Control engineering

control engineering is the technology of mechanisms, which affect technological processes after a given plan. If their purpose is automatically served by control, it concerns automation.

Table of contents

steered processes

the general purpose technological processes is transforming and transporting material, energy and information, to which over suitable technical mechanisms energyone uses and one changes. Control technical mechanisms, also controls mentioned, affect the transducers by information, which processed them in the sense of the process goal.

With the technological process of the machine laundry washing process-technical mechanisms become such as heating, Wasserzufluss and electric motor ofa control by processing of information for example over water level, time and temperature so on set and continue that clean predried laundry develops.
The technological process of a traffic light device for pedestrians has to the goal, over colored light transverseends itself to pedestrians andTo give vehicles passage information for collision-free traffic. The free passage for pedestrians and the closed for vehicles is the temporally limited exception, which is requested by pedestrians bedarfsweise with the control.

actuators and sensors

the links betweencontrol technical and process-technical mechanisms are sensors and actuators (also actuators called). Sensors convert process conditions into information and are thereby sources of information. On the other hand actuators are information lowering. They convert information-carrying energy into process energy. (In this viewpoint the information character of the assigned becomesEnergy stressed to let appear around the actuator as functional counterpart the sensor.)

the information delivered of sensors to become so often changed to it the representational form to have, which is accepted by the information-processing equipment (controller). Likewise from the controller a spent becomesInformation changed to it the form has, which an actuator accepts.

Process conditions are bivalent (binary), if they can be indicated by a statement, like article available/missing. Against it they are continuous if they can be illustrated by a real number,e.g. Temperature = 65,5°C. Binary process conditions are transformed by sensors into binary information. Continuous process conditions are converted by the sensor into similar information. If the controller needs the numerical value of the similar information, a similar to/a digital transformation is necessary. The reverse appliesfor actuators.

A signal is supplied to the actuator electric motor at the conveyor of a Ladenkasse, which is so strengthened that it can drive the engine. (That means: the driving power carries the information, which issues the controller, while the mechanical energy, thosethe engine produced, the process purpose serves and as storage medium no meaning has.) thereby the controller to decide can, whether the electric motor is be switched on or off, needs it the information of a sensor about the presence of goods within the grasp range of the cash personnel, for examplea light barrier.
The actuator lamp of an outdoor light fixture receives the signal for shining in form to sufficiently strong electricity. By the control from the information, the one sensor for the daylight strength and a sensor for those are won and strengthenedMovement of a heat source supply.
The controller of an autoengine affects continuously the fuel supply and ignition over similar actuators. It keeps similar information about sensors for the position of the gas pedal, the engine temperature and the number of revolutions, around the engine under most diverse outside circumstances optimalto operate.
Pattern of process and control _____________ _____ ______ |\ | |\ | | | | \ Sensors |  >>>> | \ |  >>>> | | | \ _______| |____ \| | | | | Process-technical. Inform. Controller mechanisms transducers| | _______ _____ | | | / | | /| | | | /Actuators |  <<<< | / |  <<<< | | |/____________| |/____| |______|

demarcation for regulation

because regulations to controls are related, must for demarcation a view of it to be thrown.

If the task exists to manufacture a certain value physical dimension such as pressure or temperature in many cases an actual value will develop, which deviates from the desired value, because disturbing influences at the work are.

ThatProblem is solved, as physical dimension with a sensor is seized. The controller, which is called in this case controller, can recognize and in such a way the actuator affect the deviation of the actual value from the desired value that the influences of noise are compensated.The effect of the actuator over physical dimension and the sensor on the controller is a feedback. Such arrangements belong to the technical field of knowledge of control engineering. The characteristic of regulated processes is the closed chain of acting elements, the automatic control loop.

Thus the actual valuewith the demanded accuracy and characteristic the desired value, must the controller the appropriate rule answer follows give, which is affected considerably also by the inertia, with which the actual value to the actuator reacted (time performance of the controlled system). Sometimes it is sufficient, ifrough actual value fluctuations in the temporal means the desired value correspond. In other cases highest regulation quality is demanded.

The constant speed of a car decreases when simply holding the accelerotor pedal to an upward gradient, which is a variable disturbance of the procedure. The controllers more modernVehicle engines can settle the necessary regulation besides. The automatic control loop for constant driving speed closes when desired the driver in the controller, as the fuel supply is extracted from the influence of the decreasing/going back accelerotor pedal and subjected but to the influence by engine speed changes.
Of a lab power supply unitit is required that it keeps an adjusted tension constant despite load and line voltage changes. In order to increase the delivered tension, an actuator decreases an internal voltage drop in the load current circle and in reverse. The automatic control loop results from the fact that the tension produced by the actuator upinfluences itself.

Regulations with controls are related, because they affect like these by actuators, sensors, transducers and information-processing devices technological processes. Also regulations are according to device often embedded in controls. The large difference exists in the specialSetting of tasks, which entails a feedback, which leads to completely different data processing. In consideration of the thing in common and differences one can quite regard control engineering as a speciality of control engineering, although this view is not generally divided.

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controls transferred and process information. The storage medium electrical tension, rare hydraulic or pneumatic pressure is predominant.

The information about binary process conditions can be truely or wrongly. True information becomes a wrong with 0, with 1 anddesignated, e.g. Key pressed = 0 means: Key is not pressed, the information is thus wrong. The two logical values 0 and 1 of binary information are illustrated by defined conditions of a storage medium, e.g. to 0 0 V correspond, to 1 correspond to 24V. A logical value is called simplified also condition (the storage medium).

Similar information from continuous process conditions is needed for the regulation, for the announcement or for the examination by limit values. A marginal check of physical dimension leads to the binary information: Limit value reached/does not reach.


of a call key over an illuminated readout the nurse can call logic control systems example a patient. Differently than with a door bell depressing the key must lead to a durable message, in order also to be still noticed if thoseCall key is no longer pressed. The illuminated readout is deleted by the nurse with a reset key.
With the draft of binary controls with the help of a Funktionstabelle, each possible combination of the logical values (entrances), supplied by sensors, becomes accordingly the logical value of an actuator (exit)the control purpose assigned. After a possible simplification the result can serve directly for the construction of the controller.
The problem definition of the example requires Speicherverhalten, so that in the Funktionstabelle beside the sensors (E1 and E2) also the actuator condition as entrance addedwill must (E3). Thus the table 2^3 = 8 receives lines.
Line call key pressed reset key pressed message--Message
_ a E1 E2 E3 -- A1
1 1 1 1 -- 1
2 1 1 0 -- 1
3 1 0 1 -- 1
4 1 0 0 -- 1
5 0 1 1 -- 0
6 0 1 0 -- 0
7 0 0 1 -- 1
8 0 0 0 -- 0
from the lines 1 to4 it is to be recognized that with pressed call key (E1 = 1) always the announcement shines (A1 = 1), which both entrances E2 and E3 play thus no role. The lines 5 and 6 show that the resetting (A1 = 0)of entrance E3 is independent. In the lines the Speicherverhalten of the control is 7 and 8: The illuminated readout keeps its (old) condition with (A1 = E3), if both tracers over one of the lines 3, 4, 5, 6 into the condition0 comes.
From it results: The illuminated readout shines only, if the call key is pressed, or if the reset key is not pressed and the illuminated readout shines. (This intuitively found simplification could have been determined also by mathematical procedures.)
usual are thosethe following representations of this statement:
  • Expression of Bool' algebra (switching algebra):
(v for OR, & for AND, here exeptionally ''for NOT)
 A1 = E1 v (“E2” & E3)
  • operating diagram:
( >=1 for OR, & for AND, O for NOT)
 ____________________________| ______ | E3 |____| | ______ | | & |______| | | E2----O| | | | | |______| |  >=1 |__|____A1 | | E1____________________| | |______|
  • Ladder diagram:
(Parallel connection for OR, series connection for AND, openers for NOT)
 _________________________ ||_ _ /---E1 /---E2// | | | | | /---- E3 | / | |________| | __|_ _ | |_____|-------A1 | ____________|____________

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While the operating diagram is ajar against a circuit from electronic switching elements, the ladder diagram supports the structure thatControl by relays.

With increased complexity in relation to the example and in particular during feedback of exits on entrances, one speaks of finite automats, which are treated in their own field of knowledge, i.e. the theory of the finite automats.

On the other hand are the simplest tables those of the basic linkages, with which, as in the example be shown, more complex tables can be described. The following table has 2 entrances and therefore 4 lines. The 3 most important linkages are represented with the exits A1 to A3.

(Tables with several exits are a shortened representation of according to many tables with only one exit. A table with 2 entrances can have maximally 16 exits and thus 16 possible linkages, about which 8 is the negations of the others.)
_ _ --AND OR XOR
E1 E2--A1 a2 A3
0 0-- 0 0 0
0 1-- 0 1 1
1 0-- 0 1 1
1 1-- 1 1 0

The logical statement of and and/or. OR operation is also applicably to more than two entrances, e.g. “If E1 AND E2 AND E3 etc. = 1, A1 = 1 follows ".

The table with an entrance can have only a meaningful linkage,the negation.

For the basic linkages there are standardized symbols, whereby the US-American differ from those to DIN.

Many developers go when simple controls not the way over linkage tables, but provide plans with linkage symbols and take possibly. Redundancies in purchase.

Logikgatter "and"
logic gate “and”
Logikgatter "or"
logic gate “or”
Logikgatter "xor"
logic gates “xor”
Logikgatter "not"
logic gate “emergency”
Logikgatter "and us"
logic gate “and US”
Logikgatter "or us"
logic gate “or US”
nn nn

controls and computer

computer are universal devices of the data processing, which outstanding as controller are suitable. One findsit depending upon task as CONTROLLERs, as programmable controller (SPS) or as industry PC (IPC). While the SPS programmer Funktions- and Kontaktpläne or also specific instructions can enter, CONTROLLERs and IPC with usual programming languages are programmed. IPCscan at smallest expenditure extensive auxiliary functions such as visualizations, loggings and statistics make available.

Example of a simplified heater control
a heating system consists of one heating circle each with circulation pump for space heating and hot water tank as well as a boiler with oil burner.
The boiler stops its Isttemperaturthe target temperature given by the respective heating circle, as the burner is switched on, if the Isttemperatur falls below the target temperature. The burner is switched off, if the Isttemperatur 5° C is higher than the desired value (on-off control). A heating circle, which does not need temperature, demands ofBoiler 0°C.
Below 16°C outside temperature runs the pump of the space heating circle and the boiler must on the average a temperature supply, which depends after a heating curve on the outside temperature. The pump switches, so long the heating circle for warm water of the boiler one offTemperature > 0°C demands. Above 17°C outside temperature is likewise switched the pump off (heating out).
The enterprise of the heating circle for warm water has priority. It is introduced, if the warm water being temperature falls below the target temperature, and terminated, if the Isttemperatur 5° C overis appropriate for the desired value (on-off control). During the water heating the pump runs, and of the boiler the maximally possible temperature is demanded.
The problem definition contains three cycles since new, which are almost from each other independent. Each of the cycles is realized by an endless program. The threePrograms run parallel, which is supported by the multitasking by operating systems and programming languages. They communicate among themselves over the global visible temperature requirements T1 and T2 of the two heating circles.
The following program structure charts show the program conception:
Boiler ________________________________________________ | Burner out _______| || | ___ | | Target being. = max (T1, T2) | | | Isttemp. < Target being. ? | | | yes | no | | | Burner | Isttemp. < Target being. + 5 ? | | | | no| yes | | | | | Burner out | | | Control room 10 s ___| | | Repeat | |________________________________________________|
Heating circle space heating global one variable T1 ________________________________________________ | Pump out, T1 = 0 _______| | | | ___ | |External temp. > 17 °C? | | | yes | no | | |Pump out| External temp. < 16 °C? | | | T1 = 0 | no | yes | | | | | T2  > 0 ? | || | | no | yes | | | | |T1= f (external temp.)|Pump out| | | | | Pump in | | | | Control room 10 s ___| | | Repeat | |________________________________________________|
Heating circle warm water global one variable T2 ________________________________________________ | Pumpout, T2 = 0 _______| | | | ___ | | Isttemp. < Target being. ? | | | yes | no | | |Pump in| Isttemp. > Target being + 5? | | | T2 = max| no | yes| | | | | Pump out, T2 = 0 | | | Control room 10 s ___| | | Repeat | |________________________________________________|

Just as most technological processes are implemented programs of expirations. Expirations need time. Only hard and software, thosealso in the most unfavorable case synchronously to the process to work can, is suitable and as real timable one designates as controller. In the closer sense real time means however that hard and software of a computer are particularly appropriate for this purpose. Computers, which steer, may never overloaded its.

see also

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