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 GEN series,
the following time base options are available:
l
Internal time base
The clock used to drive the ADC
’
s is the built
-
in clock.
l
External time base
The clock used to drive the ADC
’
s is the clock signal
presented at the external clock input on the GEN series system. The
interval between two consecutive samples may not be equidistant. This all
depends on the accuracy of the supplied clock signal.
When internal time base is selected, there are two related options:
l
Internal Clock Base Decimal
This setting is used to create time base
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.
l
Internal Clock Base Binary
This setting is used to create time base values
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.
The selections above can be found in the Perception software in the Settings
Sheet
►
Memory&Timebase
►
Mainframe
►
Clock Base and are therefore
mainframe
-
wide, i.e. the same for all recorders.
A binary clock base is a useful time base settings when doing FFTs (frequency
domain analysis).
GEN3i
I3763-3.1 en HBM: public
139
