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Anglicky v odborných předmětech "Support of teaching technical subjects in English “. Tutorial : Mechanic - electrician Topic : Electric measurement the 2nd. y ear Measuring devices 3 Prepared by: Ing. Jiří Smílek.
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Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Mechanic - electrician Topic: Electric measurement the 2nd. year Measuringdevices 3 Prepared by: Ing. Jiří Smílek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
Measuring instruments - basic properties of measuring instruments • Measuring range: • Measuring range reflects the range of values within which the instrument measures with the required accuracy • Usually the measuring range coincides with a full scale, • Instrument sensitivity : • The sensitivity of the device indicates how the deflection of the hands responds to the unit of the measured values. • Constant device for • is the reciprocal of sensitivity; • expresses the size of the measured variables at one scale interval. • formula • unit V/div, A/div, V . A/div
Measuring instruments - basic properties of measuring instruments • Changing the measuring range: • DC • Ampere meter– shaft • Voltmetr– ballast • AC - also • Ampere meter– measuring transformer current - MTP • Voltmeter-measuring transformer voltage-MTN • Calculation of constants: • Shunt, ballast - n times increases the range • kP = n k • MTP - transfer of the transformer p= I/5A • Conversion constant transformer • KT =p kA • MTN - transfer of the transformer p= U/100V • Conversion constant transformer • KT =p kV • W – meter • k= range U x range I / number of scale intervals
Measuring instruments - basic properties of measuring instruments • Accuracy of measuring instruments: • expresses the class of accuracy. • according to standard: 0,05, 0,1, 0,2, 0,5, 1, 1,5, 2,5 a 5. • These numbers indicate the measured values of variables leaving the maximum deviation from the actual size, in% of measuring range • To measure accurately, the deflection of the hands must be measured in the last third of the scale. • formula • Overload • Overload means the multiples of the rated current or voltage, that the measuring instrument will last for a period of time without damage • voltmeters doubled, • ammeters tenfold,
Measuring instruments - basic properties of measuring instruments • Power consumption devices: • Power necessary to achieve full deflection of the hands • Overload • Overload means the multiples of the rated current or voltage, that the measuring instrument will last for a period of time without damage • voltmeters doubled, • ammeters tenfold, • Rapid stabilization of displacement of the hands: • Reading measurement values - after stabilization of the position of the hands -> longer measurement time. • Prevention - damping oscillation rotation of the system.
Measuring instruments - basic properties of measuring instruments • Errors of measuring instruments: • influencing variables, which can alter the measurement data. They are for example: • ambient temperature, • strange magnetic fields, • position of the device, • frequency, • wave alternating current, • influence of ferromagnetic bar • Reference conditions • are the sum of the reference values given by the instrument manufacturer for each influence quantity, • The reproducibility of measurements • Each correct measurement must be reproducible. • This means that repetition with a certain measurement by the same device under the same conditions we get the same results.
Activities for students–questions • Describe what is a measuring range • Write how the measuring range is related to the scale • Describe what is the instrument sensitivity • Write a formula • Describe what is a constant unit • Write a formula
Activities for students–questions • Write how to express accuracy of the meter • Name the class of accuracy according to the standard • Describe what we have to watch to gauge accuracy (as far as possible)
Activities for students–questions • Write what is meant by overload (thus how we state it) • Name some variables affecting the measurement accuracy • Describe what we must do, in order for us to repeat measurements to achieve the same conditions
Bibliography • Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, 2000. ISBN 80-7361-269-7. • Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 – 2013. • Dostupné na: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-pro-konkurenceschopnost • Učebnice Elektrická měření – Ing. Pavel Vylegala, SŠE Ostrava, 2006 • Učebnice Elektrické měření – SNTL, 1981 • Elektrotechnika - Laboratorní cvičení pro bakalářské studium - Doc. Ing. Miloš Hammer, CSc.