HF Field Device Calibration for Amplifier Coupling Compensation
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Solution Overview
Problem
Conventional calibration methods fail to compensate for signal amplification couplings and undesired reflections in high frequency based field devices, leading to corrupted measured values in applications like radar-based fill level and dielectric value measurements, particularly in highly aqueous media and large separation scenarios.
Innovation Solution
A high frequency based field device with a first switching unit that can assume various switch positions to connect or isolate components, allowing for the compensation of amplifier couplings by defining and reconciling characteristic variables as calibration factors, using attenuation elements to correct for signal amplification effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If transmission amplifier and receiving amplifier are placed in compact construction, then signal amplification is improved, but coupling between transmitting and receiving paths increases causing measurement corruption
Solution Approach 1:
The patent divides the measurement process into distinct phases (transmission phase and reception phase) using switching units. During transmission, the receiving path is disconnected; during reception, the transmission path is disconnected. This temporal segmentation eliminates coupling between amplifiers while maintaining compact construction, resolving the contradiction between signal amplification and measurement accuracy.
Solution Approach 2:
The patent employs periodic switching between transmission and reception modes. The switching units alternately connect and disconnect the transmission and receiving paths in a periodic manner, ensuring that amplifiers operate in isolation during their respective phases. This periodic action prevents continuous coupling while maintaining effective signal amplification throughout the measurement cycle.
2Ease of operation
If conventional calibration methods are used, then calibration simplicity is maintained, but amplifier couplings and reflections are not compensated leading to corrupted measurements
Solution Approach 1:
The patent performs calibration measurements before actual measurements using the same switching configurations. The calibration factors are determined in advance when the system is in known states (with and without attenuation element), and these pre-determined factors are then used to correct subsequent measurements. This preliminary calibration action eliminates the need for complex real-time compensation while maintaining measurement accuracy.
Solution Approach 2:
The patent uses calibration factors derived from preliminary measurements to feedback-correct the actual measurement values. The system measures characteristic variables during calibration, computes correction factors, and applies these factors to reconcile the actual measurements. This feedback mechanism automatically compensates for amplifier couplings and reflections without requiring complex operational procedures.
3Measurement precision
If attenuation element is introduced for calibration, then amplifier coupling compensation is achieved, but device complexity increases
Solution Approach 1:
The attenuation element serves multiple functions: it provides known attenuation for calibration measurements, enables determination of calibration factors, and facilitates compensation of amplifier couplings. The same component is reused in both calibration and measurement phases, eliminating the need for separate correction components and reducing overall device complexity despite the added element.
Solution Approach 2:
The attenuation element acts as an intermediary component that mediates between the amplifiers during calibration. By inserting a known attenuation between the transmission and receiving paths during calibration measurements, the system can separately characterize the amplifier couplings and derive correction factors. This intermediary approach simplifies the calibration process compared to trying to directly measure and compensate for complex coupling effects.
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
The solution effectively compensates for amplifier-induced couplings and reflections, ensuring accurate determination of fill level and dielectric values by reconciling measured variables through precise calibration, enhancing measurement accuracy.
Implementation Method 1
an antenna arrangement placeable on a container for transmitting a high frequency signal to the medium, and after interaction with the medium, receiving a received signal
Implementation Method 2
a transmission amplifier arranged in the transmission path and/or a receiving amplifier arranged in the receiving path
Implementation Method 3
the transmission path and/or the receiving path are/is connected to an attenuation element, via which the transmission path is connectable with the receiving path
Data Source
AI summary
For calibrating high frequency based field devices, a first switching unit is provided between the antenna arrangement and the transmission amplifier and receiving amplifier of the field device. For ascertaining the corresponding calibration factors, the first switching unit can assume switch positions at which the signal production unit and/or the evaluation unit are/is connected with the antenna arrangement, and at which the transmission path and/or the receiving path are/is connected with an attenuation element via which the transmission path is connectable with the receiving path. An evaluation unit of the field device ascertains at least at these switch positions the corresponding characteristic variable to use these in the later measurement operation as calibration factors. Advantageous with this kind of calibration of the invention is that possible couplings of the amplifiers are compensable.