Eddy Current Thermometer for Noncontact Temperature Sensing
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Solution Overview
Problem
Existing remote, noncontact temperature sensing technologies face limitations, including the need for unobstructed line of sight and reliance on distance and angular orientation, making them impractical for various industrial and food heating applications.
Innovation Solution
A method and apparatus using a magnetic field with a triangular waveform to induce eddy currents in conducting members, allowing for the determination of temperature based on the characteristic time constant of these currents, independent of distance and angular orientation, through a receiving coil assembly with compensated voltage outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If infrared thermometers are used for remote temperature sensing, then noncontact measurement is achieved, but unobstructed line of sight is required which limits practical application
Solution Approach 1:
The patent replaces optical detection (infrared) with electromagnetic induction (eddy currents). Instead of using infrared radiation that requires line of sight, the invention uses magnetic fields to induce eddy currents in the target object, allowing temperature measurement without direct visual contact. The magnetic field penetrates nonconductive materials and obstacles that would block infrared signals.
2Measurement precision
If work coil impedance changes are used for temperature measurement, then temperature can be sensed, but the measurement varies significantly with distance between work coil and susceptor
Solution Approach 1:
The patent changes the measurement parameter from impedance magnitude to phase angle. Instead of measuring the absolute impedance change which is highly distance-dependent, the invention measures the phase angle between the work coil current and the voltage across the susceptor. This phase angle remains relatively stable with distance changes, providing more reliable temperature measurements.
Solution Approach 2:
The patent introduces a nonconductive susceptor as an intermediary between the work coil and the object being heated. The susceptor has specific electrical and magnetic properties that enable it to couple the magnetic field from the work coil to the target object while providing a stable phase reference for temperature measurement, reducing sensitivity to distance variations.
3Reliability
If measuring coils are placed at fixed distances to maximize phase angle, then distance effect is reduced, but mechanical adjustment is required for each measurement which is inconvenient
Solution Approach 1:
The patent makes the measurement system dynamic by continuously tracking the phase angle as distance changes occur. Instead of requiring fixed positioning, the system adapts to varying distances by measuring the phase angle in real-time, which automatically compensates for distance variations without requiring mechanical adjustment of coil positions.
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
Enables accurate, noncontact temperature measurement of conducting members and objects, providing consistent results regardless of distance or orientation, and demonstrating high accuracy in food heating applications compared to conventional thermocouples.
Implementation Method 1
It is well known that alternating magnetic fields produce electromotive forces that excite eddy currents in electrically conductive objects
Implementation Method 2
These currents are in the form of closed vortices, with the shape and space distribution of these vortices being defined by the alternating magnetic field pattern in space and time, and by the conductivity and magnetic properties of the conductive objects
Data Source
AI summary
A remote, noncontact temperature determination method and apparatus is provided, which is operable to determine the temperature of a conducting member in operative thermal communication with an object of interest. The method comprises the steps of first inducing a closed vortex eddy current in a conducting member by subjecting the member to a magnetic field, such that the corresponding eddy current magnitude changes exponentially over time. A characteristic time constant of the exponential current magnitude changes is then determined, and this is used to calculate the temperature of the object. The apparatus includes a field transmitting coil coupled with a waveform generator for inducing the eddy current, and a field receiving coil assembly which detects the corresponding induced magnetic. Temperature determinations can be made which are substantially independent of the relative distance and/or angular orientation between the conducting member and the field receiving coil assembly.