Watlow QPAC Modular SCR Power Control Service - Manual (Page 9)

WATLOW QPAC Service Manual
9 Operation Theory, Chapter 3
Q01
Chapter 3
Operation Theory of
Base and Firing Cards
Single Phase Model - Q01
Power Base Operation
The Q01 uses one pair of SCRs connected in inverse parallel to control a resistive
or inductive load. The main board contains the power supply, output drivers, and
connections for the transformer, and the control card. The Q01 accepts all control
cards. The standard Q01 power base takes any transformer from 120VAC to
480VAC. 600VAC requires a special base.
The Q01 main board provides power and FWZ (full wave zero cross) to detect
zero crossover to the control board. The control board then outputs a pulse for
each half cycle to turn ON the instrument SCRs which in turn fire the power SCRs.
Two windings of the power transformer provide power for the instrument SCRs.
See schematic 02-0655 on Page 33.
Figure 3 -
Q01 Board Layout
Figure 4 -
Q01 Block Diagram
and Typical Load
Circuit
Power
Supply
FWZ
Control Card
Opto
Opto
T1
L1
L1
L2
VAC
Heater
Load Circuit