Speed signal variance detection fault system and method

A signal fault detection method useable in electrical control sensors for shaft speed signal frequency change rate tests, detecting intermittent or “in-range” failures of the signal, comprising:

• means for measuring frequency of a shaft speed signal;
• means for estimating a short-term variance of the measured signal using the equation:
• Var[x]=E[x−E(x)]2=E[x2]−E2[x], where x is the measured signal, E(x) is the expected value of x, E[x]is the expected value of x2, calculated by estimating the average of x2 over a predefined short term, and E2[x] is the squared value of E[x], where E[x] is calculated by estimating the average of the measured signal x over the predefined short term;
• means for estimating the short-term variance Var[x]=E[x2]−E2[x] by employing the following algorithm:
• Var[x]=Filtered [(x)2]−(Filtered [x])2;
• means for comparing the estimated variance with a predefined variance limit for a predefined amount of time;
• and
• means for deeming the measured signal at least one of faulted and invalid, if the estimated variance exceeds the predefined variance limit for the predefined amount of time.