Stillpipe Radar Level Gauging Under Diameter Mismatch and Large Openings

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Solution Overview

Problem

Radar level gauging in stillpipes faces inaccuracies due to frequency dispersion and mismatch between the stillpipe inner diameter and antenna diameter, as well as interference from large openings, leading to costly manufacturing and installation requirements for stringent diameter tolerances.

Innovation Solution

The method involves calculating the phase velocity of wireless signals reflected from the material in the tank using a processing system, which allows for robust level determination by converting dispersed phase velocity into normal velocity, reducing the need for frequency interpolation and enhancing accuracy despite diameter mismatches and large openings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If strict diameter tolerance is enforced between stillpipe and antenna, then measurement precision is improved, but manufacturing cost and complexity increase

Engineering Contradiction:

Improvelevel gauging accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent changes the measurement parameter from direct time-of-flight measurement to phase velocity-based measurement. By measuring phase velocity and using the relationship between phase velocity, frequency, and wavelength, the system can calculate the distance to the material surface. This parameter change makes the measurement less sensitive to diameter mismatches between stillpipe and antenna.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional mechanical/optical time-of-flight measurement system with an electromagnetic phase velocity measurement system. Instead of measuring the direct travel time of radar pulses, the system measures the phase velocity of electromagnetic waves propagating through the stillpipe, which is less affected by geometric mismatches.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If large openings are provided in stillpipe for viscous material flow, then ease of operation is improved, but measurement precision deteriorates

Engineering Contradiction:

Improvematerial flow capabilityVSAvoidlevel gauging accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of large openings (which cause electromagnetic field disturbances and mode conversions) into a beneficial measurement approach. By using phase velocity measurement and analyzing the frequency-dependent behavior of electromagnetic waves, the system can actually utilize the field disturbances caused by large openings as additional information about the material level, rather than treating them purely as noise.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If mismatch between stillpipe and antenna diameter is allowed, then ease of manufacture is improved, but frequency dispersion increases

Engineering Contradiction:

Improveinstallation flexibilityVSAvoidmeasurement stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent introduces a dynamic measurement approach that adapts to the actual electromagnetic field conditions in the stillpipe. By measuring phase velocity across different frequencies and analyzing the dispersion characteristics, the system dynamically adjusts its measurement parameters to compensate for mismatches between stillpipe and antenna diameters, maintaining reliable measurements despite geometric variations.

Inventive Principle:

Principle #15Dynamics

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 approach provides accurate level measurements with reduced costs and increased robustness, tolerating greater mismatches between antenna and stillpipe diameters, and minimizes the impact of large openings, thereby improving measurement stability and reducing errors.

Implementation Method 1

radar signals are transmitted towards and reflected off the surface of the material in the tank

Methodology Applied

Scientific EffectRadar: Radar

Implementation Method 2

radar signals are transmitted towards and reflected off the surface of the material in the tank

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

calculating a phase velocity of the wireless signals reflected off the material

Methodology Applied

Scientific EffectPhase velocity:

Implementation Method 4

accounts for waveguide dispersion and allows for robust accuracy without stringent diameter mismatches

Methodology Applied

Scientific EffectWaveguide dispersion: Dispersion (of waves)

Data Source

PatentUS8271212B2Method for robust gauging accuracy for level gauges under mismatch and large opening effects in stillpipes and related apparatus

Publication Date: 2012.09.18 ENRAF BV

AI summary

A method includes transmitting wireless signals towards a material in a tank and receiving wireless signals reflected off the material. The method also includes calculating a phase velocity of the wireless signals reflected off the material and identifying a level of the material in the tank using the phase velocity. Calculating the phase velocity of the wireless signals could include identifying a plurality of linearly-spaced frequencies and performing linear interpolation using the data identifying the wireless signals to identify data points at the linearly-spaced frequencies. The identification of the data points at the linearly-spaced frequencies could represent the only interpolation operation performed during the calculation of the phase velocity and the identification of the level of the material. Moreover, a mismatch could exist between an inner diameter of a stillpipe through which the wireless signals are transmitted and a diameter of an antenna used to receive the wireless signals.