Campbell 227 Instruction Manual

Model 227 Delmhorst

Cylindrical Soil Moisture Block

Revision: 11/08

Copyright © 1983-2008

Campbell Scientific, Inc.

Warranty and Assistance

The 227 DELMHORST CYLINDRICAL SOIL MOISTURE BLOCK is
warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in
materials and workmanship under normal use and service for twelve (12)
months from date of shipment unless specified otherwise. Batteries have no
warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is
limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option)
defective products. The customer shall assume all costs of removing,
reinstalling, and shipping defective products to CAMPBELL SCIENTIFIC,
INC. CAMPBELL SCIENTIFIC, INC. will return such products by surface
carrier prepaid. This warranty shall not apply to any CAMPBELL
SCIENTIFIC, INC. products which have been subjected to modification,
misuse, neglect, accidents of nature, or shipping damage. This warranty is in
lieu of all other warranties, expressed or implied, including warranties of
merchantability or fitness for a particular purpose. CAMPBELL SCIENTIFIC,
INC. is not liable for special, indirect, incidental, or consequential damages.

Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
serves your country.

To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container.
CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____
815 West 1800 North
Logan, Utah 84321-1784

For all returns, the customer must fill out a “Declaration of Hazardous Material
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at
completed form must be either emailed to [e-mail]
to 435-750-9579. Campbell Scientific will not process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer’s expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

www.campbellsci.com/repair

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or faxed

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

227 Table of Contents

PDF viewers note: These page numbers refer to the printed version of this document. Use
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1. General Description.....................................................1

2. Specifications ..............................................................1

3. Installation....................................................................2

4. Wiring............................................................................2

5. Programming ...............................................................3

5.1 Excite and Measure the 227......................................................................3

5.2 Calculate Sensor Resistance .....................................................................4

5.3 Calculate Soil Water Potential..................................................................6

5.4 Programming Examples............................................................................8

5.4.1 CRBasic ..........................................................................................8

5.4.2 Edlog...............................................................................................9

List of Figures

1. 227 Schematic.............................................................................................2

2. Polynomial Fit to Typical Block Resistance vs. Water Potential ...............4

List of Tables

1. 227 Wiring..................................................................................................3

2. Excitation and Voltage Ranges...................................................................5

3. Typical Soil Water Potential, R

4. Polynomial Coefficients for Converting Sensor Resistance to Bars...........6

5. Polynomial Error - 10 Bar Range...............................................................7

6. Wiring for CR1000 Example Program.......................................................8

7. Wiring for CR10X Example Program........................................................9

and Vs/Vx................................................6

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Model 227 Delmhorst Cylindrical Soil Moisture Block

1. General Description

The 227 gypsum soil moisture block connects directly with a Campbell
Scientific datalogger; it is not compatible with our CR200-series.

The -L option on the Model 227-L indicates that the cable length is user
specified. This manual refers to the sensor as the 227.

The Delmhorst cylindrical block is composed of gypsum cast around two
concentric electrodes which confine current flow to the interior of the block,
greatly reducing potential ground loops. Gypsum located between the outer
electrode and the soil creates a buffer against salts which may affect the
electrical conductivity. Individual calibrations are required for accurate
readings of soil water potential.

The 227 circuit has capacitors in the cable that block direct current flow from
the 227 to datalogger ground. This is done to block electrolysis from
prematurely destroying the sensor.

Gypsum blocks typically last for one to two years. Saline or acidic soils tend
to degrade the block, reducing longevity. To maximize longevity, it is
recommended that gypsum blocks not used during the winter be removed from
the field. Shallow blocks may become frozen and crack, while blocks located
below the frost line may not maintain full contact with the soil. Regardless of
depth, blocks left in the field over winter are subject to the corrosive chemistry
of the soil.

2. Specifications

Approximate Cylinder Dimensions
Diameter 2.25 cm (0.88”)
Length 2.86 cm (1.25”)

Material Gypsum
Electrode Configuration Concentric cylinders

Center electrode Excitation
Outer electrode Ground

Calibration: Measurements are affected by soil salinity,

including fertilizer salts. Individual calibrations are
required for accurate measurement of soil water
potential. The soil water potential versus resistance
values in Table 2 are “typical” values supplied by
Delmhorst Corporation. Neither Delmhorst nor
Campbell Scientific make any claim as to the
accuracy of these values. The calibration equations
in Section 4.5 were fit to the values in Table 2 to
allow output of an estimated water potential.

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