Campbell Scientific 223-L Delmhorst Cylindrical Soil Moisture Block - Manual (Page 12)

223 Delmhorst Cylindrical Soil Moisture Block
10. Select the AM16/32 tab and wire the 223 sensors to the AM16/32
according to the wiring diagram generated by SCWin Short Cut.
5. Overview
The 223 gypsum soil moisture block is configured for use with multiplexers.
The –L option on the model 223–L indicates that the cable length is user
specified. This manual refers to the sensor as the 223.
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 multiplexer that the 223 is connected to leaves the circuit open when no
measurements are being made. This blocks direct current flow from the 223 to
datalogger ground and prevents electrolysis from prematurely destroying the
sensor.
The 223 should not be connected directly to the datalogger. The 227
Delmhorst soil moisture block is available for direct connection and has
capacitors in the cable that block direct current flow.
Gypsum blocks typically last for one to two years. Saline or acidic soils tend
to degrade the block, reducing longevity. To maximize longevity, gypsum
blocks not used during the winter should 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.
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