Watlow EZ-ZONE PM Integrated Controller - Manual (Page 127)

Watlow EZ-ZONE ® PM Integrated Controller • 124 • Chapter 9 Features
Manual Tuning (cont.)
5. Start with an Integral value of 6,000 and allow 10 minutes for the process temperature to reach the set
point. If it has not, reduce the setting by half and wait another 10 minutes. Continue reducing the setting
by half every 10 minutes until the process value equals the set point. If the process becomes unstable, the
Integral value is too small. Increase the value until the process stabilizes.
6. Increase Derivative to 0.1. Then increase the set point by 11° to 17°C. Monitor the system’s approach to
the set point. If the process value overshoots the set point, increase Derivative to 0.2. Increase the set
point by 11° to 17°C and watch the approach to the new set point. If you increase Derivative too much, the
approach to the set point will be very sluggish. Repeat as necessary until the system rises to the new set
point without overshoot or sluggishness.
For additional information about autotune and PID control, see related features in this chapter.
Autotuning with TRU-TUNE+ ®
The TRU-TUNE+ ® adaptive algorithm will optimize the controller's PID values to improve control of dynamic
processes. TRU-TUNE+ ® monitors the Process Value and adjusts the control parameters automatically to
keep your process at set point during set point and load changes. When the controller is in the adaptive con-
trol mode, it determines the appropriate output signal and, over time, adjusts control parameters to optimize
responsiveness and stability. The TRU-TUNE+ ® feature does not function for on-off control.
The preferred and quickest method for tuning a loop is to establish initial control settings and continue
with the adaptive mode to fine tune the settings.
Setting a controller's control mode to tune starts this two-step tuning process. (See Autotuning in this
chapter.) This predictive tune determines initial, rough settings for the PID parameters. Then the loop auto-
matically switches to the adaptive mode which fine tunes the PID parameters.
Once the Process Value has been at set point for a suitable period (about 30 minutes for a fast process to
roughly two hours for a slower process) and if no further tuning of the PID parameters is desired or needed,
TRU-TUNE+™ may be turned off. However, keeping the controller in the adaptive mode allows it to auto-
matically adjust to load changes and compensate for differing control characteristics at various set points for
processes that are not entirely linear.
Once the PID parameters have been set by the TRU-TUNE+™ adaptive algorithm, the process, if shut
down for any reason, can be restarted in the adaptive control mode.
Turn TRU-TUNE+™ on or off with TRU-TUNE+™ Enable [t;tUn] (Setup Page, Loop Menu).
Use TRU-TUNE+™ Band [t;bnd] (Setup Page, Loop Menu) to set the range above and below the set point
in which adaptive tuning will be active. Adjust this parameter only in the unlikely event that the controller
is unable to stabilize at the set point with TRU-TUNE+™ Band set to auto (0). This may occur with very fast
processes. In that case, set TRU-TUNE+™ Band to a large value, such as 100.
Use TRU-TUNE+™ Gain [`t;gn] (Setup Page, Loop Menu) to adjust the responsiveness of the adaptive
tuning calculations. Six settings range from 1, with the most aggressive response and most potential over-
shoot (highest gain), to 6, with the least aggressive response and least potential for overshoot (lowest gain).
The default setting, 3, is recommended for loops with thermocouple feedback and moderate response and
overshoot potential.
Before Tuning
Before autotuning, the controller hardware must be installed correctly, and these basic configuration param-
eters must be set:
• Sensor Type [`SEn] (Setup Page, Analog Input Menu), and scaling, if required;
• Function [``Fn] (Setup Page, Output Menu) and scaling, if required.
How to Autotune a Loop
1. Enter the desired set point or one that is in the middle of the expected range of set points that you want
to tune for.
2. Enable TRU-TUNE+.
3. Initiate an autotune. (See Autotuning in this chapter.)
When autotuning is complete, the PID parameters should provide good control. As long as the loop is in the
adaptive control mode, TRU-TUNE+ ® continuously tunes to provide the best possible PID control for the pro-
cess.