US 7,248,994 B1Granted

Digital method and apparatus for sensing position with a linear variable differential transformer

AssigneeAlliant Techsystems Inc.

InventorJohn A. Stolan

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Abstract

An apparatus and method for determining a linear position from a linear variable differential transformer (LVDT) including a primary coil driven by an excitation signal, and two secondary coils coupled to two correlated signals. The method includes converting the correlated signals to a digital estimate, for each of the correlated signals, and evaluating an amplitude of the correlated signals to determine the linear position. The process of converting the correlated signals comprises comparing the correlated signal to an analog feedback signal to generate a comparison result and incrementally adjusting the digital estimate in response to sampling the comparison result at an estimation frequency. The converting process also includes converting the digital estimate to the analog feedback signal, collecting a digital estimate history at a sample frequency that is a binary multiple of the excitation frequency, and analyzing the digital estimate history to determine the amplitude substantially near the excitation frequency.

Claims32

Dependent claims

An apparatus for determining a linear position of a movable component of a linear variable differential transformer (LVDT), which includes a primary coil driven by an excitation signal at an excitation frequency, a first positional output, and a second positional output, the apparatus comprising:

a first signal analyzer including an analog input operably coupled to the first positional output and a second signal analyzer including an analog input operably coupled to the second positional output, each of the first signal analyzer and the second signal analyzer comprising:
a feedback loop configured to generate a digital estimate that substantially tracks an amplitude of the analog input, the feedback loop comprising:
a comparator configured for comparing the analog input to an analog feedback signal and generating a comparison result;
a digital estimator, operating at an estimation frequency and configured to sample the comparison result and modify the digital estimate by an incremental adjustment amount responsive to the comparison result to reduce a difference between the amplitude of the analog input signal and an amplitude of the analog feedback signal;
and
a digital-to-analog converter configured to convert the digital estimate to the analog feedback signal;
and
an amplitude analyzer configured to collect a digital estimate history by sampling the digital estimate at a sample frequency that is a binary multiple of the excitation frequency and analyze the digital estimate history to determine an amplitude of the digital estimate substantially near the excitation frequency;
and
a result calculator configured to evaluate the amplitude of the digital estimate from the first signal analyzer and the amplitude of the digital estimate from the second signal analyzer to generate a numerical representation of the linear position of the movable component.

7 more elements

A method for determining a linear position, comprising:

generating at least two correlated signals from a Linear Variable Differential Transformer (LVDT) by stimulating an excitation input with an excitation signal, wherein the at least two correlated signals are responsive to a linear position of a movable component of the LVDT and the excitation signal;
converting the at least two correlated signals to a digital estimate for each of the at least two correlated signals, the converting comprising:
comparing the correlated signal to an analog feedback signal to generate a comparison result;
incrementally adjusting the digital estimate at an estimation frequency in response to sampling the comparison result such that the incremental adjusting reduces a difference between the correlated signal and the analog feedback signal;
converting the digital estimate to the analog feedback signal;
collecting a digital estimate history by sampling the digital estimate at a sample frequency that is a binary multiple of an excitation frequency of the excitation signal;
and
analyzing the digital estimate history to determine an amplitude of the digital estimate substantially near the excitation frequency;
and
evaluating the amplitude of the digital estimate substantially near the excitation frequency of the at least two correlated signals to determine a numerical representation of the linear position of the movable component.

7 more elements

A method for determining a linear position of a movable component of a linear variable differential transformer (LVDT), which includes a primary coil driven by an excitation signal at an excitation frequency, a first signal from a first secondary coil, and a second signal from a second secondary coil, comprising:

converting the first signal to a first digital estimate, the converting comprising:
comparing the first signal to a first analog feedback signal to generate a first comparison result;
incrementally adjusting the first digital estimate at an estimation frequency in response to sampling the first comparison result to reduce a difference between an amplitude of the first signal and an amplitude of the first analog feedback signal;
converting the first digital estimate to the first analog feedback signal;
sampling the first digital estimate at the sample frequency to generate a first digital estimate history;
and
analyzing the first digital estimate history to determine a first amplitude of the first signal substantially near the excitation frequency;
converting the second signal to a second digital estimate, the converting comprising:
comparing the second signal to a second analog feedback signal to generate a second comparison result;
incrementally adjusting the second digital estimate at an estimation frequency in response to sampling the second comparison result to reduce a difference between an amplitude of the second signal and an amplitude of the second analog feedback signal;
converting the second digital estimate to the second analog feedback signal;
sampling the second digital estimate at a sample frequency to generate a second digital estimate history;
and
analyzing the second digital estimate history to determine a second amplitude of the second signal substantially near the excitation frequency;
and
evaluating the first amplitude and the second amplitude to determine a numerical representation of the linear position of the movable component.

13 more elements

Dependencies are inferred from the claim text.