. Reference...................................................................28

Figures

5-1. 257 Soil Matric Potential Sensor with capacitor circuit and

completion resistor installed in cable. Model 253 is the same,

except that it does not have completion circuitry in the cable. ...... 13

7-1. 257 schematic.................................................................................... 14

7-2. 253 wiring example ........................................................................... 15

Tables

7-1. Excitation and Voltage Ranges for CRBasic Dataloggers................. 16

7-2. Excitation and Voltage Ranges for Edlog Dataloggers ..................... 16

7-3. Comparison of Estimated Soil Water Potential and Rs at 21°C......... 18

7-4. Conversion of Matric Potential to Other Units.................................. 19

7-5. Wiring for Programming Example #1............................................... 19

7-6. Wiring for Programming Example #2............................................... 20

7-7. Wiring for Programming Example #3............................................... 23

7-8. Wiring for Programming Example #4............................................... 24

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253-L and 257-L Soil Matric Potential
Sensors

1. Introduction

The 253 and 257 soil matric potential sensors are solid-state, electrical­resistance sensing devices with a granular matrix that estimate soil water
potential between 0 and –2 bars (typically wetter or irrigated soils).

The 253 needs to be connected to an AM16/32-series multiplexer, and is
intended for applications where a larger number of sensors will be monitored.
The 257 connects directly to our dataloggers.

Before using a 253 or 257, please study:

• Section 2, Cautionary Statements

• Section 3, Initial Inspection

• Section 4, Quickstart

2. Cautionary Statements

• The black outer jacket of the cable is Santoprene® rubber. This jacket will

support combustion in air. It is rated as slow burning when tested
according to U.L. 94 H.B. and will pass FMVSS302. Local fire codes
may preclude its use inside buildings.

• Avoid installing in depressions where water will puddle after a rain storm.

• Don’t place the 253 or 257 in high spots or near changes in slope unless

wanting to measure the variability created by such differences.

• When removing the sensor prior to harvest of annual crops, do so just after

the last irrigation when the soil is moist.

• When removing a sensor, do not pull the sensor out by its wires.

• Careful removal prevents sensor and membrane damage.

3. Initial Inspection

• Upon receipt of a 253 or 257, inspect the packaging and contents for

damage. File damage claims with the shipping company.

• The model number and cable length are printed on a label at the

connection end of the cable. Check this information against the shipping
documents to ensure the correct product and cable length are received.

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253-L and 257-L Soil Matric Potential Sensors

4. Quickstart

Please review Section 7, Operation, for wiring, CRBasic programming, Edlog
programming, and interpretation of results.

4.1 Installation/Removal

NOTE

Placement of the sensor is important. To acquire representative
measurements, avoid high spots, slope changes, or depressions
where water puddles. Typically, the sensor should be located in
the root system of the crop.

1. Soak sensors in water for one hour then allow them to dry, ideally for 1 to

2 days.

2. Repeat Step 1 twice if time permits.

3. Make the sensor access holes to the required depth. Often, a 22 mm (7/8

in) diameter rod can be used to make the hole. However, if the soil is very
coarse or gravelly, an oversized hole (25 to 32 mm) may be required to
prevent abrasion damage to the sensor membrane. The ideal method of
making an oversized access hole is to have a stepped tool that makes an
oversized hole for the upper portion and an exact size hole for the lower
portion.

4. If the hole is oversized (25 to 32 mm), mix a slurry of soil and water to a

creamy consistency and place it into the sensor access hole.

5. Insert the sensors in the sensor access hole. A length of 1/2 inch class 315

PVC pipe fits snugly over the sensor collar and can be used to push in the
sensor. The PVC can be left in place with the wires threaded through the
pipe and the open end taped shut (duct tape is adequate). This practice
also simplifies the removal of the sensors. When using PVC piping,
solvent weld the PVC pipe to the sensor collar. Use PVC/ABS cement on
the stainless steel sensors with the green top. Use clear PVC cement only
on the PVC sensors with the gray top.

2

NOTE

CAUTION

6. Force the soil or slurry to envelope the sensors. This will ensure uniform

soil contact.

Snug fit in the soil is extremely important. Lack of a snug fit is
the premier problem with sensor effectiveness.

7. Carefully, back fill the hole, and tamp down to prevent air pockets which

could allow water to channel down to the sensor.

8. When removing sensors prior to harvest in annual crops, do so just after

the last irrigation when the soil is moist.

Do not pull the sensor out by the wires. Careful removal
prevents sensor and membrane damage.

253-L and 257-L Soil Matric Potential Sensors

9. When sensors are removed for winter storage, clean, dry, and place them

in a plastic bag.

4.2 Use SCWin to Program Datalogger and Generate Wiring Diagram

The simplest method for programming the datalogger to measure the sensor is
to use Campbell Scientific’s SCWin Program Generator (Short Cut).

NOTE

Short Cut requires the use of a soil temperature sensor before the
253 or 257 sensor is added. This is needed because there is a
temperature correction factor in the equations that convert sensor
resistance. In these Quickstart examples, a 107-L temperature
probe is used to measure soil temperature.

4.2.1 257 SCWin Programming

1. Open Short Cut and click on New Program.

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253-L and 257-L Soil Matric Potential Sensors

2. Select the datalogger and enter the scan interval, and then select Next.

3. Select 107 Temperature Probe and select the right arrow (in center of
screen) to add it to the list of sensors to be measured.

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253-L and 257-L Soil Matric Potential Sensors

4. Select the 107’s units and click on OK.

5. Select 257 Soil Moisture Sensor, and select the right arrow (in center of
screen) to add it to the list of sensors to be measured.

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