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Enabling better global research outcomes in soil, plant & environmental monitoring.

WP4-T Water Potential Measurement

The WP4-T makes the difficult measurement of water potential easier. The WP4-T has a measurement range from 0 to -300MPa and 3 to 6.5 pF (saturation to airdry) with an accuracy of 0.1MPa or better.

  • Generate soil moisture release characteristics
  • Measure water potential of soil samples for the root zone, seed zone, and under mulch
  • Monitor water potential for bioremediation
  • Measure water potential dependence of seed germination
  • Monitor seed priming media
  • Study plant-water relations
  • Durable laboratory-grade instrument with integral sensor drawer.
  • Internal chilled-mirror dewpoint measurement is accurate ± 0.1 MPa from 0 to -10 MPa (3 to 5 pF), ±1% from-10 to -300 MPa (5 to 6.5 pF).
  • RS232A port allows direct data transfer to an attached computer.
  • Disposable, lidded sample cups make sample handling easy.
  • Single-point calibration; fast and simple.
  • Both water potential and sample temperature are displayed.
  • Displays water potential in MPa & pF.
  • Menu-based user interface with 10 selectable languages.


The WP4-T senses the dew point of water vapour with a cooled mirror located above a sample in a closed chamber. Sample temperature is monitored with a built-in infrared thermometer, and the WP4-T’s internal peltier cooler allows you to control the sample temperature from 15°C – 40°C. Readings for individual samples are obtained rapidly (5-10 minutes for most soil samples).

Internal Temperature Control

Your lab temperature may vary as much as 5 degrees during the day. This results in as much as a -0.5 MPa difference in water potential readings on dry soil. Most researchers know that water potential changes with temperature. When you use the WP4-T you can measure the water potential of all your samples at a pre-set temperature. Temperature control allows you to monitor small changes in water potential from one sample to the next. By removing the temperature variables from your readings you more accurately measure water potential variations from sample to sample.

Accuracy: 0 to -10 MPa (3 to 5 pF) ± 0.1 MPa
-10 to -300 MPa (5 to 6.5 pF) ± 1%
Range: 0 to -300 MPa (3 to 6.5 pF)
Resolution: ± 0.01 MPa
Measurement Time: 5-10 minutes typical for most soils, 15-20 minutes for plant tissue
Operating Environment: 5 to 43°C, 20 to 85% relative humidity
Temperature Control: 15°C to 40°C ±0.2°C
Weight: 3.2 kilograms
Shipping Weight: 5.2 kilograms
Case Material: Powder coated aluminium
Sample Dish Capacity: 15 ml full (7 ml recommended)
Enclosure Size: 25.4 x 22.8 x 11.4cm
Warranty: 1 year
Sensors: 1. Infrared sample surface temperature.
2. Cooled mirror condensation dewpoint.
Power: 110V or 220V AC, 50/60Hz
Communications: 9-pin D-subminiature, RS232A compatible, 8 data bit ASCII code, 9600 baud, no parity, 1 stopbit. Standard RS232A serial cable included