1. Wireless Control Foundation
Terrence L. "Terry" Blevins
Deji Chen

2. Wireless Control Foundation
Chapter 1 - Introduction

3. Overview
The book is written for the process or control engineer who is familiar with traditional control but has little or no experience using a wireless transmitter or wireless valve.
The control system interfaces and wireless field devices described in this book are based on wireless standards for industrial settings and can be used in monitoring and control applications.
Multiple application examples are used to show what is required to utilize wireless control. Workshops are included in the book that explores key concepts associated with wireless control. The reader may view the workshop solution by going to the website that accompanies the book.
information is provided on how a wireless network may be integrated into a legacy control system and on how the PID may be modified for wireless control
One chapter of the book addresses how a dynamic simulation of the process and wireless field devices may be easily created in a DCS.

4. Overview (Cont) Chapter Description Introduction
History and Background 5
Wireless Field Devices
Commissioning Wireless Devices and Diagnosing Field Operation 25
Control Using Wireless Transmitters 47
Control Using Wireless Throttling Valves 77
Discrete Control Using Wireless Field Devices 111
Model Based Control Using Wireless Transmitter
Wireless Model Predictive Control
Applying Wireless in Legacy Systems
Simulating Wireless Control

5. History and Background
Chapter 2
History and Background

6. Evolution of HART
The HART protocol has evolved from a 4–20mA based protocol to the current wired and wireless-based technology
Includes extensive features supporting security, unsolicited communication of field device parameters and advanced diagnostics.
Diagnostics now include information about the device and the equipment that is being monitored.

7. Architecture of WirelessHART Mesh Networks
The gateway is the interface between the wireless network and the plant automation application host.
The gateway contains the network manager that controls join, configuration, maintenance and all other network management duties.
The security manager manages the keys used at both the network layer and the data link layer

8. Layered Structure of HART Communication Protocol
In WirelessHART networks, the communication stack on each device is organized in a layered structure.
Communications are precisely scheduled using an approach known as Time Division Multiple Access (TDMA).
Scheduling is performed by the network manager, which uses overall network routing information in combination with communication requirements from individual devices and applications.

9. WirelessHART Slot Timing
All transactions occur in slots following specific timing requirements, and each 10 ms time slot is further divided into several sub time intervals.
This figure shows one time slot and provides an overview of transaction timing

10. WirelessHART Key Model
Network devices implement industry standard encryption, authentication, verification, anti-jamming and key management.
The Network management Network (NWK) layer is responsible for mesh networking
Two different scenarios are shown: 1) a new network device wants to join the network and 2) an existing network device is communicating with the network manager.

11. WirelessHART Sniffer
A wireless “sniffer” may be used to collect the network traffic of a WirelessHART network.
A sniffer was use at the Separation Research Program (SRP) plant at the J.J. Pickle Research Campus of the University of Texas, and the data collected was used to study the network.

12. Separation Research Program Processing Equipment
The SRP is an industry supported consortium focused on fluid mixture separations. The SRP has continued to evolve through support from oil, chemical, biotech, biofuel, food, power generation and process manufacturing companies.
At this site a variety of WirelessHART devices are installed; pH and conductivity and technology, vibration analysis and control over wireless.
The WirelessHART installation has expanded to multiple networks extending across the process equipment, the lab, the instrument shop and the boiler house, which is located remotely from the main process plant.

13. Separation Research Program Processing Diagram
Recent projects include process technology such as CO2 separation illustrated in this figure.
The absorber and the stripper are 16.8 inches in diameter and are approximately 35 feet tall.
The absorber contains two beds of packing. Column temperature is measured every 12–18 inches, which helps to monitor column operations

14. Device and Network Summary
The HART tag and type for the devices installed at the Separations Research Program (SRP) plant are summarized in the first two columns in this table.
The final two columns show the device Nickname, a 2-byte identifier maintained by the Network Manager, and the identified neighbor devices that are installed at various locations through the Separations Research Program (SRP) plan

15. Network Topology
The devices included in this study are located in three locations: the main process area, the instrument area and the boiler house.
The boiler house is located over 300 meters from the main processing equipment and can only be reached through routing devices
The mesh forms automatically without any need for site surveys. The network topology as set up by the network manager after two days of use in this case study is shown in this figure.

16. Network Traffic Flow by Hour
For this field test data was collected by the sniffer over a 45 hour period. During this period over 750,000 packets were collected and analyzed.
During the initial two hours of operation, the network traffic was largely dominated by Advertisements.
Once the network forms, the largest portion of the network traffic is made up of measurement data. The network traffic summary is plotted by hour in this figure.

17. Exercise: Accessing a Wireless Gateway
This workshop provides several exercises that can be used to further explore the information that may be accessed using the built-in webpage provided with the gateway. In this workshop we will login into the gateway and explore the types of information that may be accessed. .
Step 1: Open the WirelessHART gateway webpage by typing the gateway IP address in a web browser. In response a login page will be displayed
Step 2: Type in the account name and password. In response the main web page will be displayed.
Step 3: Click on different nodes of the hierarchical tree on the left pane to view different information. For example, through this interface you may access a network overview, the published device values, the network configuration and the parameters of a device that are configurable.

18. Process: Accessing a Wireless Gateway
In this workshop some features are demonstrated for monitoring the performance of a wireless gateway. Interfaces accessed in the workshop are shown below.

19. Wireless Field Devices
Chapter 3
Wireless Field Devices

20. Wireless Devices - Process Industry
Most wireless field devices designed for use in the process industry are based on either the international WirelessHART standard IEC 62591, or the ISA100.11a national standard.
All products claiming HART Protocol compliance must be independently tested and verified by the HART Communication Foundation. Devices that pass this testing and are registered may display the logo.
The ISA100 Wireless Compliance Institute (WCI) has been established by ISA to certify device conformance to the ISA100.11a standard. Successfully passing the WDI conformance test is the basis for using the ISA100 Wireless Compliant logo and registration.

21. Certified Wireless Devices
WirelessHART
ISA100

22. Battery Replacement
The power modules used in wireless devices are designed to be periodically replaced as illustrated in Figure 3-3. The power module used in some devices is designed to be intrinsically safe, which allows field replacements without the need to remove the transmitter from the process.
The lithium-thionyl chloride battery cells used by many wireless devices provide high energy density, long shelf life and a wide working temperature range.

23. Example – Wireless Pressure and Temperature Transmitter
The communication update rate that is configured for a device has a direct impact on the expected battery life, as does the service temperature.
In most cases, the communication update rate may be selected by the end user. Typical examples of how update rate and operating temperature impact battery life are shown.

24. Using an Adapter to Access Device Diagnostics and Measurement
WirelessHART adapters and ISA100 adapters have been developed that access and wirelessly communicate diagnostic information. Such adapters use power drawn from the wired transmitter current loop.
An adapter can also be installed on a traditional wired transmitter for wireless access to the measurement values of devices used for monitoring or control. This approach may be especially useful when working with an existing wired transmitter or when installing new four wire transmitters that have a local source of power.

25. Commissioning Wireless Devices
Chapter 4
Commissioning Wireless Devices

26. Field Communicator
A Field Communicator is used to configure HART devices. WirelessHART devices are preconfigured using the same tools and methods used on wired HART devices. However, WirelessHART devices require the additional configuration of the Join Key and Network ID to join the correct wireless network.
A device uses the Network ID to determine which wireless network to join in a large installation spanning multiple process areas. Once the device has heard one or more neighbors, it uses the Join Key to encrypt the join messages exchanged with the network manager.
The network manager, in turn, authenticates the device and incorporates the device into the network.

27. Connecting a Field Communicator to a Wireless Device
The Field Communicator connects to wireless devices through the devices’ FSK (frequency-shift keying) communication terminals.
The Field Communicator connects directly to the communication terminals on a wireless device.
Once connected, the field communicator automatically polls for connected devices using the selected polling options.

28. HART Online Menu and Device Dashboard Online Menu
With many devices, an online menu that appears once a device connection has been established.
This menu displays critical process information that is continuously updated, including device setup, primary variable (PV), analog output (AO), PV lower range value (LRV) and PV upper range value (URV).
Depending on the device description, the first online screen may be a standard HART menu or a Device Dashboard menu.
For WirelessHART devices, Network ID and Join Key are set within the Configure menu.

29. 1420 Wireless Gateway Explorer Page
If a wireless device was configured with the Network ID and Join Key, and sufficient time for network polling has passed, the device should be connected to the network. To verify connectivity, the user should open the gateway’s integral web interface and navigate to the Explorer page.
This page will display the transmitter’s HART tag, Primary Variable (PV), Secondary Variable (SV), Tertiary Variable (TV), Quaternary Variable (QV) and Update Rate.
A green status indicator means that the device is working properly. A red indicator means that there is a problem with either the device or its communication path.

30. 1420 Wireless Gateway Network Settings Page
The most common cause of connection problems is incorrect configuration of the Network ID and Join Key. The Network ID and Join Key in the device both must match that of the gateway.
The Network ID and Join Key may be obtained from the gateway on the Setup>Network>Settings page of the web interface as shown.
The Network ID and Join Key for the entire network can be changed from this page; the method described in the previous section a Field Communicator is used for a device joining an existing wireless network.

31. Integration of Wireless Network with DCS System
Wireless networks are integrated into plant automation systems through the gateway. Several protocols including Modbus, OPC, and HART-IP are often supported.
Connecting the wireless network to the plant automation system may be achieved in a wide variety of ways with greatly varying levels of integration. An example of a fully integrated setup is illustrated in this figure.

32. Wireless IO Network in an Explorer View
In small networks, the gateway should be located near the center of the network. For large networks or applications that require the gateway to be mounted inside a control room or rack room with remote access points, it is best practice to build the initial network around the location of the access points. The network can then be expanded to reach remote areas of the process unit. This approach will provide a solid foundation on which to expand the network
In one example of a fully integrated systems, the Wireless I/O Network appears under the Control Network in an Explorer view and can support up to 120 Wireless Gateway nodes. This figure shows the Wireless I/O Network

33. Wireless Reconcile I/O Dialog
Once a wireless network is integrated into a host system, the next step is to connect the wireless devices with the control applications. This can be achieved in a large number of ways. For example, this is achieved with the “Reconcile I/O” procedure.
Reconcile I/O links wireless devices with those configured in the host system database. The host applications then access those devices and their data points via the database configuration.

34. Network Overview Display
The WirelessHART gateway is the primary interface for communicating with network devices and host applications.
The gateway collects and maintains cached response messages from all devices in the network.
The WirelessHART gateway is accessed through web pages. These web pages provide access to a wide range of diagnostics information, and with the right login credentials to a limited set of configuration capabilities. An overview of the gateway’s diagnostics is shown

35. Device States in the Network
The network overview display provides summary information on devices connected, devices reporting power failures, devices with naming problems and other top-level diagnostics.
More detailed information can be found on devices and join failures as well as other items. This figure shows the overall state of all the devices in the network.

36. Network Statistics Display
Another important diagnostic screen is network statistics.
Network statistics show the total number of transmits, receives, burst messages and lost packets across the entire network.
An example of the network statistics display is shown in this figure

37. Host Statistics
Network statistics between the gateway and the host system are another important diagnostic.
This figure shows the User Datagram Protocol (UDP ) network statistics between the gateway and the host system. The other host statistics are not shown

38. DeltaV Diagnostics
An important measure of wireless and wired networks is the host’s ability to monitor and diagnose the overall health of the network.
The Diagnostics view supported by the control system is a starting point to diagnose nodes (controllers and workstations) and subsystems for IO access in the control system.
An example of how problems related to wireless devices are reported in the diagnostics view is shown in this example where the Fisher DVC6000 Control Valve assigned to Channel 10 has Loop Current Fixed

39. Device Communication Statistics
The screen shown in this figure is launched from the diagnostic view.
The gateway communication statistics with a valve are shown in this example.

40. Device Manager
Asset Management Suite (AMS) Device Manager is an application that allows users to view and configure wireless devices online in a wireless network.
Control system applications such as AMS Device Manager are often used as an alternative or in addition to handheld field communicator
Both Device Manager and the wireless network could be integrated with the host system, in which Device Manager would access the devices through the host. This figure shows a wireless network hierarchy in Device Manager.

41. Device Diagnostics – DVC 6200 Valve Display
For a wireless device to join a gateway's self-organizing network, it must first be provisioned (configured) for that network. Once provisioned, the wireless device joins the network and appears in Device Manager.
To diagnose the device it is only necessary to select the device and proceed to the diagnostics display. This figure shows an example of the diagnostics display for a wireless Fisher DVC 6200 device.

42. The Wi-Analys tool accepts security keys through user input and uses this key to decode messages from the Wi-Htest suite designed to exercise WirelessHART devices, thus facilitating compliance assessment.
These messages could be those intended for the Wi-Analys tool, or legitimate WirelessHART commands from the Wi-HTest suite to the device that assign keys to the device.
The Wi-Analys suite will use the keys it possesses to authenticate or decrypt. Messages that fail are indicated with different colors.

43. Exercise: Device Diagnostics
This workshop provides several exercises that will show the diagnostic information that is available from a wireless network. In this workshop we look at diagnostics information from of a wireless network. It is assumed that the wireless network is already integrated into the control system and the devices are integrated with the control modules.
Step 1: To launch DeltaV diagnostics view click Start → DeltaV → Operator → Diagnostics.
Step 2: Expand the following nodes in sequence: Control Network, Controller nNode, Assigned Wireless I/O, Wireless Gateway, C01.
Step 3: Click on individual channels under C01, check respective parameter values, observe whether the Value parameter updates.
Step 4: Expand a channel node, click on the assigned wireless device under it and check its attributes.

44. Process: Device Diagnostics
This workshop is designed to illustrate diagnostic information that is available from a wireless network. An interface used in the workshop is shown below.

45. Exercise: Commissioning Wireless Devices
This workshop provides several exercises that will illustrate the steps to add a new field device to a wireless network. In this workshop a new wireless device is added to the control system and the measurement it provides is added to a control module. It is assumed that the wireless gateway has been added to the control system LAN and assigned to the controller.
Step 1: Configure a new wireless device using a field communicator. Enable the burst mode to publish data. Power it on and let it join the wireless network.
Step 2: In the control system explorer view of field devices, open the Reconcile I/O dialog box, find the new device and, drag and drop it to an unused channel.
Step 3: Create a new control module and, assign it to the controller. Add an AI function block and assign its IO_IN to the tag of the channel assigned to the new device.
Step 4: Download the controller.
Step 5: Open the control module online and observe that the value of the AI block periodically updates. The updates come from the burst data of the new device.

46. Process: Commissioning Wireless Devices
This workshop is designed to illustrate features that are typically available in commercial products to commission a wireless network. An example tree view used in the workshop is shown below.

47. Control Using Wireless Transmitters
Chapter 5
Control Using Wireless Transmitters

48. Measurement and Control Data Sampling Rate
To achieve the best control response, the rule of thumb is that feedback control should be executed four to 10 times faster than the process response time.
Most multi-loop controllers used in the process industry are designed to oversample the measurement by a factor of 2 to 10 to minimize delay being introduced by IO access.

49. Impact of Update Rate on Battery Life
When a wireless measurement transmitter is used in a control application, it is not practical to provide the same oversampling as a multi-loop controller with a wired transmitter because it quickly depletes the battery in the wireless transmitter.
A wireless transmitter that communicates a new measurement value every 8, 16, or 32 seconds typically has a battery life in the range of 3–7 years.

50. There is also an underlying assumption in traditional PID control that a new measurement is available each time control is executed and that control is executed at least four times faster than the process response time.
Depending on the process response time it may not be possible to provide measurement updates this frequently and still achieve a 3–7 year battery life.

51. PID Control – Wireless Measurement Update Four Times Faster Than the Process Response Time
The impact of wireless measurement update rate on control performance can be illustrated by considering a control application
Lambda controller tuning rules are applied to traditional PID control for a Lambda factor = 1.
Process Gain = 1
Process Deadtime = 2 seconds
Process Time Constant = 6 seconds

52. Wireless Measurement Update Rate Two Times Faster Than the Process Response Time

53. PID Control – Wireless Measurement Update Rate Set Equal to the Process Response Time

54. Wireless Measurement Update Rate Two Times Slower Than the Process Response Time
Wireless update time exceeds the process response time, the control response to setpoint changes and disturbances becomes oscillatory.
Only for applications such as temperature control and level control that are characterized by slow process dynamics is it possible to use wireless transmitter update rates that are four times faster than the process response time and still achieve 3–7 year battery life.

55. Many of the control techniques and guidelines established during the development of single loop digital controllers in the mid-‘70s are based on providing a capability that mimics an electronic analog controller.
With the introduction of battery powered wireless transmitters, such update rates are impractical. Thus it is necessary to re-examine how control should be structured for use with wireless measurements.

56. Implementations of PID Controller Reset
Manufacturers of DCS have approached PID implementation in a variety of ways.
Many commercial products create the reset component using a positive feedback network.
In a positive feedback network the time constant of the filter in the network defines the reset time in seconds per repeat.

57. Example – Process Response Exactly Matches Reset Network Filter Response
When the PID reset is implemented using a positive-feedback network, it is easy to see that the time constant in the filter contained in this network is a direct reflection of the process dynamic response.
Take, for example, a pure lag process where the PI controller is tuned for a Lambda factor of 1. On a change in setpoint, the PI controller output changes only once because the dynamic response of the filter exactly cancels the dynamic response of the process.

58. PIDPlus for Wireless Control
To provide the best control when a measurement is not updated on a periodic basis, the PID may be restructured to reflect the reset contribution for the expected process response since the last measurement update.
This PID implementation is known as PIDPlus.

59. PIDPlus with Continuously Updated Filter
To further enhance the response for continuous changes in setpoint, the implementation of the PIDPlus algorithm can be modified as shown in this figure.
PIDPlus tuning is based on the process dynamics (for example, RESET = process time constant plus deadtime).
PIDPlus reset automatically compensates for variations in the measurement update rate and slow measurement update rates.

60. PIDPlus Implementation
For those processes that require derivative action, the contribution to the PID output should be recomputed and updated only when a new measurement is received.
The derivative calculation should use the elapsed time since the last new measurement to account for the fact that a new measurement value is not available for each execution of the PID.

61. Control for Wireless Measurement
When the PIDPlus algorithm is used with a wireless transmitter in a control application, the performance will be comparable to that achieved using a wired transmitter.
Example: PIDPlus using wireless transmitter compared to a standard PI controller where the wired measurement value.

62. Response for Measurement Loss during a Setpoint Change
The reliability of WirelessHART device communication has been well established. Even so, in the event of communication loss, the expected control behavior is of interest.
The example compares loss of communication with a PIDPlus against a PID with a wired transmitter where the wired measurement is frozen for a period of time.

63. Response for Measurement Loss after a Process Disturbance
The response observed when the measurement was lost after a process disturbance is shown
As illustrated by these tests, the PIDPlus provides superior dynamic response under these lost measurement conditions.
PID response is significantly worse and may not be acceptable in many process applications.

64. Example – Enabling PIDPlus in a Control Module
In addition, in many common applications such as flow or pressure control of a liquid or gas stream, an update rate that is four times faster than the process response time cannot be achieved if there is a requirement for a 3–7 year battery life.
In such cases the PIDPlus should be used to implement control using a slower update rate such as 8 or 16 seconds.
When PIDPlus is available as a standard feature of the distributed control system, the PIDPlus capability is selected through an option parameter of the PID.

65. Disabling Filtering in the Control Path
A timestamp accompanies new measurement values that are communicated by a transmitter to the WirelessHART gateway.
However, some distributed control systems detect the communication of a new measurement when the value changes. If the PIDPlus uses this mechanism to identify a new communication it is critical that filtering is not applied in the module processing

66. Setting Module Execution Rate Example
When control using a WirelessHART measurement is implemented, the module execution rate should be set much faster that the communication update period.
For example, the module may be set to execute every 0.5 seconds even though the communication update rate is set to 8 seconds.
Scheduling the module execution in this manner can minimize any delay in a new measurement value being used in control. This is necessary since the module execution within the DCS is not synchronized with the measurement communication.

67. Single Use Bioreactor (SUB) with Wireless Instrumentation
The benefits of using WirelessHART transmitters with a single use bioreactor have been demonstrated by Broadley James, a major manufacturer of bioreactors for product development and production.
A skid was instrumented with a 100L SUB (Single Use Bioreactor) with WirelessHART pH, temperature and pressure transmitters
The bioreactor pH and temperature were controlled over a series of batch runs using WirelessHART measurements.

68. Bioreactor Process
A wireless pressure transmitter was used to monitor pressure within the bioreactor.
The pH measurement was communicated on a 1 second window communications.
The temperature was reported on a 2 second using continuous (periodic) communications.

69. Wireless Temperature Control Response in SUB Unit
A mammalian cell culture was used for each batch run.
For the purpose of comparison, wired pH and temperature measurements were also available during each batch run.
This screen capture shows the setpoint response of temperature control based on the WirelessHART input.

70. Wireless pH Control Response in SUB Unit
Similarly good performance was seen for pH control using the WirelessHART input.
The response to 0.05 changes in pH setpoint is shown in this screen capture.

71. Stripper Column at UT
During the development of the PIDPlus, the performance was also verified in several field trials where the PIDPlus was used for control with WirelessHART transmitters.
The control of the Stripper Column shown on the left portion of the picture was addressed in a field trial conducted at the J.J. Pickle Research Campus, University of Texas

72. Stripper Pressure and Steam Flow Control
Standard WirelessHART pressure and flow transmitters were installed to demonstrate and test control using the PIDPlus.
The control system was configured to allow the operator to switch between control using WirelessHART and PIDPlus and the wired transmitters and PID.

73. The stripper column pressure control is shown in Figure 5-26 for two periods of operation:
1. PID control of steam flow and column pressure using wired measurement transmitters.
2. PIDPlus control of steam flow and column pressure using WirelessHART measurement transmitters.
The same dynamic control response was observed, as illustrated in these screen captures. For these tests, the same tuning was used for both wired and wireless control.

74. Field Evaluation of Wireless Control
The control performance is shown for column pressure and steam flow control for PIDPlus control using WirelessHART measurement transmitters (Test 2) vs PID control using wired measurement transmitters (Test 1).
Comparable control performance was achieved using WirelessHART measurements and PIDPlus vs control with wired measurements and PID. However, the number of measurement samples with a WirelessHART transmitter vs a wired transmitter was reduced by a factor of 10 for flow control and a factor of six for pressure control.

75. Exercise: Control Using Wireless Transmitters
This workshop provides several exercises that can be used to further explore the control using a wireless measurement.
Step 1: 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.

76. Process: Control Using Wireless Transmitters
A simulation of two identical heater processes is used to compare the control performance of PIDPlus using a wireless transmitter and PID using a wired transmitter.

77. Control Using Wireless Throttling Valves
Chapter 6
Control Using Wireless Throttling Valves

78. 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.

79. 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

80. 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.

81. 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.

82. 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.

83. 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

84. 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.

85. 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.

86. 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.

87. 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.

88. 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%.

89. 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.

90. 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.

91. 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 4–10 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.

92. Field Test of Wireless Control

93. 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.

94. 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.

95. Setpoint Change Response for Wired Transmitter and Valve
The response to setpoint changes using a wired transmitter and wired valve in control is shown.

96. 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.

97. 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.

98. 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

99. Setpoint Change, Wired Transmitter and Wireless Valve
The response to setpoint changes using a wired transmitter and wireless valve in control is shown.

100. Disturbance Response, Wired Transmitter and Wireless Valve
The response to an unmeasured disturbance using a wired transmitter and wireless valve in control is shown

101. Setpoint Change Response, Wireless Transmitter and Wired Valve
The response to setpoint changes using a wireless transmitter and wired valve in control is shown

102. 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

103. Setpoint Change Response, Wireless Transmitter and Wireless Valve
The response to setpoint changes using a wireless transmitter and wireless valve in control is shown

104. 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

105. 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

106. 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

107. 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

108. 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

109. 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.

110. 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.

111. Discrete Control Using Wireless Field Devices
Chapter 7
Discrete Control Using Wireless Field Devices

112. Recycle Tank Level Control Using Point Measurement
A by-product that can be used as a feedstock within a manufacturing process can be created as the result of that process or another manufacturing process
To account for any imbalance when the recycle supply and is less that the process feed requirements, the recycle tank makeup stream maybe automatically regulated
A WirelessHART vibrating fork liquid level transmitter may be used to detect low level and a WirelessHART on-off valve used to regulate the makeup flow.

113. Control Module – Discrete Point Measurement
When the discrete level control setpoint, SP_D, is set to Auto (Figure 8-2), then on detection of low level the makeup valve is opened for a period of time determined by the ON_TIME parameter and then turned off.
Makeup is only needed to prevent the level from dropping below the low level sensed by the level switch.
This ensures that sufficient room is maintained in the recycle tank to accommodate surges in tank level when the recycle flow exceeds the feed flow.

114. Recycle Tank Level Control Using Continuous Measurement
A wireless continuous level measurement provides greater flexibility in structuring the control and provides a direct indication of level. For example, a wireless guided wave radar level transmitter can be used to obtain a continuous measurement of level.

115. Control Module – Continuous Level Measurement
In Automatic mode the makeup valve opens if the tank level drops below the low level target and closes when the level reaches the setpoint.
In manual mode operators can use the OUT_D parameter to open or close the valve. The example module illustrates the implementation of this level control based on a continuous measurement of level.

116. Storage Tank Temperature Control
There is often a requirement that storage tanks for plant feedstock or, intermediate or final product be maintained at a temperature that is required for pumping or processing.
Temperature control can be automated using a wireless temperature transmitter and a wireless on-off valve to regulate the steam used to heat the tank using a wireless temperature transmitter and wireless on-off valve.

117. TIC206 Module for Tank Temperature Control
If the mode of the temperature control is set to Auto, the discrete output to the wireless on-off steam valve is opened when the tank temperature falls below the setpoint value.
When the temperature reaches setpoint, the steam valve is turned off and remains off until the temperature drops by more than the one deviation limit.
When the temperature drops below setpoint by more than the DEVIATION value below setpoint the steam valve is opened again.
When the mode of TC206 is changed to Manual the operator may manually open and close the steam valve using the OUT_D parameter.

118. Gas-cleaning Tower
A gas-cleaning tower with a feedwater inlet/outlet system plays a key role in the production of titanium dioxide in a European chemical plant.
To automate flushing water and sand from the tower, an on-off valve with a 4320 wireless valve positioner mounted to an on-off valve was installed at the bottom of the tower. A 2160 wireless vibrating fork liquid level switch was installed to detect when the water level reached overfill conditions when the vessel was full and was ready to be drained.
On detection of an overfill condition, the control sends an “open” command to the wireless positioner to open the drain valve. After 30 seconds, it sends a “close” command to the valve positioner to complete the draining cycle

119. Wireless Control of Tank Temperature
At the AkzoNobel surfactants processing plant in Belgium, the fatty nitriles and amines products produced by the plant are stored in 40 tanks before they are shipped to customers. To facilitate loading the products into road tankers, the fatty nitriles and amines must be maintained within specific temperature parameters.
Four WirelessHART temperature transmitters have been installed so far (at the time of this writing) to control the temperature of four storage tanks.
Temperature is transmitted every minute to a wireless gateway and is then integrated into the existing DCS. The DCS automatically controls a simple On-Off steam valve that heats the tanks. The temperature of the tanks can now be maintained using this wireless closed-loop control, enabling the final product to be delivered at the appropriate temperature.

120. Pulse Duration Modulation
In many areas of the process industry, pulse duration modulation capability may be required to regulate field devices such as on-off valves.
This output capability may be applied to an on-off valve to be turned on for a precise period of time. The maximum time that the pulse output may be turned on in one request is determined by the length of the duty cycle.
The time over the duty cycle that the output is turned on determines the pulse width (% time on).

121. Increase-Decrease Control for Motorized Actuator
Motorized actuators may be used for applications that require larger valves may be preferred in some applications that require precise positioning of the valve. The motor is designed to run in a forward or reverse direction to open or close a valve.
The length of time the motor remains on and its direction of rotation determine how much the valve is closed or opened. This type of regulation is known as increase-decrease control
In these types of applications, the time-to-apply command can be used to tell the motor when to turn on and off..

122. Exercise: Discrete Control Using Wireless Field Device
This workshop provides several exercises that can be used to further explore wireless discrete control. In the workshop a module is used that addresses the tank temperature control using a wireless temperature transmitter and wireless on-off valve. The tank heat loss is a disturbance to control operation that can be adjusted in the workshop.
Step 1: Open the module that will be used in this workshop and observe the control and simulated processes.
Step 2: Change the mode of the discrete control block, TC206, from Manual to Auto and observe how the steam valve is regulated to raise the tank temperature. Does the tank temperature control allow the temperature to overshoot setpoint.
Step 3: Observe the variation in temperature and the frequency at which the valve must be opened and closed to maintain the temperature. Change the tank heat loss rate and observe the impact on the frequency at which the valve must be opened.
Step 4: Change the value of the Deviation parameter and examine the impact on temperature variation and the frequency at which the valve must open to maintain temperature.

123. Process: Discrete Control Using Wireless Field Device
A simulated storage tank is used to demonstrate discrete control of tank temperature using a wireless transmitter and a wireless discrete on-off steam valve.