Watlow EZ-ZONE RMC - Manual (Page 164)

Watlow EZ-ZONE ® RMC Module • 161 • Chapter 7 Features
When the dead band value is a negative val-
ue, both heating and cooling outputs are active when
the temperature is near the set point.
Time
Temperature Negative Dead Band
Set Point
Heat Output Active
Cool Output Active
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;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
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.
Ramping to set point starts from the process value
and increments or decrements to the closed loop set
point at the defined rate.
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
Temper
atur
e
Temperature reaches Set Point quickly
Heating System without Ramping
Set Point
Time
Temper
atur
e
Heating System with Ramping
Temperature ramps to Set Point at a set rate
degrees
per minute