Two-Wire Field Device Connection Circuit for Inrush Current Limiting

Solution Overview

Problem

Two-wire field devices experience unpredictable fluctuations in available power, leading to unstable voltage and current peaks during startup, which can violate safety standards and disrupt communication.

Innovation Solution

A connection circuit with a supply capacitor, first and second current limiting elements, and bridging elements to manage inrush currents and current changes, ensuring compliance with Ethernet-APL standards by limiting input current and temporal current changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a two-wire field device is started up, then power supply is established, but excessive inrush current peaks occur that violate safety standards

Engineering Contradiction:

Improvecompliance with safety standardsVSAvoidinrush current peaks

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by pre-charging the supply capacitor through the first current limiting element before the main power switch is closed. This preliminary charging action limits the inrush current to a safe level, and only after the capacitor is charged does the bridging element close to establish full power supply, thus preventing excessive current peaks while ensuring compliance with safety standards

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses the first current limiting element as an intermediary component between the power source and the supply capacitor during startup. This intermediary element restricts the charging current to a permissible level, acting as a mediator that allows safe charging of the capacitor without generating harmful inrush current peaks that would violate safety standards

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If a supply capacitor is used to stabilize internal voltage, then voltage stability is improved, but current peaks occur during capacitor charging

Engineering Contradiction:

Improveinternal voltage stabilityVSAvoidcharging current peaks

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by pre-charging the supply capacitor through the first current limiting element before the main power switch is closed. This preliminary charging action limits the inrush current to a safe level, and only after the capacitor is charged does the bridging element close to establish full power supply, thus preventing excessive current peaks while ensuring compliance with safety standards

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses the first current limiting element as an intermediary component between the power source and the supply capacitor during startup. This intermediary element restricts the charging current to a permissible level, acting as a mediator that allows safe charging of the capacitor without generating harmful inrush current peaks that would violate safety standards

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

Stabilizes internal voltage and power supply, preventing excessive current peaks and ensuring compliance with Ethernet-APL standards by efficiently managing startup currents.

Implementation Method 1

a supply capacitor (5) which is connected upstream of the voltage converter (4), wherein the supply capacitor (5) is configured to absorb electrical energy when the connection circuit (1) is started and to use it to supply the voltage converter (4)

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a first current limiting element (6) which is connected upstream of the supply capacitor (5), wherein the first current limiting element (6) is designed to limit an input current below a permissible limit current when the connection circuit (1) is started

Methodology Applied

Scientific EffectElectrical Resistance: Electrical Resistance

Data Source

PatentUS20250390078A1Connection circuit for a field device, and field device

Publication Date: 2025.12.25 ENDRESS HAUSER FLOWTEC AG

AI summary

A connection circuit for a field device comprises two connections forming a two-wire interface, a microcontroller for operating the field device, a voltage converter connected upstream of the microcontroller and configured to operate the microcontroller with an operating voltage, a supply capacitor connected upstream of the voltage converter and configured to absorb electrical energy when the connection circuit is started and to use it to supply the voltage converter, a first current limiting element connected upstream of the supply capacitor and designed to limit an input current below a permissible limit current when starting the connection circuit, a first bridging element connected in parallel with the first current limiting element and configured to bridge the first current limiting element if a first criterion is satisfied, and a test element configured to check whether the first criterion is satisfied.