rs3™ to deltav™ tuning - instrumentation and...
TRANSCRIPT
Slide 1
RS3™ to DeltaV™ Tuning
Conversion
by
James F. Beall
Emerson Process Management
February 26, 2013
Slide 2
“ All PIDs are not Created Equal”
• Units of RS3 and DeltaV Tuning Constants,
including PV filter
• PID Form
• RS3 – Standard
• DeltaV – Standard (default) or Series
• ARW settings
• PID “Structure” Options
Slide 3
RS3 and DeltaV Tuning Constant Units
RS3 DeltaV
• Gain %PB1 or Gain1,2 Gain2
• Reset Second, minute or hour3 Second
• Rate Second, minute or hour3 Second
• PV_Filter Note 4 Second
• Notes
1. Selected on a system wide basis
2. Gain has units of %OUT/%PV
3. Selected on a loop by loop basis, Rate and Reset units can be
different
4. See next slide
Slide 4
RS3 PV Filtering
• PV filtering is provided on the Analog-In block. It is a first
order filter, enter the time constant in seconds
• Additional filtering is provided in the PID block if
Derivative is activated (PID, PD or ID), even if Rate = 0.
• The PID filter is non adjustable and its first order time
constant is the greater of (2*Sample time) or (Rate/8).
Note “sample time” is the greater of the ControlBlock
sample time, if configured, or the Controller Processor
card scan time. Units are selectable as seconds, minutes
or hours.
• Note the PID filter applies to the value being acted upon
by the Proportional, Integral and Derivative terms. This is
different than DeltaV where this filter (α*Rate) is applied
only to the value going to the Derivative function.
Slide 5
PID Form – Parallel, Standard, or Classical
• Three Common PID Forms
– Parallel Form
– Standard (aka ISA) Form,
– Series (aka Classical) Form.
• The same tuning constants may produce
different response in each PID Form
Slide 6
PID “Form” Selection
• RS3 has a “Standard” form
• DeltaV is selectable – “Series” or “Standard”
– “Standard” is the DeltaV default selection
• If the Derivative is not used (Rate = 0 min),
then “Series” and “Standard” are the same
• Use the “Standard” Form in DeltaV!
Slide 7
Series and Standard Forms
• Series
• Standard
PROCESS
PV +
- SP
Output
+
Error
+
+
P
I
D SD
T
sR
T1
CK
Slide 8
RS3 Tuning Conversion
• Choose DeltaV Form = Standard (default) for
ease of conversion
• So, DeltaV Tuning will be simply a conversion of
units:
Parameter RS3 DeltaV (Standard Form)
Gain %PB Gain = 100/%PB
Gain Gain = Gain
Reset Ti - seconds Reset = Ti
Ti - minutes Reset = 60*Ti
Ti - hours Reset = 3600*Ti
Rate Td - seconds Rate = Td
Td - minutes Rate = 60*Td
Td - hours Rate = 3600*Td
Slide 9
RS3 PV Filtering
• The default α in DeltaV for filtering ONLY the
signal to the derivative function only is 0.125
(1/8). This is the close to the equivalent of PV
filtering in RS3 when Derivative is active (PID,
PD or ID even if Rate = 0) and you are using a
typical Derivative setting.
• Consider the filter setting in the RS3 Analog-In
block also.
• The DeltaV PID block has a first order PV_Filter,
set in seconds, in addition to the Derivative
filtering above.
Slide 10
Anti-Reset Windup (ARW) Settings
• IMPORTANT!!!!!!!!
• RS3 performs ARW limits based on the 0-100%
out limits. There are not separate ARW limits.
• DeltaV ARW settings are “OUT EU’s”. Set ARW
limits to OUT LIMITS in DeltaV (range is -10 to
110% of OUT_SCALE, in EU’s)
– If OUT_SCALE = 0-15,000 lb/hr, example ARW
settings would be ARW_LO_LIM= 0 (lb/hr) and
ARW_HI_LIM= 15000 (lb/hr)
• Incorrect DeltaV ARW Limits will cause poor
control action!!
Slide 11
Anti-Reset Windup (ARW) Settings
ARW Limits use
OUT_SCALE EU’s
Slide 12
PID “Structure”
• The PID “Structure” has to do with whether the
Gain and Derivative act on the Error (SP-PV) or
on the PV. (Integral (I) action is always on
Error.)
• The RS3 allows you to choose whether the
Proportional (P) acts Error, PV or SP
• The RS3 allows you to choose whether the
Derivative (D) acts Error, PV or SP.
• There are several DeltaV PID Structure options
though it does not allow P and D on SP. The
most common is PI on error, D on PV
Slide 13
DeltaV PID Structure Options
Slide 14
Other RS3 PID Considerations
• The RS3 PID has a both the “positional” (default)
and a “velocity” PID implementation. DeltaV has
only the “positional” PID implementation. The
two implementations may act differently when the
output comes out of a limit.
• Check the feed forward scaling systems. Both
RS3 and DeltaV use a “Feed forward Gain” but
the DeltaV PID block has a “feed forward scale”.
Slide 15
Other RS3 PID Considerations
• RS3 has several more options like error squared,
gap, etc. that can be implemented in DeltaV.
• Gain and Ratio functions in the RS3 Control
Block are implemented in separate blocks in
DeltaV