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

MP306 Moisture Sensor

Measure volumetric soil moisture for scientific research, agriculture and civil engineering

The MP306 has a compact body and the needles are arranged in a single plane making it ideal for use in soil columns. It is also ideally suited to measuring pots in glasshouses and growth cabinets. The MP306 can also be installed in the field, with a lifespan of 20+ years in the most extreme conditions.

The MP306 can be used to take continuous measurements over time through permanent or temporary burial and connection to a SMM Soil Moisture Meter. The sensor has a compact body and the needles are arranged in a single plane making it ideal for use in soil columns, enabling measurement of discrete soil layers within the column. Similarly in soil profiles, narrow layers can be precisely measured.

The MP306 is also used to measure the moisture content in materials used in mining, roadway and buildings. The material that can be measured is often soil but can be any composition of non-metallic powdered, liquid or solid substance into which the needles are inserted. It is especially suitable for mineral stock piles, mine tailings and sand for batch mixing of concrete.

The MP306 Soil Moisture Sensor can also measure soil water potential via the SMM Soil Moisture Meter and a soil water characteristic curve.

MP306 Soil Moisture Sensor Features

  • Volumetric Soil Water Content (%) or can simultaneously measure soil water potential
  • Highly accurate and precise
  • Robust, stainless steel needles and epoxy body
  • Measures in saline, toxic and high temperature soils
  • Rapid measurement
  • Can be buried for up to 20 years

 

Utilising the MP306 sensor in a custom IoT (Internet of Things) package

The SNiP-MP3 is a ‘Sensor Node Integrated Package’ for LoRaWAN or CAT-M1 communication of real-time soil moisture measurements for continuous soil, plant and environmental monitoring. The base SNiP-MP3 integrates 1 MP306 Sensor with an MFR-NODE to a site’s unique network, communication and power requirements. An extended SNiP-MP3 can support up to 4 MP306 sensors or 3 additional compatible sensors.

 

mp306-oven-01

MP306 uses the standing wave principle of measurement. It is equivalent to a Time Domain Reflectometry (TDR) sensor without the need for a complex and expensive pulse generator. MP306 is a high accuracy, precision sensor with +/- 1% VWC accuracy following soil-specific calibration and 0.01% VWC resolution.

The MP306 is ideally supported by the SMM Soil Moisture Meter, a wireless, stand-alone logging instrument available from ICT International. With the SMM, MP306 sensors can be individually calibrated for maximum accuracy.

MP306 Accuracy

The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil samples using the MP306 are given below (Figure 1). This result is typical of the results obtained from comparative testing of the MP306 in prepared soil samples, for a wide range of agricultural soils. Standing Wave Technology and hence the MP306 are not affected by changes in temperature or salinity of the soil or material being measured and hence the values of VSW% are equivalent to oven dried water content.

What is Standing Wave?

The standing wave technique uses an oscillator to generate an electrical field in order to detect the dielectric properties of a substrate of interest. The parallel needles of an MP306 act as a coaxial transmission line to generate a signal. The amplitude of the signal is related to the dielectric constant which in turn is directly related to moisture content.

Results

The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil samples using the MP306 are given below. This result is typical of the results obtained from comparative testing of the MP306 in prepared soil samples, for a wide range of agricultural soils. Standing Wave Technology and hence the MP306 are not affected by changes in temperature or salinity of the soil or material being measured and hence the values of VSW% are equivalent to oven dried water content.

Polynomial Look-up Table

Linearisation tables can be added to Data Loggers using the following data:
Converting Data Table for MP306. From VSW% to mV & mA

Soil moisture VSW%
Millivolts Volts
0% 120 0.120
5% 210 0.210
10% 310 0.310
15% 415 0.415
20% 510 0.510
25% 610 0.610
30% 720 0.720
35% 825 0.825
40% 895 0.895
45% 955 0.955
50% 1005 1.005
55% 1015 1.015
60% 1025 1.025
65% 1035 1.035
70% 1045 1.045
75% 1055 1.055
80% 1065 1.065
85% 1070 1.070
90% 1080 1.080
95% 1095 1.095
100% 1106 1.106

 

MP306 Soil Moisture Probe

Measurement

Measurement Range 0-100 VSW%
Accuracy +/- 1%
Resolution 0.01% VSW%
Response Time Less than 0.5 seconds
Stabilisation Time 3 seconds approximately from power-up

Interface

Input Requirements 9-18 V DC unregulated
Power Consumption 14 mA typical, 16mA max
Output signal 0-1160mV for 0-100 VSW%

Mechanical

Total Length 199 mm
Needle Length 60 mm
Needle Seperation 8 mm
Needles Stainless Steel (Grade 316) – does not corrode in saline solutions
Exterior ABS Plastic
Cable 4.5m Standard

Other

Environment Designed for permanent or temporary burial

MP406 and MP306 Wiring R1-1

Adrien Guyot, Kasper T. Ostergaard, Mothei Lenkopane, Junliang Fan, David A. Lockington, (2013) Using electrical resistivity tomography to differentiate sapwood from heartwood: application to conifers