Page 177 - Electrical Engineering Dictionary

This capacity is particularly important for evant equation is
polymericmaterials, whichhavetowithstand y(jω)u (jω)
∗
the chemical degrading effect promoted by ˆ g(jω) =
∗
u(jω)u (jω)
ozone generated by the corona effect. See
also corona effect. in terms of the FFTs of the input and output
signals. The ∗ superscript indicates the com-
corona ring a toroidal metal ring con- plex conjugate. As the system output y(t)
nected to discontinuities on high-voltage generally contains terms in addition to those
conductors to reduce local field intensity and caused by the input u(t), its Laplace trans-
thus discourage the formation of corona dis- form is
charge.
y(s) = g(s) × u(s) + d(s)
coronal projection a projection image
Thus the correlation of input and output can
formed on a plane parallel to the chest and
enhance the accuracy of the estimate for the
perpendicular to the transverse and sagittal
system frequency response function g(jω),
planes.
since the correlation function then yields
the following estimate of the actual process
corporate feed also known as parallel
model:
feed, a method of feeding a phased array an- ∗
d(jω)u (jω)
tenna in which the signal from a transmitter is ˆ g(jω) = g(jω) + ∗
successively split until there are enough feed- u(jω)u (jω)
lines to carry the signal to each array element. Clearly, the effect of the disturbance d(t) is
The name comes from the resemblance of the readily reduced if the input is chosen either
feed structure to the organizational chart of a to be large in amplitude, compared to the dis-
corporation. turbance, or to be pseudo-random so that it
does not correlate with the disturbance and
correction layer control layer of a mul- the second numerator becomes zero, by def-
tilayer controller, usually situated above the inition.
direct control layer and below the optimizing (2) the temporal or spatial function or
control layer, required to make such modifi- sequence resulting from integrating lagged
cations of the decisions supplied by the op- products of two signals, i.e., the products of
timizing layer — before these decisions are a signal with the time-inverted version of a
passed to the direct layer — that some speci- second signal at various relative delays with
fied objectives are met; for example, a correc- respect to each other. If the two signals
tion layer of the industrial process controller are identical, a maximum correlation output
may be responsible for such adjustment of a amplitude results at full overlap. See also
particular set point value that an important convolution.
constraint is satisfied by the controlled pro-
cess variables — in case when the optimizing correlation bandwidth the frequency
layer is using inaccurate model of this con- for which the autocorrelation of the transfer
trolled process. function reaches a given threshold, for exam-
ple x% of the central value.
correlation (1) the mathematical opera-
tion of comparing the behavior of two signals correlation coefficient a measure of the
to determine how closely they are related. It ability to predict one random variable x as the
is usefully applied to system identification linear function of another y. The correlation
when the input and output signals of a given coefficient
system are compared by correlation to give E[xy]− E[x]E[y]
ρ =
the system transfer function model. The rel- σ x σ y

c
2000 by CRC Press LLC