Turbidity Sensor Calibration Using Historical Data
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Solution Overview
Problem
Turbidity measuring devices installed for monitoring drinking water face challenges in calibration due to impracticality of removing them for standard samples, leading to outdated parameters and measurement deviations, which are not effectively addressed by current methods that only correct zero-point offsets without considering changes in slope or other mapping specification parameters.
Innovation Solution
A method that updates the mapping specification of a measuring device by recording current and historical calibration values, using laboratory reference samples, and incorporating their age as weighting factors to correct for drift, allowing periodic or event-triggered recalibrations, and storing value pairs for robust characteristic curve updates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If only the zero-point parameter is updated during calibration, then the calibration process is simple and quick, but measurement accuracy deteriorates when slope or other mapping parameters have drifted
Solution Approach 1:
The patent extends calibration from updating only the zero-point parameter to updating multiple mapping parameters including slope, curvature, and higher-order terms. This allows the system to adapt to comprehensive drift behaviors while maintaining calibration simplicity through automated polynomial fitting procedures.
Solution Approach 2:
The system uses historical measurement data and laboratory reference values as feedback to automatically determine which mapping parameters require updating. By analyzing deviations between measured and reference values over time, the system intelligently adjusts the appropriate parameters without requiring manual intervention.
2Measurement precision
If frequent calibrations are performed to maintain accuracy, then measurement precision improves, but loss of time and operational disruption increase
Solution Approach 1:
The patent implements partial calibration by updating only the necessary mapping parameters based on actual drift patterns rather than performing complete recalibration each time. This reduces calibration time and operational disruption while maintaining sufficient measurement accuracy through targeted parameter adjustments.
Solution Approach 2:
The system performs preliminary analysis of measurement data to predict when calibration is actually needed, rather than following fixed schedules. By monitoring drift trends and only triggering calibration when parameters exceed acceptable thresholds, the system minimizes unnecessary calibration interruptions while maintaining accuracy.
3Measurement precision
If complete recalibration is performed each time, then measurement accuracy is maintained, but device complexity and calibration effort increase
Solution Approach 1:
The patent implements dynamic calibration that adapts to the actual state of the measuring device. By continuously monitoring measurement data and determining which mapping parameters have drifted beyond acceptable thresholds, the system selectively updates only those parameters, reducing calibration complexity while maintaining accuracy.
Solution Approach 2:
The calibration process is segmented into independent parameter updates rather than requiring complete recalibration. Each mapping parameter (zero-point, slope, curvature) can be updated independently based on its specific drift characteristics, simplifying the overall calibration process while maintaining comprehensive accuracy.
Data Source
AI summary
In a method for calibrating a measuring device, a signal of a first sensor is mapped to a measured value based on a mapping specification. A current measured value of the measuring device is recorded as current calibration measured value; a laboratory reference sample of the measured medium with properties of the calibrated measured value at the point in time of the recording is supplied to a laboratory reference measuring device; the actual value of the measured variable is ascertained based on the laboratory reference sample and made available and recorded as current laboratory reference measured value; and, based on the current calibration measured value, as well as the current laboratory reference measured value, the mapping specification is updated. At least one earlier value pair of a calibration measured value and an associated laboratory reference measured value ascertained in an earlier calibration is considered in updating the mapping specification.