Watlow QPAC Modular SCR Power Control Service - Manual (Page 4)

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WATLOW QPAC Service Manual
Overview, Chapter 1
Overview
Chapter 1
QPAC Modular SCR Power Control
Figure 1 -
The QPAC-01
SCR Power Control
General Description
The QPAC Power Controls are a family of solid state controls used for electric
heating applications. A solid state power control provides output power that is pro-
portional to the input command signal from a temperature control. This proportion-
al output power helps to produce a closely controlled heater temperature, which
saves energy and prolongs heater life by holding heater elements at a nearly con-
stant temperature.
The QPAC has a modular construction with plug-in features for flexibility. The
three modules of the QPAC are the power base, transformer, and control card.
See Figure 2. Power bases are available in 30 to 300
Ω
ratings in single phase,
three phase-two leg and three phase-three leg configurations. A transformer
plugged into the power base allows the QPAC to operate on any voltage from 120
to 480VAC. The plug in control card sets the QPACs firing mode. Control cards
are available in solid state contactor, burst firing (zero cross), or phase angle
modes with a wide variety of input options. This modular approach, using a stan-
dard power base with plug-in transformers and control cards, allows power control
users, distributors and OEMs to maintain minimum inventories while still providing
rapid service.