Siemens 353, User Manual

Page: 59 / 246

UM353-1B Function Blocks
April 2012 3-29
3.2.20 BIAS - Bias
BIAS
function blocks can be used on a one per loop basis
and provide a means to bias a signal, such as the setpoint in
an external set application. Inputs A and E (external bias)
are summed and then added to the operator adjustable bias
B.
Track Command input TC, asserted high (1), will cause the
block output to track input TV and BIAS to be recalculated
as B = TV - (A+E). The value of B will be clamped at the
HI and LO LIMIT settings. It is important to realize that the
inputs and outputs are in engineering units and the limits
must be adjusted accordingly with the expected minimum
and maximum required range values. The default values
have been set to -150.00 and +150.00, which might be the
normal expected limits when using the default range of 0.0
to 100.0. These values can be set lower but have a
maximum setting of +/-150% of the range pointer value.
The default range is 0.00 to 100.00 if the pointer is not
configured.
If, for example, the BIAS block is used to bias a flow setpoint with a range pointer (input R) of 0-6.00 GPM, the
maximum bias adjustments would be +/-9.00. If limit adjustments of +/-50% of this range are desired, then the
BIAS block LO LIMIT should be set at -3.00 and the HI LIMIT at +3.00. If a range change is made the current
LIMIT settings and the current BIAS value will be changed to be the same % value within the new range.
The BIAS can be adjusted using the QUICKSET feature if the parameter QUICKSET is set to YES. The BIAS
value will continuously change as the knob is adjusted but the STORE button must be pressed when the final value
is reached to insure that the new BIAS setting will be retained on a Cold power up condition.
Any unused inputs to the block will be set equal to 0.
The TO (Tracked Output) is normally used in applications where an external device is being used to set a bias in
place of the BIAS parameter (B is then set to 0.0). When it is desired to have the output of the BIAS block track the
TV variable, the external device is forced to track TO. Input E will then equal TV- [A+(0.0)] and, therefore, the
BIAS block output O1 will equal TV.
BLOCK DIAGRAM
B
A + E
A
E
TC
TV
TV - (A + E)
A + E + B
TO
O1
O utput 1
T
racked
TC
+
-
+
+
-
TV - (A + B)
+
+
+
+
+
O
utput
T rack C ommand
T rack V ariable
.
.
Rev 2
When a configuration containing the BIAS function block is edited in i|config and then downloaded to an on-line
controller, the controller will ignore a change to the BIAS parameter value and continue to run with the pre-
download value.
Input A
BIAS
S B
L
L I
I H I
O L
C
I N U A
K E S T
BIAS
(S)
..................................... Real (0.00)
HI gh Bias LIMIT
(S)
.................... Real (150.0)
LO w Bias LIMIT
(S)
.................... Real (-150.0)
INPUT A
(H)
......
loop tag.block tag.output (null)
QUICK SET bias
(S)
............. NO/YES (YES)
O1 O utput 1
BIAS
BIAS ESN = 000
A I
T P
U I
A
E
TC
TV
O = B + A + E
B
Input E
T rack C ommand
T rack V ariable
TO
T racked O utput
I
I
I
N
N
N
P
P
P
U
U
U
T
T
T
E
C
T
INPUT E
(H)
......
loop tag.block tag.output (null)
INPUT TC
(H)
...
loop tag.block tag.output (null)
INPUT TV
(H)
....
loop tag.block tag.output (null)
E S N
E
xec.
S
eq.
N
o.
(H)
............ 001 to 250
M I T
T I M
Q
V
T
R G P T R
R an G e P oin T e R
(S)
...
loop tag.block tag (null)
R ange R