Campbell Scientific 253-L and 257-L (Watermark 200) Soil Matric Potential Sensors - Manual (Page 8)

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
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. NOTE
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.
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. NOTE
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. CAUTION
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