Anglicky v odborných předmětech "Support of teaching technical subjects in English “

1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Mechanik - elektrotechnik Topic: Electric measurement the 2nd. year Oscilloscope2 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.

2. Measurements using an oscilloscope • The oscilloscope measures only the voltage against the ground (earth). • Measurement of DC voltage • Procedure : • Set the horizontal time axis. • Positive voltage - zero horizontal axis at the lowest grid line, • Negative voltage– zero horizontal axis on the top grid line. • The size of deflection read from the screen grid, • Grid – lattice with centimetre and millimetre divisions • Determination of the measured voltage – deducted length multiplied by the set measure (V/cm) and possibly even evaluate the factor of the measuring probe. • Dividing (ratio) reduces the input voltage of the probeand itis also less taxing on the measured object.

3. Measurements using an oscilloscope • Measurement of AC voltages • AC voltage on the Y-axis deflects the beam up and down alternately. • Periodic signal – course of time • Aperiodic signal- light band • Display of measured voltage- current value (e.g. peak) AC signal. • Voltage peak – peak = difference between the highest and lowest deflection beam traces on the screen • Voltage size – deducted distance multiplied by the set measure in V/cm.

4. Measurements using an oscilloscope • Measurement of current • A current waveform can be measured indirectly by measuring the voltage drop caused by resistance in a small current • Ohm’s law applies • I=U/R

5. Measurements using an oscilloscope • Display AC values • The input signal is applied to the Y-input and the ground(GND). • Timebase is set so that the image was still standing still.

6. Measurements using an oscilloscope • Measurement of frequency • Measurement of the length of period and thus the frequency of AC signal • Set the fine regulation of the time base • switch the VARIABLE to the cal. position • Set the time base so that one period of the signal occupies the greatest part of the screen. • Set the time base starting threshold (LEVEL) so that the process started at zero voltage. • Measuring the length of the period on the screen grid • The calculation of frequencies using the formula f=1/T

7. Measurements using an oscilloscope • Measurement of phase shift • Two AC electrical quantities is best viewed simultaneously on the two-beam or dual-channel oscilloscope. • The inputs of both channels are connected to periodic signals (same frequency), for which we want to measure the phase shift.

8. Measurements using an oscilloscope • Imaging characteristics • For a dual channel oscilloscope switch the second channel to the horizontal deflection system (instead of the time base) • Then it is possible to arbitrarily change the scale on both axes.

9. Activities for students- Questions • How does the beam move on the screen when the time base is turned on? • What shape is produced by an impulse time base? • What is the danger of an idle X or Y amplifier?

10. Activities for students - Questions • What advantage does a driven starting time base have (triggering)? • What is the oscilloscope probe or probe ratio? • What is the sampling time (Chopper) of an oscilloscope? • For which signal frequencies is an alternating mode used (Alternate)?

11. Bibliography • Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, 2000. ISBN 80-7361-269-7. • Wikipedie • Příručka elektrotechnika, Europa 2000 • Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 – 2013. • Available at: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-pro-konkurenceschopnost