Various Controls - Mitsubishi Electric MELSEC iQ-R Series Programming Manual

Various controls

Cascade control
The cascade control consists of the primary loop and secondary loop. This control detects disturbance entering secondary
loop in an early stage and absorbs them into secondary loop to remove the effect on the process and improve the whole
control performance.
Generally, the response speed of the secondary loop should be three times or more than that of the primary loop.
When tracking is required, connect CASOUT_T of the primary loop with CASIN_T of the secondary loop. In
addition, settings for the following operation constants of the secondary loop are necessary.
• PID_TRK
• PID_SVPTN_BO
• PID_SVPTN_B1
For details, refer to the following.
Page 604 Cascade connection when tracking is required
Ex.
When controlling the furnace temperature
The fuel supply variation is absorbed by flow control of the secondary control loop, and the response characteristics of the
whole temperature control are improved.
Flow fluctuation
Fuel tank
SV
TIC
Primary control loop (temperature control)
001
PV MV
FIC
PV
002
Flow sensor
SV
Secondary control loop
(flow control)
MV
Valve
Appendix 3 Related Functions of Process
Thermocouple
Burner
Furnace
APPX
A
601