Shaft feedback sensor error detection
View Patent ↗Methods and apparatus for detecting a sensor angle error in a system in which a measured quantity is determined on the basis of a phase of a signal. A signal derived from the measurement of multiple sensors is ascribed to a vector in a two-dimensional space, and a norm is calculated characterizing that vector. A value is calculated characterizing variation of that norm over a specified period of time and that value is compared with a threshold in order to identify a sensor fault.
1. A method for detecting a sensor angle error in a system employing a rectangular-to-polar coordinate conversion, the method comprising:
a. ascribing multiple sensor measurements to a vector in a two-dimensional space;
b. calculating a norm characterizing the vector;
c. determining a single scalar value characterizing variation of the norm over a specified period of time, the single scalar value amenable to scalar comparison; and
d. comparing the single scalar value characterizing variation of the norm to a specified threshold value; and
e. enabling fault-handling procedures in case of variation of the norm exceeding the specified threshold.
2. A method in accordance with claim 1 , wherein the step of determining a single scalar value characterizing variations of the norm includes:
i. determining a first value characterizing a time-averaged minimum of the norm;
ii. determining a second value characterizing a time-averaged maximum of the norm; and
iii. calculating the single scalar value characterizing variation of the norm as a function of the maximum and minimum of the norm.
3. A method in accordance with claim 2 , wherein the function of the maximum and the minimum of the norm is a ratio of the maximum to the minimum.
4. In a sensor system of the type employing a rectangular-to-polar coordinate conversion, an improvement comprising;
a. a plurality of sensors for generating analog sensor signals together defining a vector in a two-dimensional space;
b circuitry for combining the analog sensor signals to create a plurality of demodulated signals of known phase relationship;
c. a norm processor for combining the plurality of demodulated signals to derive a single scalar norm characterizing the vector; and
d. a comparator for comparing a function of the single, scalar norm to a specified threshold, wherein the function characterizes behavior of the norm over a specified period of time.
5. The improvement of claim 4 , wherein the function is a ratio of a maximum to a minimum of the norm over the course of a cycle.