C7-8
IM 34M06H62-02E 2nd Edition : June 2008-00
C7.4.1 Cascade Mode
In cascade mode control, the output value of the primary loop is used as the set point of
the secondary loop.
The primary loop uses the control set point (CSP1) of the odd-numbered loop and the
process value (PV1) of the odd-numbered loop to perform control and computation
(PID1) of the odd-numbered loop.
The secondary loop uses the control output value (OUTPUT1) of the odd-numbered loop
as the control set point (CSP2), uses the process value (PV2) of the even-numbered loop
to perform control and computation (PID2) of the even-numbered loop, and outputs the
control output value (OUTPUT2).
Figure C7.11 Schematic Diagram for Cascade Control
When switching from Automatic or Manual mode to Cascade mode, as the PID1 output
from the primary loop is set equal to CSP2 of the secondary loop beforehand, the PID
control output from the secondary loop will change smoothly in cascade mode starting
with the current output value.
C7.4.2 Automatic Mode
In Automatic mode, only the secondary loop is operating.
The secondary loop uses the control set point of the even-numbered loop (CSP2) and
the process value of the even-numbered loop (PV2) to perform control and computation
in the even-numbered loop (PID2) and output the control output value (OUTPUT2).
The primary loop has no effect on control but its measured value can still be read.
Figure C7.12 Schematic Diagram in Automatic Mode
When Cascade mode is switched to Automatic mode, the value of CSP2 is determined
by the SP value of the secondary loop (even-numbered loop). Therefore, it is
recommended that you temporarily set the SP value equal to the CSP2 value
immediately before transiting from Cascade to Automatic mode. To inherit the set point in
Cascade mode, set SP Tracking Mode (SP.TR) of the secondary loop to "0: ON".
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