[...]... values 1. 8.3 Maintaining constant values by operation As already discussed in Chapter 1. 3, “Operation and control , a parameter can be kept constant by suitable operation An example could be to maintain a constant furnace temperature Assuming a constant voltage, i.e a steady power supply to an electrically heated furnace, the setting of an energy regulator can be varied to provide different furnace temperatures... leads to a loss of information about the measured signal Binary signals In their simplest form the signals can only have two states, and are therefore called binary signals The control engineer is already familiar with this type of signal The two states are normally described as “0” and 1 Every switch used to turn a voltage on and off produces a binary signal as its output variable Binary signals are... requirement for very high accuracy, and where the required features of the controller, such as its dynamic action, are already known at the planning stage Because of its speed of reaction, the analog controller has clear advantages in extremely fast control loops In digital controllers a microprocessor converts all analog inputs into numerical values, and uses them to calculate the manipulating variable This... with automatic control If the process is subjected to a disturbance, or there is a change in the transfer characteristic of the manipulating device, there can be undesirable changes in output, even with a fixed transfer action between input and output variables 1. 9 Main areas of control engineering Today, control engineering has applications in almost every area of technology In Chapter 1. 1 we have already... chapters (see Fig 4) - Continuous controllers (usually referred to as proportional or analog controllers) Controllers which receive a continuous (analog) input signal, and produce a controller output signal that is also continuous (analog) The manipulating signal can take on any value within the manipulation range They usually produce output signals in the range 0 — 20mA, 4 — 20mA or 0 — 10 V They are... and usually also linearizes the signal In this case the controller need only have an input for standard signals The process value is normally displayed on the controller This can be in the form of a digital display (numerical indication), which has the advantage of being readable from a longer distance The advantage of the analog display (pointer movement) is that trends such as rising or falling of... Indicating devices such as process value display or relay status LEDs are not usually provided, as the operator does not normally have access to these controllers - Rack-mounting controllers are intended for use in 19 -inch racks They are only fitted with a front panel and do not have a complete housing - Card-mounted controllers consist of a microprocessor with suitable peripherals, and are used in various... variable This has certain advantages compared with analog processing: - increased accuracy of control, depending on the measurement signal and the technology used (e.g A/ D converter) Unlike components which are affected by tolerances and drift, the mathematical relationships used have a constant accuracy and are unaffected by ageing, variations in components and temperature effects - high flexibility... structure and characteristics of the controller Instead of having to adjust parameters or unsolder components, as in analog controllers, a digital controller can be modified by simply programming a new linearization, controller structure etc by inputting numerical values - facility for data transfer There is often a need to modify or store information about process status variables, or pass it on for different... uses, and this is very simple to achieve using digital technology Remote setting of parameters through data systems, such as process management systems via a digital interface, is also quite simple - control parameters can be optimized automatically, under certain conditions Digital controllers also have disadvantages compared with controllers operating on analog principles The digital display, normally . Ratio control 11 0 6.8 Multi-component control 11 1 Inhalt 7 Special controller functions 11 3 7 .1 Control station / manual mode 11 3 7.2 Ramp function 11 4 7.3 Limiting the manipulating variable 11 4 7.4. action 11 1. 5 Construction of controllers 12 1. 6 Analog and digital controllers 18 1. 6 .1 Signal types 18 1. 6.2 Fundamental differences 20 1. 7 Manipulating devices 23 1. 8 Other methods of achieving. constant values 25 1. 8 .1 Utilizing physical effects 25 1. 8.2 Constructional measures 25 1. 8.3 Maintaining constant values by operation 26 1. 9 Main areas of control engineering 27 1. 10 Tasks of