Siemens Module B3 manual Basic Types of Continuous Controllers

Automation and Drives - SCE

2.7.3 Basic Types of Continuous Controllers

The discrete controllers just discussed have, as mentioned before, the advantage of being simple. The controller itself as well as the actuator and the final control element are of a simpler nature and thus less expensive than for continuous controllers. However, discrete controllers have a number of disadvantages. If high loads, such as large electrical motors or cooling systems have to be operated, high peak loads can occur that can overload the power supply. For these reasons, we often don’t switch between “Off“ and “On“, but between a full load and a base load -with a clearly lower use of the actuator or final control element. But even with these improvements, a continuous controller is not suitable for many applications. Imagine a car engine whose speed is governed discretely. There would be nothing between idle and full throttle. Aside from it probably being impossible to transfer the power during a sudden full throttle suitably over the tires onto the road, such a car would probably be quite unsuitable for street traffic. For such applications, continuous controllers are used for that reason. Here, the mathematical relationship that the controlling element establishes between system deviation and controller output variable is theoretically virtually limitless. In practice, however, we differentiate among three classical basic types that are discussed in greater detail below.

	Preface	Fundamentals	Discontinuous Action Controller Controller Block (S)FB41	Setting the System Appendix
	T I A Training Document		Page 21 of 64	Module
				B3
Issued: 02/2008				Control Engineering with STEP 7