Campbell Scientific 253-L and 257-L (Watermark 200) Soil Matric Potential Sensors - Manual (Page 20)

253-L and 257-L Soil Matric Potential Sensors
Range: 0 to –200 kPa
Dimensions: 8.26 cm (3.25 in)
Diameter: 1.91 cm (0.75 in)
Weight: 363 g (0.8 lb)
7. Operation
7.1 Wiring
7.1.1 257 Wiring
The 257 wiring diagram is illustrated in FIGURE 7-1. The red lead is inserted
into any single-ended analog channel, the black lead into any excitation
channel, and the white lead to analog ground (CR10(X), CR510, CR500) or to
ground (CR1000, CR800, CR850, CR3000, CR9000(X), CR5000, CR23X,
CR7, 21X).
Installed in the cable is a capacitor circuit that stops galvanic action due to the
differences in potential between the datalogger earth ground and the electrodes
in the block. Such a difference in potential would cause electrical current flow
and lead to rapid deterioration of the sensor block.
BLACK
RED
WHITE
CLEAR
100 μfd
Rs
1K Ω 1%
EX
SE
Gnd
FIGURE 7-1. 257 schematic
7.1.2 253 Wiring
An example of wiring for the 253 is illustrated in FIGURE 7-2. The 253 is for
use with analog multiplexers including models AM32, AM416, and AM16/32
series. Sensor leads are connected to channels on the multiplexer and the
common channels of the multiplexer are connected to the datalogger wiring
panel. The sensor has two green leads. One of the green leads has a ridged
strip while the other is smooth. Campbell Scientific connects a white lead to
the ridged green lead, a black lead to the smooth green lead, and adds clear
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