FMCW Fill Level Sensor Fault Detection via Correlation
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Solution Overview
Problem
FMCW-based fill level measuring devices face challenges in distinguishing response signals from disturbance fractions, leading to incorrect measurements due to reflections from disturbing objects and internal apparatus issues, particularly in critical process plants requiring high reliability.
Innovation Solution
A method involving the transmission of a radar signal, reception of a response signal, creation of a measurement signal, calculation of a correlation coefficient with a reference signal, and detection of a faulty state when the correlation coefficient falls below a predefined minimum value, using cross-correlation and potentially predicting the remaining operating time through regression analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FMCW radar signal is transmitted for fill level measurement, then continuous contactless measurement with high resolution is achieved, but disturbance signals from reflecting objects and internal feedback cause measurement errors
Solution Approach 1:
The patent applies preliminary action by performing a reference measurement in an absorbing environment before actual measurements. This reference measurement captures the internal disturbance signals of the measuring device, which are then stored and subtracted from subsequent measurements to eliminate their harmful effects on measurement accuracy and reliability
Solution Approach 2:
The patent converts the harmful internal disturbance signals into a beneficial component by measuring and storing them as a reference signal. Instead of being error sources, these disturbance signals are systematically removed from actual measurements through subtraction, thereby improving measurement reliability
2Measurement precision
If correction of disturbance signals is performed using reference measurements, then measurement accuracy is improved, but aging and fouling of the device change disturbance signals over time requiring ongoing correction
Solution Approach 1:
The patent performs preliminary reference measurements at different fill levels to establish correction curves before actual operation. These correction curves pre-compensate for device characteristics and aging effects, enabling automatic correction during operation without complex real-time adjustments
Solution Approach 2:
The patent changes the approach from attempting to physically prevent aging and fouling to adapting to parameter changes over time. By periodically updating correction curves based on reference measurements and tracking changes in disturbance signal characteristics, the system maintains measurement accuracy despite device aging and environmental changes
3Reliability
If distinction between response signal and disturbance fraction is made without doubt, then measurement correctness is ensured, but disturbance signals from stirrers and internal feedback make this difficult
Solution Approach 1:
The patent extracts the internal disturbance signals from the total measured signal by performing reference measurements in an absorbing environment where only internal feedback is present. This separated disturbance component is then subtracted from actual measurements, leaving only the genuine response signal from the fill substance surface
Solution Approach 2:
The patent introduces an intermediary reference measurement process that acts as a mediator between the raw measurement signal and the corrected result. This reference measurement captures the disturbance component, which serves as an intermediary element to be subtracted, thereby enabling clear differentiation between response signal and disturbance
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 method enables reliable detection of faulty states in fill level measuring devices, ensuring accurate measurements even in high-reliability process plants by differentiating between correct and incorrect fill level assessments and predicting potential failures for predictive maintenance.
Implementation Method 1
A continuous radar signal is transmitted and the response signal, which is reflected on the surface of the fill substance, is compared with the frequency of the instantaneously transmitted radar signal
Implementation Method 2
the response signal in the ideal case should be produced exclusively by reflection of the radar signal on the fill substance surface
Implementation Method 3
An established measuring principle, in such case, is the FMCW measuring principle (wherein FMCW stands for Frequency Modulated Continuous Wave). In such case, a continuous radar signal is transmitted and the response signal, which is reflected on the surface of the fill substance, is compared with the frequency of the instantaneously transmitted radar signal
Data Source
AI summary
Disclosed is a method for detecting a faulty state of an FMCW-based fill level measuring device. For this, a correlation coefficient is ascertained by correlation, especially cross correlation, of the measurement signal with a reference signal. The faulty state is accordingly detected when the correlation coefficient subceeds a predefined minimum value. In this way, the functioning of the fill level measuring device can be monitored with a degree of safety allowing the fill level measuring device to be applied also in process plants and measuring environments, which require extremely reliable measuring apparatuses, and measurement data.