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Automation and Drives - SCE
T I A Training Document Page 21 of 64 Module
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
B3
Issued: 02/2008 Control Engineering with STEP 7