PCC-IV Instruction Manual (Rev. 0.1)
Page 6-15
Section 6
– Blockware Functions
Technical Reference
F42
[F(X)] Function of X Generator with Learn Mode
Function
F(X)
generates a Block Output based on a user generated Output vs Input profile (i.e., y=f(x)). The
parameters provide 11 (X, Y) breakpoint pairs. Between adjacent breakpoints,
F(X)
“draws” a straight line from
breakpoint to breakpoint (see the figure below).
Less than 11 breakpoints: All eleven breakpoints do not have to be used. Starting from X1,
F(X)
ignores all
breakpoints after the first X
i
= -150.00 is encountered. Example: Y1=10%, X1=0.00%; Y2=22%, X2=20.00%;
Y3=29%, X3=30.0; Y4=0%, X4=-150.00. Breakpoints 4 through 11 (inclusive) would be ignored in this example.
The X coordinates can be any value; however, the X values must be entered in ascending order (i.e. X1 < X2 < X3
< X4
…).
First/Last Segments: For X Inputs below the first or above the last defined breakpoints, the Block Output can be
held at the last valid Y value (Hold mode), or the Block Output can vary per the last valid line segment equation
(Linear mode). Parameter 1 (First/last Segment) = 0 holds the Output, Parameter 1 = 1 varies the Output linearly.
The figure above illustrates Linear mode. At least two points must be entered to activate Linear Mode.
Learn Mode
X and Y coordinates may be entered or modified at any time from the PCC-IV front panel editor, the USB port, or
the MODBUS communications port (via PLINK).
F(X)
also has a
Learn
mode for automated entry and editing of
characterizing curves.
Learn
mode is particularly useful for setting up the various curves associated with
combustion applications: fuel/air ratio, oxygen setpoint, flue gas recirculation curves, furnace draft feedforward, and
feedwater valve characterizer curves.
When Input 2 (Learn Enable) = 1 the
Learn
mode is activated and Inputs 3, 4, and 5 determine how
Learn
mode
operates. Inputs 3-5 are ignored when Input 2 (Learn Enable) = 0. The Block Output continues to be calculated
based on the X input and the current parameters throughout
Learn
mode. See the truth table below:
Learn Enable
Input
Learn
Input
Clear
Input
Action
0
not used
not used
Learn mode is disabled
1
0
not used
No (X, Y) data is stored in the parameters
1
1
not used
No (X, Y) data is stored in the parameters
1
^1
0
The current X and Y Input values are stored in a pair of
parameters (see below)
1
^1
1
All X and Y parameters are reset to the default values
NOTE:
^1
means: on the rising edge (i.e., only once during the scan that the Input changes from 0 to 1)
-20
0
20
40
60
80
100
120
-20
0
20
40
60
80
100
120
O
ut
pu
t
(Y)
Input (X)
F(x): 10 Breakpoints Entered, First/Last=Linear
X1,Y1
X2,Y2
X10,Y10
