Page 172 - Electrical Engineering Dictionary

ulation direct control layer and the set point for n →∞, then the sequence x n tends to x
optimizing control layer. in probability.
See also controller.
convergent state the equilibrium state of
controller (1) the entity that enforces the a dynamic system described by a first order
desired behavior — as specified by the con- vector differential equation is said to be con-
trol objectives — of the controlled process by vergent if there exists a δ = δ(t 0 ), such that,
adjusting the manipulated inputs. The values
of these inputs are either predetermined or k x (t 0 ) − x e k<δ ⇒ lim x(t) = x e
t→∞
decided upon (computed) using on-line, i.e.,
real time, decision mechanism of the con- See also stable state.
troller — based on the currently available in-
formation. See also controlled variable. converter a generic term used in the
(2) a device that generates the input to the area of power electronics to describe a recti-
plant or process. The role of the controller fier, inverter, or other power electronic device
is to force the controlled variable of the plant that transforms electrical power from one fre-
or process to behave in a desired manner. quency and voltage to another.
(3) a unit that directs the operation of a
subsystem within a computer. For instance, convex fuzzy set (1) a fuzzy set that has
a disk controller interprets data access com- a convex type of membership function.
mands from host computer (via a bus), and (2) a fuzzy set in which all α-level sets are
sends read/write, track seeking, and other convex. See also α-level set.
control signals to the drive. During this time,
the computer can perform other tasks, un- convolution the mathematical operation
til the controller signals DATA READY for needed to determine the response of a sys-
transfer via the CPU bus. tem from its stimulus signal and its weighting
function. The convolution operation is de-
convection current a current in which noted by the symbol “∗.” The convolution of
electrons are released for movement outside two continuous time signals f 1 (t) and f 2 (t)
of a material. is defined by
Z ∞
convective heat transfer the process by
f 1 (t) ∗ f 2 (t) = f 1 (τ)f 2 (t − τ)dτ
which a moving fluid transfers heat to or from −∞
a wetted surface. Z t
= f 1 (τ)f 2 (t − τ)dτ if f 1 (t), f 2 (t)
0
convergence the condition when the elec-
= 0,t < 0
tron beams from a multi-beam CRT meet at a
single point. For example, the correct regis-
The integral on the right-hand side of the
tration of the three beams in the color picture
above equation is called the convolution in-
tube.
tegral, and exists for all t ≥ 0if f 1 (t) and
f 2 (t) are absolutely integrable for all t> 0.
convergence in probability for some se- f 1 is the weighting function that character-
quences of random numbers, the tendency to izes the system dynamics in the time domain.
a single number. It is equivalent to the response of the system
To wit, for a sequence of numbers x n , and when subjected to an input with the shape of a
a random variable x, if for all > 0, Dirac delta impulse function. Laplace trans-
formation of the weighting function yields
P {| x n − x |> } → 0 the transfer function model for the system.

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