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Control Using Wireless Throttling Valves

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Title: 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.
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