On/Off - On/Off Controller - Siemens 353 User Manual

Function Blocks

3.2.59 ON/OFF - On/Off Controller

ON/OFF is an on/off controller with deviation function. It
is one of five controller types that can be used on a one per
loop basis.
When P-S (Process - Setpoint) reaches the HDEV limit, the
Boolean output HO will go high (1) and when S-P (Setpoint
- Process) reaches the LDEV limit, the output LO will go
high (1). When the deviation drops to less than the
DEADBAND setting, the outputs will go low (0).
Derivative action is added to the process variable when the
TD parameter is other than 0.0.
When single ended action (gap action) is desired, set the
DEADBAND equal to the gap and the HDEV parameter for
half the gap. For example, if DEADBAND = 20.0, set
HDEV to 10. If the setpoint S is 50.0, output HO will go
high (1) when P equals 60.0 and HO will go low (0) when P
equals 40.0.
Input E asserted high (1) will enable the block outputs;
when low (0) all outputs will be set low (0).
The process range pointer parameter points to another function block that has range scaling, such as the analog
input that is providing the process variable. This enables the controller to normalize the tuning parameters for the
range of the process input. If this parameter is not configured, the controller will use a range scaling of 0.0 - 100.0.
POWER UP - During a warm start, outputs and comparator functions will be initialized at the state prior to power
down and all dynamic elements will be initialized at the current input on the first scan. During a cold start all
outputs and comparator states will be set to zero, to be activated by the block functions. All dynamic elements will
be initialized at the current input on the first scan.
Process
Engineering
P
INput units
scaling
RanGe
PoinTeR
+
-
Engineering
S
INput units
scaling
.
Setpoint
Absolute Value
3-62
ON_OFF Controller
Lead
t
+
D S
+
t
D
+ 1
S
D G
Engineering
High
INput units
DEViation
scaling
Engineering
Low
INput units
DEViation
scaling
Absolute Error
BLOCK DIAGRAM
AE
ON_OFF CONTROLLER
ONOFF
R
Range
Process P
Setpoint S
E
Enable
R G P R
T
T D
D G
H D E V
L D E V
D E A D B A N D
I N P U T P
I N P U T S
I N P U T E
E S N
A
HI Comparator
IF A>=B THEN H=100
B
IF A>=(B-DB) AND A<B THEN H=H
IF A<(B-DB) THEN H=0
+
Engineering
DB
INput units
+
scaling
A
LO Comparator
+ IF A<=B THEN L=100
B
IF A<=(B+DB) AND A>B THEN L=L
IF A>(B+DB) THEN L=0
-
UM353-1B
ESN = 000
AE Absolute Error
ON_OFF
HO High Output
CONTROLLER
O1 Output 1
LO Low Output
RanGe PoinTeR ..................
(S) loop tag.block tag (null)
Time - Derivative ........... 0.00 to 100.00 min
(S)
Derivative Gain ....................... 1.00 to 30.00
(S)
High DEViation .................................... Real
(S)
Low DEViation ..................................... Real
(S)
DEAD BAND ....................................... Real
(S)
INPUT P .....................
loop tag.block tag.output (null)
(H)
INPUT S .....................
(H) loop tag.block tag.output (null)
INPUT E .....................
loop tag.block tag.output (null)
(H)
Exec. Seq. No. ........................... 001 to 250
(H)
H
AND
1
Dead
OR
Band
AND
L
AND
1
Enable
r3
April 2012
(0.00)
(10.00)
(5.00)
(5.00)
(0.5)
HO
O1
LO
.
E