Calibration and Testing of the MPS-1 Matric Potential Sensor.

In this study, we evaluated the performance of the MPS-1 matric potential sensor (Decagon Devices, Pullman, WA).  Ten MPS-1 sensors were selected and pressure/suction measurements were carried out for a wide range of soil environmental conditions to determine the effects of temperature, hysteresis, and differences between pressure and suction.  Four separate experiments (I through IV) were conducted, to determine the measurement range, sensitivity, repeatability, accuracy, and variation among the ten sensors.

Experiment-I was conducted to obtain a universal calibration equation for all sensors using the 1.0-bar pressure point. Experiment-II showed that temperature effects were not significant, relative to the variations between the 10 sensors.  In experiment-III we determined that the sensors were slightly affected by the way they were equilibrated, i.e. by either suction or pressure.  In experiment-IV we noted significant hysteresis effects on the sensors. In summary, we determined that there was much consistency between the sensors and measurements were repeatable. However, we also determined that the calibration curve is highly nonlinear, so that the sensitivity of the MPS sensor between the wet and dry measurement ranges.  Field measurements of the MPS will be compared with tensiometric data, with and without the one-point laboratory calibration.