Two-wire Process Variable Indicator Using Electrophoretic Display

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Solution Overview

Problem

Existing tank level indicators, particularly those using magnetic floats, are costly, bulky, and limited to liquid measurements, as they require custom engineering and cannot effectively measure solid materials or provide reliable daylight visibility with high contrast.

Innovation Solution

A two-wire process variable indicator utilizing a microencapsulated electrophoretic display powered by a 4-20 mA current loop, which provides high-contrast, low-power local indications without the need for process fluid connections, suitable for both liquids and solids, and can be flexibly mounted or placed near the tank.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a magnetic float indicator is used for tank level indication, then local visual indication is provided, but the device becomes costly, bulky, and limited to liquid measurements only

Engineering Contradiction:

Improvelocal visual indicationVSAvoidcustom engineering requirements

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical magnetic float system with an electronic display system. The magnetic float mechanism is substituted by a microencapsulated electrophoretic display that receives signals from the process control loop, eliminating the need for custom-engineered float chambers and magnetic coupling mechanisms while enabling measurement of both liquids and solids.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The electronic display system provides universal applicability for measuring both liquid and solid materials in tanks, whereas the magnetic float system was limited to liquids. The display can represent various process variables including tank level for different material types through electrical signals from the control loop.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If a magnetic float indicator is used, then tank level can be indicated, but the device is bulky and requires custom engineering

Engineering Contradiction:

Improvetank level indicationVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The bulky mechanical float chamber and magnetic coupling components are replaced by a compact electronic display unit. The display housing contains only essential electronic components (display module, circuit board, power supply), dramatically reducing device size and weight while maintaining reliable tank level indication through electrical signaling.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Loss of information

If traditional display technologies are used, then process variables can be displayed, but power consumption is high and backlight is required

Engineering Contradiction:

Improvedisplay visibilityVSAvoidpower consumption

Core Design Contradiction:

Loss of informationVSUse of energy by moving object

Solution Approach 1:

The microencapsulated electrophoretic display uses color changes of microcapsules in response to applied voltage to display information. The microcapsules contain charged particles that migrate to create visible contrast (typically black and white) without requiring backlight, enabling passive reflection-based display that consumes minimal power.

Inventive Principle:

Principle #32Color changes

4Measurement precision

If magnetic float system is used, then liquid level measurement is achieved, but it cannot measure solid materials

Engineering Contradiction:

Improveliquid level measurementVSAvoidmaterial type measurement

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The electronic display system is coupled to the process control loop in a manner that allows it to display process variables for both liquid and solid materials. The display receives electrical signals representing tank level or other process variables and can represent these visually regardless of material type, providing versatile measurement capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 cost-effective, high-contrast, and reliable local displays of process variables, including solid materials, with reduced power consumption and no requirement for backlight, suitable for various industrial lighting conditions and applications.

Implementation Method 1

A two-wire process variable indicator utilizing a microencapsulated electrophoretic display

Methodology Applied

Scientific EffectElectrophoresis: Electrophoresis

Data Source

PatentEP2795267B1Two-wire process variable indicator with microencapsulated electrophoretic display

Publication Date: 2020.12.09 ROSEMOUNT INC

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AI summary

A two- wire process variable indicator (106, 200) includes a housing (202) having a plurality of terminals disposed therein. The terminals (204, 206) are coupleable to a two-wire process control loop. A power module (202) is coupled to the plurality of terminals (204, 206) to receive current flow from the process control loop. Driver circuitry (210) is coupled to the power module (202) and a microencapsulated electrophoretic display (109, 212) is coupled to the driver circuitry (210).