TDR Sensor Foam Layer Measurement via Signal Integration
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Solution Overview
Problem
Conventional filling level measurement methods using time domain reflectometry (TDR) struggle to accurately determine the filling level in containers with multiple media layers, particularly when foam forms, as it leads to confused or merged reflection signals, resulting in inaccurate or unreliable measurements.
Innovation Solution
The method integrates the signal curve over a reference position, using an integral that accounts for the history of signal reflections, allowing for robust measurement independent of signal curve shape and enabling the use of TDR sensors for foam measurement by compensating for varying dielectric constants and environmental influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional TDR evaluation algorithms are used to recognize individual reflection signals, then the measurement process is simple, but the algorithm cannot handle measurement situations with foam or multiple media layers where reflection signals are confused or merged
Solution Approach 1:
The patent changes the evaluation parameter from detecting individual reflection signal peaks to integrating the entire reception signal curve. The filling level is determined by finding where the integral of the reception signal equals a predetermined threshold value, rather than searching for discrete reflection peaks. This parameter transformation allows the system to reliably measure through foam and multiple media layers where traditional peak detection fails.
2Measurement precision
If the bandwidth of the transmitted pulse is increased to separate echo pulses from closely spaced boundary layers, then echo separation improves, but the demands on electronic design and sampling rate increase significantly
Solution Approach 1:
The patent extracts the essential measurement information from the entire reception signal curve through integration, rather than relying on separated echo pulses. By integrating the signal over time and comparing to a threshold, the system obtains filling level information without requiring high bandwidth pulses or complex electronics for pulse separation. This extracts the necessary measurement data while avoiding the complexity of high-bandwidth signal processing.
3Area of stationary object
If a monoprobe is used for TDR measurement, then the sensor can cover the full measurement region, but the signal-to-noise ratio becomes insufficient at very high frequencies due to skin effect damping
Solution Approach 1:
The patent uses periodic pulsed electromagnetic signals for measurement. By transmitting short pulses at appropriate intervals and integrating the reception signal over each pulse duration, the system maintains good signal-to-noise ratio without requiring continuous high-frequency operation. The pulsed nature allows the monoprobe to function effectively while avoiding the skin effect damping problems of continuous high-frequency signals.
4Reliability
If chemical agents are added to reduce foam formation, then foam formation is suppressed, but the process medium is influenced and chemical agents are usually inconceivable in the food sector
Solution Approach 1:
The patent replaces chemical foam suppression methods with a mechanical/electromagnetic measurement approach. Instead of adding chemical agents to prevent foam, the system uses integrated TDR signal processing that can accurately measure through existing foam layers. The integration method is insensitive to foam presence, allowing food industry applications where no chemical additives are permitted.
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 enables accurate filling level measurement up to the surface of a medium with interfering layers, such as foam, by integrating the signal curve and adapting for dielectric constant changes, providing a stable and reliable measurement even when pulses are not easily recognizable, thus overcoming the limitations of conventional methods.
Implementation Method 1
The invention relates to a method of filling level measurement in a container having a first medium and at least one second medium, in particular a foam layer, arranged thereabove in accordance with the preamble of claim 1... based on transmitting an electromagnetic signal into the container having the filling level to be measured and on evaluating the reflected signal
Implementation Method 2
It is based on the determination of times of flight of an electromagnetic signal to determine the interval of a discontinuity of the characteristic impedance of a line... the electromagnetic waves are not irradiated into the open, but are rather conducted along a conductor
Implementation Method 3
If the pulse is incident on an interference site, which is equal to a change in the local characteristics impedance, a portion of the transmitted energy is reflected back to the conductor inlet
Implementation Method 4
In addition, at very high frequencies above 10 GHz, the damping in a monoprobe increases greatly due to the skin effect so that the signal-to-noise ratio can be insufficient
Data Source
AI summary
A method of filling level measurement in a container (12) having a first medium (14) and at least one second medium (16) arranged thereabove, in particular a foam layer, wherein an electromagnetic signal is transmitted, in particular along a probe (28) arranged in the container (12), and a signal curve (S) of the signal reflected in the container (12) is recorded, wherein a signal time of flight (t) up to a border transition (18, 20) to the first medium (14) and/or up to the second medium (16) is determined with reference to the signal curve (S) and a filling level of the first medium (14) and/or a filling level of the second medium (16) is determined from the signal time of flight (t). In this respect, the border transition (18, 20) is recognized from the integral over the signal curve (S), the integral starting from a reference position (t0).