point was selected to reduce the chance of overshoot at setpoint when
Auto-Tuning at start-up. If Auto-Tuning from setpoint and 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 point.
To Initiate Auto-Tune:
1. Make sure that Auto-Tuning is enabled in Lockouts Parameter Module
(3-LC).
2. Place the controller into the Normal Display Mode.
3. Press P for 3 seconds from Normal Display Mode.
4. Scroll to “tUNE” by use of P, if necessary.
5. Select “YES” and press P.
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 P for 3 seconds from normal display mode.
3. Scroll to “tUNE” by use of P, if necessary.
4. Select “NO” and press P.
5. Auto-Tune canceled.
B) Or reset the controller by disconnecting power.
Auto-Tune Of Heat/Cool Systems
During Auto-Tune of heat/cool systems, the controller switches the
cooling output (O2) on and off in addition to the heat output (O1). The
heat/cool overlap deadband parameter (db-2) determines the amount of
overlap or deadband between the two outputs during Auto-Tune. For most
applications, set this parameter to 0.0 prior to starting Auto-Tune. 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 Cooling Relative Gain
parameter (GAN2) for heat/cool systems.
Some water cooled processes exhibit an extreme non-linear gain
characteristic. That is, the process cooling gain starts very high and flattens out
deeper into the cooling region. This effect may result in regular oscillations at
setpoint as the controller applies heat to counteract the effect. These processes
may benefit from a lower cooling fan setting and/or reduced water flow in the
jacket or manifold. The process heat and cool gains should be balanced as much
as possible, and the controller gains adjusted to the process.
Auto-Tune Of Cascade Control
The following procedure may be used to tune cascaded controllers:
1. Place the Secondary controller into Local Setpoint mode and Manual
(USEr) mode of operation
2. Adjust output power level of the secondary until primary variable is close
to primary setpoint (5% of range).
3. Key-in secondary setpoint value equal to secondary process value.
4. Auto-Tune the secondary controller while in Local Setpoint mode.
5. Place the secondary controller into Remote Setpoint mode and Automatic
(Auto) mode of operation.
6. Auto-Tune the primary controller while the primary is in Automatic mode
of operation.
7. Initial tuning of system is complete.
After the process has stabilized, the primary and secondary may be
re-tuned in Automatic mode of operation. Normally, the primary requires
re-tuning whenever the secondary PID constants are changed.
Note: For Remote Setpoint controllers, the Auto-Tune control point is derived
from the Remote Setpoint when in Remote Setpoint mode and from the Local
Setpoint when in Local Setpoint mode.
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