Inductive Sensor Demodulator Circuit Noise Reduction
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Solution Overview
Problem
Existing eddy current sensors suffer from high noise levels, limited accuracy, and increased power consumption due to the transconductor's noise generation, limited common mode voltage range, and temperature sensitivity, which degrades performance especially in high radiation environments.
Innovation Solution
A current commutating demodulator circuit with a unique topology that replaces the transconductor with coupling capacitors, converting the voltage-to-current circuit to a current-mode operation, reducing noise, non-linearity, and temperature sensitivity, and allowing for larger AC signals without increasing power supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transconductor is used in the demodulator circuit, then voltage-to-current conversion is achieved, but noise is generated and temperature sensitivity increases
Solution Approach 1:
The patent removes the transconductor from the demodulator circuit and replaces it with a capacitor-based voltage-to-current conversion mechanism. This extraction of the problematic component eliminates the noise and temperature sensitivity it generated, while preserving the essential signal conversion function through alternative means.
Solution Approach 2:
The patent substitutes the electronic transconductor with a capacitor-based conversion mechanism. This replacement uses fundamental electrical properties (capacitance) instead of active electronic components, achieving voltage-to-current conversion without the harmful effects of transconductors in terms of noise and temperature dependence.
2Device complexity
If the common mode voltage range is limited, then circuit design is simplified, but accuracy degrades in high radiation environments
Solution Approach 1:
The patent changes the operational parameters of the demodulator circuit by using capacitor-based conversion instead of transconductor-based conversion. This parameter change enables the circuit to handle broader voltage ranges including high common-mode voltages, improving accuracy in radiation environments while maintaining circuit simplicity.
3Power
If AC signal amplitude is increased, then signal strength improves, but power supply voltage requirements increase
Solution Approach 1:
The patent replaces the transconductor with a capacitor-based voltage-to-current conversion system that can handle larger AC signal amplitudes without requiring proportionally higher power supply voltages. The capacitor-based approach naturally accommodates signal amplitude variations within the existing power supply range.
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 significantly reduces noise, improves accuracy, and enhances power efficiency by eliminating radiation-induced drift and minimizing post-amplification needs, resulting in higher sensitivity and stability for eddy current sensors.
Implementation Method 1
An inductive sensor is comprised of an induction loop that, when electric current passes through it, generates a magnetic field. The inductance of such a loop changes according to the material inside the magnetic field and since metals are much more effective inductors (conductors) than other materials the presence of metal in the magnetic field increases the current flowing through the loop.
Implementation Method 2
Eddy currents are created when a conductor experiences changes in the magnetic field. If either the conductor is moving through a steady magnetic field, or the magnetic field is changing around a stationary conductor, eddy currents will occur in the conductor. Therefore, eddy currents will be generated wherever a conducting object experiences a change in the intensity or direction of the magnetic field at any point within it.
Implementation Method 3
Parallel capacitors Cp resonate with the inductance of the sensors, improving linearity, temperature coefficient, and noise while reducing power consumption.
Data Source
AI summary
A transconductor converts voltage on an inductive sensor to a proportional current using two “coupling” capacitors. Responsive to movement of an electrically conductive target from the null position a resonant current is formed between the two sensor coils. A single differential transistor pair switched by periodic drive signals commutes the net alternating current at the single input to direct current.