User guide

Watlow EZ-ZONE
®
PM PID Controller • 94 • Chapter 9 Features
Auto (closed loop) and Manual (open loop) Control (cont.)
Bumpless transfer will allow the controller to transfer to the manual mode using the last power value cal-
culated in the auto mode if the process had
stabilized at a ±5 percent output power level
for the time interval of Time Integral (Op-
erations Page, Loop) prior to sensor failure,
and that power level is less than 75 percent.
Input Error Latching [`i;Er] (Setup
Page, Analog Input Menu) determines the
controller’s response once a valid input
signal returns to the controller. If latch-
ing is on, then the controller will continue to
indicate an input error until the error is
cleared. To clear a latched alarm, press the
Advance Key ‰ then the Up Key ¿.
If latching is off, the controller will au-
tomatically clear the input error and return
to reading the temperature. If the controller
was in the auto mode when the input error occurred, it will resume closed-loop control. If the controller was
in manual mode when the error occurred, the controller will remain in open-loop control.
The Manual Control Indicator Light % is on when the controller is operating in manual mode. You can
easily switch between modes if the Control Mode [`C;M] parameter is selected to appear in the Home Page.
To transfer to manual mode from auto mode, press the Advance Key
‰
until [`C;M] appears in the lower
display. The upper display will display [AUto] for auto mode. Use the Up ¿ or Down ¯ keys to select [Man].
The manual set point value will be recalled from the last manual operation.
To transfer to auto mode from manual mode, press the Advance Key
‰
until [`C;M] appears in the lower
display. The upper display will display [MAn] for manual mode. Use the Up ¿ or Down ¯ keys to select
[AUto]. The automatic set point value will be recalled from the last automatic operation.
Changes take effect after three seconds or immediately upon pressing either the Advance Key
‰
or the
Infinity Key ˆ.
On-Off Control
On-off control switches the
output either full on or full
off, depending on the input,
set point and hysteresis val-
ues. The hysteresis value indi-
cates the amount the process
value must deviate from the
set point to turn on the out-
put. Increasing the value de-
creases the number of times
the output will cycle. Decreas-
ing hysteresis improves con-
trollability. With hysteresis
set to 0, the process value
would stay closer to the set
point, but the output would
switch on and off more fre-
quently, and may result in the
output “chattering.”
On-off control can be se-
lected with Heat Algorithm [`h;Ag] or Cool Algorithm [`C;Ag] (Setup Page, Loop Menu).
On-off hysteresis can be set with Heat Hysteresis [`h;hY] or Cool Hysteresis [`C;hY] (Operations Page,
Loop Menu).
Time
Temperature
Bumpless Transfer
40%
Sensor
Break
2 minutes
Locks in
Output
Power
0%
Set Point
Actual Temperature
Output Power
Power
100%
Set Point
Time
Temperature
The heating action switches off when the process
temperature rises above the set point.
The heating action
switches on at startup.
Hysteresis
Process Temperature
The heating action switches on when the process temperature
drops below the set point minus the hysteresis.