Presented by Emerson's James Beall, Nikki Bishop, and Barabara Hamilton at the 2011 Emerson Exchange conference in Nashville, Tennessee.

1. Smooooth Operations
Configuration Tips for Analog Blocks

2. Presenters
 James Beall
Principal Process Control Consultant
 Barbara Kerr Hamilton
Senior Industrial Energy Consultant
 Nikki Bishop
Senior Applications Consultant

3. Introduction
 Discuss useful features and options of the PID Block
 Explain how to use BKCAL’s in Cascade Control and
explain the various options
 Identify additional uses of BG and RTO blocks and
how to use them
 Demonstrate examples of these features and options

4. TOPIC 1: The simple PID block
“I don’t understand all I know about this”

5. PID “Form”
 Three Common PID Forms
– Standard, aka ISA Form (DeltaV default)
– Series, aka Classical Form
– Parallel Form (not available in DeltaV)
 Read the fine print…
FORM None Selects equation form (series or standard). If
Use Nonlinear Gain Modification is
selected in FRSIPID_OPTS, the form
automatically becomes standard,
regardless of the configured selection of
FORM.

6. Series and Standard Forms
Error
TDS D Output
 Series P + PV
+ KC + PROCESS
SP
+
-
1
TR s
I
I
1
 Standard Error = SP - PV TR s OUTPUT
P
SP + PV
KC + PROCESS
-
TDS D

7. PID “Form” Choice
 Prior system experience and/or migration
 Personal Preference - Standard (RS3, etc) or
Series (Provox, etc.)
 Series is identical to Standard form if
Derivative action is NOT used
 Can impact conversion of tuning constants
from previous control system

8. Convert Series (Classical) to Standard
 Series is identical to Standard form if Derivative
action is NOT used
 TR should be time/rep; units = seconds
 TD should be in seconds
 Be sure to convert to your tuning constant units
after form conversion
TR Classical + D Series
Series + T TD Classical
KC Standard = KC Series *
TR Classical
Series
0
TR Standard = TR Series ++ TTD Series
D Classical
0
TR Classical TD Series
Series * * TD Classical
TD Standard = 0
( TR Classical + D Series ) )
Series + T TD Classical

9. PID “Structure”
Used most.
Default

10. Structure: PI on error, D on PV
Controller Output – Flow to reactor
SP

11. Structure: I on error, PD on PV
Controller Output – Flow to reactor
SP

12. Structure: 2 Degrees of Freedom
 BETA - determines the degree of proportional
action that will be applied to SP changes.
– Range = 0-1
– BETA=0 means no proportional action is applied to SP change.
– BETA=1 means full proportional action is applied to SP change.
 GAMMA - determines the degree of derivative
action that will be applied to SP changes.
– Range = 0-1
– GAMMA=0 means no derivative action applied to SP change.
– GAMMA=1 means full derivative action is applied to SP change.

13. Structure: 2 Degrees of Freedom

14. PID “IDEADBAND” (Integral Deadband)
 Limits the movement of the controller output
when the error is less than the IDEADBAND
– Integral action stops
– Proportional and Derivative action continue
– Same Engineering Units as PV Scale
 Uses:
– Mitigates effect of valve “stiction” (but leaves offset)
– Allows P-only control if within deadband

15. PID: Setpoint Processing
 SP_FTIME: Time constant of 1st order SP filter
– seconds
– Applies in AUTO, CAS and *RCAS (*not specified in BOL)
 SP_RATE_DN: Ramp rate for SP decreases
 SP_RATE_UP - Ramp rate for SP increases
– PV units per second
– If set to 0.0 then SP is used immediately.
– Applies only in AUTO (not CAS or RCAS)

16. Set Point Limits
 SP_HI_LIM- The highest SP value (EU’s)
allowed.
 SP_LO_LIM - The lowest SP value (EU’s)
allowed.
 CONTROL_OPTS – allow you to specify if SP
Limits to be obeyed in “CAS and RCAS”
 Can use “Output Limits” of Master loop in
cascade pair to limit SP to Slave loop ONLY
in CAS and RCAS

17. Gain Scheduler
 Provides up to 3 regions of different PID tuning
parameters based on a selected state variable
(output, PV, error, or “other”)
 Provides a smooth transition between regions
 Create PID module using Module Templates:
Analog Control/PID_GAINSCHED
 OR, add function to existing PID module
– Expose Gain, Reset and Rate parameters on PID
function block
– Copy all function blocks from template except the
PID FB and link as needed.

18. Gain Scheduler

19. Gain Scheduler

20. Gain Scheduler – Detail Display

21. FRSIPID_OPTS: Non-linear Gain
 Modifies the proportional
Gain as a function of the
error (PV-SP)
 Makes the tuning more
aggressive as the PV is
farther from the set point
 Can create the “error
squared” PID function

22. FRSIPID_OPTS: Non-linear Gain
The PID “Gain” is multiplied by “KNL” which has a value between 0
and 1 as a function of the error (SP-PV).
Knl
Knl=1
Knl=NL_MINMOD
e= PV-SP
NL_GAP NL_HYST
NL_TBAND

23. FRSIPID_OPTS: Non-linear Gain
TIP: I typically set NL_HYST = 0 unless it is a for a
“valve position controller.

24. FRSIPID_OPTS: Non-linear Gain
 GAIN ≥ modified PID gain ≥ GAIN * NL_MINMOD
But neither GAIN nor GAIN_WRK show the modified gain
value!
 Caution – Integrating Processes
– May cause oscillation at reduced gain
– For these applications, the reset time should be based
on “Gain*MINMOD” which will result in a larger reset
time to prevent oscillations.
– Consider using the Gain Scheduler instead (so you can
change gain and reset)

25. FRSIPID_OPTS: Non-linear Gain
Caution! PID Form is set to Standard regardless
of the configured FORM parameter value
– Also, if the Non-linear Gain option is enabled, the
STRUCTURE will be “PID on error” regardless of
the PID Structure chosen (including 2 degrees of
freedom).
– So if you move the SP such that the error is outside of
NL_GAP+NL_HYST, there will be a “proportional
kick” of the output
– Test this on your application!

26. FRSIPID_OPTS: Non-linear Gain “Error2”
 “Error squared” PID function – error*abs(error)
 Proportional = error*abs(error)*gain
= error* (abs(error)*gain)
 Proportional = error*(Modified Gain) Non-linear Gain
 Modified Gain = abs(error)*Gain Settings for E2
Modified
Gain
Activate NL Gain
NL_MINMOD = 0
NL_GAP = 0
NL_TBAND = 100%
of PV Span (EU’s)
Error
NL_HYST = 0

27. Topic 2: Block Initialization and Options
The single most
BKCAL_IN and BKCAL_OUT misused and
misunderstood
How to use it …. connection in
DeltaV!!
When to fool it….

28. Don’t Be Frightened by BKCAL’s!
 Don’t let BKCAL’s scare you away! They are quite
useful little “critters” and can make your life a lot
easier.

29. What is a BKCAL?
 Downstream loop “talks” to the upstream loop and tells it what’s
going on. Information such as:
– Can the downstream loop receive a setpoint?
– If not, why? And where should the upstream output
be to match the local downstream setpoint?
“Hey there, Mr. “No problem, Mr. “Sound great, Mr.
Upstream, I am Downstream. Just Upstream. That
not quite ready for tell me what your way, when I am
your SP. I’ll let current SP is so that ready for your SP,
you know when I I can make my we will be all
am ready.” output match.” matched up.”

30. What’s in a BKCAL?
 BKCAL_OUT Value
– SP (default)
– PV (selected in CONTROL_OPTS of downstream PID block)
 BKCAL_OUT Status :  BKCAL_OUT SubStatus :
– Bad – NotLimited
– Uncertain – LowLimited
– GoodNonCascade – HighLimited
– GoodCascade – Constant

31. BKCAL’s and Block Initialization
“Ok. Where
should my
output be to
LT FT “bump-less” –
match your
local setpoint?”
neither the setpoint
A nor the valve on
the flow loop will
K f
bkcal
jump to a new
T
A T “I am not ready
value when placed
for your SP right
now. I’ll let you
in CAScade
output know when I am
ready.”
A T
“balance-less” –
setpnt
operator does not
K f
have to “line up”
T
A T
level output with
F(x)
flow setpoint to
F(x)
change modes

32. Important Control Options
FRSIPID_OPTS CONTROL_OPTS
 Dynamic Reset Limit  Use PV for BKCAL_OUT
 SP-PV Track in LO or IMAN
 SP-PV Track in MAN

33. But what do those things mean?
 Use PV for BKCAL_OUT
– Use this on slave loops to send the actual PV upstream to
the master instead of the SP when in CAScade mode.
– In AUTO, MAN, IMAN, and LO the SP is still used for the
BKCAL_OUT
– If used in conjunction with DRL on the master, will prevent
reset windup if/when the slave loop cannot make setpoint.
 SP-PV Tracking
– SP will be set equal to PV in the modes selected.
– Separate checkboxes for MAN and LO / IMAN. Usually
check both.

34. Output limiting and reset windup
 Dynamic Reset Limiting on PID block:
– BKCAL_IN will be used for reset feedback instead of the
internal “OUT” of the PID algorithm.
– If BKCAL_IN is not changing, reset cannot “wind”.
– Default DeltaV PID blocks use internal “OUT” for reset
feedback and the internal reset calculation can continue past
the OUT limit
 Example - Flow loop with cascade setpoint
– PID configured with low output limit of 20%
– If loop cannot make setpoint, output will clamp at 20%
– But internal reset action will continue
– Internal PID output will “wind” all the way to 0%

35. How can you prevent windup?
 What to do
– Set the Anti-Reset Windup (ARW) limits equal to OUT limits
• Reset action will return 16X faster than normal
– Use Dynamic Reset Limit on PID block
• BKCAL_IN will be used for reset feedback instead of internal
“OUT”
• If BKCAL_IN is not changing, reset cannot “wind”.

36. Enabling PID External Reset
 Utilized most often
in the primary loop
of a cascade
 Compensates for
“unexpected” slow
secondary loop
response or
secondary PV
limited before its
OUT limited

37. Anti Reset Windup
 Standard
– Limited conditions in the Slave loop are taken care of
through the BKCAL feature
– Integral action is turned off in the direction of the limited
status
 Dynamic Reset Limiting
– Prevent reset windup with external reset
– Select “Dynamic Reset Limit” in FRSIPID_OPTS on the
Master loop
– Select “Use PV for BKCAL_OUT” in CONTROL_OPTS
on the Slave loop

38. Anti-Reset Windup Limits
 Improves process recovery from saturation
 ARW_LO_LIM must be >= OUT_LO_LIM
– When OUT is between above numbers, reset action
to increase the output is decreased by 16X
– Process recovery from low limit is faster until output is
> than anti-reset windup limit
 ARW_HI_LIM must be <= OUT_HI_LIM
– When out is between above numbers, reset action to
decrease the output is decreased by 16X
– Process recovery from high limit is faster until output
is < than anti-reset windup limit

39. Setting ARW limits
 Default values are 0 and 100
– Units are the same as
OUT_SCALE
– Set ARW limits are equal to
OUT limits or scale as a start
 Example:
– Master loop: OUT_SCALE is
0-25,000 lbs/hr.
– Set ARW_HI_LIM = 25,000
Set ARW_LO_LIM = 0

40. Setting ARW Limits – IMPORTANT!
 Control Instability
– If the ARW limits are “inside” the OUT limits, reset action
can be based upon RESET in one direction and
RESET∕16 in the other
– poor control and loop instability can result.
 WARNING – Version Upgrade!!
– Early DeltaV (V6 and before) this feature did not work
– If you violated above guidelines prior to V7, it didn’t
cause problems until you upgraded to a later version!

41. Setting ARW limits
 Example: ARW_LO_LIM > OUT_LO_LIM
PV
SP
ARW_LO_LIM
OUT
OUT_LO_LIM
 Example: ARW_HI_LIM < OUT_HI_LIM
– Dampers passes only slightly more flow at 100% than 75%
– Set ARW_HI_LIM to 75%, but keep OUT_HI_LIM at 100%

42. Topic 3: Additional Control Strategies
Override
Control
< PC
Valve F(x)
FC Characterization FC
PT
Hot Cold
FT FT
Water Water
TT LT
To Reactor

43. Start Simple – a single PID loop
PC
PT
Hot Cold
Water Water
TT LT
To Reactor

44. Valve Characterization
PC
F(x)
FC FC
PT
Hot Cold
FT FT
Water Water
TT LT
To Reactor

45. Output Characterization to Valve
 Use a “Signal Characterizer” function block to
change valve characteristics
– Note the best solution is to change valve trim to
proper characteristic
SGCR
•Characterizes IN_1 to OUT_1
•Reverse Char. IN_2 to OUT_2

46. Output Characterization to Valve
 See Books On Line for rules for
the X and Y curves
 Set “SWAP_2” = TRUE to
provide a “reverse”
characterization for the BKCAL
signal (The answer in V9.3 and
later is “Change X by Y axis on
IN-2”.)
 BOL: The SWAP_2 parameter swaps the X and Y axes used for
OUT_2. When the SWAP_2 parameter is True, IN_2 references the
CURVE_Y values and OUT_2 references the CURVE_X values. In
addition, the IN_2 units change to Y_UNITS and the OUT_2 units
change to X_UNITS.
 IF YOU DON’T SELECT THIS OPTION, IT WILL APPEAR TO WORK
BUT THE AO OUTPUT WILL CHANGE DURING A DOWNLOAD!!!

47. Override Control
< PC
F(x)
FC FC
PT
Hot Cold
FT FT
Water Water
TT LT
To Reactor

48. Using CTLSL for Override Control
 One valve – two controllers
 Example: low pressure override on a flow loop
– Master control loop determines flow setpoint
– Flow loop determines valve position to control flow as long as
header pressure can be maintained.
– If header pressure gets too low, pressure override loop “takes over”
and determines valve position.
 The Good News: No Windup
– DeltaV “turns off” the integral action if a controller is not the
selected controller in a CNTLSL block. No windup!
 The Bad News: What happens when switching to MAN?
– The valve “belongs” to the flow controller
– If override is active, you will get a bump when switching to MAN
– The fix: pulse flow loop to LO with BKCAL_IN as TRK_VAL when
target mode transitions to MAN
– Defeat override in MAN using output limits and DRL

49. Topics 4: BG and RTO blocks
 RULE #1
NEVER EVER use SUB, ADD, MUL, DIV, or CALC
blocks to modify a setpoint
 RULE #2
When modifying a setpoint ALWAYS use BG or RTO
blocks
 RULE #3
If you break Rules #2 and #3, you MUST provide
your own BKCAL values and they MUST include
the right status.
Good luck with that.

50. Bias-Gain (BG) Function Block
OUT = (SP + IN_1) * Gain

51. Bias-Gain (BG) Function Block
Typical Use of BG Block
B/G Boiler 1
PIC B/G Boiler 2
B/G Boiler 3

52. Make your own PV on a BG block
 Some bias strategies require a “PV” for BKCAL_OUT
 Example:
– To optimize the use of a lower cost energy source, configure the
demand of the higher cost source using a BG block
– Higher Cost Demand = Total Energy Demand – Actual Lower Cost
Flow
 Use BG block for higher cost setpoint calculation
– Connect OUT of master loop to CAS_IN
– Connect (0 - actual MBTU / HR) of lower cost source to IN_1
– This will subtract the actual low cost value from the demand.
– Compute the “PV” of the BG block by summing the actual MBTU /
HR of each energy source.
– Use a CALC block to transfer the correct BKCAL_OUT status and
use the “PV” for BKCAL_OUT value.

53. Bias-Gain Function Block
 CONTROL_OPTS
– “Act on IR” (act on initialization request)
• If checked, when Bias/Gain Block transitions from non-automatic to
automatic, the current Bias will remain as the SP.
• If not checked, when Bias/Gain transitions from non-automatic to
automatic, an internal register is used to move from the actual Bias
from the current value to the retained Bias SP in the “Balance Time”
– “Use BKCAL_OUT With IN_1” – check if the OUTPUT of a
Controller goes to IN_1 AND you want it to operate in Cascade
with the Ratio Block
 FRSIBG_OPTS
– “Treat IN_1 as wild” –if True, IN_1 is treated as a non-cascade
input and if “Use_BKCAL_OUT With IN_1” is True, BKCAL_OUT
sub-status will be set to keep cascade closed.
Be careful with this one!

54. Ratio (RTO) Function Block
OUT = SP * IN_1 * Gain

55. Ratio Control
Typical Use of RTO Block
Main Flow
Ratio SP IN1
From RTO Block
Operator X
OUT
SP to
Manipulated FIC

56. Using the PV of a RTO block
 RTO blocks are not just for ratio control
– Use RTO blocks to compute setpoints that require a change
in engineering units
 Example:
– The OUT_SCALE of the master loop is in MBTU / HR
– The PV_SCALE of the flow loop in is GPM
 Use RTO block to convert from MBTU / HR to GPM
– Connect OUT of master to CAS_IN
– Connect the inverse of the heating value to IN_1
– Use GAIN for unit conversion (MLB to GAL and HR to MIN)
– Connect actual flow to IN
– The PV of the RTO will equal the actual MBTU / HR flow

57. Business Results Achieved
 PID block features can be used to significantly
improve the performance of your control schemes
 Providing advanced control strategies that do not
bump with mode changes:
– Prevents the controls from introducing upsets
– Gives the operators confidence in the controls
– Allows the operators to react quickly to process issues
 Preventing reset windup:
– Allows the controls to be more responsive when “changing
directions”
– Allows for more aggressive tuning without instability
 Bottom line: Better control performance = $$$$

58. Summary
 DeltaV has many useful control features of the PID
block
 Block Initialization is essential for good control
 If there is a connection to CAS_IN…
There needs to be a connection from BCKAL_OUT
 “Easy DeltaV” can get you in trouble with multi
cascaded loops unless you take care to connect up
the BKCAL’s correctly and check the right
CONTROL_OPTS and FRSIPID_OPTS.
 BG and RTO block are useful for providing much
needed BKCAL’s

59. Where To Get More Information
 EGUE Exhibit Area – Industry Solutions Group
 Emerson Process Management Education Services:
http://www2.emersonprocess.com/EN-
US/brands/edservices/Pages/EducationalServices.aspx
 Emerson Process Management, Industry Solutions Group
 DeltaV Books Online
 Emerson Process Improvement and Optimization Consulting:
http://www2.emersonprocess.com/en-
US/brands/processautomation/consultingservices/ProcessImprovem
entOptimization/Pages/ProcessImprovementOptimization.aspx
 Ask for a copy of this .FHX and play with the simulation.
 James.Beall@Emerson.com
 Barbara.Hamilton@Emerson.com
 Nikki.Bishop@Emerson.com

60. SAMA for Demonstration