Watlow Integrated Controller Rev C EZ-ZONE PM, User Manual

Wa t l o w   E Z - Z O N E

®

  P M   I n t e g r a t e d   C o n t r o l l e r  

•

    5 5    

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C h a p t e r   9   F e a t u r e s

Manual Tuning

In some applications, the autotune process may not 
provide PID parameters for the process characteris-
tics 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 Pro-

portional 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 Propor-
tional Band or Cool Proportional Band value in 3 
to 5° increments until it stabilizes, allowing time 
for the system 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 reach-
ing the set point. The difference between the set 
point and actual process 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 re-
ducing the setting by half every 10 minutes until 
the process value equals the set point. If the pro-
cess becomes unstable, the Integral value is too 
small. Increase the value until the process stabi-
lizes.

6.  Increase Derivative to 0.1. Then increase the set 

point by 11° to 17°C. Monitor the system’s ap-
proach to the set point. If the process value over-
shoots 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 with-
out 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 dy-
namic processes. TRU-TUNE+

®

 monitors the process 

variable and adjusts the control parameters auto-
matically to keep your process at set point during set 
point and load changes. When the controller is in the 
adaptive control mode, it determines the appropriate 
output signal and, over time, adjusts control param-
eters 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 contin-
ue 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 
automatically 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 automatically adjust to load changes and compen-
sate 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 adap-
tive tuning calculations. Six settings range from 1, 
with the most aggressive response and most poten-
tial overshoot (highest gain), to 6, with the least ag-
gressive 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 pa-
rameters 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+

®

.