Transcript DeltaV Control Performance Suite

Chapter 10
Applying Wireless in Legacy
Systems
PID Support for External Reset

When the PID supports external reset capability, a parameter is
provided to select whether the PID output or an input to the PID is
used as the input to the positive feedback network to calculate the
reset component of the PID.
Use of External Reset in Override Control

Support for external reset becomes necessary for implementing
override control. In this case external reset is enabled and the output
of the control selector is the external reset input to the PID block. used
in the override control.
Construction of PIDPlus Capability

In a legacy control system it is possible to construct PIDPlus capability
if the PID supports external reset. This is done by setting the Reset of
the PID to a value that eliminates the impact of the filter in the positive
feedback network and then constructing the external reset input to
duplicate that used in the PIDPlus
Example – External Reset in
Foundation Fieldbus PID

PID function blocks based on the Fieldbus Foundation specification may use
the BKCAL_IN parameter for the external reset input. For example, in one
manufacturer’s implementation, the use of BKCAL_IN as the external reset is
enabled by selecting Dynamic Reset in a PID parameter, FRSIPID_OPTS.
When external reset is enabled the BKCAL_IN value is used in the positive
feedback network rather that the PID output
Composite for Calculation Outside the PID

As a starting point in
constructing the
required calculation
outside of the PID, a
composite block
EX_RESET was
created that
contains parameters
to support
connection with the
PID block and a
calculation block
Composite Created to Detect New Measurement

A composite block may be created to set a flag when a new
measurement is detected based on a change in value. An example of
the composite NEW_VAL that was created to detect a new
measurement
Enabling External Reset in the PID

When control uses a wireless measurement then the EX_RESET and
NEW_VAL composites can be added to the control module and
external reset can be enabled in the PID as illustrated.
Exercise: Adding PIDPlus to Legacy Control Systems
This workshop provides several exercises that are used to explore how PIDPlus
functionality may be added to a control module in a legacy control system and then tested in
a simulation environment. In this workshop it is assumed that the PID supports external
reset.

Step 1: Open a module that contains a standard PID function block and examine the
parameters of the PID block that are used to enable external reset capability and to
connect the external reset input. Enable external reset in the PID.

Step 2: Identify the two composites that were added to the module that enable the PID
to provide functionality that is equivalent to PIDPlus (for PI control). Examine the
construction of these composite blocks.

Step 3: Examine the parameters and composite block that are used to simulate a first order- plus- deadtime process and wireless communication..

Step 4: Enable wireless control in the composite, switch the PID to Auto and on a trend
observe the response to changes in setpoint and process disturbances. Disable
wireless control and on a trend observe the response for a change in setpoint and
process disturbance .
Process: Adding PIDPlus to Legacy Control Systems
This workshop is designed to illustrate how PIDPlus capability may be added to a legacy
control system. The resulting module is shown below.
Gateway Connection with the Controller

The gateway supports
both Modbus remote
terminal unit RTU over
the RS485 serial port and
Modbus Transmission
Control Protocol TCP
over Ethernet.

It functions as a subdevice on the Modbus
network and must be
polled by a Modbus
master or client (host
system).
Gateway Terminal Block Diagram

The gateway is wired to an RS485 bus which typically leads to a serial
I/O card or a Modbus I/O card. The interface allows a maximum of 31
gateways to be connected to a single I/O card in this manner. The
Modbus connectors in the gateway terminal block are shown below
.Modbus Communications Page

It is important that the
Modbus communication
settings in the gateway
match the settings in the
controller I/O card. The
Modbus communication
settings can be found by
navigating to

Setup>Modbus>Commun
ications in the gateway’s
webpage as shown
Modbus Register Mapping Interface

After configuring
communications, the next
step is to configure register
mappings.

Register mapping is the
process of assigning
parameters from wireless
field devices to Modbus
registers. These registers
can then be read by a
Modbus master or client.

The Modbus register
mapping interface can be
found by navigating to
Setup>Modbus>Mapping in
the gateway’s webpage as
shown
Typical System Architecture Using
Security Setup Utility
To connect the gateway with a
workstation, a Security Setup Utility
must be installed in the workstation
that is linked to the gateway.
The Security Setup Utility enables
secure communications between the
gateway and the host system, asset
management software, data historians
or other applications.
The Security Setup Utility can support
multiple gateways at once and each
proxy can support multiple client
application connections. A typical
system architecture using the Security
Setup Utility is shown.
OPC Browse Tree

A list of device tags
may be accessed
using the OPC
Browse Tree. This
speeds up the work in
the site integration
phase.

The tag count is the
basis for estimating
the cost of integrating
the asset health
information and
alarms into the DCS.
OPC Mirror Connecting Two OPC Servers

OPC Mirror connects OPC servers on multiple control systems and
enables bi-directional data traffic from one system to another .

OPC defines two kinds of applications: servers and clients. Servers
provide data services to control systems, industrial buses or
proprietary devices. The OPC proxy for the gateway is also a
server. Clients access servers to make use of their data.
Map Parameters in OPC Mirror

OPC Mirror's
standard Windows
interface makes it
easy to learn and
requires no custom
code to transfer data
between all standard
OPC systems.

The user interface
(UI) mapping
parameters from both
servers is shown.