Substrate Moisture Sensor Modeling Inductance for Accurate Readout
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Solution Overview
Problem
Conventional measurement systems for monitoring water content and nutrient concentration in substrates used in agriculture and horticulture are inaccurate due to the neglect of inductance values associated with sensing elements, which significantly impact measurement accuracy, especially at higher frequencies and in thicker substrates.
Innovation Solution
A sensing system that models the impedance formed by sensing elements and substrates as a distributed RLC network, incorporating inductances Lp1 and Lp2, capacitance Cp, and conductance Gp, and uses a processing unit to solve a system of equations to determine water content and nutrient concentration by accounting for these inductances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional measurement systems neglect inductance values, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The measurement system is segmented into distinct electrical components (resistance R, capacitance C, inductance L) that form an RLC circuit model. Each component is measured separately using specific excitation frequencies, allowing the complex impedance to be broken down into manageable parameters that can be individually characterized and combined to determine water content and nutrient concentration.
Solution Approach 2:
The system changes measurement parameters by using multiple excitation frequencies to separately determine resistive, capacitive, and inductive components of the impedance. By varying frequency and analyzing the resulting impedance changes, the system extracts accurate values for R, C, and L parameters, which are then used in the RLC model to calculate substrate properties with high precision.
2Measurement precision
If inductance effects are accurately modeled, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system replaces direct physical measurement of inductance with an electrical substitution method. Instead of mechanically measuring L, the system uses electrical excitation and measures the resulting impedance phase and magnitude changes, then mathematically extracts the inductive component. This electrical field-based approach substitutes complex physical measurement with simpler electrical measurements and computational analysis.
Solution Approach 2:
The system introduces an intermediary RLC circuit model that mediates between the raw impedance measurements and the final water content/nutrient concentration calculations. The model acts as a mathematical intermediary that translates measured electrical parameters (R, C, L) into meaningful substrate properties, simplifying the overall measurement process while maintaining high accuracy.
3Measurement precision
If higher frequencies are used for measurement, then measurement precision may be improved, but the impact of inductance increases causing measurement errors
Solution Approach 1:
The system uses feedback by measuring impedance at multiple frequencies and using the results to iteratively determine the R, C, and L parameters. The measured impedance data feeds back into the RLC model, allowing the system to adjust and refine its parameter estimates. This feedback mechanism enables the system to compensate for inductance effects and maintain accurate measurements even at higher frequencies where inductance would normally cause significant errors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides high-accuracy measurements of water and nutrient levels by accurately modeling the inductance effects, enabling precise control of plant growth conditions.
Implementation Method 1
sensing elements 3A and 3B, combined with the part of substrate 1 between said sensing elements 3A and 3B, form a capacitive element Cp
Implementation Method 2
capacitance Cp can be written as a multi-variable function Cp(W, εs, εw), wherein W is the water content in substrate, εs is the dielectric constant of substrate 1 without any water, and εw is the dielectric constant of water
Implementation Method 3
due to a particular concentration of nutrients in the water inside substrate 1, which nutrients take the form of mobile ions, there exists a non-zero electrical conductivity (EC) between sensing elements 3A and 3B
Data Source
AI summary
The present invention relates to a sensing system (10) for monitoring a substrate (1), comprising a sensing unit (4) with first and second sensing elements (3A, 3B) configured to be inserted into the substrate (1); a signal generation unit (5) configured to apply an electrical signal to the sensing elements; a readout unit (6) configured to determine at least one electrical parameter as a result of the electrical signal being applied to the sensing elements (3A, 3B); and a processing unit (7) configured to determine at least an amount of water inside the substrate (1) among an amount of water in the substrate (1) and a nutrient concentration in the substrate (1), based on the determined at least one electrical parameter and an electrical model of a combination of the sensing elements (3A, 3B) and the substrate (1) in which they are inserted, wherein the electrical model comprises a first inductor modelling a first inductance (Lp1) of the first sensing element (3A) and a second inductor modelling a second inductance (Lp2) of the second sensing element (3B); a capacitor modelling a capacitance (Cp) between the sensing elements (3A, 3B); a resistor modelling a conductance (Gp) between the sensing elements (3A, 3B); wherein the first inductance (Lp 1) is modelled as a known first function of the amount of water inside the substrate (1), wherein the second inductance (Lp2) is modelled as a known second function of the amount of water inside the substrate (1), wherein the capacitance (Cp) is modelled as a known third function of the amount of water inside the substrate (1), and wherein the conductance (Gp) is modelled as a known fourth function of the amount of water inside the substrate (1) and an amount of mobile ions representing the amount of nutrients inside the substrate (1).