Moisture-Barrier Coated Strain Gauges for Stable Measurement

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Solution Overview

Problem

Conventional strain gauges used in load cells are susceptible to moisture penetration, leading to drift in measurement accuracy and increased manufacturing costs due to hermetic sealing methods like bellows or metallic foils, which affect the metrological performance, especially in low-capacity load cells.

Innovation Solution

A strain gauge with a polymer substrate and a moisture barrier coating applied via deposition processes on all sides, encapsulating the resistor track and base layer, reducing the exposed polymer surface and minimizing moisture absorption, while maintaining measurement accuracy and reducing costs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If hermetic sealing methods like bellows or metallic foils are used to protect strain gauges against moisture, then moisture protection is improved, but manufacturing cost increases and metrological performance deteriorates

Engineering Contradiction:

Improvemoisture protectionVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies a thin polymer film cover layer over the strain gauge to provide moisture protection. This flexible film approach replaces complex hermetic sealing structures like bellows or metallic foils, significantly reducing manufacturing cost and complexity while maintaining effective moisture barrier properties.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent creates a composite structure by combining the strain gauge with a polymer film cover layer. This composite approach integrates moisture protection functionality into the existing strain gauge design, eliminating the need for separate hermetic sealing components and reducing overall manufacturing cost.

Inventive Principle:

Principle #40Composite materials

2Reliability

If hermetic sealing methods like bellows or metallic foils are used to protect strain gauges against moisture, then moisture protection is improved, but measurement accuracy deteriorates

Engineering Contradiction:

Improvemoisture protectionVSAvoidmetrological performance

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The polymer film cover layer is designed to be flexible and thin, allowing the strain gauge to deform naturally with the test object without introducing artificial constraints. This flexibility ensures that the measurement reflects true strain conditions, maintaining measurement accuracy while providing moisture protection.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent uses a simple polymer film cover layer that can be easily applied and removed without affecting the strain gauge's performance. This approach avoids the complexity of hermetic sealing that introduces measurement errors, while still providing adequate moisture protection for the measurement duration.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If polymer materials are used in strain gauges for their suitable properties, then ease of manufacture is improved, but moisture absorption increases causing drift in measurement accuracy

Engineering Contradiction:

Improveease of manufactureVSAvoidmeasurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The polymer film cover layer acts as a moisture barrier that prevents ambient humidity from reaching the strain gauge's polymer materials. This protection eliminates moisture absorption-induced swelling and elastic modulus changes, thereby preventing measurement drift while maintaining the ease of manufacture advantage of polymer-based strain gauges.

Inventive Principle:

Principle #30Flexible shells and thin films

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 moisture-insulated strain gauge maintains measurement accuracy over extended periods and passes stringent humidity tests, ensuring compliance with international standards without significant cost increases, even in low-capacity load cells.

Implementation Method 1

a moisture barrier coating is formed, by means of a depositior process, on all sides of the cover layer

Methodology Applied

Scientific EffectDeposition (physical): Physical Vapour Deposition

Implementation Method 2

When humidity is adsorbed, the volume of polymer materials in strain gages will swell

Methodology Applied

Scientific EffectAbsorption (physical): Absorption (physical)

Data Source

PatentEP3844467B1Moisture-insulated strain gauge and method of insulating a strain gauge against moisture penetration

Publication Date: 2025.10.01 METTLER TOLEDO (CHANGZHOU) PRECISION INSTR CO LTD

Figure 1~5
Figure 6~9B
Figure 10~14

AI summary

A strain gauge (12, 21A, 21B, 25A, 25B, 31, 35, 41, 45) and method of manufacturing a strain gauge (12, 21A, 21B, 25A, 25B, 31, 41, 35, 45) against moisture penetration comprises or includes the step of producing a coated base or cover layer (14, 34, 44) by forming a moisture barrier coating (17) on the surface the latter.