MPS-2 DIELECTRIC WATER POTENTIAL

Measurements: Water Potential

Applications:

Maintenance-Free Water Potential and Temperature Sensor

The MPS-2 measures a wide range of soil water potentials (-10 to -500 kPa (pF 2.01 to pF 3.71)) without user maintenance and factory calibration.

 

Install Sensor, Log Data

Unlike tensiometers, which need a skilled operator, this dielectric water potential sensor needs no care or feeding. Instead, it can simply be packed into a hole, plugged into a data logger, and left to log water potential data. While the MPS-2 doesn't have the accuracy of UMS tensiometers, its extended range makes this sensor ideal for measuring the water potential in natural systems or other drier systems where cavitation of tensiometers is a concern.  The added temperature measurements can be used to determine approximate soil water potential in partially frozen soils.

 

Plug and Read

Get straight to the data with the Em50 series of data loggers. Just install the sensor, plug it into the Em50, set the clock and measurement intervals, and start logging data. No programming required.

 

Using a Different Logger? No Problem

The MPS-2 can be integrated with systems manufactured by other companies  (such as Campbell Scientific) using serial or SDI-12 communication modes. Some programming is required; sample programs are available.

 

Accuracy Trade-offs

The MPS-2 has much higher accuracy with the factory calibration (±25% of reading from -10 kPa to -100 kPa*) than the MPS-1 and other matrix sensors available on the market.  User calibration is difficult, however it can improve accuracy significantly.  Aside from the tensiometer, the MPS-2 is the only calibrated water potential sensor on the market.

 

Best For:

  • Deficit irrigation monitoring and control.
  • Water potential monitoring in the vadose zone.
  • Crop stress.
  • Waste water drainage studies.
  • Plant water availability.

*please refer to the user manual for more details on the accuracy at different water potentials

 

Case Study: Water potential measurements in a Swiss forest.

The data below were taken with MPS-2 sensors in a Beech and Dry Oak forest, respectively.  Both the MPS-2 and the MPS-6 share the same ceramic plate and technology; only the calibration methodology is different.  The data sets show excellent sensor agreement down to permanent wilting point (-1,500 kPa) with a range that extends well beyond permanent wilting point. 

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Figure 1. Time series MPS-2 water potential data collected at 80 cm depth under a dry oak forest in Switzerland. Note the excellent sensor agreement down to permanent wilting point (-1,500 kPa)

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Figure 2. Time series MPS-2 water potential data collected at 20 cm depth under a dry oak forest in Switzerland. Note that the range extends well beyond permanent wilting point.

Figures 1 and 2 were reproduced with permission from Walthert, L. et al. (2013): Soil as a site factor in Swiss forests (project title).  Swiss Federal Institute for Forest, Snow, and Landscape Research, WSL.​

 

ACCURACY

Soil Water Potential: ± 25% of reading from -10 kPa to -100 kPa, see user manual for more details on accuracy

Soil Temperature: ± 1°C

RESOLUTION

Soil Water Potential: 0.1 kPa

Soil Temperature: 0.1°C

RANGE

Soil Water Potential: -10 to -100,000 kPa (pF 2.01 to pF 3.71)

Soil Temperature: -40 to 60 °C*

*Sensors can be used at higher temperatures under some conditions.  Contact Decagon for more details.

MEASUREMENT SPEED 150 ms (milliseconds)
EQUILIBRATION TIME 10 min to 1 hr depending on soil water potential
SENSOR TYPE Frequency domain with calibrated ceramic discs, thermistor
OUTPUT RS232 (TTL) with 3.6 volt levels or SDI-12 communication protocol
OPERATING ENVIRONMENT

-40 to 60 °C*

*Sensors can be used at higher temperatures under some conditions.  Contact Decagon for more details.

POWER 3.6 to 15 VDC, 0.03 mA quiescent, 10 mA max during 150 ms measurement
CABLE LENGTH 5 m, custom cable lengths available
CABLE CONNECTOR TYPES 3.5 mm "stereo" plug or stripped and tinned lead wires (3)
SENSOR DIMENSIONS 9.6 cm (l) x 3.5 cm (w) x 1.5 cm (d)
DATA LOGGER COMPATIBILITY (NOT EXCLUSIVE) Decagon Em50 Series, ProCheck, Campbell Scientific, any SDI-12-capable data logger
WARRANTY One year, parts and labor

 

 

  MPS-6 MPS-2 T5/T5x* T4 T8 TS1
COST $$ $ $$$ $$$ $$$$ $$$$$
ACCURACY ± 10% of reading + 2 kPa from -9 to -100 kPa ± 25% of reading + 2 kPa from -9 to -100 kPa ±0.5 kPa ±0.5 kPa ±0.5 kPa ±0.5 kPa
RANGE -9 to -100,000 kPa -9 to -100,000 kPa +100 kPa to -85 kPa (-200 kPa*) +100 kPa to -85 kPa +100 kPa to -85 kPa +100 kPa to -85 kPa
POWER REQUIREMENTS 3.6-15 V, 10 mA 3.6-15 V, 10 mA 5-15 VDC 5-15 VDC 3.6 V-15 VDC 5-15 VDC
MEASUREMENT OUTPUT Digital SDI-12 Digital SDI-12 Analog Analog Digital SDI-12, RS-485 Digital SDI-12, RS-485
METHOD USED FOR DETERMINING WATER POTENTIAL Capacitance of a ceramic matrix, 6 point calibration Capacitance of a ceramic matrix, 2 point calibration Piezoelectric pressure sensor, Wheatstone full bridge
BEST FOR

- Long term research studies

- Natural environment monitoring

- Low cost irrigation monitoring

- Column & Spot Measurements in the Laboratory

- Small point measurements

- Long term field studies

- Vadose zone hydrology

- Long term field studies

- Vadose zone hydrology

- Long term field studies

- Vadose zone hydrology

- Monitoring in remote sites

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