User guide
Watlow EZ-ZONE
®
PM PID Controller • 87 • Chapter 9 Features
Manual Tuning
In some applications, the autotune process may not provide PID parameters for the process characteristics
you desire. If that is the case, you may want to tune the controller manually.
1. Apply power to the controller and establish a set point typically used in your process.
2. Go to the Operations Page, Loop Menu, and set Heat Proportional Band [`h;Pb] and/or Cool Proportional
Band [`C;Pb] to 5. Set Time Integral [``ti] to 0. Set Time Derivative [``td] to 0.
3. When the system stabilizes, watch the process value. If it fluctuates, increase the Heat Proportional
Band or Cool Proportional Band value in 3 to 5° increments until it stabilizes, allowing time for the sys-
tem to settle between adjustments.
4. When the process has stabilized, watch Heat Power [`h;Pr] or Cool Power [`C;Pr] (Operations Page,
Monitor Menu). It should be stable ±2%. At this point, the process temperature should also be stable, but
it will have stabilized before reaching the set point. The difference between the set point and actual pro-
cess value can be eliminated with Integral.
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 variable 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 variable 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 automati-
cally adjust to load changes and compensate for differing control characteristics at various set points for pro-
cesses 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.