LeCroy LSA1000, Operator'S Manual, Page: 18 / 115

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About the LSA1000
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Processor
— a PowerPC 603e microprocessor controls the
entire system and performs computations and special
monitoring.
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Interfaces
— Ethernet port transfers processed data to the
host computer and receives remote control instructions.
Finding the “Right Fit”
For optimum results there must first be a good “fit” between the
character of the signals under analysis and the primary specifications
of the LSA1000. In assessing the overall signal representation,
particular consideration needs to be given to these three cardinal
parameters:
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Bandwidth: The bandwidth specification of an LSA1000
indicates the ability of its front-end amplifier to faithfully track an
incoming signal. The LSA1000's bandwidth is defined as the
frequency at which a sinusoidal input signal has been attenuated
to about 70 % of its real amplitude. This point, at which the
vertical amplitude error is about 30 %, is called the
–3 dB point.
➢
Sample Rate: The higher the sample rate the better the signal
resolution. This is particularly important for single-shot waveform
capture and measurement. The danger with low sample rates is
that important information may be lost between samples. A
sample rate of at least twice the highest frequency component of
the signal is required to avoid aliasing. A sample rate of at least
five times is advisable for accurate waveform capture.
➢
Memory Length: Acquisition memory length determines the
number of input signal samples that can be stored. The greater
the capacity for stored samples, the faster the possible sample
rate for a given waveform duration. The signal captured with a
long-memory LSA1000 has a greater resolution, whereas in the
case of other short-memory instruments, such high sample rates
are only available on short waveform-capture time settings.
Long-memory LSA1000s allow operation at the highest possible
sample rate, and over a far longer capture time.
The LSA1000’s fidelity in reconstructing the input signal is affected
mainly by these three parameters. The bandwidth must be sufficient
to allow all the signal components to pass through the signal-
conditioning system. And the sample rate has to be high enough to
provide a good definition of the signal. Long memory maintains the
sample rate for large time windows.