Batsw - Batch Switch - Siemens Moore 353 User Manual

UM353-1

3.2.23 BATSW - Batch Switch

BATSW function blocks can be used on a one per loop
basis. Each is used with a PID function block to eliminate
overshoot during startup conditions. When placed in the
feedback path of the controller it causes the reset
component of the controller to be reduced (if controller
action is Rev). Without the use of a batch switch during
startup, the controller output (O1 = GE + R) will equal
full output since the reset will wind up. This requires the
process to overshoot the setpoint in order to bring the
controller output back down. With a batch switch in the
feedback path, a lower reset value will be present when
crossover occurs, thus reducing or eliminating overshoot.
As input A equals or exceeds the HI or LO LIMIT setting,
the output of the batch switch will be either decreased (HI
LIMIT) or increased (LO LIMIT), changing the feedback signal and therefore the controller reset signal. This
maintains controller output at the batch switch limit setting and eliminates reset windup.
If a controller has a large proportional gain setting, the reset can be modified too much, such that the process may
under shoot the setpoint during a startup condition. The BPL (Batch Pre-Load) is adjusted to optimize the controller
for startup conditions by limiting how much the batch switch can adjust the controller feedback signal.
When the controller output is within its normal operating output, the batch switch has no effect on the controller.
This allows the controller to be tuned optimally for normal operating conditions and the batch switch to add
additional compensation, very similar to derivative action, only during startup.
A
-
.
HI LIMIT
-
LO LIMIT
March 2003
+
GAIN
+
+
Batch Pre-Load
+
GAIN
+
+
BLOCK DIAGRAM
BATCH SWITCH
ESN = 000
BATSW
BATCH SWITCH
Input A
A
H I L I M I T
HIgh LIMIT ........................... Real (100.0)
(S)
L O L I M I T
........................... Real
LOw LIMIT
(S)
P
B L
Batch Pre-Load
(S)
G A I N
GAIN .................................... Real
(S)
I N P U T A
INPUT A ....
loop tag.block tag.output
(H)
E S N
Exec. Seq. No.
(H)
HI LO
Selector Selector
LO HI
Selector Selector
Output
Function Blocks
O1 Output 1
(0.0)
.................. Real (50.0)
(32.0)
(null)
........... 001 to 250
O1
.
3-33