TABLE OF CONTENTS We have now covered all the features of the IEC 1131-3 standard. In this chapter, we will look more closely at the application of IEC 1131-3 to industrial control problems. In particular, the chapter will focus on the following aspects of designing IEC 1131-3 based systems:
The definition of external interfaces;
The analysis and breakdown of the control problem into more manageable components, that can be defined as programs and function blocks;
The partitioning of the control software to run in different PLC resources;
Selecting the most appropriate programming language;
Defining the total configuration.
The example application that we will review in some detail concerns the control of a boiler water feed pump. A water feed pump is used to maintain the water level in the steam drum of a large boiler, as might be found in an oil- or coal-fired power station. The water level in the main boiler must be controlled within safe operating limits.
The level can fluctuate as the steam from the main boiler is used by the power generation turbine or by other services. If the level drops, there is a danger that the boiler riser tubes that absorb heat from the burners will overheat and distort. If the level goes too high, there is a danger that water droplets will pass into the superheated steam supply and damage the main generator turbine blades.
The boiler water feed pump which is driven by a small steam turbine off the...
