5 . 2
■
Wa t l o w P o w e r S e r i e s
F e a t u r e s , C h a p t e r 5
Variable Time Base - Zero Cross
In the variable time base control method, an optimal
ratio of cycles on to cycles off is used to generate the
desired power output. The number of cycles needed
to completely generate a desired power level is
variable in single cycle increments. Line voltage
compensation algorithms are used to adjust the
percentage power output while operating in this
mode. Variable time base operation gives the best
response time and resolution and provides for the
longest heater life.
In single cycle variable time base below 50 percent
power, the unit is never on for more than one consec-
utive full cycle. Above 50 percent power, the unit is
not off for more than one consecutive full cycle while
maintaining the proper output.
Line voltage compensation is active if selected; how-
ever, it can be disabled.
Setup Page:
• Enter the Setup Page by holding
± ¬
for 2 seconds.
• When the display reads
[algo]
, press
®
until
[`Off]
[`set]
[Algo]
is displayed. Press
Ó Î
to select
[Urtb]
variable
time base, zero cross.
Figure 5.2a — 50% variable time base
1 cycle on, 1 cycle off.
Figure 5.2b — 40% single cycle variable time base
1 cycle on, 1 cycle off, 1 cycle on, 2 cycles off.
DC Contactor - Zero Cross
DC contactor control mode is a specialized version of
zero cross control in which the analog control input
is always used and percentage power output is fixed
at 100 percent or 0 percent.
The off/on thresholds are 2.0V/3.5V for voltage
input; 5.0mA/8.0mA for current input. This means
the unit is off for an input voltage (current) of
2.0V(5.0mA) or lower, and 100% on for an input volt-
age (current) of 3.5V(8.0mA) or higher. Maximum
input voltage is 10.0V.
In contactor mode use a four second cycle time to
improve heater diagnostics operation.
Line voltage compensation is not used under dc con-
tactor control, the output is either 100 percent on or
100 percent off.
Setup Page:
• Enter the Setup Page by holding
± ¬
for 2 seconds.
• When the display reads
[algo]
, press
®
until
[`Off]
[`set]
{Algo]
is displayed. Press
Ó Î
to select
[cont]
dc
contactor.
NOTE: Heater Tolerance, Heater Open and Load Balance
alarms
do not work in DC
Contactor control mode.
The phase angle control method gates a limited
portion of the line voltage cycle to the load based on
percentage power selected. Soft start is always
included when phase angle is selected.
Phase angle control may not be selected in a 3
phase, 2-leg system.
Line voltage compensation will be used to adjust the
percentage power output while operating in this
mode if selected.
Current limiting is a valid option with phase angle if
the unit is equipped with heater diagnostics.
Setup Page:
• Enter the Setup Page by holding
± ¬
for 2 seconds.
• When the display reads
[algo]
, press
®
until
[`Off]
[`set]
[Algo]
is displayed. Press
Ó Î
to select
[PH2t]
phase
angle.
Figure 5.2c— Phase angle firing.
NOTE: The maximum output power is 99%. This is consid-
ered full on for the Power Series.
Phase Angle
NOTE:
Do not use variable time base settings
in
the temperature
controller to drive a Power Series in c
ontactor mode.
Summary of Contents for PC1X-N20
Page 4: ...ii Watlow Power Series Table of Contents...
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