• Senseur de l’humidité du sol et lecteur numérique

Senseur de l’humidité du sol et lecteur numérique

Watermark sensor

In use since 1978, the patented WATERMARK sensor is a solid-state electrical resistance sensing device that is used to measure soil water tension. As the tension changes with water content the resistance changes as well. That resistance can be measured using the WATERMARK Sensor.

The sensor consists of a pair of highly corrosion resistant electrodes that are imbedded within a granular matrix. A current is applied to the WATERMARK to obtain a resistance value. The WATERMARK Meter or Monitor correlates the resistance to centibars (cb) or kilopascals (kPa) of soil water tension.

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. Internally installed gypsum provides some buffering for the effect of salinity levels normally found in irrigated agricultural crops and landscapes.



The WATERMARK sensor is a resistive device that responds to changes in soil moisture. Once planted in the soil, it exchanges water with the surrounding soil thus staying in equilibrium with it. Soil water is an electrical conductor thereby providing a relative indication of the soil moisture status. As the soil dries, water is removed from the sensor and the resistance measurement increases. Conversely, when the soil is rewetted, the resistance lowers.

The WATERMARK 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 unique feature allows the sensor to have a stable and consistent calibration that does not need to be established for every installation.

The relationship of ohm of resistance to centibars (cb) or kilopascals (kPa) of soil water tension is constant and built into the reading devices that are used to interrogate the sensor. The sensor is calibrated to report soil water tension, or matric potential, which is the best reference of how readily available soil water is to a plant. The WATERMARK sensor consists of stainless steel electrodes imbedded in a defined and consistent internal granular matrix material that acts like a soil in the way it moves water. This matrix is encased in a hydrophilic material that establishes good hydraulic conductivity with the surrounding soil and is held in place by a durable stainless steel perforated shell with plastic end caps.



The soil moisture measurement device, or sensor, shall represent soil moisture status in units of soil water tension or matric potential, registering in centibars (cb) or kilopascals (kPa) when read with a compatible reading device. Its construction shall be of the Granular Matrix Sensor (GMS) type and require no on-site calibration or routine maintenance. It shall be durable, long-lasting, not subject to dissolving in a wet soil environment with an outer surface of stainless steel and ABS plastic. It shall be the WATERMARK sensor as manufactured by the IRROMETER Company, Inc. of Riverside, California.


  • Proven stable calibration
  • Range of measurement from 0 to 239 cb (kPa)
  • Fully solid-state
  • Will not dissolve in soil
  • Not affected by freezing temperatures
  • Internally compensated for commonly found salinity levels
  • Inexpensive, easy to install and use
  • Compatible with AC or DC reading devices (specialized circuit required)
  • NO maintenance required



  • Irrigation Scheduling
  • Water Table Monitoring
  • Leak Detection
  • Agronomy Research
  • Environmental Monitoring
  • Anywhere you need to know when or if the soil moisture status is changing




ABS plastic caps with stainless steel body over a hydrophilic fabric covered granular matrix.



.875 in. (22 mm) LENGTH: 3.25 in. (83 mm)



.147 lb. (.067 kg) – with 5 ft. lead


AWG 20, 2 leads


One year



The WATERMARK Meter is a hand held device designed for reading WATERMARK sensors in the field. The digital readout displays the sensors’ soil moisture status in centibars (cb) or kilopascals (kPa) of soil water tension. This value represents the energy a plant’s root system uses to draw water from the soil. Whereas higher tension values indicate dryer soil, lower tension values indicate wetter soil. The meter’s replaceable cable assembly has spring loaded clips for attaching to sensor leads. Users only need one meter to read any number of WATERMARK sensors. The meter comes in its own nylon case, padded and zippered for safe keeping when not in use.



The WATERMARK meter is designed to read all WATERMARK soil moisture sensors exclusvely. These sensors have an output of 500 – 30,000 ohms of electrical resistance which is non-linear. The meter uses a solid-state alternating current resistance bridge meter for reading the sensors and converts the resistance value into centibars (cb) or kilopascals (kPa) of soil water tenson. The reading is displayed on an LCD screen [range 0 –199 cb (kPa)]. Soil temperature values can be input by the user to compensate for their effect on sensor reading.



The soil moisture monitoring system shall incorporate Granular Matrix Sensors (GMS) to measure soil water tension. The sensors shall use a digital meter to read sensor values. The meter shall have a soil temperature compensation feature and self test functions on its tactile keypad. The meter shall be the model #30- KTCD-NL WATERMARK digital meter as manufactured by the IRROMETER Company, Inc. of Riverside, California.


  • Large LCD display is easy to see in sunlight
  • Touch pad operating panel is simple to use and has a self-test function
  • Quick release cable assembly is field changeable
  • Adjustable for soil temperature variations




The WATERMARK meter is designed to read WATERMARK sensors exclusively


Self powered 9 VDC internal battery


ABS plastic case with touchpad controls (tactile switches)



4.750 in. (121 mm) [ 5.25 in. (140 mm) including cable recepticle ]



2.75 in. (70 mm)



1.0 in. (25 mm)


50 OHM coaxial cable [ 24 in. (.6 m) ] with bayonet type connection (BNC) on the meter end and two alligator clips on the sensor end


0 –199 cb (kPa) of soil water tension

IR30KTCDNL Digital Readout
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