Control Using Wireless Throttling Valves

1
Chapter 6

• Control Using Wireless Throttling Valves

2
Future Vision WirelessHART Throttling Valves in
Closed Loop Control

• Based on the broad acceptance of wireless
  transmitters, manufacturers have developed and
  introduced wireless actuators for on/off valves.
  These devices are being used to implement closed
  loop discrete control .
• In the future, it is envisioned that
  manufacturers will introduce wireless throttling
  valves that may be used with a wireless
  transmitter to implement closed loop control.

3
PIDPlus for Control with Wireless Transmitter
and Valve

• The PIDPlus features may be combined with the
  modifications for control using a wireless valve
  to address these different combinations of wired
  and wireless field devices.
• The changes in the PIDPlus for use with a
  wireless valve and wireless transmitter are
  illustrated.
• The use of the implied or actual response
  indication as the input to a positive feedback
  filter enables the reset contribution to
  automatically compensate for delays in the
  positioner response

4
PIDPlus Structured to Minimize Changes in Target
Valve Position

• The PID may be modified to minimize the number of
  changes made in the target valve position when
  control is implemented using a wireless valve and
  a wireless transmitter.
• To minimize the power consumed by the valve
  positioner, calculated PID output is transmitted
  to the wireless valve only if the criteria
  determined by non-periodic control communications
  have been met.
• The PID is typically scheduled to execute much
  faster than the minimum period at which the
  target valve position may be communicated to
  the wireless valve.

5
Wireless Communication to the Valve

• The key to applying non-periodic control
  communications is understanding that the PID
  reset calculation is implemented using a positive
  feedback network based on the implied valve
  position, which is communicated to the PID with
  minimal delay as the feedback in response to a
  change in the target position.
• Ideally, this feedback of implied valve position
  (i.e., the target position that the valve
  accepted and is working to achieve) would be
  communicated by the wireless valve back to the
  wireless gateway in the response to the target
  position write request.

6
Example Control Implementation Using Wireless
Valve

• A new WirelessHART command has been proposed that
  supports the inclusion of a time to apply field
  with the output value communicated to a wireless
  valve.
• This added field specifies a time in the future
  when the output value takes effect. The time to
  apply value is selected to ensure that the valve
  receives the output communication before this
  future time.
• Thus, it is possible to calculate the implied
  valve position based on the target position
  communicated to the valve and the specified time
  when the valve takes action on the new target
  position.

7

• The command sent to the valve will contain the
  new target value and the time that the valve is
  to act on the new target position.
• This time value will be based on the time at
  which the new target value was accepted plus the
  delay time configured by the user or set by the
  manufacturer.
• The sequence in which the AO output is processed,
  communicated to the valve and then acted on by
  the valve is shown in this example

8
Control Structure Used in Field Trial

• Field trails were conducted to evaluate a
  wireless positioner for a throttling valve
• In these field trails the functionality
  associated with determining the target to
  minimize valve movement and calculation of the
  external reset input used in the PID was done in
  the control module.

9
Test Module Control Using a Wireless Valve

• As part of the applied research into control
  using a wireless valve positioner that was
  conducted by Emerson Process Management in the
  spring of 2014, a module was created that
  allows control using a wireless valve to be
  tested in a simulation environment.
• Composites within the module are used to simulate
  the Controller Output Processing (using the new
  HART command), the communications and delay
  associated with the wireless gateway, and the
  wireless valve. In addition, a composite is
  provided to simulate the dynamic process.

10

• In the first two tests, the control performance
  was evaluated using a wired transmitter and a
  wireless valve vs a wired transmitter and a wired
  valve. Identical changes in setpoint and
  unmeasured disturbances were introduced into both
  control loops during the tests.
• In the first test, the wireless valve
  communication to the valve was set to 3 seconds
  and the delay in the PID seeing the valve
  response was set to 3 seconds in the simulation
  of wireless communication.
• In the second test, the delay to the valve and
  the valve response were set in the simulation to
  6 seconds.

11
Performance Using a Wireless Valve with a Wired
Transmitter

• During the test, statistics on the number of
  communications, valve movement and IAE were
  captured in the module by the PERFORMANCE
  composite.
• Stable control was observed for changes in
  setpoint and load disturbances using the wireless
  valve. Through the use of valve minimization the
  number of changes in valve target was reduced by
  a factor of 23.

12
PID Control Using Wired Valve and Transmitter vs
Wireless Valve and Transmitter

• The tests were repeated using a wireless
  transmitter with the wireless valve.
• The transmitter used window communications mode
  where the period was 6 seconds, default report
  time was 12 seconds and deadband in reporting was
  3.

13
Performance Using a Wireless Valve with a
Wireless Transmitter

• The results achieved for wireless control using
  PIDPlus with the modifications for the wireless
  transmitter and valve vs a wired transmitter and
  valve using PID are summarized in this table.
• Stable control was observed for changes in
  setpoint and load disturbances using the wireless
  transmitter and valve. Through the use of
  minimization of valve movement, the number of
  changes in valve target was reduced by a factor
  of 23.

14
Flow Lab Where Wireless Control Was Tested

• A prototype wireless valve was tested in one of
  Fisher Controls flow labs located in
  Marshalltown, Iowa using a DeltaV control system
  and its embedded PIDPlus algorithm.
• In these tests, closed loop flow control was
  evaluated using both wireless and wired flow
  measurement.
• Communications with the wireless valve used a new
  HART command that allows a time to apply to be
  specified.
• The PIDPlus external reset input was modified to
  allow delay to be used optionally to compensate
  for the time to apply. In addition, a new
  technique for minimizing valve movement was
  evaluated using a wired and wireless input to the
  valve.

15
Field Trial Summary

• The test results can be summarized as follows
• PID tuning was set strictly based on the process
  gain and dynamics. The fact that the tuning was
  never changed throughout the wireless test
  illustrates that the PIDPlus tuning is not
  impacted by transmitter and valve update rate and
  delay introduced by communications. Good control
  was achieved in all wireless valve and wireless
  transmitter tests using this tuning.
• Using a wired transmitter and valve and then
  applying valve minimization reduced the number of
  changes in valve position by a factor of 70 for
  0.1 second loop execution and cut total valve
  travel by over 50. Introduction of valve
  minimization had no impact on loop stability and
  had minimal impact on control performance less
  than 50 increase in IAE.
• The wireless transmitter update rate was set to 8
  seconds for most of the tests and introduced 410
  seconds variable delay in the flow measurement
  used in control. However, this had no impact on
  the stability of PIDPlus control and had minimal
  impact on control performance
• When a wireless transmitter was used with
  PIDPlus, the number of changes in valve position
  was reduced by a factor of 47 since the output of
  the PIDPlus only changes when a new measurement
  is received or the setpoint is changed.
• Changing the wireless transmitter update rate
  from 8 seconds to 16 seconds had minimal impact
  on control performance increasing IAE
  approximately 60 for setpoint changes.

16
Field Test of Wireless Control
17
Control Module for Wireless Field Trial

• Modules created for the field test allow the
  selection of a wireless valve and/or wireless
  transmitter in a test run and the selection of a
  modified DeltaV wireless interface to the
  Rosemount 1420 or the standard output cards to be
  used in control.
• The apply delay may be optionally selected to
  compensate for the delay in the time the target
  valve position is acted on when control uses
  wireless communication to the device.

18
Time to Apply Arrival During Test

• The time to apply was set to 8 seconds in all
  wireless valve tests. The chart in Figure 6-15
  shows a log of normalized Time to Apply as
  published by the modified 4320 over the course of
  testing.
• It shows when the command was received by the
  device in relation to when the new setpoint would
  be applied via the Time to Apply variable.
• Most commands were received before the Time to
  Apply but a few arrived late. It shows that the
  command had a range of unpredictable arrival
  times.

19
Setpoint Change Response for Wired Transmitter
and Valve

• The response to setpoint changes using a wired
  transmitter and wired valve in control is shown.

20
Response to Unmeasured Disturbance for Wired
Transmitter and Valve

• The response to an unmeasured disturbance using a
  wired transmitter and wired valve in control is
  shown.

21
Setpoint Change, Valve Movement Minimized, Wired
Transmitter and Wired Valve

• The response to setpoint changes when valve
  movement is minimized using a wired transmitter
  and wired valve in control is shown.

22
Disturbance Response, Valve Movement Minimized,
Wired Transmitter and Wired Valve

• The response to an unmeasured disturbance when
  valve movement is minimized using a wired
  transmitter and wired valve in control is shown

23
Setpoint Change, Wired Transmitter and Wireless
Valve

• The response to setpoint changes using a wired
  transmitter and wireless valve in control is
  shown.

24
Disturbance Response, Wired Transmitter and
Wireless Valve

• The response to an unmeasured disturbance using a
  wired transmitter and wireless valve in control
  is shown

25
Setpoint Change Response, Wireless Transmitter
and Wired Valve

• The response to setpoint changes using a wireless
  transmitter and wired valve in control is shown

26
Disturbance Change Response, Wireless Transmitter
and Wired Valve

• The response to an unmeasured disturbance using a
  wireless transmitter and wired valve in control
  is shown

27
Setpoint Change Response, Wireless Transmitter
and Wireless Valve

• The response to setpoint changes using a wireless
  transmitter and wireless valve in control is
  shown

28
Disturbance Change Response, Wireless Transmitter
and Wireless Valve

• The response to an unmeasured disturbance using a
  wireless transmitter and wireless valve in
  control is shown

29
Response to Setpoint Change

• The response to setpoint changes using a wireless
  transmitter and wireless valve in control with
  minimization of valve movement enabled is shown

30
Response to Unmeasured Process Disturbance

• The response to an unmeasured disturbance using a
  wireless transmitter and wireless valve in
  control with minimization of valve movement
  enabled is shown

31
Setpoint Change Response

• The response to setpoint changes using a wireless
  transmitter with a reporting rate of 16 seconds
  and a wired valve in control is shown

32
Setpoint Change Response, Wireless Transmitter at
16 sec, Wireless Valve, Two-Hop Network

• The response to setpoint changes using a wireless
  transmitter with a reporting rate of 16 seconds
  and a wireless valve in control is shown

33
Exercise Control Using Wireless Throttling
Valves

• This workshop provides several exercises that can
  be used to further explore the control using a
  wireless measurement and wireless valve.
• Open the module that will be used in this
  workshop and observe the control and simulated
  processes.
• Step 2 Initialize the Performance Index (IAE)
  and then change the SP parameter of both control
  loops by 10. Observe the control response using
  a plot of the setpoint, control measurements and
  output.
• Step 3 Note the IAE and the number of
  communications for the wireless and wired
  control. A significant difference should be seen
  in the number of communications for wired vs
  wireless control that were required to respond to
  the setpoint change.
• Step 4 Initialize the Performance Index and
  change the Disturbance input from zero to 10.
  Observe the response of the PID and PIDPlus to
  this unmeasured process disturbance.
• Step 5 Note the IAE and the number of
  communications for the wireless and wired
  control. A significant difference should be
  observed in the number of communications for
  wired vs wireless control that were required to
  respond to the unmeasured process disturbance.

34
Process Control Using Wireless Throttling Valves

• A simulation of two identical flow processes is
  used to compare the control performance of
  PIDPlus using a wireless transmitter and wireless
  valve to PID using a wired transmitter and wired
  valve.