Chapter 11
Simulating Wireless Control
Simulate Parameter – Analog Input Block

The current or digital outputs
of these transmitters and
switches are normally
accessed in a control system
using the analog and discrete
input blocks.

The normal processing of
analog and discrete input
blocks can be altered by
enabling the Simulate
parameter
Transfer of Simulation Parameters

Simulation modules
may be added without
modifying existing
modules if control
systems include the
capability for a module
to read and write
parameters contained
in another module.

Using this capability,
simulation modules
may read the output
value of analog and
discrete output
function blocks

.The results of the
simulation modules
may then be written
back to the simulation
input parameters.
Breaking a P&ID into Small Processes

Thus, a first step in
developing a process
simulation is to break
down the equipment
and piping shown on
the P&ID into multiple
processes that may be
simulated in one or
more simulation
modules.

An example of how the
equipment and piping
shown on the P&ID
may be broken into
smaller sets of
equipment that
represent processes is
illustrated in the
Recycle Tank example
is shown
Simulation Diagram for Recycle Tank Example

The circled areas of the P&ID will be simulated processes that are
interconnected and can be documented along with the simulated
wireless communications in a simulation diagram.
Simulation Module Construction for
Recycle Tank Example

The simulation diagram may be implemented as a simulation module
that references the existing control modules. The simulation module
construction for the recycle tank example is shown
Module LIC134 – Recycle Tank Level Control

For the recycle tank example, tank level control LC134 and makeup
on-off valve, LV134, are contained in one module, LIC134, as
illustrated
Module FIC133 – Reactor Flow Control

The flow loop to the reactor in the recycle tank example is
implemented as one module, FIC133, as illustrated
Flow Composite

It is appropriate to design a process simulation to duplicate the step response.
For example, a filter block, a deadtime block and a multiplier block may be
used to simulate the process deadtime, time constant and gain of a single
input-single output (SISO) self-regulating process. The construction of the
composite used to simulate the makeup flow through the valve in the recycle
tank is shown in this example
Recycle Tank Level Simulation

The simulation of an integrating process may be created using a combination
of standard function blocks and a calculation block to implement the recycle
tank level simulation shown in the Simulation diagram
COM_TRANS Composite to Simulate
Communication of a Wireless Measurement

A single composite may be created to simulate the communication of a
measurement value from a wireless transmitter to the gateway and its access
by the control system.
COM_VALVE Composite for Simulating
Communications to a Wireless Valve

The wireless communication of target position to an on-off valve and a
throttling valve may be simulated using a single composite.
Example Simulation Interface

Some control systems
provide simulation
environments that allow
process simulation
modules and control
modules to provide faster
than real-time response.

Such tools may also allow
the input block’s Simulate
parameter to be enabled
or disabled in all modules
or in selected modules
with one click of a button.

This is an example of the
interface provided for such
a simulation environment
Exercise: Simulating Wireless Control
This workshop exercise is designed to further explore the implementation of the process and
wireless communication simulation for a recycle.

Step 1: Open the module that simulates the recycle tank process and wireless
communication and compare this to the P&ID shown below.

Step 2: Examine the off-line and on-line view of the composites that were created to
simulate the wireless communication from a transmitter to the control system. Examine
the composites created to and to a simulation the communication of the target valve
position to the wireless valve.

Step 3: Using a trend of the tank level, the on-off valve position and the flow to the
reactor, examine how the on-off recycle valve is manipulated by LC134 to keep the tank
level from going below a level setpoint..

Step 4: Adjust the setpoint of FIC133 to change the flow rate to the reactor. Using a
trend of the flow measurement and valve position, examine how PIDPlus regulates the
valve to achieve the new flow setpoint. How does the flow change impact the level
control?

Step 5: Reduce the recycle flow input and observe the impact on how frequently the
recycle flow is activated.
Process: Simulating Wireless Control
This workshop exercise is designed to show how a simulation of a process and associated
wireless field devices may be constructed and used in control system checkout. A recycle
tank is used as a process example.
First Order-Plus-Deadtime Process

Many of the basic thermal and
physical mechanisms
reflected in the design of
process equipment – such as
heat transfer or the blending
of gases or liquids – tend to
provide a first order response
to input changes.

In addition, because of
physical equipment size,
some transportation delay is
often seen in the output
response
Heater Example – First Order-PlusDeadtime Process

For purposes of analysis
and control system design ,
the operation of the process
equipment that makes up a
plant can usually be broken
into processes that are
characterized as having a
first order-plus-deadtime
response.

One example of a process
that may be characterized
as having a first order-plusdeadtime response is a feed
stream heater
Process Made up of Three Non-interacting Lags

Multiple mechanisms
working together within a
process often combine to
provide what may be
approximated as a first
order-plus-deadtime
response, even when no
transport or measurement
delay is involved.

This example illustrates a
process that is made up of
three lags in series (a
third-order system) but can
be approximated as a first
order-plus-deadtime
process
Approximating Higher Order Systems

In this example, a
change in the output
of a lag process
begins immediately
when the process
input changes.

However, the
combined impact of
the three lag
processes in series
gives a level output
response that closely
approximates the
response of a first
order-plus-deadtime
process
Integrating Process Response

When an input to an
integrating process
changes, the output may
not begin to respond for a
period of time because of
measurement or transport
delay.

Thus, one parameter that
may be used to
characterize an integrating
process is the process
deadtime.

Once the process output
begins to change in
response to a change in
input, the observed rate of
change in the output is
used to characterize an
integrating process.
Example – Integrating Process

Integrating processes are also
described as non-self-regulating
processes.

An example of an integrating
process is a tank in which the
flow into the tank is the
manipulated input, the tank
level is the controlled output,
and the discharge from the tank
is a gear pump.

In this process, the outlet flow
rate is determined by the speed
of the gear pump and thus is
not affected by the tank level.
Simulation of a Multivariate Process

When the response of a process that has multiple inputs and/or outputs is
addressed, the assumption made in simulating the process by step responses
is that the process is linear and possesses the two properties of superposition
and homogeneity. These properties are the basis on which the process output
of a multivariable process may be represented by the sum of the step
responses for a change in the process inputs, as illustrated. Every process
output is the sum of input actions.