Watlow QPAC Modular SCR Power Control Service - Manual (Page 13)

WATLOW QPAC Service Manual
13 Operation Theory, Chapter 3
Cards
AF - Phase Angle Fired (08-5288)
The AF card provides a delayed SCR turn ON, pro-
viding an infinitely variable voltage and current from
full OFF to full ON. The AF card can be used on
resistive, inductive, or Tungsten lamp loads. It
includes a 10 second soft start, and a missing half
cycle detector to put it into emergency shut down
(ESD), and retrigger the soft start. A low signal on
the ESD terminals puts the QPAC in ESD. The
input is factory set for 4 - 20mA into 250
Ω
. It can be
converted to a voltage input by removing R3 and
readjusting the bias and gain potentiometers for
any voltage fan 0 - 3VDC to 0 - 15VDC.
AL - Phase Angle
Fired with Current Limit (08-5411)
The AL card incorporates all of the features
of the AF card with the addition of a two
mode controller to hold the output current at
a pre-set maximum level. The load current is
monitored by a CT (current transformer) and
the maximum output can be set by a poten-
tiometer on the card.
Zero Cross Control Cards
(work on all bases)
BF - Burst Fired with
a Four Second Time Base (08-5289)
The BF card is designed for time proportioning with a 4 second
time base. It can be field changed to a 1 second time base by
removing R17. A 4 - 20mA input is standard, and can easily be
changed to accept a voltage input by removing R8 and read-
justing the bias and gain pots for any voltage input from 0 -
3VDC to 0-15VDC. The output of the card is disabled if the
emergency shut down goes low.
Figure 9 -
QAF Board Layout
Figure 10 -
QAL Board Layout
Figure 11 -
QBF Board Layout