Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1992-08-21
1995-05-23
Tyz, Marcus
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324333, 324439, 331 65, G01R 2726, G01V 308
Patent
active
054184665
DESCRIPTION:
BRIEF SUMMARY
This invention relates to moisture and salinity measurement and in particular to a sensor and its method of use which may provide values for the moisture/complex dielectric constant and/or salinity of a variety of mediums in which it is placed, which may include soils, cotton, grain, coal dust and concrete.
BACKGROUND OF THE INVENTION
The invention is primarily directed towards a sensor for determining the moisture/complex dielectric constant and/or salinity of the medium in which the sensor is placed. To assist in the description of the invention we will use the example of one of its many uses, that of measuring the water and salinity content of soil but it will be understood that this is only an example and is not intended to be limiting in any way upon the scope of the invention as later claimed herein.
The efficient use of irrigated water for food production should be a primary objective of irrigators where the basic resources i.e. water, fertilisers, etc., are finite, degradable and/or costly. Efficient irrigation involves applying known amounts of water at frequencies which achieve optimum crop yield and quality, in a way which sustains and protects the resources being used. If irrigations are not correctly scheduled, food quality can be reduced, yields suppressed, perched water tables can rise, the degradation of irrigable land hastened and resources wasted. (The technique used to achieve this is referred to as "irrigation scheduling").
Proper irrigation scheduling requires decisions to be made regarding when to irrigate, how much water to use, and where it should be applied. Throughout the world, the irrigation industry recognises that there is a need for the development of an irrigation scheduling system which is inexpensive, accurate, reliable and repeatable. Gathering relevant information as part of this system is currently a very labour intensive and expensive undertaking, due partly to the instrumentation available and partly to the complexity of the situation.
There are many factors which influence irrigation scheduling techniques and the decision making process, comprising the climatic setting (arid, semi-arid etc.), soil texture, spatial variability, water supply (constraints on availability, cost of pumping, water quality), crop (flowering habit, harvest index, stress sensitivity at each stage of growth), irrigation system (degree of control, level of automation), weather (current, short term expected), economics (profit maximising level of irrigation) and last but not least the level of salinity in the soil water solution. The relationship between these factors can be highly complex, and the development of an integrated expert modelling system for practical irrigation scheduling and crop production has therefore been limited.
Much of the aforesaid problem has been due to the difficulty of collecting accurate and extensive data from the field. The development of a successful irrigation scheduling system based on monitoring will depend on the quantity and quality of the information collected. Some of the information related to the needs of a system is readily available and capable of being collated and understood by the agricultural decision maker without the need for specialised equipment.
This includes inventory information about the soil, water supply quantity and quality, the irrigation system, the physiology of the crop and environmental variables such as climatic details.
Of major significance to the success of an irrigation scheduling system is that part of the system which measures the response of the soil to the applied water and the rate of its depletion by the crop grown. Several devices and procedures have in the past been used to obtain soil moisture/complex dielectric constant measurements from which predictive models have been used to assist the irrigation decision making process. The most commonly used equipment and methods of collecting this type of data from the soil are outlined below.
The simplest but most labour intensive method for directly determining soil water co
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Smith-Rose, R. L. "The Electrical Properties of Soil for Eight Alternating Currents at Radio Frequencies", Proceedings of the Royal Society of London, 140,359 (1993) (no month).
Hoekstra, P. and Delaney, A. "Dielectric Properties of Soils at UHF and Microwave Frequencies", Journal of Geophysical Research, vol. 79, No. 11 Apr. 24, 1990.
Buss Peter
Gatto Rick
Watson Keith
Weir Peter
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