535-PROF User's Manual
Chapter 7
103
Applications
control parameters, which in turn helps to eliminate overshoot of the Setpoint.
Software Configuration
1. Go to the
TUNING
menu.
2. Set
POWR.BACK
parameter to ENABLED.
3. Go to the
SELF TUNE
menu.
4. For
DEAD TIME
, set the value (time) that the controller should wait before
invoking an output change. This value is typically the dead time of the
process. Or, let Pretune calculate the dead time, then complete just steps
1 and 2 above.
N. SELF TUNE—POWERTUNE
®
The Self Tune function of the 535 consists of two distinct components, Pretune
and Adaptive Tune. These components may be used independently or in
conjunction with one another. For best results, we recommend using them
together.
Pretune
This algorithm has three versions. Choose the type that most closely matches
the process to optimize the calculation of the PID parameters. The three Pretune
types are:
• TYPE 1
Normally used for slow thermal processes
• TYPE 2
Normally used for fast fluid or pressure processes
• TYPE 3
Normally used for level control applications
Pretune is an on-demand function. Upon initiation, there is a five second period
during which the controller monitors the activity of the process variable. Then
the control output is manipulated and the response of the process variable is
monitored. From this information, the initial Proportional Band, Reset and Rate
(P, I and D values) and dead time are calculated. When using TYPE 2 or TYPE
3 Pretune, the Noise Band (
NOISE BND.
) and Response Time (
RESP. TIME
)
will also be calculated.
In order to run this algorithm, the process must fulfill these requirements:
• The process must be stable with the output in the manual mode;
• For tuning a non-integrating process, the process must be able to reach a
stabilization point after a manual step change; and
• The process should not be subject to load changes while Pretune operates.
If these conditions are not fulfilled, set the Adaptive Tune to run by itself.
Adaptive Tune
Adaptive Tune continuously monitors the process and natural disturbances and
makes adjustments in the tuning parameters to compensate for these changes.
In order to make accurate calculations, Adaptive Tune needs noise band and
response time values. Pretune TYPE 2 and TYPE 3 automatically calculate
these values. These values may also be entered or changed manually in the
Self Tune
menu. For Pretune TYPE 1, Noise Band and Response Time
parameters must be entered manually.
Figure 7.13 illustrates the relationship between Pretune and Adaptive Tune.
CAUTION
!
Disable Adative Tuning before
altering process conditions (e.g., for
shutdown, tank draining, etc.).
Otherwise, the 535 will attempt to
adapt the Tuning parameters to the
temporary process conditions.
Adaptive Tune can be disabled via
digital input (if applicable—see Digital
Inputs in this chapter), or via menus:
1. Go to the
TUNING
menu.
2. Go to parameter
ADAPTIVE.
Change the value to DISABLED.
