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Flow-X─ Function Reference
4-266
Flow-X General functions - fxPID
Logic
Symbols
PV
process value in current cycle [EU]
CUR
PV
process value in previous cycle [EU]
PREV
SP
required setpoint value [EU]
REQ
SP
in-use setpoint value in current cycle [EU]
CUR
SP
in-use setpoint value in previous cycle [EU]
PRV
e
error in current cycle [EU]
CUR
e
error in previous cycle [EU]
PRV
Δu
control output deviation value [%]
v
required control output value in current cycle [%]
CUR
v
required control output value in previous cycle [%]
PRV
u
actual control output value in current cycle [%]
CUR
u
actual control output value in previous cycle [%]
PRV
u
low limit for control output [%]
MIN
u
high limit for control output [%]
MAX
Δt
calculation cycle time [s]
K
Proportional gain factor
P
K
Integral gain factor
I
K
Derivation gain factor
D
P
Proportional part of current cycle
I
Integral part of current cycle
CUR
I
Integral part of previous cycle
PRV
D
Derivative part of current cycle
Control output logic
The logic for the control output depends on the current manual and tracking modes.
Manual mode = Enabled
Manual mode = Disabled AND Tracking mode = Enabled
Manual mode = Disabled AND Tracking mode = Disabled
Set current output equal to manual input value
v
= 'Manual output %'
CUR
Set current output equal to tracking input value
v
= 'Tracking value' (input)
CUR
Determine the current setpoint
If cascade mode enabled then
SP
= Cascade input value * (High scale value - Low scale value) + Low scale value
CUR
Else
SP
= SP
CUR
REQ
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