Page 295 - Electrical Engineering Dictionary

Forward converter.

foundry for semiconductor manufactur- protection should shut down the motor in the
ing, a vendor providing wafer processing. event of field loss.

four connected See pixel adjacency. four-quadrant operation (1) a signed
representation of electrical or mechanical
four-level laser laser in which the most variables in the phase plane in order to sit-
important transitions involve only four en- uate the different modes for energy transfer.
ergy states; usually refers to a laser in which This term can be used both for power elec-
the lower level of the laser transition is sepa- tronics and electrical machines. For electri-
rated from the ground state by much more cal variables, the four-quadrant operation is
than the thermal energy kT (contrast with defined by the voltage–current (or current–
three-level laser). voltage) characteristic with the two variables
expressed as instantaneous or mean values.
four-point starter a manual motor starter For mechanical variables, the term is defined
that requires a fourth terminal for the holding by the torque–speed (or speed–torque) char-
coil. Because of its independent holding coil acteristic with the same time-domain repre-
circuit, it is possible to vary the current in the sentation as previously explained. The en-
field circuit independently of the holding coil ergy transfer is defined with electrical power
circuit. The disadvantage is that the motor in the voltage–current curve and with me-
starter holding relay will not drop out with chanical power in the torque–speed curve.
loss of the field; however, proper overcurrent The four-quadrant operation is related to re-

c
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