Time Base; Real-Time Sampling And Time Base - HBM Genesis GEN5i User Manual

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9.4

Time base

The power of modern data acquisition techniques is achieved by digitizing
analog information. Digitizing is the conversion of the instantaneous value of
an analog signal (static or dynamic) into a numeric value. When the signal
varies, sampling the instantaneous amplitude at sufficiently rapid intervals
converts this signal into a series of numbers that can represent the original
analog signal.
9.4.1

Real-time sampling and time base

Real-time sampling is a straightforward sampling method and is the only
method to record non-periodical phenomena. In this method, the intervals
between the samples taken of the original signal are as short as possible and
equidistant. If the sample rate used is high enough, the original signal can be
reconstructed without any additional processing.
The sample rate is determined by the time base: the time base is a clock that
generates pulses used to drive the A-to-D Convertor. Within the GEN5i you
have the following time base options:
Internal time base When you select the internal time base, the clock used
l
to drive the ADC's is the built-in clock.
External time base When you select the external time base, the clock used
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to drive the ADC's is the clock signal presented at the external clock input
BNC on the GEN5i Controller/Interface module. When you select this
mode, the interval between two consecutive samples may not be
equidistant. This all depends on the accuracy of the supplied clock signal.
For more details see "IM1 - I/O connectors" on page 178 and "IM2 - I/O
connectors" on page 148.
The above selection is made in the Perception software in the Settings Sheet
► Recorder ► Time base Source.
When internal time base is selected there are two related options:
Internal Clock Base Decimal This setting is used to create time base
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values that are base 10, e.g. 1 MHz, 100 kHz, 50 kHz, 2.5 Hz, etc. These
values are derived from a main oscillator that operates at a base 10
frequency, e.g. 1 MHz.
Internal Clock Base Binary This setting is used to create time base values
l
that are base 2, e.g. 1.024 MHz, 512 kHz, 64 Hz, etc. These values are
derived from a main oscillator that operates at a base 2 frequency, e.g.
1.024 MHz.
GEN5i
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