Ratio - Ratio - Siemens 353 User Manual

UM353-1B

3.2.72 RATIO - Ratio

RATIO function blocks can be used on a one per
loop basis. They provide a means of setting a ratio in
an external setpoint application, for example,
controlling a captive flow while maintaining the ratio
between a wild flow and the captive flow at the
desired value. Inputs A and E (external ratio) and the
operator set ratio R value are multiplied and become
the function block output O1.
Track Command input TC, asserted high (1), causes
the ratio block to track the input variable TV. The
ratio value to be recalculated is then R = TV / (A x
E). The value of R will be limited at the HI or LO
LIMIT range settings. The factory default settings of
the ratio limits are 0.00 - 30.00.
The RATIO can be adjusted using the QUICKSET
feature if parameter QUICKSET is set to YES. The
RATIO will continuously change as the knob is
adjusted. Press the STORE button when the final value is reached to insure that the new RATIO setting will be
retained on a Cold power up condition. The QS DPP parameter enables setting of the Ratio adjustment resolution
when in the QUICKSET mode.
If input A or E is not configured, its value will be set to 1. When input TC or TV is not configured, its value will be
set to 0.
The TO (Tracked Output) is normally used in applications where an external device is being used to set a ratio in
place of the RATIO parameter (R is then set to 1.0). When it is desired to have the output of the RATIO block track
the TV variable, the external device is forced to track TO. Input E will then equal TV/[Ax(1.0)] and, therefore, the
RATIO block output O1 will equal TV.
A
E
TC
.
TV
When a configuration containing the RATIO function block is edited in i|config and then downloaded to an on-line
controller, the controller will ignore a change to the RATIO parameter value and continue to run with the pre-
download value.
April 2012
A x E
X
X
TV
÷ R
A x E
Track Command
Track Variable
BLOCK DIAGRAM
RATIO
RATIO
Input A A
R
Input E E
RATIO
TC
Track Command
O = R x A x E
TV
Track Variable
R A T I O
RATIO
(S)
H I L I M I T
HIgh Ratio LIMIT
L M I
O L I T
LOw Ratio LIMIT
Q S D P P
QuickSet Dec. Pt. Pos.
I N P U T A
INPUT A
(H)
I N
P U T E
INPUT E
(H)
I N P U T T C
INPUT TC
I N P U T T V
INPUT TV
Q U I C K S E T
QUICK SET Ratio
E S N
Exec. Seq. No.
R x A x E
Output 1
X
TV
÷
A x R
Tracked
Output
Function Blocks
ESN = 000
O1 Output 1
TO Tracked Output
..................................... Real (1.00)
..................... Real (30.00)
(S)
..................... Real (0.00)
(S)
.. 0.0.0.0.0.0 (0.00)
(S)
........
loop tag.block tag.output (null)
........
loop tag.block tag.output (null)
......
loop tag.block tag.output (null)
(H)
......
loop tag.block tag.output (null)
(H)
............. NO/YES (YES)
(S)
.............. 001 to 250
(H)
O1
TO
.
.
.
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