Capacitive Ground Fault Detection for Isolated PCB Systems

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Solution Overview

Problem

Integrated circuit electronics face damage from electrical interference, such as electrostatic discharge, and existing protection mechanisms like grounding can disrupt operations in applications like automation, necessitating a non-intrusive method for ground fault detection.

Innovation Solution

A capacitive sensing system that includes a capacitive sensor coupled to the system isolation ground and a capacitance/data converter to detect ground faults by measuring changes in sensor capacitance, allowing for real-time detection without interrupting system operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If off-line circuit diagnostics are performed through current injection, then ground fault detection capability is improved, but system operation is disrupted

Engineering Contradiction:

Improveground fault detection capabilityVSAvoidsystem operation continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent replaces the mechanical/current-based diagnostic approach with a capacitive sensing system that uses electrical field interactions. The capacitive sensor detects ground faults through changes in capacitance caused by proximity to the isolation ground, eliminating the need for disruptive current injection while maintaining detection capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a capacitive sensor as an intermediary element that indirectly detects ground fault conditions. Instead of directly injecting current through the system, the sensor measures capacitance changes in the electrical field, providing fault detection information without disrupting normal system operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If PCB ground is isolated from chassis ground, then protection from electrical interference is improved, but ground fault detection complexity increases

Engineering Contradiction:

Improveprotection from electrical interferenceVSAvoidground fault detection complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces complex electrical injection methods with capacitive sensing technology. The capacitive sensor measures changes in electrical field capacitance caused by proximity to the isolation ground, providing a simpler and less invasive detection method that works effectively in isolated ground systems.

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

Enables effective ground fault detection in electrically isolated systems, preventing damage from shorts while maintaining continuous operation by converting capacitance measurements into digital data for immediate signaling of faults.

Implementation Method 1

a capacitive sensor capacitively coupled to the system isolation ground, and a capacitance/data converter that captures sensor capacitance measurements for conversion to sensor data representative of a ground short

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

the capacitive sensor includes a sensor electrode capacitively coupled to the system isolation ground by one of projected capacitance and a floating capacitor

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Data Source

PatentUS9995781B2Ground fault detection for PCB and isolation grounds

Publication Date: 2018.06.12 TEXAS INSTRUMENTS INC

AI summary

A ground fault detection system based on capacitive sensing suitable for use in detecting a ground fault condition in electronic equipment (such as a PCBA) with a circuit ground electrically isolated from an isolation ground (such as chassis ground). The capacitive sensing system includes a capacitive sensor capacitively coupled to the system isolation ground, and a capacitance/data converter that captures sensor capacitance measurements for conversion to sensor data representative of a ground short. In one embodiment, the capacitive sensor includes a sensor electrode capacitively coupled to the system isolation ground by one of projected capacitance and a floating capacitor (such as 33 pf), and the CDC unit further includes sensor excitation circuitry configured to drive the sensor electrode, such that a sensor capacitance (projected or floating capacitance) is representative of an electrical condition of the system isolation ground. For sensing by projected capacitance, the capacitive sensor can include a driven shield.