Photoacoustic Sensor Drift Correction via Transfer Function

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Solution Overview

Problem

Photoacoustic detectors experience drift over time, leading to variations in measurement accuracy and repeatability, as their response changes post-manufacture and initial calibration, causing them to deviate from specified performance.

Innovation Solution

The method involves establishing an initial transfer function for a photoacoustic detector and periodically measuring subsequent transfer functions to determine span and baseline correction values, which are used to compensate for output variations, without requiring significant changes in gas concentration, utilizing a closed-loop control system with an infra-red source and dual microphones for accurate gas concentration detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If photoacoustic detectors are used for gas detection over time, then detection capability is maintained, but measurement precision deteriorates due to detector drift

Engineering Contradiction:

Improvedetection capabilityVSAvoidmeasurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The system performs preliminary characterization by measuring the detector's transfer function at multiple known gas concentrations to establish baseline response characteristics. This preliminary data collection enables the system to predict and correct for future drift without requiring continuous external calibration gases, thereby maintaining measurement precision over time while preserving detection capability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements feedback by continuously monitoring the detector's transfer function and using the characterized drift patterns to adjust measurements in real-time. The microprocessor compares current detector responses against the stored transfer function model and applies corrections accordingly, creating a closed-loop system that maintains measurement accuracy despite detector aging and environmental variations.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If traditional calibration methods are used, then initial measurement accuracy is achieved, but repeatability deteriorates over time due to drift out of specification

Engineering Contradiction:

Improveinitial measurement accuracyVSAvoidmeasurement repeatability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the operational parameter from static calibration to dynamic transfer function characterization. By measuring detector response across multiple gas concentrations and storing the complete transfer function, the system adapts to detector drift by updating correction factors based on the full response curve rather than relying on single-point calibration, thus maintaining both accuracy and repeatability.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If span and baseline correction is implemented, then measurement precision is maintained over time, but device complexity increases

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidcorrection circuitry complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system replaces complex hardware correction mechanisms with software-based processing. Instead of using additional physical components or complex circuitry to correct for drift, the patent uses a microprocessor to perform mathematical corrections on the detector output based on the stored transfer function, significantly reducing device complexity while maintaining measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system creates a digital copy or model of the detector's transfer function characteristics and uses this model to correct measurements. By storing the transfer function data in memory and using it for corrections, the system avoids the need for complex real-time hardware correction circuits, simplifying the overall device architecture while maintaining accuracy.

Inventive Principle:

Principle #26Copying

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 ensures precise and repeatable performance by continuously correcting for drift and maintaining measurement accuracy over time, ensuring consistent gas concentration detection without the need for known gas concentrations during calibration.

Implementation Method 1

Photoacoustic detectors experience drift over time

Methodology Applied

Scientific EffectPhotoacoustic effect: Photoacoustic Effect

Data Source

PatentUS9086364B2Photoacoustic sensor with baseline and span correction

Publication Date: 2015.07.21 HONEYWELL INTERNATIONAL INC

AI summary

A photoacoustic detector wherein a detector response transfer function can be measured at various times under predetermined conditions during the life of the detector. One or more of the time related transfer functions each can, when acquired, be compared to the stored initial transfer function established at initial manufacture and calibration of the detector. Span and baseline correction values can be determined. These values can be used to compensate detected output values during normal operation. Time related transfer functions can be compared to each other as well as to the stored initial transfer function.