ABB COMMANDER C355 - A4 Single Loop Controller with Feedforward

118
…APPENDIX A – CONTROL TEMPLATES
CSPt
PV
Process Variable
Low Signal Select
(Alarm A1)
•1
•2
•1 Template 5 only. Alarm A1 trip value can be set to give the desired low signal detection
•2 Template 6 only.
Master Output
Digital Select
Manual Output
L
LR
ao1
OP1
PV–
CSPt
Local Set Point
Profile
Set Point
I/P1
I/P2
di.1
PID
Controller
Local/
Remote
Select
A2.3 Analog Backup (Templates 5 and 6)
The Analog Backup provides a backup for a master controller. In normal operation (remote control mode selected) the COMMANDER 350’s current
output follows the master controller’s output value. A fault in the master system can be identified either by detecting a low s
ignal on the master output
(template 5) or via a digital signal (template 6). When a fault is detected the COMMANDER 350 switches into local control mode
and the process is
controlled by the PID output of the COMMANDER 350. The COMMANDER 350 PID algorithm continually tracks the master output value t
o ensure
bumpless transfer from remote to local mode operation. When the master signal is restored or the digital input returns to its n
ormal state the COMMANDER
350 switches back to remote control mode (i.e. COMMANDER 350 output = master output).
The analog backup station can be used in series or in parallel with the master output signal. (See Fig. A1). Parallel operation
is achieved by using
relay 1 in the COMMANDER 350 to energize an external relay (with suitable changeover contacts for switching low level signals)
which selects the output
to be routed to the actuator.