Reading from an Oscilloscope

The Oscilloscope•An oscilloscope is a piece of scientific equipment which is used to measure voltage which is changing. They are very useful for studying waveforms.

•The screen looks similar to a piece of graph paper.•The controls set the

scale of the display.

How does it work?1. Electrodes which deflect

the electron beam. (make the dot move on the screen)

2. Electron gun – fires electrons towards the screen.

3. Beam of electrons (tries to spread out as electrons repel each other)

4. Coil produces a magnetic field which focuses the beam.

5. Phosphor atoms on the inside of the screen glow green when electrons hit them.

Reading from the oscilloscope

•Y-axis displays amplitude of a voltage.

•X-axis displays units of time•AC – a current that is continuously

changing between positive (+) and negative (-) voltage. Mains AC has the shape of a sine wave, because of the way it is generated.

Wavelength and Amplitude

•Voltage peak-peak

0 V

•Amplitude of wave

•Period (distance between two equivalent points on wave)

Frequency•Frequency of a wave is the number of waves passing a fixed point per second.

•Measured in Hz – number per second.

frequency = number of waves / time for waves to pass

•One Hz

•Two Hz

•X-axis 0.005s per division. ?Hz

Frequencyfrequency = number of waves / time for waves to pass

= period / time

•X-axis 0.005s per division.

•One wave passes in 4 x 0.005s = 0.02s

•Frequency = 1 wave / 0.02s = 50Hz

Mains in the UK

•UK mains supply is 230V amplitude, 50Hz.

•The ‘live’ voltage supply is the one which is continuously changing between +230V and -230V at 50Hz. *This varies above and below neutral which is at approximately 0V but can be different as neutral is earthed at the sub-station which can be some distance away.

*HT only