Red Lion PCU - Manual (Page 73)

As shown in Figure 37, Auto-Tune Operation, Auto-Tune cycles the
process at a control point 3/4 of the distance between the current process
signal value (at the instant Auto-Tune is started) and the setpoint. The 3/4
control point was selected to reduce the chance of signal overshoot at setpoint
when Auto-Tuning at start-up. If Auto-Tuning from setpoint and signal
overshoot is unacceptable, temporarily lower the setpoint by an amount of the
oscillation and then Auto-Tune. Reset the setpoint to the original value when
Auto-Tune is complete. After starting Auto-Tune, the secondary display
indicates the current phase (Aut1, Aut2, Aut3 & Aut4). If the controller
remains in an Auto-Tune phase unusually long, the process or connections
may be faulty. Additionally, during Auto-Tune it is important that
disturbances to the system be minimized, as these may have an effect on the
parameter determination.
INITIATE AUTO-TUNE
Auto-Tune may be initiated at start-up, from setpoint, or at any other
process signal point.
To Initiate Auto-Tune:
1. Make sure that Auto-Tuning is enabled in parameter lockouts module.
2. Place the controller into the normal display mode.
3. Press PAR for 3 seconds from normal display mode.
4. Scroll to “tUNE” by use of PAR, if necessary.
5. Select “YES” and press PAR.
Auto-Tune is initiated.
To Cancel Auto-Tune: (Old PID settings remain in effect).
A) Make sure that Auto-Tuning is enabled in parameter lockouts module.
1. Place the controller into the normal display mode.
2. Press PAR for 3 seconds from normal display mode.
3. Scroll to “tUNE” by use of PAR, if necessary.
4. Select “NO” and press PAR.
5. Auto-Tune canceled.
B) Or reset the controller by disconnecting AC power.
Note: If using the linear DC output for control, full power is applied (+100% OP1
or -100% OP2) regardless of the output power limit settings. Set the Linear DC
Output scaling points to limit the magnitude of the output, if desired.
AUTO-TUNE OF SECONDARY OUTPUT (OP2) / MAIN
OUTPUT (OP1) SYSTEMS
During Auto-Tune of OP2/OP1 systems, the controller switches the
secondary output (OP2) on and off in addition to the main output (OP1). The
deadband parameter (db-2) determines the amount of overlap or deadband
between the two outputs during Auto-Tune. Refer to
ON/OFF CONTROL ,
page 62, for the operation of this parameter. The deadband parameter remains
unchanged after Auto-Tune is complete. Therefore, when proportional
control is started after the completion of Auto-Tune, this parameter may need
to be reset.
It is important that external load disturbances be minimized, and if present,
other zone controllers idled as these may have an effect on the PID constant
determination. The controller additionally sets the Relative Gain parameter
(GAN2) for OP2/OP1 systems.
AUTO-TUNE OF INTERNAL CASCADE CONTROLLERS
Auto-Tune of Internal Cascade controllers involves tuning of the Primary
PID and Secondary PID parameters. Each set of parameters is tuned
individually with the secondary parameters normally tuned first. For
Internal Cascade controllers, Auto-Tune offers the option of tuning the
Primary or Secondary:
tunE
no – No Auto-Tune or abort Auto-Tune
Pri – Start Auto-Tune of primary or Auto-Tune of primary in
progress
SEC – Start Auto-Tune of secondary or Auto-Tune of
secondary in progress
The Auto-Tune status display indicates the set of parameters actively
Auto-Tuned:
TunePhase
Display
(Primary)
Display
(Secondary)
1 APr1 ASC1
2 APr2 ASC2
3 APr3 ASC3
4 APr4 ASC4
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