Watlow EZ-ZONE ST User Manual download pdf (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

1 2 ... 68 69 70 71 72 73 74 75 76 77 78 ... 96 97

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