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Watermark Soil Moisture Sensor, 200SS, 1.5m Cable US$154.00

Watermark Soil Moisture Sensor, 200SS, 1.5m Cable

Watermark Soil Moisture Sensor

Moisture and temperature of soil are two main concerns in the agricultural arena. This sensor is prepared for applications that require precise monitoring over moisture and temperature conditions. With a copper sintered mesh over the sensor, you have no worry about its anticorrosion performance.

The Watermark sensor by Irrometer is a resistive-type sensor consisting of two corrosion-resistant electrodes embedded in a granular matrix below a gypsum wafer. The resistance value of the sensor is proportional to the soil water tension, a parameter dependent on moisture which reflects the pressure needed to extract the water from the ground.

The Watermark is designed to be a permanent sensor, placed in the soil to be monitored and read as often as necessary with a portable or stationary device. The internally installed gypsum provides some buffering for the effect of salinity levels normally found in irrigated agricultural crops and landscapes.

This sensor is unique in that it takes its resistive measurement within a defined and consistent internal matrix material, rather than using the surrounding soil as the measurement medium. This feature allows the sensor to have a stable and consistent calibration that does not need to be established for every installation.

Different lengths available

This version of the sensor has a 1.5-meter cable (about 5 feet). Combine this with the 4.5-meter and the 8-meter versions to detect soil moisture at different depths.

If extended range to the reading system is required, use at least gauge AWG 18 wire up to 1000 feet (304.8m), AWG 16 wire if between 1000 and 2000 feet (914.4m), AWG 14 wire if between 2000 and 3000 feet, and AWG 12 wire if between 3000 and 4000 feet (1219m).

Soil Moisture Sensor Features

  • 0-200 centibar range
  • Frequency Range: 50 to 10000 Hz approximately
  • Diameter: 22mm
  • Length: 83mm
  • Stainless steel enclosure
  • Fully solid state
  • Will not dissolve in soil
  • Not affected by freezing temperatures
  • Internal compensation for commonly found salinity levels
  • Easy to use
  • No maintenance

Watermark Documentation


Always "plant" a wet sensor! For best response over the first few irrigations, follow this routine prior to installation ("planting" the sensor):
  • 1. Wet the sensor for 30 minutes in the morning and let dry until evening.
  • 2. Wet it again that evening for 30 minutes and let dry overnight.
  • 3. Wet once more for 30 minutes that next morning and let dry until evening.
  • 4. Soak overnight, then install while wet.
Make a sensor access hole to the desired depth with an Irrometer installing tool or a 7/8" (22 mm) O.D. rod. Fill the bottom of the hole with a thick slurry made of soil removed from the hole and water, then firmly push the sensor down into the mud in the bottom of the hole. This will "grout in" the sensor to ensure maximum surface contact between the sensor surface and the surrounding soil. A length of 1/2" class 315 PVC pipe can be coupled onto the sensor and can be used to push it into the soil. A good snug fit in the soil is important. This PVC pipe can be solvent-welded to the sensor.

If your PVC extension pipe is not left on the sensor, backfill the hole so the sensor is buried. If your PVC pipe is left on, make the soil compact around the surface to seal off the hole. The PVC pipe acts as a conduit for the sensor's wires. Label each sensor wire to indicate the measurement depth.

For very coarse or gravelly soils, an oversized hole (1 to 1.25 inches; 25 to 32 mm) may be needed to prevent abrasion damage to the sensor membrane. In this case, auger a hole to the desired depth and make a thick slurry with the soil and some water. Fill the hole with this slurry and then install the sensor. This will "grout in" the sensor to ensure a snug fit.

If sensors are removed, clean by rinsing with water and wiping with a soft cloth. Air dry and store indefinitely in a clean, dry location. Always soak before re-installation.

Compatible with Waspmote

This sensor can be used in a Waspmote wireless sensor platform by plugging it into the Waspmote Agriculture Sensor Board PRO.

This product was added to our catalog on Wednesday 20 August, 2014.


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