Request Quote | Specification Sheet | Reference List

MP406 Soil Moisture Probe

The MP406 can be used to measure the soil moisture for scientific research or irrigation management. In either situation the MP406 can:

rapidly measure soil moisture by pushing the needles of the sensor into the soil surface or soil profile. (MPKit)
make measurements over time by permanently burying the MP406 and connecting it to a data logger. (FieldStation logging system)
control irrigation by permanently burying the MP406 and connecting it into an irrigation controller. (MP406C)

The MP406 Moisture Probe can also be used to measure the moisture content in many materials such as soil, food and materials used in roadway and building construction.

Theory of Operation

The MP406 has a high frequency moisture detector, which uses the standing wave principle to indicate the ratio of two or more substances forming a body of material, each substance having a different electric constant (Ka).

The moisture measurement of the material is based upon the fact that in a water:soil:air matrix, the dielectric constant is dominated by the amount of water present. Then the soil water content can be measured exactly because changes in water content of the soil result in changes in the dielectric constant of the soil.

The material that can be measured by the MP406 is often soil but can be any composition of non-metallic powdered, liquid or solid those substance into which the needles are inserted.

MP406 measurement of VSW% using soil samples as a standard

Soil sample volumetric soil water (%)
MP406 = 1.0136x + 0.4298
R² = 0.9931

Results

The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil samples using the MP406 are given above. This result is typical of the results obtained from comparative testing of the MP406 in prepared soil samples, for a wide range of agricultural soils.

Typical Installations

Teaching: Sampling soil water percent (VSW%) in soil pits, greenhouse pots and trays and surface soil.
Crop water use and forest hydrology : Frequently MP406 are connected in groups of 4 via a SMD4-V or SMD4-P Smart Interface to the Smart Logger, enabling four depths to be measured continuously in the soil profile.
Road building: MP406 probes can be permanently installed in the soil profile to monitor soil water movement.
Slope Monitoring: MP406 are commonly installed on slopes with tensiometers as a soil moisture and suction-logging system.

Smart interface

Up to 4 MP406 probes are fitted to each external smart interface that consists of an integrated microprocessor. This interface contains all the required information to allow autonomous operation of the probe, including power requirements and logging interval. The smart interface resolution is 16 Bit (1 in 65,536) offering highly precise and accurate recording of the MP406 moisture probe.

Each interface is fitted with a standard cable length of 5 m, extension cables of any length can be interchanged as different experiments demand.

Polynomial Look-up Table

Linearization tables can be added to Data Loggers using the following data:

A: Converting Data Table for MP-406. From VSW% to mV & mA in mineral soil

VSW%	mV MP406	mA MP406C	VSW%	mV MP406	mA MP406C
0%	0	4.00	55%	1015	18.5
2%	120	5.71	60%	1025	18.64
5%	210	6.99	65%	1035	18.785
10%	310	8.43	70%	1045	18.93
15%	415	9.93	75%	1055	19.07
20%	510	11.285	80%	1065	19.21
25%	610	12.71	85%	1075	19.28
30%	720	14.285	90%	1085	19.43
35%	825	15.785	95%	1105	19.64
40%	895	16.785	100%	1160	20.00
45%	955	17.64
50%	1005	18.35

Ordering Information

MP406	Connection to SMD4-P or SMD4-V, 4.5 m cable, Con-X-All connector
MP406/W	Bare wire cable end for use with analogue data logger, 4.5 m cable
MP406/D	DIN connector for use with MPM-160 Moisture Probe Meter, 4.5m cable
MPADA	MP406 Adaptor cable, Con-X-All to DIN connectors, allows probes designed for SMD interfaces to connect to the MPM-160 Moisture Probe Meter

Applications Image Gallery

Click the thumbnail for full-sized image