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Example 2: Dual Set Point / PID
A heat treating furnace is required to harden the mold at a high temperature
( 1000 C ) for 30 minutes, then the mold is cooled down with a
programmable ramp ( 20 C / minute ) toward a lower set point ( 200 C ).
Use the dual set point / PID and ramp / dwell functions for this application.
( 1 ) Set the following parameters in the Setup menu:
FUNC= FULL
A1FN= TIMR
EIFN= SP.P2
PVMD= PV1
SPMD= MINR
( 2 ) Adjust the following parameters in the User menu:
TIME= 30.0 ( Minutes )
RAMP= 20.0 ( C/Minute )
SP1= 1000 C
SP2= 200 C
PL1= 100 ( % )
( 3 ) Set the proper values for PB1, TI1, TD1,PB2, TI2 and TD2 directly according
to the previous records. For a new system tune first PID set at SP1=800 C
and tune second PID set at SP2=400 C.
The circuit diagram is same as shown in Figure 5.14. The temperature profile
is shown as below:
C
30
minutes
40
minutes
Figure 5.16
Dual Set Point /PID Profile
1000
200
Use SP1,PID1
Use SP2,PID2
Time ( Minutes )
95