A method and a system is provided, useable in electrical control sensors for
shaft
speed signal frequency change rate tests, detecting intermittent or "in-range"failures.
The method estimates a short-term variance of the measured signal or signal rate
of change, using the equation: Var[x]=E[x2]-E2[x], where
E[x2] is an estimated average of the squared measured signal or rate
of change over the short term, and E2[x] is a squared estimated average
of the measured signal or rate of change over the short term. The estimated variance
is compared with a predefined variance limit for a predefined amount of time, and
if the estimated variance exceeds the predefined variance limit for the predefined
amount of time, the measured signal is deemed invalid. A latching counter is used
for timing, and its time out rate is preferably proportional to the time period
the measured input is true. The step for estimating a short-term variance of the
measured signal uses several filters performing averaging function.
