PicoScope 3425 PC Oscilloscope
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Glossary
AC/DC control. Each channel can be set to either AC coupling or DC coupling. With
DC coupling, the voltage displayed on the screen is equal to the true voltage of the
signal across the differential inputs. With AC coupling, any DC component of the
signal is filtered out, leaving only the variations in the signal (the AC component).
Aggregated values. In
driver can
use a method called aggregation to reduce the amount of data your application
needs to process. This means that it replaces a number of consecutive raw samples
with a pair of values, which are the minimum and maximum values of all the raw
samples. You can set the aggregation parameter when you call
for real-time capture, and when you call
to obtain post-processed data.
Aliasing. An effect that can cause digital oscilloscopes to display fast-moving
waveforms incorrectly, by showing spurious low-frequency signals ("aliases") that do
not exist in the input. To avoid this problem, choose a sampling rate that is at least
twice the frequency of the fastest-changing input signal.
Analogue bandwidth. All oscilloscopes have an upper limit to the range of
frequencies at which they can measure accurately. The analog bandwidth of an
oscilloscope is defined as the frequency at which a displayed sine wave has half the
power of the input sine wave (or, equivalently, about 71% of the amplitude).
Block mode. A sampling mode in which the computer prompts the oscilloscope to
collect a block of data into its internal memory before stopping the oscilloscope and
transferring the whole block into computer memory. This mode of operation is
effective when the input signal being sampled is high frequency. Note: To avoid
effects, the maximum input frequency must be less than half the sampling
rate.
Buffer size. The size, in samples, of the oscilloscope buffer memory. The buffer
memory is used by the oscilloscope to temporarily store data before transferring it to
the PC.
Common-mode overflow. The scope measures the difference between the positive
and negative input voltages on each channel. The voltage of each input with respect
to ground does not affect the measurement as long as it does not exceed the
common-mode voltage limit. If this limit is exceeded, a common-mode overflow
occurs and the scope will not measure the signal accurately. PicoScope 6 shows a
when this happens.
Common-mode voltage. The common-mode voltage of two points is the average
voltage of the two points with respect to ground. A differential oscilloscope accurately
measures the voltage difference between its two inputs and ignores their
common-mode voltage, as long as the input voltages with respect to ground remain
within a defined range. Outside this range the accuracy of the measurement cannot
be guaranteed.
Differential oscilloscope. A differential oscilloscope measures the voltage
difference between two points, regardless of the voltage of either point with respect to
ground. This is unlike a conventional oscilloscope, which requires one of the two
points to be at ground potential.
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