Strain Gage Differential Pressure Measurement in Flow Meters

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Solution Overview

Problem

Flow meters with plenums and impulse lines are prone to leakage and clogging, requiring frequent monitoring and calibration, which affects the accuracy and reliability of fluid flow rate measurements.

Innovation Solution

The use of electrical strain gages attached to the structure of differential pressure flow meters, such as pitot tubes, V-cone, and orifice plates, to measure structural strain as a function of differential pressure, eliminating the need for fluid-conducting plenums and impulse lines by converting fluid pressures into electrical signals through a Wheatstone bridge configuration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If plenums and impulse lines are used to convey pressure data in flow meters, then fluid pressure transmission is achieved, but leakage and clogging occur requiring frequent monitoring and calibration

Engineering Contradiction:

Improvemeasurement reliabilityVSAvoidleakage and clogging

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes the plenums and impulse lines from the flow meter system, replacing them with strain gages that directly measure pressure on the sensing element. This eliminates the fluid-conducting pathways that cause leakage and clogging, while maintaining the ability to transmit pressure data electrically through the strain gage circuitry.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical fluid-conducting system (plenums and impulse lines) with an electrical measurement system (strain gages). The strain gages convert mechanical strain caused by pressure differential directly into electrical signals, eliminating the need for physical fluid pathways and their associated reliability problems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If strain gages are used to convert fluid pressures to electrical signals, then leakage and clogging are eliminated, but the complexity of electrical measurement apparatus increases

Engineering Contradiction:

Improvemeasurement reliabilityVSAvoidelectrical measurement complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the pressure sensing function and the signal generation function into a single integrated system. The strain gages are directly mounted on the sensing element, combining the mechanical response to pressure with the electrical signal conversion in one location, thereby simplifying the overall system architecture despite the sophistication of the measurement electronics.

Inventive Principle:

Principle #5Merging (Combining)

3Volume of moving object

If a small area sensing element is used, then the device is compact, but accuracy and range suffer due to weak signal

Engineering Contradiction:

Improvesensing element volumeVSAvoidflow measurement accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The patent employs strain gage technology, which uses composite material structures (typically a fine metallic grid bonded to a flexible substrate) to create highly sensitive pressure sensors. This allows the sensing element to maintain a compact form factor while achieving high measurement precision through the enhanced sensitivity of the strain gage material composition.

Inventive Principle:

Principle #40Composite materials

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 reduces the risk of leakage and clogging, maintains the averaging effect of pitot tubes, and enhances measurement accuracy and sensitivity by directly converting fluid pressure into electrical signals, improving the reliability of fluid flow rate measurements.

Implementation Method 1

Electrical strain gages are the logical choice to convert fluid pressures and the resulting meter strain to electrical signals. Fluid flow produces a strain on the sensing tube, compressing the leading side strain gages and tensing the trailing side strain gages, causing their resistance to decrease and increase respectively.

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Data Source

PatentUS7308832B1Strain gage differential pressure measurement in a fluid flow meter

Publication Date: 2007.12.18 DIETERICH STANDARD INC

AI summary

Apparatus and method for strain gage measurement of differential pressure across a body inserted into a flowing fluid where the body includes an exterior upstream facing portion, an exterior downstream facing portion and interior surfaces. At least one first electrically resistive strain gage having connecting terminals is disposed on one or more of the interior surfaces of the upstream facing portion and at least one second electrically resistive strain gage having connecting terminals is disposed on one or more of the interior surfaces of the downstream facing portion. The first and second strain gages are electrically connected to form the legs of a full Wheatstone Bridge, the electrical output of which is directly related to the differential pressure across the inserted body.