Capacitive Voltage Indicator for Power Cord Detection

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Solution Overview

Problem

Existing voltage indicators for AC power distribution systems often damage power cords, require physical contact with metal conductors, or need a battery source, making them inconvenient for determining the presence of voltage on appliances like coffee makers and clothes irons.

Innovation Solution

A flexible AC voltage indicator with a high impedance display device and conductive elements, one insulated from the power cord and the other for human contact, allowing capacitive coupling to indicate voltage presence without physical contact or battery, mounted on a power cord using a sheet-form insulating material.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Difficulty of detecting and measuring

If a knife blade contact is used to detect voltage, then voltage detection is achieved, but the insulation on the wire is permanently damaged

Engineering Contradiction:

Improvevoltage detectionVSAvoiddamage to power cord insulation

Core Design Contradiction:

Difficulty of detecting and measuringVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a non-contact voltage sensor as an intermediary device that detects voltage through electromagnetic field coupling without requiring physical contact with the conductor. This mediator enables voltage detection while avoiding direct contact that would damage the insulation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the mechanical contact-based voltage detection method (knife blade physically touching the conductor) with a field-based detection method using electromagnetic coupling. This substitution eliminates mechanical contact and its associated damage to the power cord insulation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Difficulty of detecting and measuring

If an alligator clip is used to complete the circuit, then voltage detection is achieved, but a grounded electrical terminal is required

Engineering Contradiction:

Improvevoltage detectionVSAvoidrequirement for ground terminal

Core Design Contradiction:

Difficulty of detecting and measuringVSEase of operation

Solution Approach 1:

The patent replaces the mechanical circuit-completion method (alligator clip requiring ground terminal connection) with a field-based detection system. The non-contact sensor detects voltage through electromagnetic coupling, eliminating the need for physical circuit completion and ground terminal requirements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Difficulty of detecting and measuring

If a thin electrical connecting wafer is slid over the plug, then voltage detection is achieved, but the quality of the electrical connection is decreased

Engineering Contradiction:

Improvevoltage detectionVSAvoidelectrical connection quality

Core Design Contradiction:

Difficulty of detecting and measuringVSReliability

Solution Approach 1:

The patent introduces a non-contact voltage sensor as an intermediary that detects voltage without interfering with the electrical connection. The sensor couples to the electromagnetic field around the conductor, enabling voltage detection while leaving the original electrical connection undisturbed and maintaining its quality.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Difficulty of detecting and measuring

If a screwdriver or pen type indicator is used, then voltage detection is achieved, but physical contact between the probe tip and metal conductors is required

Engineering Contradiction:

Improvevoltage detectionVSAvoidmetal-to-metal contact

Core Design Contradiction:

Difficulty of detecting and measuringVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical contact-based probe indicator with a non-contact sensor that detects voltage through electromagnetic field coupling. This substitution eliminates the need for metal-to-metal contact between the probe tip and conductors, avoiding potential damage or safety hazards.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

5Difficulty of detecting and measuring

If metallic contacts pierce the conductors, then voltage detection is achieved, but the power cord insulation is permanently damaged

Engineering Contradiction:

Improvevoltage detectionVSAvoiddamage to power cord insulation

Core Design Contradiction:

Difficulty of detecting and measuringVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a non-contact voltage sensor as an intermediary detection method that senses voltage through electromagnetic field coupling without piercing or contacting the conductors. This mediator enables voltage detection while preserving the integrity of the power cord insulation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the mechanical piercing method with a field-based detection system. The non-contact sensor detects voltage through electromagnetic coupling, substituting the destructive mechanical piercing action with a non-intrusive field measurement approach.

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

Provides a simple, battery-free, and non-damaging method to determine AC voltage presence on power cords, usable anywhere along the cord, enhancing troubleshooting convenience without damaging the insulation or requiring a ground terminal.

Implementation Method 1

A first conductive element in physical proximity to, and electrically insulated from, said power cord... whereby the presence or absence of voltage on the insulated hot conductor of the power cord is indicated

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

a second conductive element that is exposed for touching by a human being and is electrically connected to said second electrode of said display device, whereby the presence or absence of voltage... is indicated... when said second conductive element is connected to ground through a human being

Methodology Applied

Scientific EffectCapacitive coupling to ground: Capacitance

Data Source

PatentUS7893686B1Power cord voltage indicator

Publication Date: 2011.02.22 ATHERTON JOHN C

AI summary

A voltage indicator for mounting on a power cord (FIG. 3) for indicating the presence or absence of a single-phase AC voltage potential on a monitored power cord for a grounded AC power distribution system. The indicator comprises; a housing (16,18), an electronic display (10), a static suppression resistor (12), a first conductive element (14) in physical proximity to the monitored power cord, and a second conductive element (22) meant to be touched by a human being to provide a visual indication of the presence or absence of a voltage potential on the monitored power cord. A capacitive coupling (FIG. 1) takes place between the “hot” conductor of the power cord and the first conductive element (14) of the indicator. This causes a voltage drop across the display (10) and the resistor (12) in parallel with the display (10). The current flow from the display (10) and the resistor (12) merge together to return to ground through a human being touching a second conductive element (22). The path of current flow is completed by the power source ground connection. The indicator is electrically insulated from the power cord it monitors due to the insulation on the power cord at the location of the indicator. The monitored power cord can be a two conductor power cord (“hot” and neutral) or a three conductor power cord (“hot”, neutral, and ground).