Development of PC-Based SCADA Training System

Development of PC-Based SCADA Training System

Syed Umer Abdi, M.Eng.
University of Ottawa
Ottawa, ON, Canada
Email: [email protected]

Kamran Iqbal, Ph.D.
University of Arkansas at Little Rock
Little Rock, AR, USA
E-mail: [email protected]

Jameel Ahmed, Ph.D.
Riphah International University
Islamabad, Pakistan
E-mail: [email protected]



Abstract— This paper describes successful and cost effective design &
implementation of PC-based SCADA training system for the natural gas
transmission and distribution industry. The design provides robust and
automated environment for centralized control of a geographically scattered
process. Microcontroller based data acquisition (DAQ) control units for
distributed data processing are designed and serially connected with COM
port of the remote terminal units (RTUs) via RS485/232 convertor. The real-
time information gathered in RTU from sensors is fed to the master terminal
unit (MTU) through a dedicated communication link. Visual Basic (VB) is
used to develop Human-Machine Interface (HMI) environment for technicians
and operators. The in-house HMI development aimed at reliable, cost
effective, user friendly and easy to troubleshoot and update software. PC-
based SCADA training system and HMI were developed to meet the training
needs of Sui Northern Gas Pipelines Ltd. (SNGPL). The design work supports
future updates and provides opportunities of research in rapidly evolving
field of industrial automation and control.

Keywords— HMI, PC, SCADA, Training


Introduction

SCADA (Supervisory Control and Data Acquisition) system can formally be
defined as a system that allows the collection of data from remote sites
coupled with supervisory control over various decisions that need to be
made using the collected information [1]. SCADA provides the combination of
data acquisition and telemetry to incorporate information gathering,
transferring it back to central location, functioning essential control and
analysis, and exhibition of information on screens and displays for
operators and decision makers. Control actions required to tune the process
are then fed back to process [2]. SCADA is utilized for remote measurement
and control on modern industrial facilities in addition to critical
infrastructures [3]. In practice, SCADA is an industrial control system
which consists of an HMI, computer system monitoring, data acquisition and
processing, and advanced visualization [4,5] (Fig. 1).

The aim of the SCADA system is collection of real-time data to monitor
and control equipment and processes in a critical infrastructure. Examples
include oil and gas production, telecommunication, distribution and
transmission, pollution and soil fertility and moisture monitoring,
railways, industrial plant control, distribution and management of fresh,
irrigation and waste water, system control of communication network
(SYSCON), early warning siren system, process monitoring, transportation
management, mass transit system, energy management system, electrical power
distribution from nuclear, renewable resources, gas or coal fired, and so
on.


1. The general SCADA system [5].

SCADA system includes analytical instruments which senses process
variables across field data interface devices, or RTUs. The RTUs connect to
sensors, convert sensor signals to digital data, and transmit digital data
to the supervisory system. Host computers, called SCADA servers or MTUs,
enable human control and monitoring of the processes by keeping databases
and displaying statistical process control charts and reports. The HMI is
used to display process data to a human operator who has the ultimate
responsibility to monitor and control the process [6]. SCADA systems are
employed to collect real-time data from pipeline sensors, such as valves
and pumps, and present it to operators, who observe data from pipeline
control equipment [7].


1 Evolution of SCADA Systems

SCADA system has progressed with the increasing complexity of latest
computational technology. First generation SCADA systems lacked
connectivity to other systems and employed wide area networks (WAN) for
connecting with RTUs. The communication protocols used in those networks
were designed by RTU vendors and were proprietary in nature. Redundancy in
the first generation systems was furnished by using two mainframe systems,
i.e., dual primary and backup systems connected at bus level.

Second generation SCADA systems benefited from advancement in system
miniaturization and development of LAN technology, whereby multiple
stations with explicit functions could be connected to LAN and shared
information in real-time. A few distributed stations served as
communication processors for field devices/RTUs. Other units functioned as
operator interfaces, catering to the HMI for system operators. SCADA
systems' distribution utilities interconnecting multiple systems provided
more processing power at system level as compared to a single processor.

Third generation SCADA systems include the networked systems enabled by
the application of WAN/ Internet Protocols (IP) for communicating between
MTUs and the RTUs. This allowed separation of the communication function
from the monitoring functions. Disaster survivability enabled through
distributed processing has been a major improvement in distributed SCADA
systems. Today's SCADA system can survive complete loss of one or more
locations, which accords SCADA a super-critical function.


2 PC based SCADA Systems

PC-based SCADA systems are extensively used in oil and gas industry due
to the enhanced power and lower price of PCs, and extensive use of PCs in
field operations and offices. PCs are therefore preferred for SCADA
networks for making the process data accessible all over company's
operations. As PCs have become more powerful, it has prompted SCADA
software developers to add novel features to system. PC based SCADA systems
facilitate field operators to execute their work more proficiently and thus
assist in optimizing production wells. PCs deliver active interface to
monitor and control plants and compressors, and deliver real-time and
historical data to operators to facilitate them in developing strategies
for optimization of field operations.

A model that has significantly decreased design and execution time of
regular SCADA systems has been reported in [8] that comprises of an MTU and
a single RTU. Its core methodology is to place regular PC configuration on
both MTU and RTU sides of a dedicated communication link. Development of a
PC-based SCADA research and training laboratory was reported in [9]. PC-
based SCADA systems comprise PC-based RTU with customized software that
permits communication with MTU. The key benefits of PC-based SCADA are
reduced design and maintenance cost, significant reduction of development
time and implementation complexity, and its effectiveness with
sophisticated SCADA systems available in market.

Traditional SCADA systems utilize PC with proprietary software for data
collection from RTUs and displaying it through HMI. The architecture
requires PC to be available to serve and display data, and take HMI
requests for reliable operation. Additional software installed on SCADA PC
and remote PC permits remote access to multiple users. New features in
SCADA software includes the web server feature. It enables remote users to
access common HMI/SCADA views on remote computers that are serviced by MTU.
Furthermore, advanced tele-control system may propose embedded SCADA and
HMI at remote stations, thus permitting remote and local users the
proficiency to directly access individual outstations.


3 HMI in SCADA Systems

HMI, or the interface between industrial control systems and human
operators, is a vital element in the operation and configuration of
industrial facilities [10] (Fig 2). Balanced and well managed interfaces
results in business benefit and safety achievement; an unbalanced interface
spells potential danger and loss of control [11]. Engineers and operators
use HMI for set point configuration, control algorithms and to adjust
controller parameters. HMI also displays historical and process status
information. It allows human operators to observe the state of the process,
modify control settings to meet changing control objectives, and manually
override automatic control in state of emergency.

2. Interaction of Equipment, Process and People

HMI computer proficiently manages higher level control functions that are
dependent on central monitoring station of SCADA [12]. HMI design offers
wide functionality including graphical displays to deliver information
about the operation and status of the process to the operator in a format
that enables easy interpretation, and determining the need for action. It
facilitates inputs from operator to adjust the operation, perform machine
setups, and respond to events. It offers data logging and storage of
historical machine operating data for part traceability and analyzing
methods of quality improvement and productivity. HMI is also used to store
and retrieve machine setup data; trending to offer means for analyzing
visually the data on present or previous machine operation and alarm
function to provide notification to operator of abnormal operating
conditions and events [13].

The prime objective of HMI development is to support the operator in the
execution and management of an industrial process. A well-developed HMI
will enhance productivity of operator and process, rise uptime, and
facilitate in providing constant product quality. Requisite functionality
of HMI will vary depending on the type and complexity of product
manufactured, the type of equipment used, skill-set of operator, and degree
of automation of the process. Object oriented technologies and VB
programming language have gained worldwide recognition for designing HMIs.
Features such as COM, ActiveX and OPC are used with applications developed
in VB to solve these problems and offer flexible and economical information
delivery system.


4 SCADA Communication Links

Historically, microwave links have been used in SCADA communication
networks. Microwave radio link employs high frequency, line of sight (LoS)
terrestrial radio transmission medium using parabolic dishes as antennas.
Microwave link has advantages like high data rate and bandwidth
transmission, easy linkage with remote areas and, most importantly, a
constant dedicated connection, which is mandatory for SCADA systems. Sui
Northern Gas Pipelines, Ltd., uses Microwave Radio Link for their
nationwide network (Fig 3). Microwave repeaters regenerate, re-time, re-
synchronize and re-strength the signals and pass it to SCADA stations (Fig
4).


3. SCADA System in SNGPL.

Interference and noise are significant factors in planning and
installing data communication systems. As SCADA systems normally use
small operating voltage they are intrinsically vulnerable to noise.
Compared to radio links, optical fiber offers many advantages such as
high speed reliable communication, high security, data rate and
bandwidth; resistance against EMI, radio interference, and noise,
elimination of spark hazards, immunity against ground faults and
transients, etc. Optical fiber has high capital cost but low recurring
cost. Fiber optic cables also reduce the risk of interception and
modification of SCADA system's data [14]. SNGPL is using optical fiber
link in some parts of its network mainly in Punjab and KPK provinces of
Pakistan.


4. Microwave Repeater in SNGPL's SCADA Network.


System Architecture and Design

PC-based SCADA training system was designed and developed to meet the
training needs of SNGPL, the largest integrated natural gas distribution
and transmission company in Pakistan. The architecture of the PC-based
SCADA training system includes a central monitoring and control station
connected to PC-based RTUs via Industrial Ethernet (Fig. 5).


5. Architecture and design of SCADA System.


1 Visual Basic: WinSock Control

The Winsock control in Visual Basic 6.0 is used to connect multiple
terminals to each other and provide easy access to network services.
WinSock control of Visual Basic enables the connection to remote machine
and interchange data using Transmission Control Protocol (TCP). TCP can be
used to generate server and client applications. Similar to Timer control,
WinSock control does not possess visible interface at run time. Utilization
of Winsock in this project is to create client application that collects
user information prior to sending it to central server and to create server
application that acts as central collection point for data. TCP protocol
control is a connection-based protocol similar to telephone in which user
should establish a connection before continuing.


2 Industrial Ethernet

Industrial Ethernet protocol is commonly used in industrial environment.
Industrial Ethernet uses LAN UTP Cat 5 Cable with mesh and ring topologies
for communication between PC-based RTU & MTU. Industrial Ethernet has
robust devices and high level of traffic prioritization. Industrial
Ethernet equipment is designed for harsh environment to sustain high
temperature, high pressure, high voltage, vibration and shocks. Use of
Industrial Ethernet in SCADA systems (Fig 6) offers several advantages
including faster speed (1 G bit/s with IEEE 802 over Cat5e/Cat6 cables or
optical fiber), enhanced performance and communication distance, use of
standard access points, routers, switches, hubs, cables and optical fiber,
capacity of having 2 or more nodes on link (only possible with RS-485),
peer-to-peer architecture that may swap master-slave roles, and improved
interoperability. Network topology of SCADA system is static. Communication
paths between nodes are identified in advance.


6. Industrial Ethernet Application in SCADA System.


3 RS-485 and RS-232 Communication:

RS-232 serial link is commonly used for connecting DCE (Data Circuit-
terminating Equipment) and DTE (Data Terminal Equipment). RS485 is a two-
wire, half-duplex, multipoint serial communications channel; it employs a
differential balanced line over twisted pair, and can cover comparatively
large distances. RS-485 can be designed for either half or full duplex.
Half duplex typically uses one pair of wires; full duplex requires two pair
(similar to RS-232, which is used for single mode transmission). The
relevant features of RS-232 and RS-485 are compared in Table 1.

"PARAMETERS "RS-232 "RS-485 "
"Operation Mode "Single "Differen"
" "Ended "tial "
"Total No. of "1 Driver 1"32 "
"Drivers and "Receiver "Driver "
"Receivers on One " "32 "
"Line (One driver " "Receiver"
"active at a time " " "
"for RS485 " " "
"networks) " " "
"Max. Cable Length "50 ft. "4000 ft."
"Max. Data Rate "20kb/s "10Mb/s-1"
" " "00Kb/s "
"Maximum Driver "+/-25V "-7V to "
"Output Voltage " "+12V "
"Driver "Loaded"+/-5V to "+/-1.5V "
"Output " "+/-15V " "
"Signal " " " "
"Level " " " "
"(Loaded " " " "
"Min.) " " " "
"Driver Load "3k to 7k "54 "
"Impedance (Ohms) " " "
"Max. Driver"Power "N/A "+/-100uA"
"Current in "On " " "
"High Z " " " "
"State " " " "
"Slew Rate (Max.) "30V/uS "N/A "
"Receiver Input "+/-15V "-7V to "
"Voltage Range " "+12V "
"Receiver Input "3k to 7k ">=12k "
"Resistance (Ohms)," " "
"(1 Standard Load " " "
"for RS485) " " "


Comparing Parameters of RS-232 and RS-485 Cable


DATA ACQUISITION AND CONTROL UNIT DESIGN

Data acquisition and control units (DAQs) consisting of 8 digital inputs
and outputs and two analog inputs were designed and developed to connect
MTU to a PC-based RTU through RS 485/232 convertor and RS 485 Bus. A
photograph of the DAQ Card with Inputs/Outputs appears in Fig. 7. The
layout of the DAQ unit is shown in Fig. 8.


7. Final implementation of DAQ Cards with I/O's

Regulators: Series Voltage Regulators LM78XX were used to supply 05 and
12 Volts DC. Bipolar Analog Integrated Circuit UPC 1093 Adjustable
Precision Shunt Regulators were used. The output voltage can be set at any
reference voltage between 2.5v and 36v by two external resistors. These ICs
can apply to error amplifier of switching regulators.

Converters: 0832 8-bit Buffered D/A Converter was used having an advance
CMOS 8-Bit Multiplying D/A Conversion. 8 bit 0831 series successive
approximation A/D converters with 8 channels were used.

Sensors: LM 35 precision temperature sensors with LM 358 dual operational
amplifier were used as sensors. LM 358 consists of two independent, high
gain, internally frequency compensated operational amplifiers.

Triac BT 136 is a bidirectional thyristor commonly used in ac-phase
control. It can be considered as two SCRs connected in anti-parallel with a
common gate connection.

Octal D-Type Latch has 3-state bus-driving true outputs, buffered control
p-n-p inputs reduce dc loading on data lines. It is suitable for
implementing buffer registers, I/O ports, bidirectional bus drivers and
working registers.

Transceivers: Octal Bus Transceiver with 3-State Output SN74LS245 were
used which drive bus lines directly. It has p-n-p inputs that reduce dc
loading. Low-Power RS-485/RS-422 Transceivers have been used in hardware
design.

MAX485 is low-power transceivers for RS-485 and RS- 422 communication.
Each part contains one driver and one receiver. MAX232 Dual EIA-232
Driver/Receivers were used. MAX232 device is a dual driver/receiver which
contains voltage generator to provide EIA-232 voltage levels from a single
5-V supply. Each receiver converts EIA-232 inputs to 5V TTL/CMOS levels







8. Block Diagram of the DAQ Unit


9. Opto-Couplers: PC 817 Series High Density Mounting Type Photo-coupler is
used in signal transmission between circuits of different potentials and
impedances. MOC 3021 Opto-Couplers / Opto-Isolators were used for 250V
Photo Triac Driver Output.

Microcontroller: AT89C52 is a powerful microcomputer for providing highly
flexible and cost effective solution to many embedded control applications.
AT89C52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a
parallel address space to the Special Function Registers. Microcontroller
was programmed in C language. Flow chart of Source Code embedded in Micro
Controller is shown (Fig. 11).


Human-Machine Interface Design

This section describes the design and development of VB-based human-
machine interface (HMI) for the PC-based SCADA training system. Fig. 9
shows typical operation of the HMI in a SCADA system.



10. Operation of HMI in SCADA System

The prime objective of the HMI is to support operator in execution and
management of process. A well-developed HMI will enhance productivity of
operator and process, rise uptime, and facilitate in providing constant
product quality. Requisite functionality of HMI will vary depending on the
type and complexity of product manufactured, the type of equipment used,
skill-set of operator and degree of automation of process.

In this study a Visual Basic (VB) based HMI environment for PC based
SCADA Training system is developed that enables real-time monitoring and
control of industrial parameters and process variables. The central
monitoring and control / MTU display is shown in Figure 10. The proposed
HMI design allows real sense monitoring of pressure, temperature, level,
light, humidity, security switches, AC input, A/D and D/A conversion
values, whereas fire alarm, start/stop of water pump, speed control of DC
motor are carried out through emulation and human interaction through
dedicated Graphical User Interface (GUI).


11. VB-based central monitoring & control/MTU display


12. Flowchart for the 8052 Microcontroller program.


DISCUSSION AND CONCLUSION

PC based SCADA Training System was successfully designed and implemented
as required by the sponsors (SNGPL). This training system will facilitate
understanding of real-time monitoring and control of natural gas
transmission and distribution network by trainee engineers, technologists
and operators who desire hands on experience on SCADA Systems. DAQ cards
are with time stamping which would lead to SOE monitoring. It will also
provide better understanding of Industrial SCADA systems to undergraduate
students. Regular Training programs for industries in Pakistan like PARCO,
SSGCL, IRSA, WAPDA/NTDC have been proposed.

In house built HMI environment has shown promising results, and is cost
effective compared to more expensive proprietary software. Compared to
Lab View; Visual Basic based HMI Environment which is compatible with
Windows Operating System, is particularly designed to facilitate and ease
the learners in real time user-friendly environment. "Winsock" control in
visual basic performs the main function to connect multiple terminals to
each other. The interactive and descriptive HMI software has the ability
to remotely issue monitoring and control commands, generate reports,
fault diagnosis and troubleshooting can be carried out, modified, re-
installed and improved for future upgradation easily. Functional Block
Diagrams can be displayed in backend as well to program process variables
and industrial parameters.


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http://www.softwaretoolbox.com/ims99/swtoolboxims99final.pdf
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