- Introduction
Contemporary Industrial Control Systems consist
of the following components:
(a)
A
PLC, which communicates with field equipment through a variety of telemetry
devices
(b)
A
SCADA System, which reads the values stored in memory locations (Tags) of PLC
and provide a Human-Machine Interface (HMI) for users to monitor the various
Plant Parameters in real-time
(c)
An
MIS (Management Information System) which captures the data from PLC or SCADA
and stores it in a Database. The user can view historical data as well as near
real-time data in form of various Reports and Trends.
2. System Description
A simple view of the architecture is as
follows:
· The data from an Industrial Plant is
communicated to PLC through a variety of Telemetric Systems.
· The data from PLC is transferred and
archived in the MIS Database either through SCADA or through OPC Software.
2.1 Data Transfer through SCADA / HMI
In case of data transfer through
SCADA, the steps traversed are as follows:
o
Step
1 à Scripts written in SCADA / HMI fetch the data
from PLC through SCADA Server, to either display in HMI in real-time, or to
forward to MIS
o
Step
2à The data is temporarily stored in SCADA / HMI
Database in designated database tables
o
Step
3 à Global Scripts written in SCADA / HMI fetch
the data from the SCADA / HMI Database
o
Step
4 à The data is stored in MIS Database based on
the data rate set in SCADA / HMI Scripts, or on the basis of triggering of an
event.
Here, the SCADA / HMI carries out two major
functions – real-time updating of HMI Screens, and data transfer to MIS
Database from the SCADA / HMI Database.
2.2 Data Transfer through OPC
In case of data transfer through
OPC, the steps covered are:
o
Step
1 à OPC Client maps the PLC Tags with Columns in
MIS Database
o
Step
2 à OPC Client transfers data from PLC to Database
directly
In this case, SCADA / HMI carries out only one
function – real-time updating of HMI Screens. The task of data transfer to MIS
Database is handled by OPC Client Software.
3. Functional Classification of SCADA – MIS System
Setting up a SCADA – MIS infrastructure
involves the following different types of activities / skill-sets:
(a)
Engineering
o
This
involves the overall design of the System including:
§ Liaison with Client and various
Teams, facilitation
§ Industrial Plant Design
§ Telemetry Design
§ Selection of PLC & SCADA
§ Selection of Infrastructure,
Hardware & Networking for the System (with inputs from other teams)
§ Design of MIS Output Requirements in
form of Reports and Graphs
(b)
PLC
Programming
o
This
involves assigning PLC Tags to various Telemetry Devices. The PLC has a dual
role – acquiring data from the field, and sending control / actuation commands
to devices in the field. The PLC programming is done through SCADA Interface:
§ Plant Control Design
§ PLC Programming
(c)
HMI
Designing & Development
o
This
involves creating a graphical mock-up of the Plant on the Computer, and associating
tag values to the mockup and screens. Data from PLC is rendered on the screens.
The functions involved here are:
§ HMI Screens Design
§ Programming in HMI for data import
from PLC
§ (In case OPC is NOT provided)
Scripting in “Global Script” to transfer data to MIS Database
(d)
MIS
Development
o
This
involves creating a Web or Windows Application which fetches data from SCADA or
OPC and archives it in the Database. Reports and Trends are generated from the
archived data. The functions involved here are:
§ Database Design & Development
for MIS
§ Application Development for MIS
§ Generation of Reports and Trends
§ Interfacing with SAP / ERP
4. Workforce Allocation
The Workforce allocation for development of
SCADA – MIS System is shown in the figure below:
5. Recapitulation & Concluding Remarks
Building
an integrated SCADA – MIS System involves a number of teams with diverse
skill-sets who work together to create an Industrial Control System. The key
for success lies in each team understanding the broader view of the project in
hand, and a detailed understanding of their function area.
