How to Prepare and Condition Watermark 200SS Soil Water Tension Sensors
Hydrate your soil water tension sensors before installation. rEMEMBER TO ONLY SUBMERGE THEM HALFway TO SPEED UP THE HYDRATION.
QUESTION: How to prepare Watermark 200SS soil water tension sensors for installation, so they show accurate readings immediately after installation?
ANSWER: Always install soaking wet soil water tension sensors and only after performing the sensor conditioning procedure which follows. Do not install dry sensors! After installation, connect them to the MeteoAG wireless IoT sensor node.
Soil water tension sensors are constructed of an open-cell porous substrate (similar to an open-cell foam, but rigid) whose pores are initially filled with air. For the sensor to function correctly and accurately, the air must be replaced by water, not to offset the soil water tension (pressure) readings. Replacing all of the air molecules with water takes some time inside the dense inner labyrinth of thousands of pores. The following hydration procedure will enable the Watermark sensors to show accurate soil water tension readings within one or two irrigation cycles, depending on the soil's wetness.
Soil water tension sensors need some time to reach an equilibrium with the surrounding soil moisture following an installation. This time can be minimized using the following procedure of hydrating the sensors in multiple short cycles.
Sensor Hydration Before Installation (RECOMMENDED)
Wet the sensor the 1st time by submerging less than halfway for 30 minutes in the morning.
Fully submerging the sensor will trap air inside it and will require drying the sensor completely and restarting this procedure.
Submerging it only halfway lets air escape out of the pores above the water. It allows the capillary action to pull water into the inner pores. It is the fastest way to get the sensor prepared for installation.
Let it dry until the evening.
Wet the sensor a 2nd time by submerging less than halfway for 30 minutes that same evening.
Let it dry overnight.
Wet the sensor a 3rd time by submerging less than halfway for 30 minutes the next morning and let dry until the evening.
Finally, fully submerge the sensor over the 2nd night and install soaking wet in the 3rd morning.
Full sensor accuracy will be reached after 2 or more irrigation cycles, depending on the soil’s wetness.
Shortened Hydration Procedure (NOT-RECOMMENDED)
Soak the sensors overnight in irrigation water before installing the next day. A minimum of 8 hours should be allowed to let water penetrate into most of the inner matrix pores and for most of the air to get pushed out or dissolved in the water.
Full sensor accuracy will be reached after 5 or more irrigation cycles, depending on the soil’s wetness.
REFERENCES
More details on the recommended conditioning procedures can be found on the manufacturer’s website at Irrometer.com at the following links.