Siemens 353, Руководство пользователя

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Function Blocks UM353-1B
April 2012 3-28
3.2.19 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.
BLOCK DIAGRAM
A
O utput
-
GAIN
HI
Selector
LO
Selector
+
+
+
GAIN
LO
Selector
HI
Selector
+
+
+
B atch P re- L oad
HI LIMIT
LO LIMIT
-
O1
.
.
Rev 2
Input A
BATCH SWITCH
T I H I
O L
I N U A
I A G N
HI gh LIMIT
(S)
........................... Real (100.0)
LO w LIMIT
(S)
........................... Real (0.0)
INPUT A
(H)
....
loop tag.block tag.output (null)
GAIN
(S)
.................................... Real (32.0)
O1
O utput 1
BATCH SWITCH
BATSW ESN = 000
I M L
T P
A
L I M I T
E S N
E xec. S eq. N o.
(H)
........... 001 to 250
P B L
B
atch
P
re-
L
oad
(S)
.................. Real (50.0)