Rain Sensor Expansion Rate Algorithm for Irrigation Control

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Solution Overview

Problem

Conventional rain sensors, particularly those using hygroscopic materials, often falsely trigger shut-off commands due to activation by fog, dew, or light sprinkles, leading to unnecessary suspension of irrigation, as they cannot accurately differentiate between these conditions and actual rainfall.

Innovation Solution

An intelligent rain sensor employing a processor and hygroscopic members with an electronic sensor that measures the expansion and rate of expansion of hygroscopic materials, using algorithms to generate a shut-off command only upon determining measurable rainfall, thereby avoiding false triggers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If hygroscopic materials are used to detect rainfall, then the sensor can detect moisture, but it falsely triggers on fog, dew, or light sprinkles instead of accurate rainfall

Engineering Contradiction:

Improverainfall detection accuracyVSAvoiddifferentiation between rainfall and environmental moisture

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the detection parameter from simple moisture presence to rate of expansion. By measuring how quickly the hygroscopic material expands rather than just whether it expands, the system can distinguish between rapid expansion caused by rainfall and slow expansion caused by dew or fog, thereby resolving the contradiction between reliability and measurement precision.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional mechanical switch-based rain sensor with an electronic sensor system that uses algorithms to process expansion data. This substitution allows for more sophisticated analysis of the expansion rate and pattern, enabling accurate differentiation between rainfall and other moisture conditions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the sensor triggers shut-off on any moisture detection, then irrigation is suspended during rain, but unnecessary suspension occurs during dew or fog

Engineering Contradiction:

Improveirrigation suspension accuracyVSAvoidunnecessary irrigation suspension

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent introduces dynamic thresholding based on expansion rate. Instead of using a fixed threshold for moisture detection, the system adjusts its sensitivity based on how quickly the hygroscopic material expands. Rapid expansion triggers shutdown while slow expansion (dew/fog) does not, eliminating unnecessary time loss while maintaining reliable rain detection.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system continuously monitors the expansion rate of the hygroscopic material and uses this feedback to determine whether to trigger shutdown. The algorithm processes ongoing expansion data in real-time, allowing the system to respond appropriately to different moisture conditions without unnecessary suspension of irrigation.

Inventive Principle:

Principle #23Feedback

3Device complexity

If conventional rain sensors are used, then the system is simple, but it cannot differentiate between measurable rainfall and light sprinkle

Engineering Contradiction:

Improvesensor system complexityVSAvoidrainfall intensity differentiation

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces simple mechanical switch contacts with an electronic sensing system that measures expansion rate. This substitution adds minimal complexity while enabling the system to differentiate between rainfall intensities based on the rate at which the hygroscopic material expands, resolving the contradiction between simplicity and measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 intelligent rain sensor effectively differentiates between rainfall and environmental moisture, ensuring timely and accurate suspension of irrigation during rain events while minimizing false shut-offs, thus optimizing water usage.

Implementation Method 1

at least one hygroscopic member and an electronic sensor that detects an amount of expansion of the hygroscopic member upon absorbing moisture

Methodology Applied

Scientific EffectHygroscopic absorption: Absorption (physical)

Implementation Method 2

an electronic sensor that detects an amount of expansion of the hygroscopic member upon absorbing moisture

Methodology Applied

Scientific EffectPhysical expansion detection:

Data Source

PatentUS8744773B2Rain sensor with variable shut off

Publication Date: 2014.06.03 HUNTER INDUSTRIES INC

AI summary

An intelligent rain sensor incorporates at least one hygroscopic member and a sensor that generates signals representative of its amount of expansion due to absorption of moisture. A microcontroller executes a pre-programmed algorithm that determines at least the rate of expansion and uses that information to distinguish between actual rainfall events on the one hand, and high humidity, dew or a light sprinkle on the other hand, and sends a shut off command to an irrigation controller.