Watlow EZ-ZONE ST - Manual (Page 73)

Watlow EZ-ZONE ® ST • 71 • Chapter 7 Features
Variable Time Base
Variable time base is the preferred method for con-
trolling a resistive load, providing a very short time
base for longer heater life. Unlike phase-angle firing,
variable-time-base switching does not limit the cur-
rent and voltage applied to the heater.
With variable time base outputs, the PID algorithm
calculates an output between 0 and 100%, but the out-
put is distributed in groupings of three ac line cycles.
For each group of three ac line cycles, the controller
decides whether the power should be on or off. There
is no fixed cycle time since the decision is made for
each group of cycles. When used in conjunction with a
zero cross (burst fire) device, such as a solid-state pow-
er controller, switching is done only at the zero cross of
the ac line, which helps reduce electrical noise (RFI).
Variable time base should be used with solid-state
power controllers, such as a solid-state relay (SSR)
or silicon controlled rectifier (SCR) power controller.
Do not use a variable time base output for control-
ling electromechanical relays, mercury displacement
relays, inductive loads or heaters with unusual resis-
tance characteristics.
The combination of variable time base output and a
solid-state relay can inexpensively approach the effect
of analog, phase-angle fired control.
Select the AC Line Frequency [AC;LF] (Setup Page,
Global Menu), 50 or 60 Hz.
100 percent output
10 ON, 0 OFF
50 percent output
3 ON, 3 OFF
66 percent output
6 ON, 3 OFF
Phase Angle
The phase angle control method gates a limited por-
tion of the line voltage cycle to the load based on the
percentage power selected. Phase angle control is
variable inside the sine wave. This control method
provides a variable voltage output with soft start ca-
pabilities as well.
Soft Start Time
Soft start is an additional feature of phase angle con-
trol executed whenever a power increase is called for.
The output will gradually increase in power until the
final selected power output is reached. The soft start
time is the time it takes to go from 0 to 100 percent
power.
Single Set Point Ramping
Ramping protects materials and systems that can-
not tolerate rapid temperature changes. The value of
the ramp rate is the maximum degrees per minute or
hour that the system temperature can change.
Select Ramp Action [``rP] (Setup Page, Loop
Menu):
[`oFF] ramping not active.
[`Str]
ramp at startup.
[StPt] ramp at a set point change.
[both]
ramp at startup or when the set point
changes.
Select whether the rate is in degrees per minute
or degrees per hour with Ramp Scale [`r;SC]. Set the
ramping rate with Ramp Rate [`r;rt] (Setup Page,
Loop Menu).
Set Point
Time
Temperature
Heating System without Ramping
Temperature reaches Set Point quickly