Isolation Transformer for Wireless Antenna in Grounded Housing

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Solution Overview

Problem

Field devices in industrial process control systems face challenges in maintaining accurate measurements and communication in harsh environments with potential interference from ground loops and electromagnetic interference, while also requiring protection from corrosive and explosive conditions.

Innovation Solution

The implementation of electrically isolated wireless communication circuitry within a grounded housing, using an antenna connected via a shielded electrical conductor and an isolation transformer to prevent interference and ensure reliable signal transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If wireless communication circuitry is directly connected to the antenna within a grounded housing, then the device structure is simple, but ground loop interference and electromagnetic interference occur that degrade signal quality

Engineering Contradiction:

Improvesignal qualityVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

An isolation transformer is introduced as an intermediary component between the wireless communication circuitry and the antenna. The transformer's primary winding connects to the communication circuitry while the secondary winding connects to the antenna, providing galvanic isolation that blocks ground loops and electromagnetic interference while still allowing signal transmission through magnetic coupling.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrical connection between the wireless communication circuitry and the antenna is segmented into two electrically isolated parts: the primary side connected to the communication circuitry and the secondary side connected to the antenna. This segmentation through the transformer allows each side to be independently grounded without creating interference paths.

Inventive Principle:

Principle #1Segmentation

2Object-affected harmful factors

If the housing is electrically grounded for protection in harsh environments, then protection from electromagnetic interference is improved, but ground loops are created that interfere with sensitive measurement circuitry

Engineering Contradiction:

Improveprotection from electromagnetic interferenceVSAvoidmeasurement accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The isolation transformer acts as a mediator that allows the housing to be grounded for electromagnetic protection while preventing ground loop currents from reaching the sensitive measurement and wireless communication circuitry. The magnetic coupling through the transformer blocks galvanic connection paths that would otherwise create interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If an antenna is attached to a grounded housing for signal transmission, then wireless communication capability is achieved, but electromagnetic interference from the housing affects the transmitted signals

Engineering Contradiction:

Improvewireless communication capabilityVSAvoidelectromagnetic interference

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The isolation transformer provides a galvanically isolated connection between the wireless communication circuitry and the antenna mounted on the grounded housing. This allows the antenna to benefit from the housing's grounding for mechanical support and RF reference while preventing harmful electromagnetic interference and ground loop currents from affecting the communication signals.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

This solution prevents ground loop interference and electromagnetic interference, allowing for accurate and reliable wireless communication in harsh environments while protecting sensitive measurement circuitry.

Implementation Method 1

The field device includes an antenna in communication with the wireless communication circuitry via an electrical conductor having a shield. The shield of the electrical conductor is grounded to the housing of the field device.

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Implementation Method 2

The electrical circuit is electrically isolated from the housing of the field device

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7787921B2Link coupled antenna system on a field device having a grounded housing

Publication Date: 2010.08.31 ROSEMOUNT INC

AI summary

A field device in an industrial process control system having an electrically grounded housing with an electrical circuit located within the housing is described. The electrical circuit includes wireless communication circuitry and is electrically isolated from the housing. The field device also includes an antenna that is attached to the housing and a cable having a shield positioned between the wireless communication circuitry and the antenna. The cable provides electrical communication between the electrical circuit and the antenna. The electrical circuit is electrically isolated from the housing, and the shield of the cable is electrically grounded to the housing.