The MPS-6 is a matrix water potential sensor that provides long term, maintenance-free soil water potential and temperature readings at any depth without sensitivity to salts. The range of the MPS-6 goes from field capacity to air dry. Lab and field tests indicate that it can make accurate measurements at water potentials at least as dry as permanent wilting point.
The MPS-6 features:
|Accuracy||Soil Water Potential: ±(10% + 2 kPa) from -9 to -100 kPa (see manual for additional accuracy specifications past -100 kPa)
Soil Temperature: ± 1°C
|Resolution||Soil Water Potential: 0.1 kPa
Soil Temperature: 0.1°C
|Range||Soil Water Potential: -9 to -100,000 kPa
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. Water potential measurements will not be accurate below 0°C.
|Power||3.6 – 15 VDC, 0.03 mA quiescent, 10 mA max during 150 ms measurement|
|Cable Length||5m, 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 (rev 2.13+), ProCheck (rev 1.53+), any SDI-12-capable data logger|
|Warranty||One year, parts and labour|
MPS-6 sensors are composed of a moisture content sensor and a porous substrate with a known moisture release curve. After the porous material has equilibrated with the surrounding soil, the moisture sensor measures the water content of the porous material, and the sensor uses the moisture release curve to translate moisture content into water potential.
A sensor’s range depends on the variation in pore sizes in the porous substrate; the wider the range of pore sizes, the bigger the measurement range. Commercially available ceramics are designed to have a uniform pore size, which limits their range. The MPS-6 uses a ceramic specifically designed with a wide pore size distribution for wider measurement range.
However, a sensor’s accuracy depends on how well the moisture release curve characterises the porous substrate in that particular sensor. The more consistent the substrate is from sensor to sensor, the more accurate each sensor will be. Widely varied pore sizes lead to inconsistency from sensor to sensor, putting these two critical sensor goals in conflict.
This conflict can be resolved by individually calibrating each sensor. This has always been a time-consuming and expensive process, however.
The MPS-6’s accuracy comes from breakthrough calibration methods that allow sensors to be individually calibrated using an automated calibration apparatus. These new techniques make the MPS-6 the first low cost matrix potential sensor with research-grade accuracy