Web of Things in an Industrial Environment
Leandro F. Rojas-Peña and Reinhard Langmann
University of Applied Sciences Düsseldorf, Josef-Gockeln-Straße 9, 40470, Düsseldorf, Germany
Keywords: Web of Things, WoT, Websocktes, Web-automation, WOAS, Automation Services.
Abstract: This paper summarizes the work around enhancing an existing Web-oriented Automation System (WOAS)
that provides automation services; to support Virtual Devices (VD) that communicate directly with automa-
tion components like industrial controllers via Websockets. The presented architecture is a Cyber Physical
System (CPS) oriented to production environments in the industry. After a short introduction a quick over-
view about the currently used technologies is presented. The central part of the work focuses on the imple-
mentation of the required interfaces on both sides of the system. The physical side uses a Programmable
Logic Controllers (PLCs) as automation device. In the other side JavaScript and PHP are used to develop
the client and server modules respectively. A simple demo application was created for the first tests and at
the time, some basically delay measurements were realized.
1 INTRODUCTION
In the last years the concepts and paradigms of Web
of Things (WoT), Internet of Things (IoT), and In-
dustry 4.0 has been quickly grown and expanded
challenging the technology and its applications. At
present, we find ourselves at the beginning of a
stage, which is characterized by so-called “Cyber-
Physical Systems” (CPS). These systems are a con-
sequence of the far-reaching integration of produc-
tion, sustainability and customer-satisfaction form-
ing the basis of intelligent network systems and
processes (Bloem, 2014).
Automation technologies are confronting big
challenges due to the increasing penetration of such
tendencies. The emphasis on the product portfolio of
industrial automation is expected to decline over the
next few years in the factory of the future. In con-
trast, the requirement for globalized service & sup-
port is set to gain importance, together with the cost
factors. The introduction of secure Cloud computing
technology enables access to relevant strategic data
via the Internet, which can be used to make deci-
sions in real time as well as boost the operational
efficiency (Langmann, 2013).
Many companies and projects has been focus on
developments to fulfil the new requirements regard-
ing to the Web-based control applications. Since a
few years many alternatives have been used to guar-
antee the short response time required in such appli-
cations using HTTP as standard protocol. HTML-5
brings improvements to the development of Web
applications; one of them is the Websockets (WS)
specification. WS provide an enormous reduction in
unnecessary network traffic and latency compared to
other technologies. It accounts for network hazards
such as proxies and firewalls, making streaming
possible over any connection, and with the ability to
support upstream and downstream communications
over a single connection. HTML5 WebSockets-
based applications place less burdens on servers,
allowing existing machines to support more concur-
rent connections (Kaazing). This makes it suitable
for many applications requiring fast and frequent
action in both direction client/server/client; like
those which involve multiple users communicating
with each other, or those where the server-side data
constantly change (Freeman, 2013).
As consequence, Ethernet is nowadays used as a
standard protocol for the factory floor and other
industrial applications. But it is important to note
that the timing is a quite critical in the industrial
environments networks. “Time critical” refers to a
system’s dependency on a deterministic latency - or
better, absolute knowledge of time to a very high
degree of accuracy. This is the major difference
between information exchange and control applica-
tions (Zarr, 2014).
The main objective of this development was to
upgrade the WOAS system to support Virtual De-
533
F. Rojas-Peña L. and Langmann R..
Web of Things in an Industrial Environment.
DOI: 10.5220/0005491105330539
In Proceedings of the 11th International Conference on Web Information Systems and Technologies (WEBIST-2015), pages 533-539
ISBN: 978-989-758-106-9
Copyright
c
2015 SCITEPRESS (Science and Technology Publications, Lda.)
vices that communicate directly with automation
components like PLCs via Websockets. The test and
demo scenarios as well a simple real application
were also part of the initial objectives.
2 RELATED TOPICS
This section will briefly introduce some related
concepts and technologies and its state of the art.
2.1 Trends on the Nowadays Web
Automation
Nowadays there are several topics that have been the
subject of numerous articles focused on this field.
These include Internet and Web of Things (IoT,
WoT), Big Data, Cloud Computing and Industry 4.0.
All of these trends involve a lot of devices net-
worked together and a lot of data available to do
things. They also include deciding whether data is
stored and applications accessed from the computer
next to you or from a server located somewhere else
(Oulton, 2014).
Industrial automation spans a wide range of con-
trol systems from simple Programmable Logic Con-
trollers (PLC) to Supervisory Control and Data-
Acquisition (SCADA) systems and distributed con-
trol systems (Joby, et al., 2011). Automation systems
frequently control multiple devices in a synchro-
nized fashion. PLCs generally are end nodes for
more complex control systems. They are simple to
program and these days; PLCs are microcontroller-
based systems that may have a procedural program-
ming interface. In any case, a typical PLC will offer
rugged I/O and real-time synchronization. Today’s
PLCs may have network connectivity as well. A
network does not affect the I/O side, but timing and
synchronization will be an issue (Wong, 2014).
Figure 1: Decomposition of the automation hierarchy by
CPS with distributed services.
The conventional automation hierarchy is in-
creasingly transforming into a flat automation
"Cloud" as Figure 1 shows. Service-oriented archi-
tectures (SOA) provide a good solution for creating
uniform interfaces, while allowing collaboration
from the field level to the enterprise level. Cloud
computing is the provision of jointly usable and
flexibly scalable IT services using IT resources via
networks. Typical features are provision in real time
as a self-service based on Internet technologies and
charges according to use. Cloud computing enables
users to redistribute from investment to operational
expense, while paving the way for completely new
business models and their prompt implementation
(Langmann, 2014).
Current automation systems such as process vis-
ualization systems, SCADA/HMI systems and pro-
cess control systems are proprietary and manufac-
turer-specific systems that are created with conven-
tional programming languages and mostly have
manufacturer-specific internal interfaces and data
formats, making them hardly to accept as an open
industrial model. Also the increasing standardization
and opening of interfaces and description methods
(OPC UA, FDT/DTM etc.) does not change the fact
of the unity of an automation system, but comple-
ment them only in the direction of openness of a
given environment. Not the systems themselves are
more open, but rather only the interfaces and de-
scription methods are more standardized and
opened. Only the new and standardized IT technolo-
gies with Web/Internet at the forefront established
the prerequisites for a spatially unlimited distribu-
tion of functions/services and are now also increas-
ingly interesting for automation technology (Lang-
mann, 2013).
2.2 WOAS
In general all functions which are required for the
execution of an automation system could be used as
services. These can be such simple functions as a
measuring algorithm, operating or visualization of
process data, but also complex functions from higher
levels (Figure 1) could be used as AS. Looking at an
automation system from this perspective there is still
some open points; the new automation structure is a
vision for the future. At present, no application-wide
systems are available on the market, which imple-
ment a CPS-based and service-oriented automation.
Between 2011 and 2014, however, the prototype
of a Web-based platform was created, which can
integrate worldwide distributed services also with
worldwide distributed CPS components (device
components) into a functional system (Langmann,
2013). This was within the framework of the R&D
project "Architecture and Interfaces of a Web-
Oriented Automation System (WOAS)" and in-
volved the participation of 10 industrial companies.
WEBIST2015-11thInternationalConferenceonWebInformationSystemsandTechnologies
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The WOAS platform can also be referred to as CPS
integration platform. On the client side (browser) the
platform is completely implemented in HTML5 and
JavaScript runnable in each browser and device.
For the CPS-based automation, the automation
devices (AD) like controls, sensors, actuators etc.,
can be considered as CPS components after adding
corresponding interfaces to the IP network. This
results in the CPS structures as shown in Figure 2
for different AD. A Virtual Device (VD), which
maps the real device in the virtual world, functions
as an interface from the CPS components to services
distributed in the network (Langmann, 2014, p. 133).
Figure 2: Automation Devices as a CPS components.
The VD is used to map the process data of an au-
tomation device via event-based channels onto Web-
or Internet-suitable objects in a uniform manner and
makes this available in a Web browser. Via integrat-
ed protocol or device gateways, any industrial inter-
faces can therefore be made available in the IP net-
work. For the process data transfer between a VD
and an AD via HTTP, a specific protocol was devel-
oped. The VD and the protocol- or device-gateway
together form a Web Connector for the AD as a CPS
interface.
This work describes the development and evalua-
tion of an integrated PLC Web Connector according
to a Type 1 VD (Figure 2) and its application in the
WOAS portal for creating Web-oriented automation
systems.
2.3 The WSS4ILC Library
Even when the Websocket (WS) protocol is not
anymore so young in the world of the standard Web
applications, it is so in the automation world, espe-
cially in the industrial controllers like PLCs. All the
more, most automation manufacturers provide a
Web server in their devices, but usually it is only for
managing purposes or simply do not support WS. To
be able to explode the benefits of the WS protocol in
the automation devices it is necessary its complete
implementation.
Fortunately, for the PLCs of the Phoenix Contact
family (ILC series) exist a library that provides a
basis implementation of the WS protocol which
main technical specifications are: data frames can be
up to 125 byte long; support the Ping/ Pong signals
and last one is a kind of limitation but enough for
this application; it allows only one client at a time.
The use of the library is a quite simple and re-
quires just to instantiate the WSS4ILC FB and set or
connects all input and output parameters properly
(Rojas-Peña, 2014).
3 SCIENTIFIC-TECHNICAL
CONTRIBUTION
Once covered a few obligatory topics around the
concepts related to this work it is possible to present
its global conceptual idea. Figure 3 shows how in-
dustrial controllers or any automation device in
general can be directly connected to the Cloud al-
lowing its control and/or supervision by any client
user using an Internet browser. Any user can access
the WOAS portal, but to access the services provid-
ed by the controller as a VD must be properly regis-
ter in the WOAS server and be subscribed to the
desired channels.
Figure 3: Conceptual idea.
3.1 The VD4PLC Concept
To be able to successfully fulfil the proposed objec-
tives it is necessary to properly understand the com-
plete structure of the architecture and its functionali-
ties. Figure 4 shows the connections between the
different parts of the automation system and the used
protocols. Note this corresponds to a single automa-
tion device, in this case, the industrial controller
used for the test, an ILC 150 ETH PLC. In this
sense, VD4PLC is the VD developed to allow
WOAS connects directly with industrial controllers.
Let’s take a closer look to each part of the sys-
tem and decide how to realize its implementation. In
one side is the automation device (AD) and in the
WebofThingsinanIndustrialEnvironment
535
other side the Virtual Device (VD) which is a JavaS-
cript dynamic Web page created by the WOAS sys-
tem kernel. Once a user logs in to the WOAS client,
an instance of the registered VDs is created. In this
process a WS communication is established between
both entities allowing the bidirectional data ex-
change. As a particularity for PLCs must be consid-
ered that the programming standard IEC 61131-3 do
not allows using the device’s Ethernet interface with
unknown entities. For this reason it was necessary to
find a way how to set the client's IP that is starting a
session in the PLC.
Figure 4: Structure of the system.
3.2 VD4PLC Interfaces
Implementation
To communicate both sides of the system correctly it
is necessary not only to use the WS protocol for the
communications between the PLC and the VD in the
WOAS client but also to implement a higher level
protocol to properly perform the data exchange ac-
cording to the WOAS specifications.
To be congruent with WOAS it is necessary to
process the commands Subscribe, Unsubscribe,
Read and Write (CCAD-VD, 2013) as they will be
sent by the WOAS server, or a test client during the
development phase. This process is implemented
very simple; the first byte in the sent/received data
string is a command field and codifies this function-
ality as Table 1 shows.
Table 1: WOAS commands.
Command Description
Subscribe
Data can be sent when they change or be
explicitly requested
Unsubscribe No data will be sent (stops sending)
Read
Explicit data update requested. A frame
should be sent with current value of one
or all subscribed channels
Write
Contains the updated/new values of one
or all subscribed channels
Also note that the frames with the commands
Subscribe, Unsubscribe and Read are considered
command frame’s that contains no process data,
while frames with de command Write are considered
as data frames and should contain process data.
With the use of the library WSS4ILC the heavy
work is already guaranteed in the side of the AD
because it provides the required WS server as basic
unit for the communication. It is only necessary to
implement the protocol previously described in the
AD or PLC and to interact with the process I/O as
the automation function requires.
The WOAS protocol was programed as a modu-
lar function block (FB), which in correspondence
with the WSS4PLC, use parameters for its configu-
ration, facilitating its portability. The used develop-
ment environment was PC WORX from the Phoenix
Contact company. At this point the interface with the
WOAS VD is ready to be used.
In the client side, the VD4PLC is programmed in
JavaScript and of course implement the above de-
scribed protocol as the other edge of the communi-
cation channel. Its main module is the file
vd4plc.js, including functions for sending and
processing messages to or from the industrial con-
troller. Those functions are:
sendToPLC: Prepares the messages (strings)
to be sent to the PLC when commands are
generated. Write commands with process da-
ta; the others without.
getFromPLC: Decode the messages (strings)
received from the PLC when an explicit read
command is generated or the automation de-
vice sends new process data automatically
due to its own functionality or data updates.
A third function has an important role in this
main module; it is the initialization function which
by means of Ajax requests to the WOAS server
setting the client IP in the PLC.
An IEC 61131-3 programmable industrial con-
troller needs to know the IP of its partner before
starting a connection. To overcome this problematic
or limitation it is necessary to fetch the client IP at
the moment the user logs in to the WOAS portal and
send it to the PLC. After, the WS library can connect
with the VD allowing direct data exchange between
the user somewhere in the Cloud and the automation
device (AD) in a certain physical process. Two
things must be done in this direction; the VD4PLC
also includes a PHP module (vd4plc.php) which
at the proper time fetches the client IP and sends it to
the PLC (function sendCmdToPLC) via HTTP.
Therefore the AD also requires a Web server; it was
also part of this development and with quite rudi-
mentary functionalities allows setting the IP for the
WOAS server
VD4PLC
JavaScript
PHP
WOAS client
VD4PLC instance
Java
Script
IOs
HTTP
HTTP
WS
PLC
Process
Web browser
WEBIST2015-11thInternationalConferenceonWebInformationSystemsandTechnologies
536
proper WS communication and also to know the stay
of the WS server in the WSS4ILC library.
4 TEST-DEMO APPLICATION
For the initial test a Phoenix Contact EduNet devel-
opment kit was used as an automation device. This
kit has a PLC of the low range ILC (150 ETH) series
of the same company. The digital inputs (DIs) are
connected to a block of switchers allowing its manu-
al operation. The analog input is connected to a
linear potentiometer and the analog output to a led
bar with 12 indications levels. To have a direct feed-
back of the hardware functionalities one of the DOs
is physically connected to one of the DI's.
A simple program was written to combine the
WSS4PLC library, the developed WOAS FB written
in the IEC 61131-3 programming language and a
dummy automation function that basically forward
the values of the inputs every time they change and
in the other direction reflex the received values to
the outputs. The idea was to simply show how to
create automation services that will be available for
the WOAS users in the Cloud.
Figure 5: Test Web page.
To test the WOAS client was used a standalone
Web page. This is possible because WOAS is com-
plete modular and the VD4PLC implementation can
be used out of it. This has a big advantage allowing
control automation developers to easily access its
process from the Web. The unique requirement is to
use Web server to host the PHP component of the
VD.
The Web page used as user interface to test the
developed system is a quite simple, see Figure 5.
Note some of the VD properties are shown in the
upper tables while the data channels equivalent to
the automation services provided by WOAS are in
the lower table. The two controls at the bottom facil-
itate the tests; a Status field indicating if the WS is
connected to the server or not and a Disconnect
button to close the connection explicitly.
In the middle there are three buttons which are
equivalent to the WOAS commands Read, Subscribe
and Unsubscribe respectively. Note that the Read
command is also triggered with a mouse click over
the channel Value column in the bottom table. For
the Write command it is necessary to click over the
button ‘W’ in the Channel Type column.
During the days of WEBIST‘2015 the link
http://vd4plc.ccad.eu will be available for online
tests with this demonstration application.
5 DELAY TEST
A delay test was performed to have an idea about the
time performance of the implemented system. This
test was realized in two different environments, the
first one in local closed scenario in intranet and a
second one in an open scenario in the Internet. In
both cases was used the same web page on the PC
and the same program on the PLC. The physical
measurements were based on the loopback connec-
tion of one output and one input on the automation
device which guarantees that certain information
received will be automatically echoed. Around 2500
messages (pulses) were sent; while some values
were computed: maximum and minimum delay, total
of pulses lost (no pulse confirmation received), and
the frequency distribution of the delay according to
the number of pulses with a same delay.
Figure 6: Delay analisys.
Figure 6 shows the results of both tests graph
WebofThingsinanIndustrialEnvironment
537
ically in different interesting time windows accord-
ing to the delay range in the abscise axis. The blue
curve (left) represents the obtained values for the
test realized in the intranet with a very good time
response. Most measured delays were between 23
and 37 milliseconds for a 72% of the total sent puls-
es. The minimum value is really small and can be
considered ideal for some applications. The maxi-
mum value is still acceptable for some applications
but has not so important significance because it is
just a punctual value.
The green curve (right) depict the values for the
test realized in the Internet with bigger delays and
also minor repetitions for smaller delays but also
acceptable for the used scenario. In this case, most
of the values were between 42 and 54 milliseconds
for a 56,4% of the total sent pulses. Here is also
interesting to note that between 55 and 79 millisec-
onds there is an important amount of values equiva-
lent to the 24,8% of the total sent pulses. The mini-
mum value is not so small like in the intranet test but
can be also considered ideal for some applications.
The maximum value is much bigger than in the other
test and should be considered significant depending
on the application to be used.
In both cases the values are considered very well
for “soft” real time applications in automation
(Home, 2014). The percent of delay values above
180 ms is only 0,9% in the intranet test and a 2.1%
in the Internet test. The lost pulses in both cases are
around 0.2 percent.
6 CONCLUSIONS AND FUTURE
WORK
The present work describes the implementation and
test of an automation system which is services ori-
ented and CPS-based to be used in the WoT as an
enhancement of the WOAS project.
The new developed Web connector for the PLC
(Virtual Device and WOAS Function Block) allows
to connect automation devices directly to the Cloud,
and therefore to be controlled and supervised by a
user with the valid and with the required rights from
the Cloud. The tests realized with a demo applica-
tion show the feasibility of the implementation to be
used in the production environments in the industry.
On the other hand the time measurements results are
very promising in comparison with previously tech-
nologies, suggesting this architecture to be used in
control automation Web-based applications where
the time constraints are considered soft with relative
small jitter on medium-low network's load.
There are still a lot to do in this direction. The
first steps are directed to allow the WSS to support
more clients simultaneously and at the same time
improve the WOAS protocol designed for the
VD4PLC allowing longer frames and better han-
dling of the modified or read data. As a generaliza-
tion both, the WSS library and the VD should be
extended to other types of industrial controllers with
the respective tests.
Cloud-based Industrial Control Services (CICS)
is a new R&D project focused to a complete Web-
oriented control system (see control level on Fig.1).
Industrial control programs according the standard
IEC 61131-3 should be executed as control services
from the Cloud. The described WoT solution for
PLC will be evaluated in the CICS project as one of
the possibilities for a direct connection of PLCs as
CPS component to a Cloud-based and distributed
control system.
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