Inductive Sensor Signal Conditioning Using Reference Coil Compensation
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Solution Overview
Problem
Conventional signal conditioning systems for inductive sensors, particularly in electronic throttle applications, face challenges in providing a stable output signal that is independent of production variations in the gap between the coupler element and the coil assembly, and are prone to common mode signals such as electromagnetic interference and temperature variations, which can lead to inefficiencies and mechanical wear issues.
Innovation Solution
A signal conditioner system that includes a reference coil to correct for common mode variations, a differential structure to cancel out induced voltages, and a ratiometric approach to generate a linear output signal, which is then adjusted using trimmable resistors and non-volatile memory to meet specific signal specifications, eliminating the need for microprocessors and digital processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional signal conditioning system is used for an inductive sensor, then the system structure is simple, but the output signal is unstable and dependent on production variations in gap spacing and susceptible to common mode signals
Solution Approach 1:
The system segments the sensing function into three separate coils: a transmitter coil for generating the electromagnetic field, a receiver coil for detecting position-dependent signals, and a reference coil for detecting common mode variations. This segmentation allows independent optimization of each coil's function and enables compensation for environmental variations through the reference coil.
Solution Approach 2:
The reference coil acts as an intermediary that detects common mode signals (temperature variations, electromagnetic interference, gap spacing changes) and provides a reference output that is used to compensate the receiver coil output. This intermediary element enables the system to distinguish between position-dependent signals and environmental disturbances.
2Measurement precision
If microprocessors and digital processing are used to correct signal variations, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The system replaces complex digital processing and microprocessor-based correction with an elegant electrical solution: the reference coil output is electrically combined with the receiver coil output through analog circuitry. This substitution achieves the same compensation function as digital processing but with simpler hardware, lower cost, and improved reliability.
Solution Approach 2:
The system changes the electrical parameters (voltage, current, impedance) of the coil outputs through analog processing to achieve signal compensation. By manipulating these electrical parameters through the reference coil and analog circuits, the system achieves precise position measurement without requiring digital conversion and processing.
3Measurement precision
If the receiver coil is made highly sensitive to coupler element position, then measurement precision improves, but the coil becomes more susceptible to common mode signals from temperature and electromagnetic interference
Solution Approach 1:
The system uses the reference coil output as feedback about common mode variations. This feedback signal is combined with the receiver coil output to compensate for environmental effects. The reference coil continuously monitors the electromagnetic field conditions and provides corrective information that cancels out common mode interference from temperature and electromagnetic sources.
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 a stable, linear output signal that is independent of supply voltage and temperature variations, effectively compensating for geometrical changes due to mechanical wear, and maintains high reproducibility across a range of temperatures and gap variations, while reducing complexity and cost.
Implementation Method 1
a transmitter coil powered by an AC source to produce an electromagnetic carrier flux
Implementation Method 2
A receiver coil receives the carrier flux, and generates a receiver signal
Implementation Method 3
a third coil, a reference coil that generates a reference signal due to the carrier flux, but is wound to be unaffected by the position to be measured of the coupler element
Data Source
AI summary
An apparatus and a method for providing an output signal correlated with a part position for a moveable part over a positional range, the apparatus includes a transmitter coil, the transmitter coil producing an electromagnetic field when excited by an exciter signal; a receiver coil located proximate to the transmitter coil, the receiver coil generating a receiver signal when the transmitter coil is excited due to inductive coupling between the transmitter coil and the receiver coil, the receiver signal being sensitive to the part position; a reference coil, providing a reference signal substantially independent of the part position; a signal conditioner receiving the receiver signal and the reference signal, the signal conditioner including an analog divider generating a ratio signal from the receiver signal and the reference signal, the output signal being obtained from the ratio signal.