Patent ID: 6885923

Claim:
A signal fault detection system useable in electrical control sensors for shaft speed signal frequency change rate tests, detecting intermittent or “in-range” failures of the signal rate of change, comprising: means for measuring frequency of a shaft speed signal; means for calculating a rate of change (time derivative) of the measured signal; means for estimating a short-term variance of the measured signal rate of change using the equation: Var[x]=E[x−E(x)] 2 =E[x 2 ]−E 2 [x], where x is the measured signal rate of change, E(x) is the expected value of x, E(x) is the expected value of x 2 , calculated by estimating the average of x 2 over a predefined short term, and E 2 [x] is the squared value of E[x], where E[x] is calculated by estimating the average of the measured signal rate of change over the predefined short term; means for estimating the short-term variance Var[x]=E[x 2 ]−E 2 [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 invalid, if the estimated variance exceeds the predefined variance limit for the predefined amount of time.