20
4–3 Heat-Cool Control
An injection mold is required to be controlled at 120°C to ensure a consistent
quality for the parts. An oil pipe is buried in the mold. Since plastics are
injected at a higher temperature (e.g., 250°C), the circulation oil needs to be
cooled as its temperature rises. Here is an example:
The PID heat-cool operation is used for the above
example. To achieve this, set the following parameters
in the setup menu:
INPT=PT.DN
UNIT=°C
DP= 1-DP
OUT1=REVR
O1TY=RELY
CYC1=18.0 (sec.)
O1FT=BPLS
OUT2=COOL
O2TY=4–20
O2FT=BPLS
Set SV at 120.0°C, CPB at 125(%) and DB at -4.0(%).
Apply auto-tuning at 120°C for a new system to get
optimal PID values. See section 3-11.
Adjustment of CPB is related to the cooling medium
used. If water is used as the cooling medium instead of
oil, the CPB should be set at 250(%). If air is used as
the cooling medium instead of oil, the CPB should be
set at 100(%). The adjustment of DB is dependent on
the system requirements. A higher positive value of DB
will prevent unwanted cooling action, but will increase
the temperature overshoot, while a lower negative
value of DB will result in less temperature overshoot,
but will increase unwanted cooling action.
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