Variable Time Base; Single Set Point Ramping - Watlow EZ-ZONE PM User Manual

Set Point
Heat Output Active
Time
Adjust the dead band with Dead Band [``db]
(Operations Page, Loop Menu).

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 algo-
rithm calculates an output between 0 and 100%, but
the output 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 conjunc-
tion with a zero cross (burst fire) device, such as a
solid-state power controller, switching is done only at
the zero cross of the ac line, which helps reduce elec-
trical 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 ef-
fect of analog, phase-angle fired control.
Select the AC Line Frequency [AC; L F] (Setup Page,
Global Menu), 50 or 60 Hz.
100 percent output
10 ON, 0 OFF
®
Wat lo w EZ-ZO NE PM In t eg r a te d Co n tr o lle r
Cool Output Active
Negative Dead Band
50 percent output
3 ON, 3 OFF
66 percent output
6 ON, 3 OFF
Note:
When output 1 is a universal process output, output 2 cannot
use variable time base, fixed time base only. When output 3 is
configured as a universal process, output 4 cannot use variable
time base, fixed time base only.

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; S C]. Set
the ramping rate with Ramp Rate [`r; r t] (Setup
Page, Loop Menu).
Set Point
Temperature reaches Set Point quickly
Time
Heating System without Ramping
Set Point
degrees
per minute
Temperature ramps to Set Point at a set rate
Time
Heating System with Ramping
1 0 8
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Chapter 9 Fe a ture s