Velleman projects EDU06 Assembly instructions - Manual (Page 21)

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Noise: Undesired random addition to a signal.
Ripple: Unwanted periodic variation of a DC voltage.
Signal: Voltage applied to the input of the oscilloscope. The subject of your measurement.
Sine wave: Mathematical function that represents a smooth repetitive oscillation. The waveform shown at the start of
this glossary is a sine wave.
Spikes: Fast, short duration transients in a signal.
AC voltage: (AC: Alternating Current) With AC, the fl ow of the current periodically reverses, as opposed to DC, where
the current fl ows in one direction. An AC source does not have a polarity.
Bandwidth: Usually expressed in MHz. It is the frequency at which an applied sine wave will be displayed at an am-
plitude of around 70% of its original amplitude. More expensive scopes feature a higher bandwidth. Rule of thumb:
the bandwidth of an oscilloscope needs to be at least 5 times higher than the frequency of the signal applied to the
input of the scope. The HPS140 bandwidth goes up to 10MHz.
DC reference: DC measurement is always performed with respect to a ground level, so we need to defi ne this
ground level. If you do not set the DC reference, the readout might not be correct. In most cases, this ground level
will be the center of the screen, however this is not mandatory.
DC voltage: (DC:Direct Current) With DC, the current fl ows in a single direction, it does not reverse. A DC source
has a polarity, (+) and (-).
Input coupling: The drawing shows typical oscilloscope input circuit. There are 3 possible settings: AC-coupling, DC
coupling and GND. With AC-coupling, a capacitor is put in series with the input signal. This capacitor blocks any DC com-
ponent of the signal and passes only AC. With DC coupling, the capacitor is bypassed and both the AC and DC compo-
nent of the signal are passed. Low frequency signals (<20Hz) should always be displayed using DC coupling. Should AC
coupling be used, the internal coupling capacitor will interfere with the signal and the displayed signal will not be correct.
Sample rate: Usually expressed in samples or megasamples/second, sometimes in MHz. It is the number of times
per second the digital oscilloscope ‘looks’ at the signal at the input. The more it ‘looks’, the better it is able to recre-
ate a faithful image of the waveform on the screen. Theoretically the sample rate needs to be twice the max.
frequency of the applied signal, however, for best results a sample rate of 5 times the max. frequency is recom-
mended. The HPS140 samplerate is 40Ms/s or 40MHz.
Sensitivity: Indicates the smallest change of the input signal that makes the trace move up or down on the
screen. Usually expressed in mV. The HPS140 sensitivity is 0.1mV.
Slope: It determines where the scope will trigger. This can be on the rising or on the falling slope of the signal.
Vrms: The rms voltage of an AC source represents the required DC voltage to generate the same amount of
heat in a resistor as the AC source would do. For sinusoidal signals, Vrms = Vpeak / sqrt(2)
rising slope falling slope
Glossary
ple rate: Usually expressed in samp
DC coupling
or megasamples/second sometim
AC coupling
in MHz It is the number of times
GND coupling