Digital Two-Wire Proximity Transmitter Linearization
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Solution Overview
Problem
Existing vibration monitoring systems for rotating machinery, particularly those using eddy current proximity probes, face challenges such as non-linear impedance measurements, complex and inaccurate circuitry, high power consumption, and the need for frequent recalibration due to component variations and temperature drift, which complicates maintenance and reduces system reliability.
Innovation Solution
A digital two-wire proximity transmitter system that generates a customized linearization table based on the specific electrical characteristics of each probe and cable configuration, eliminating the need for phase locked loop circuits and allowing for in-field reconfiguration, thereby improving accuracy and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a phase locked loop circuit is used to maintain resonance, then the system can adapt to varying equipment configurations and target materials, but the power consumption increases significantly
Solution Approach 1:
The patent removes the phase locked loop circuit from the system entirely. Instead of using a PLL to maintain resonance, the system uses a fixed frequency oscillator that operates at a predetermined resonant frequency. This extraction of the PLL circuit directly reduces power consumption while maintaining the core functionality of probe resonance.
Solution Approach 2:
The system changes the operating parameter from dynamic frequency adjustment (via PLL) to fixed frequency operation. By operating the oscillator at a predetermined resonant frequency determined during calibration, the system eliminates the need for continuous frequency tracking while maintaining probe resonance, thereby reducing power consumption.
2Ease of manufacture
If standardized linearization tables are used across all transmitters, then manufacturing and deployment is simplified, but measurement precision decreases due to system-specific variations
Solution Approach 1:
The system performs preliminary calibration during the manufacturing process, determining the specific resonant frequency and electrical characteristics of each probe-cable-transmitter combination. This preliminary action creates a customized linearization table for each system, ensuring measurement precision while maintaining ease of manufacture through automated calibration procedures.
Solution Approach 2:
The patent implements local quality by customizing the linearization table for each specific probe and cable configuration rather than using a universal table. Each transmitter is configured with parameters specific to its hardware components, accounting for variations in cable capacitance, probe impedance, and resonant frequency, thereby improving measurement precision.
3Reliability
If complex circuitry is used to handle component variations and temperature drift, then reliability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces complex analog compensation circuits with a digital approach. Temperature sensors provide digital temperature data that is processed by a microprocessor, which then applies digital compensation to the linearization table and oscillator frequency. This substitution of digital processing for analog circuitry reduces device complexity while maintaining or improving reliability.
Solution Approach 2:
The system implements feedback through temperature sensors that continuously monitor the transmitter environment and provide data to the microprocessor. The microprocessor uses this feedback to dynamically adjust the oscillator frequency and linearization parameters, compensating for temperature drift and component variations without requiring complex passive compensation circuits.
4Measurement precision
If frequent recalibration is performed to account for component variations, then measurement precision is maintained, but loss of time and productivity decrease
Solution Approach 1:
The system performs comprehensive calibration during the manufacturing process, storing the results in non-volatile memory. This preliminary calibration accounts for component variations and establishes a baseline that remains valid throughout the transmitter's operational life, eliminating the need for frequent recalibration and reducing maintenance time.
Solution Approach 2:
The patent creates a digital copy of the probe-cable system's electrical characteristics during calibration, storing the resonant frequency, impedance values, and linearization parameters in memory. This digital representation allows the system to compensate for component variations through software algorithms rather than requiring physical recalibration, thereby maintaining precision while minimizing downtime.
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 system provides consistent and accurate vibration monitoring with reduced power consumption, improved reliability, and simplified recalibration, enabling more precise detection of machinery conditions and minimizing downtime by accounting for unique probe and cable configurations.
Implementation Method 1
Eddy current probes comprise an inductor, or coil, situated at the probe tip driven with a radio frequency (RF) signal which in turn creates a varying magnetic field in any adjacent conductive target material.
Implementation Method 2
This magnetic field produces eddy currents in the material that induce a counter-electromotive force (emf) in the eddy probe inductor
Implementation Method 3
This magnetic field produces eddy currents in the material that induce a counter-electromotive force (emf) in the eddy probe inductor, thereby altering the effective impedance of the inductor.
Data Source
AI summary
A digital based two wire proximity transmitter system and a method for calibrating the system, wherein the transmitter includes a customized linearization table uniquely generated during calibration to take into account the unique impedance properties of a particular probe/coaxial cable configuration. During calibration, the probe is positioned adjacent a calibration target. The calibration target is selected to have the same material characteristics as the target to be monitored during actual operation of the transmitter in the field. At a fixed distance between the probe and calibration target, the resonant frequency of the probe/cable system is determined. Thereafter, utilizing this resonant frequency to excite the probe, the voltage response of the probe/cable system is determined as the distance between the probe and the target material is incrementally changed. The voltage output is used to build a table for incremental distances, wherein each distance is characterized by a non-linear output that has been equated to a linear output. This uniquely generated table is subsequently downloaded into the transmitter for reference during monitoring.