Rockwell Automation 1771-TCM TEMPERATURE CONTROL - Manual (Page 39)

5–4 Configuring the Loops
Publication 1771Ć6.4.5 - January 1997
If you make the selection for barrel temperature control, you also
have a selection for whether it is an inner zone or an outer zone. An
outer zone is a zone at either end of the barrel. An inner zone is any
zone other than at the very end of the barrel (between two other
zones). The PID gain calculation algorithm for an inner zone is
slightly different from that for an outer zone to account for an inner
zone being more affected by adjacent zones. The inner zones are
treated as more of an integrating process than are outer zones.
НН
НН
Н
Н
НН
НН
НН
НН
Н
Н
Н
Н
НН
НН
H
n
H1 H2 H3
Nozzle
Zone 1 Zone 2 Zone 3
T
s
T
n T
1
T
2
T
3
T
f
T = temperature measurement point (thermocouple)
H = heater band (element)
Typical plastic injection
barrel with multiple temperature
zones
Ram
(Screw)
Outer
Zone
Outer
Zone
Inner
Zone
Inner
Zone
The loss of thermal integrity is detected when the loop M output is at
100% while the temperature rate of change measured by the module
is below the minimum expected rate. Detecting the loss of thermal
integrity requires an assumption of a minimum rate of change in the
temperature input value (C) when the M output is at 100%. An
example of a loss of thermal integrity could be because the contactor
for a heating band fails open; or the sensor is not in proper position
to measure the true temperature.
The values you enter for period and temperature change establish a
minimum rate of change (
°
/min) in the temperature input value that
you will allow when the M output is at 100%. The temperature
change value you enter divided by the period value you enter is the
thermal integrity rate. You select a mode for switching the M output
to a forced value when the rate of change of the temperature does not
reach the minimum for thermal integrity. The selections are:
•
disable the PID loop by forcing the M value to zero
•
set the output to the thermal runaway forced M value
•
set the output to the manual-mode M value by setting the loop
into manual mode
If a thermal integrity loss is detected, you must disable the affected
loop and then re-enable it to clear the condition. You can do this
from the Change Settings screen.
Inner/Outer Zone
Thermal Integrity Loss
Detection