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isolating rate and the false alarm rate are the important performance figures in the BIT
system design, and the false alarm rate is the key figure for the BIT performance
evaluation. The false alarm rate is near to 20% in most aviation electronic equipment.
And the phenomena that the fault can't be recur and the function is normal when
re-testing appear frequently. So inducing the false alarm rate is the key problem to
improve the BIT system performance .
The BIT system can be expressed by math as follow:
y(t) = f { x (t) , u (t) , m (t) , n (t) }
(1)
x (t) the system input.
y (t) the system output.
n (t) the process noise of the system.
u (t)
the state variable of testing object.
m(t) the model parameter of the dynamic process.
x(t) and y(t) can get by sensor. u(t) is a state variable, some can be test and some
can't. The model parameter m(t) can't be test directly, it can be calculated only by the
model suppose, state estimate or parameter distinguish. The process noise of the
system, n(t) can't be test directly for its incertitude and instantaneous.
Formula (2) can get by predigesting formula (1).
y(t) = f{ x(t) , m(t) }
(2)
y(t) the output of BIT system.
x(t) the input of BIT system.
m(t) the uncertainty input of the BIT system.
The input of BIT system is composed by two parts, the certainty input and the
uncertainty input. The uncertainty input is the main reason for the false alarm
appearance in the BIT system.
The uncertainty input is composed by all kinds of system noise, uncertainty and
instantaneous, just as temperature noise, humidity noise and signal burr and so on. The
noises produce the false alarm, reduce the correct rate of the BIT testing. The important
solution for this question is the self-adapt filter of testing passageway, wiping out the
influence of noise or interferential. It is the important way to reduce the false alarm rate
and assure the system's performance testing and fault diagnosing intelligently.
The fault rate of BIT circuit influenced the reliability of system directly. The fault
rate of system is influenced little by the BIT circuit of lower fault rate. Otherwise the
high fault rate of BIT circuit would produce the high false alarm of system. Then the
BIT test can't get a confidence result, the security and reliability of the system will
reduced mostly.
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