Red Lion TCU - Manual (Page 77)

As shown in the Auto-Tune Operation Figure 40, Auto-Tune cycles the
process at a control point 3/4 of the distance between the current process
temperature (at the instant Auto-Tune is started) and the temperature
setpoint. The 3/4 control point was selected to reduce the chance of
temperature overshoot at setpoint when Auto-Tuning at start-up. If
Auto-Tuning from setpoint and temperature overshoot is unacceptable,
temporarily lower the setpoint by an amount of the temperature 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 temperature 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 Heat/Cool Systems
During Auto-Tune of heat/cool systems, the controller switches the
cooling output (OP2) on and off in addition to the heat output (OP1). The
heat/cool deadband parameter (db-2) determines the amount of overlap or
deadband between the two outputs during Auto-Tune. Refer to
ON/OFF
CONTROL, page 66, for the operation of this parameter. The heat/cool
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 Cooling Gain
parameter (GAN2) for heat/cool 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:
Tune
Phase
Display
(Primary)
Display
(Secondary)
1 APr1 ASC1
2 APr2 ASC2
3 APr3 ASC3
4 APr4 ASC4
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