FMCW Sensor IF Channel Equalizer for Close-Range Accuracy
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Solution Overview
Problem
FMCW level sensors face accuracy issues due to dynamic compression caused by Sensitivity Time Control (STC) amplification, which distorts echo signals and affects measurement precision, especially in close range applications.
Innovation Solution
An FMCW level sensor with an intermediate frequency channel equipped with an equalizer that convolves or multiplies digitized signals with a time or frequency domain equalization function, and optionally uses a sensitivity frequency control filter and windowing, to correct for signal distortions and improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If STC amplification is applied to process echo signals with high dynamic range, then the receiver can handle both small and large echo signals, but the curve shape of the echo curve is influenced and measurement accuracy deteriorates in close range
Solution Approach 1:
The equalization function is pre-calculated and stored based on the known STC amplification characteristics. This preliminary preparation allows the equalizer to immediately compensate for distortions without requiring real-time complex calculations, thus maintaining measurement accuracy in close range while preserving the dynamic range capability provided by STC amplification.
Solution Approach 2:
The system uses the known STC amplification characteristics as feedback information to design the equalization function. By understanding how the STC filter modifies the echo signals, the equalizer can apply the appropriate inverse compensation to restore the original echo curve shape, thereby maintaining measurement precision while benefiting from the extended dynamic range.
2Quantity of substance
If time-dependent gain regulation is used to compress dynamic range, then echo signals with different propagation times are differently amplified, but the amplification becomes dependent on distance and affects accuracy
Solution Approach 1:
The equalizer acts as an intermediary component between the STC filter and the echo curve generation process. It receives the distorted intermediate frequency signal, applies the pre-calculated equalization function to compensate for the distance-dependent amplification effects, and produces a corrected signal that maintains measurement accuracy independent of distance while preserving the dynamic range compression benefit.
3Measurement precision
If STC filter function is measured and correction values are applied, then device-specific distortions can be compensated, but the system complexity increases
Solution Approach 1:
The equalization function is pre-calculated during the manufacturing or initialization phase based on the specific STC filter characteristics of the device. This preliminary action stores the compensation data in a compact form that can be efficiently applied during operation, avoiding the need for complex real-time measurements and calculations, thus maintaining measurement precision while minimizing system complexity.
Data Source
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AI summary
A FMCW fill level sensor comprising an equalizer that equalizes the intermediate frequency signal digitalized by an analog-digital converter. Equalizing is carried out, for example, in the form of convoluting the digitalized intermediate frequency signal by an equalizing function in the time domain. It is also possible to equalize the digitalized intermediate frequency signal by multiplying the signal by an equalizing function in the form of a transfer function G(ωk) to form the discrete frequency in the frequency domain. A digital filter can also be used. This can increase the accuracy with which the fill level is determined.