CONTROL ENGINEERING

• Systems are arrangements of parts within some boundary which work together to provide some form of output from a specified input or inputs.
• A boundary divides the system from the environment and the system interacts with the environment.
• A block diagram is a useful way of representing a system.
• An electric motor system has an input of electrical energy and an output of mechanical energy.
• An instrumentation system for making measurements has an input of the true value of the variable being measured and an output of the measured value.
• Examples of instrumentation systems include pressure measurement, speedometer, and flow rate measurement.
• An instrumentation system used for making measurements is to give the user a numerical value corresponding to the variable being measured.
• A sensor is an element of the system which is effectively in contact with the process.
• A signal processor is an element that takes the output from the sensor and converts it into a form which is suitable for display or onward transmission in some control system.
• The term signal conditioner is used for an element which converts the output of a sensor into a suitable form for further processing.
• Data presentation presents the measured value in a form which enables an observer to recognise it.
• Transducers are defined as an element that converts a change in some physical variable into a related change in some other physical variable.
• Accuracy is an indicator of how close the value given by a measurement system can be expected to be to the true value.
• Error of a measurement is the difference between the result of the measurement and the true value of the quantity being measured.
• The range of variable of a system is the limits between which the input can vary.
• Precision is used to describe the degree of freedom of a measurement system from random errors.
• Repeatability of a system is the ability to give the same output for repeated applications of the same input value.
• Reproducibility of a system is the ability to give the same output when it and/or elements of the system are disconnected from the input and then reinstalled.
• Sensitivity indicates how much the output of an instrument system or system element changes when the quantity being measured changes by a given amount, i.e the ratio output/input.
• The mass standard, the kilogram, is defined as being the mass of an alloy cylinder (90% platinum-10% iridium) of equal height and diameter, held at the International Bureau of Weights and Measures at Sevres in France.
• The length standard, the metre, is defined as the length of the path travelled by light in a vacuum during a time interval of duration 1/299 792 458 of a second.
• The time standard, the second, is defined as a time duration of 9 192 631 770 periods of oscillation of the radiation emitted by the caesium-133 atom under precisely defined conditions of resonance.
• The current standard, the ampere, is defined as that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 x 10-7 N per metre of length.
• The kelvin (K) is the unit of thermodynamic temperature and is defined so that the temperature at which liquid water, water vapour and ice are in equilibrium (known as the triple point) is 273.16K.
• The candela is defined as the luminous intensity, in a given direction, of a specified source that emits monochromatic radiation of frequency 540 x 10'^ Hz and that has a radiant intensity of 1/683 watt per unit steradian.