Rockwell Automation 1771-TCM TEMPERATURE CONTROL - Manual (Page 38)

5–3 Configuring the Loops
Publication 1771Ć6.4.5 - January 1997
Under control type, you select between barrel and non-barrel control.
Barrel control can be used for either heat-only or heat/cool
applications. Non-barrel control can be used for either heat-only,
cool-only, or heat/cool applications.
Barrel control is for multiple-zone applications in which there is
thermal conduction between the zones. Injection molding and
extruding are good examples of this because there are multiple heater
bands (zones) mounted on one thermal conductor (the metal barrel).
The barrel conducts heat between the different zones. If you select
barrel control, you must also select between inner and outer zone. If
you select barrel control, the non-barrel auto-tune disturbance size
does not apply. A barrel loop is auto-tuned as the temperature rises
from ambient to a fixed set point during startup.
Non-barrel control is for independent loops with no thermal
conduction between the zones. If you select non-barrel control, the
inner/outer zone selection does not apply. If you select non-barrel
control, the loop is auto-tuned as it reacts to the set point disturbance
you enter.
Switch to Barrel Control?
For some applications, even though the loops are independent with
no thermal conductivity between zones, barrel control may provide
better performance than non-barrel control. If a loop has any of
these characteristics, you may want to try switching it to barrel
control.
•
The time constant is greater than 100.0 seconds. (You can read
the time constant for each loop in the auto-tune block.)
•
The loop has a problem overshooting the set point.
•
The loop output is saturating (the M at 100%) for a significant
duration.
If you switch a loop to barrel control for one of these reasons, select
it to be an outer zone.
!
ATTENTION: If you switch a loop between
non-barrel control and barrel control, you must
auto-tune the loop again before operating it. If you fail
to auto-tune the loop after making such a switch, the
auto-tuning values will be wrong for the application
and the gains will be greatly distorted.
Barrel/NonĆBarrel Control