Open-loop controller

The control system includes the design and implementation of control systems. It is a part of automation technology.

The control is a plan under which the technical products ( equipment, apparatus, machinery, equipment, and biological systems ) occurring in principle changeable ( dynamic ) variables are affected.

Depending on input variables ( for example, position of a switch rocker, a hand wheel, the mixing lever or knob ) output values ​​(e.g., lighting, temperature, pressure or speed) by means of an actuator set (for example, switches, valve or the motor).

In contrast to the control is absent in the control, the feedback of the output to the input. If, however, in the communication between human and machine based on a displayed output, the input variable is changed, we find a settlement with the people rather than control.

The sizes of the input and output can be both analog and digital ( especially binary). Binary, for example, the input and output variables of a lighting: The switch has two positions, the light is on or off. Use of controls used to monitor, so the output of the controller is also binary: Achieved the size to be monitored ( input control ) a dangerous level, a process is often turned off.

• 3.1 Truth Table
• 3.2 Other forms of representation

Basics

The following diagram shows the major components of technical control facilities and their information flow:

In technical control facilities information is transmitted and processed. Mostly the information of electric voltage, rare hydraulic or pneumatic pressure.

Sensors convert process states into information and are therefore sources of information. On the other hand actuators are information sinks: they convert information into process energy.

The signals emitted by sensors information is changed so that they are suitable for the respective transmission section and can be processed by the controller as an input variable. Issued information is also converted before the actors intervene in the process.

Demarcation between the control and regulation

In contrast to the control is absent in the control, the continuous feedback of the output to the input of the controller ( control means ). Due to the absence of the actual value is spoken in the art of an open chain of effects or timing chain.

Example:

In English literature, the word control is used both for control and for control. For translations of this word is often translated as " control ". In English the exact meaning is only apparent when explicitly from a open loop control ( " control") or closed loop control ( " control" ) is spoken, otherwise the knowledge of the context for the correct translation as " control " or " control " is required.

In colloquial German regulation and control are often not exactly distinguished. This inaccuracy also takes place in specialized languages ​​that do not require this precise definition: In the Business Administration control on the one hand includes measures to achieve specific objectives within the framework of leadership, performance management, administration and controlling, for example, as a feedforward control - namely, before the entry of interference control in the strict sense - and as a readjustment ( control in the technical sense ), eg by comparing the nominal values ​​with the actual values ​​to derive from the results of new measures.

Binary signals

Process states are divalent (binary) if they only have two possible truth values ​​, such as " key " or " not pressed " object present or not present. The two truth values ​​are mapped by defined states of an information carrier, " not pressed ", for example, corresponds to 0 V, " down " corresponds to 24 V. These states are using { 0,1} or { false, true } described.

Analog signals

Process states are continuous, if it can be represented by a real number, eg temperature = 65.5 ° C. A continuous process is implemented by the sensor state into an analog signal. When the control unit requires the value of the analog signal, an analog-to- digital conversion is required.

Control types

By type of signal processing is divided into:

• Sequential control ( flow control ): sequence of individual steps according to logical decisions

• Time program control: sequence of events according to a time schedule

• Course program control: sequence of events after a Wegschema

Classification of control systems according to their structure:

• Hard-wired control mechanical control: eg pen rolling a barrel organ, Cam
• Electrical control: for example, contacts and relays
• Pneumatic, hydraulic control
• Electronic control: for example, logic gates, programmable logic device

• Programmable logic controller (PLC ), for example, the microcontroller It is the control type most commonly used today.

Draft control

Taxes means that each possible combination of input variables according to the control purpose, the truth value is assigned for each output. These assignments are presented in greatest detail in a truth table.

After a possible simplification of the rules of Boolean algebra or Karnaugh Veitch diagram, the result can be used directly for the realization of the controller.

Truth table

The adjacent truth table has 2 inputs and therefore 22 = 4 possible combinations. Shown are the 3 most important links to the outputs A1 to A3. Tables with multiple outputs are a condensed version of a corresponding number of tables with only one exit. A table with 2 inputs can have 16 different links (see Boolean function ).

The following example illustrates the control design is to be considered in more detail:

The problem of the example requires storage behavior, so that, in the truth table in addition to the sensors ( E1 and E2) and the checkback itself needs to be added as an input ( E3). Thus, the table 23 = 8 rows.

From lines 1 to 4, it is seen that pressing the call button ( E1 = 1) is always the indicator lights (A1 = 1), the two inputs E2 and E3 do not play a role. Lines 5 and 6 show that the rear position ( A1 = 0) is independent of the input E3. In lines 7 and 8, the memory behavior of the control enemies: The indicator retains its ( old ) condition if (A1 = E3), if both keys are 0.

This is why: The indicator lights up only when the call button is pressed, or when the reset button is not pressed and the indicator is lit.

Other forms of presentation

Usual, the following representations this statement:

• Expression of Boolean algebra ( Boolean algebra ):   stands for OR for AND - NOT for

• Function Block Diagram ( logic diagram ): ≥ 1 stands for OR, & for AND, O for NOT For the basic logic there are standardized symbols are described in detail in the article logic gates.

While the function block diagram of a circuit modeled from electronic switching elements, the ladder is supporting the development of the control with the help of relays.

• Ladder: Here a parallel circuit for OR, series connection for AND, NC for is NOT used as a wiring diagram.

LDN E2 A A1 O E1 = A1   LD E2 R A1 LD E1 S A1 Instruction List Version 1 variant 2 Instruction list PLC: LD stands for charge, N for NO, A for AND, O for OR, S for Set ( latching), R for reset

With increased complexity relative to the example and in particular repatriation of outputs to inputs, one speaks of finite automata, which are in a separate area of ​​knowledge, namely, the theory of finite automata, treated.

Programmable logic controllers

Computers are universal information processing equipment, which are excellent as a control device. They are found depending on the task as a controller, as programmable logic controller ( PLC ) or the Industrial PC (IPC). During the PLC programmer can input logic and ladder diagrams or instruction list, and IPC controller are programmed using high-level languages ​​. IPCs can provide extensive additional functions such as visualization, logging and statistics with minimal effort. Running Programs need time. Only hardware and software that can work even in the worst case, synchronous to the process, is suitable as a control device and is referred to as real-time capability. In a narrower sense, real-time, however, it means that the hardware and software of a computer for this purpose are especially designed. Computers that control must never be overloaded.

Applications and Examples

Examples of controlled technological processes:

• In a washing machine, heating, water supply and electric motor of a control by processing of information on water level, time and temperature are set and stopped that clean pre-dried laundry arises in transition.
• The control unit of an automobile engine, the fuel supply is continuously influenced and the ignition timing via analog actuators. It receives analog information by means of sensors for the throttle position, the engine temperature and the speed in order to operate the engine under a variety of external conditions optimal.
• Safety Control: The structure is redundant and fail-safe.
• Remote control: large distance between the controller and device
• Valve control: a mechanism for controlling the gas exchange of a four-stroke reciprocating engine
• Steering: influencing the direction of travel of vehicles of all kinds Flight control: the control of aircraft
• Blast-off
• Control of the model railway

History

The Greek inventor Heron of Alexandria (ca. 20-62 AD) describes in his book " Automata ", a door control in the open by the lighting of a fire temple door, and automatic theater controlled by uncoiling ropes perform various movements could. He also designed a holy water dispenser in accordance with the insertion of a coin, a small amount of holy water spent. These ideas have been but forgotten and not further developed.

At the beginning of 18th century music boxes were controlled with pin rollers. Middle of the 18th century were controlled by wooden punch cards, which were significantly improved in 1805 by Joseph -Marie Jacquard with a revolving perforated tape looms.

See also: History of Automation, Robotics, NC