Question

What are the four major components of a SCADA/ICS System?

Draw a simple graphic to describe their relationship (e.g. flow chart)

Answer 1

SCADA stands for Supervisory Control and Data Acquisition. In this type of system, first data is collected from different sensors located at various industries, load centres and remote or inaccessible locations and then data is sent to central computer which manages and controls the data. It consists of number of remote terminal units (RTUs) by which the data is collected and sent to central computer through communication link (wired or wireless). With the help of the data, central computer continuously monitors the process and have real time control over the system operations and it provides automatin and protection.

The four Major components of SCADA system are :

1.Sensors :- The function of sensor is to collect the data from remote locations and make users able to measure it. Usually A/D converters are employed between sensors and Remote Terminal Unit (RTU). The output of sensor may be analog or digital. SCADA systems contain different type of sensors.

For e.g they can measure inputs (filling of fluid or gas in a tank) or outputs (preasure from the release of fluid or gas). Analog sensors sense continuous change of a signal and provides accurate measurement. Digital sensors measure "discrete inputs" e.g. detects the alarm conditions which can be reported as on or off.

2. Conversion Units:- After getting data from sensors, conversion unit converts it into digital form which is then sent to user. There are two types of conversion units in SCADA depending upon applications.

a) Remote Terminal Unit (RTU) :- RTU is the main component which has direct connection with various sensors. This unit is used to transmit terminal data to the supervisory system and receive the message from the central system to contro the connected objects.

b) Programmable Logic Controllers (PLC) :- These are also connected to sensors for collecting output signals and convert those signals into digital format. It has advantages over RTU like flexibility, configuration, versatile and affordability.

3.Master Units (MU) :- Master Unit acts as the heart of SCADA system. Master Unit controls the RTU/PLC by issuing commands which are located at remote places. It gathers the required data, stores and process the information in the form of images, graphs and tables which helps user to take control decisions. The communication between MU and RTU is biderectional but RTU cannot start sending the signals.

4. Communication Netwoks :- To connect SCADA master unit and conversion units, we need some type of communication networks ( wired or wireless). Usually, the combination of radio and wired connections is used for SCADA systems. The standard protocol used in SCADA communication network is to send information only whe the maser station polls the RTUs.

diagram showing relationship between various components of SCADA is shown below :-