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72 UDC3200 Universal Digital Controller Operator Manual 04/08
Operation
The Accutune III algorithm provides user-friendly, on-demand tuning in this
controller. No knowledge of the process is required at start-up. The operator simply
initiates the tuning while in the automatic mode.
Once Accutune III has been enabled in the TUNE setup group, either “SLOW” or
“FAST” tuning may be used. Which one is used is selected via the lower display
during normal operation.
For the SLOW selection, the controller calculates conservative tuning constants with
the objective of minimizing overshoot. If the controller determines that the process
has appreciable dead time, it will automatically default to use Dahlin Tuning, which
produces very conservative tuning constants. The SLOW selection may be useful for
TPSC and Position Proportional applications, as it reduces “hunt” problems for the
motor. This selection is also recommended for applications that have significant
deadtimes.
For the FAST selection, the controller calculates aggressive tuning constants with the
objective of producing quarter damped response. Depending upon the process, this
selection will usually result in some overshoot. For this reason, it may be desireable
to enable the FUZZY tune selection. See Section 4.6. When Fuzzy tune is enabled, it
will work to suppress or eliminate any overshoot that may occur as a result of the
calculated tuning parameters as the PV approaches the setpoint. This selection is best
suited for processes with a single lag or for those that do not have any appreciable
deadtime. FUZZY tuning does not work well for processes that have appreciable
deadtime.
The Accutune III tuning process will cycle the controller’s output two full cycles
between the low and high output limits while allowing only a very small Process
Variable change above and below the SP during each cycle. A “T” shows in the upper
display until tuning is completed.
At the end of the tuning process, the controller immediately calculates the tuning
constants and enters them into the Tuning group, and begins PID control with the
correct tuning parameters. This works with any process, including integrating type
processes, and allows retuning at a fixed setpoint.
4.5.1 Tune for Simplex Outputs
After “TUNE” has been enabled, you can start Accutune as shown in Table 4-5.
Table 4-5 Procedure for Starting “TUNE”
Step Operation Press Result
1
Configure LSP1
Lower
Display
Lower
Display
Lower
Display
Until SP (Local Setpoint 1) shows
in the lower display.
2
or
Until LSP1 is to the desired value.
3
Switch to
“Automatic” Mode
Man
Auto
Man
Auto
Man
Auto
Until the “A” indicator is lighted (on
controllers with Manual option).
4
Show Tuning
Prompt
Lower
Display
Lower
Display
Lower
Display
Until “TUNE OFF” is shown on
lower display.