Radar Level Gauging via Correlation Analysis
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Solution Overview
Problem
Radar level gauges face limitations in accurately detecting surface echoes due to the reliance on amplitude detection, which requires high-resolution pulse modulation and precise delay control, leading to system complexity and increased energy consumption.
Innovation Solution
The method involves using a common pulse repetition frequency (PRF) for both the reference and reflected signals to determine the target distance based on the 'time of flight,' allowing for quick regulation and reducing the complexity and cost of the system by using only one transmitter and PRF generator, thereby relaxing the demand on precision and control of delay circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If amplitude detection is used to identify echo location, then the method is simple, but the measurement precision deteriorates due to difficulty in detecting small waveform shifts
Solution Approach 1:
The patent changes the detection parameter from amplitude-based to phase-based detection. By measuring the phase difference between transmitted and received signals, the system can detect small time shifts (δ) that correspond to small distance changes, thereby improving measurement precision while maintaining methodological simplicity
Solution Approach 2:
The patent replaces the mechanical/amplitude-based detection system with a signal processing approach using correlation analysis. Instead of relying on amplitude peaks, the system uses cross-correlation of signal waveforms to precisely determine time delays, substituting a more sophisticated detection mechanism that overcomes the limitations of simple amplitude detection
2Measurement precision
If strict requirements for pulse modulation and high-resolution A/D conversion are imposed, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent changes the critical parameter from pulse modulation strictness and A/D resolution to signal correlation analysis. By focusing on phase/delay measurement through correlation rather than requiring high-resolution amplitude sampling, the system achieves comparable or better precision with relaxed hardware requirements and reduced system complexity
Solution Approach 2:
The patent uses correlation analysis which effectively creates a reference copy of the transmitted signal and compares it with the received signal. This copying approach allows precise delay measurement without requiring the receiving system to have high resolution, as the comparison is done in the signal processing domain rather than requiring high-resolution hardware
3Measurement precision
If multiple transmitters and signal sources are used, then the measurement precision improves, but the energy consumption increases
Solution Approach 1:
The patent makes a single transmitter perform multiple functions by using it to generate both the transmitted signal and the reference signal for correlation analysis. This universal use of one signal source eliminates the need for multiple transmitters while maintaining the precision benefits of having reference signals for comparison, thereby reducing energy consumption
Solution Approach 2:
The patent merges the function of multiple signal generators into a single transmitter that produces both the outgoing signal and the reference signal used for correlation. By combining these functions and using signal splitting and time-delay techniques, the system achieves the same measurement precision with only one active transmitter, reducing overall power consumption
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 enhances sensitivity and reduces power consumption while maintaining accurate measurements, independent of pulse waveform and modulation, allowing for improved detection of surface echoes with lower system requirements.
Implementation Method 1
These devices utilize an antenna or a probe to transmit electromagnetic waves toward the material being monitored and to receive electromagnetic echoes which are reflected at the surface of the material being monitored
Implementation Method 2
a target distance or a distance to a surface may be estimated by varying a PRF common for both a reference signal and a reflected signal, in order to determine coincidence between the reference signal and the reflected signal, and thereafter calculate the target distance from the 'time of flight' based on the PRF value(s) that correspond(s) to a coincidence
Data Source
Figure 1~2a
Figure 2b~3
Figure 4a~4c
AI summary
Method for determining product surface distance in a tank comprising: i) generating a transmission signal as a first pulse train; ii) generating a reference signal having a second pulse train by time delaying said first pulse train; wherein each pulse in said first and second pulse trains have essentially identical waveforms and pulse repetition frequency; iii) guiding said transmission signal towards the product surface; iv) receiving a reflected signal; v) forming a correlation value based on a time correlation between the reference signal and the reflected signal; vi) carrying out steps i) to v) in sequence for at least three different pulse repetition frequencies, until at least three pairs of correlation values and associated pulse repetition frequencies have been stored; vii) determining said distance based on said at least three pairs of correlation values and associated pulse repetition frequencies, and said fixed time delay.