Chemical Engineering January 2023 - 40

function blocks, IEC 61499 eventbased
programming, IEC 62714 (AutomationML)
for control applications,
and DMTF Redfish for systems management.
The connectivity framework,
information and exchange
models are based on IEC 62541
(OPC UA). Notably, the OPC Foundation
has taken a step beyond the
liaison agreement by joining OPAF as
a member.
The benefits of standards deployment
are far-reaching. The latest
O-PAS version tightly defines and
controls system data and requires
uniform alarm reporting. Yokogawa's
Dave Emerson, who is co-chair
of OPAF's Enterprise Architecture
Working Group, explains it by saying
that in the past, each supplier used
to publish alarms and event conditions
in different formats, so users
had to waste time with different
types of messages. Now, consistent
reporting means they can save time.
Scope and vision
O-PAS enables the development
of systems composed of cohesive,
loosely coupled, severable functional
elements from independent
suppliers. The elements are easily
integrated via a structured modular
architecture. O-PAS does not define
the functional intellectual property
(IP) in the products; the IP can remain
proprietary to their suppliers.
Instead, the objective is to define
open standard interfaces. Interoperability
is the key.
As shown in Figure 1, the O-PAS
scope encompasses today's distributed
control systems (DCS) and programmable
logic controllers (PLC) for
continuous and hybrid process industries.
Out-of-scope are business
systems and communication protocols
between the input-output (I/O)
and field instruments. OPAF also decided
that safety instrumented systems
(SIS) would be out-of-scope
because there must be separate and
independent combinations of sensors,
logic solvers and final elements
to achieve required safety integrity
levels per the ISA84 and IEC 61511
standards.
An Open Process Automation
(OPA) system is a software-defined
control system. It is an open system
with all the benefits of a traditional
DCS or PLC system and more -
but without the limitations resulting
40
FIGURE 1. The scope of the O-PAS includes the DCS, PLC and manufacturing execution system. Business
systems, safety instrumented systems and field devices are outside the O-PAS scope
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from supplier hardware or software
locking. End-users or integrators
can design, operate and expand
functions with a wide range of interoperable
software and hardware
capabilities from multiple suppliers
and technologies.
By decoupling hardware and
software and employing a serviceoriented
architecture, the necessary
software functions can be situated in
many different locations or processors.
Not only can software applications
run in most hardware, but they
can also access any I/O to increase
flexibility when designing a system.
Figure 2 shows a reference OPA
architecture with O-PAS-compliant
products and non-compliant or legacy
products. A realistic scenario for
many end-users is to " start small, "
using a hybrid system with a combination
of OPA and proprietary components,
followed by a steady transition
from the legacy system to one
that is completely open, interoperable
and sustainable.
In an OPA system, most applications
and workloads are containerized
to run flexibly and in an interoperable
manner, utilizing the O-PAS
Communication Framework (OCF).
The OCF provides a secure, standardized
interconnection between
O-PAS-compliant software functions.
Based on the OPC Unified
Architecture (UA), the OCF provides
protected, standards-based, reliable
data transport.
The distributed control node
(DCN) is considered the fundamental
O-PAS building block. An edge
device, it is a scalable controller, I/O
or gateway device that can handle
I/O and computing functions. Since
hardware and control software are
decoupled, the exact function of a
particular DCN is up to the system
architect. A DCN consists of hardware
and system software that enables
it to communicate on the OCF
and run control software. A DCN can
be hardware or virtual. A system can
use a few or several thousand DCNs.
Device suppliers are allowing endusers
to add, configure and program
the software components of
the hardware devices based on their
requirements. In order to make the
device visible as a DCN to the rest
of the system, the O-PAS Communication
Interface (OCI) software layer
can be added as an embedded application
to any such non-compliant,
flexible architecture-based device.
The advanced computing platform
(ACP) enables DCN functionality,
but includes scalable computing
components, such as CPU cores,
memory and storage media to handle
applications that require more resources
than are typically available in
a DCN. ACPs may also be used for
applications that cannot be easily or
efficiently distributed. ACPs can be
on-premise servers or in a cloud
Gaining momentum
O-PAS is gaining momentum on a
daily basis. Don Bartusiak, co-chair
of OPAF and president of Collaborative
Systems Integration has reported
that OPAF has 110 organization
members, as of the beginning of
Yokogawa

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