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.

 

 

 

 

 

 

 

Set Point

Cool Output

 

Active

 

 

 

 

 

 

 

 

 

Temperature

Heat

Output Active

 

 

 

 

 

 

 

 

 

 

 

Negative Dead Band

 

 

 

 

 

 

 

 

 

 

Time

Adjust the dead band with Dead Band [``db] (Operations Page, Loop Menu).

Variable Time Base

Variable time base is the preferred method for controlling 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 current and voltage applied to the heater.

With variable time base outputs, the PID algorithm 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 conjunction 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 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 controlling electromechanical relays, mercury displacement relays, inductive loads or heaters with unusual resistance 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

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 cannot 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

Temperature

Temperature reaches Set Point quickly

Time

Watlow EZ-ZONE®PM Integrated Controller

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Chapter 9 Features