Practical SCADA for Industry David Bailey - FER-a

2.1 Introduction
2
SCADA systems,
hardware and firmware
This chapter introduces the concept of a telemetry system and examines the fundamentals
of telemetry systems. The terms SCADA, distributed control system (DCS),
programmable logic controller (PLC), smart instrument are defined and placed in the
context used in this manual.
The chapter is broken up into the following sections:
• Definitions of the terms SCADA, DCS, PLC and smart instrument
• Remote terminal unit (RTU) structure
• PLCs used as RTUs
• Control site/master station structure
• System reliability and availability
• Communication architectures and philosophies
• Typical considerations in configuration of a master station
The next chapter, which concentrates on the specific details of SCADA systems such as
the master station software, communication protocols and other specialized topics will
build on the material, contained in this chapter. As discussed in the earlier chapter, the
word telemetry refers to the transfer of remote measurement data to a central control
station over a communications link. This measurement data is normally collected in
real-time (but not necessarily transferred in real-time). The terms SCADA, DCS, PLC
and smart instrument are all applications of the telemetry concept.