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PicoScope 4000 Series Automotive Oscilloscope User's Manual8
© Copyright 2008 Pico Technology Ltd. All rights reserved.ps4000a.en
3 Advanced features
3.1
Sampling modes
PicoScope 4000 Series Automotive Oscilloscopes run in various sampling modes. At
high sampling rates, the oscilloscope collects data much faster than a PC can read it.
To compensate for this, the oscilloscope stores a block of data in an internal memory
buffer, delaying transfer to the PC until the required number of data points have been
sampled. This is called block mode. At very low sampling rates, you may want to
switch to streaming mode. This allows data to be transferred back to the PC as it
is collected.
3.2
More on block mode
In block mode, the computer prompts a PicoScope 4000 Series Automotive
Oscilloscope to collect a block of data into its internal memory. When the oscilloscope
has collected the whole block, it will signal it is ready and transfer the whole block into
the computer memory via the USB port. The maximum number of samples in each
block depends upon the size of the oscilloscope's memory.
3.3
More on streaming mode
In streaming mode, the computer prompts the PicoScope 4000 Series Automotive
Oscilloscope to start collecting data. The data is then transferred back to the PC
without being stored in oscilloscope memory. Data can be sampled with a period of
between 1 ms and 60 s, and the maximum number of samples is limited only by the
amount of free space on the PC's hard disk.
3.4
AC/DC coupling
Each channel can be set to either AC or DC coupling. When AC coupling is used, any
DC component of the signal is filtered out. This mode is useful for viewing ripple on
signals such as the alternator and fuel pump currents, where the DC level of the
signal is of no interest. DC coupling is recommended for most other automotive
measurements.
To switch from alternating current to direct current, or vice versa, select AC or DC
from the control on the oscilloscope toolbar of the PicoScope software application. The
setting should be adjusted to suit the characteristics of the input signal.
3.5
Oversampling
When the oscilloscope is operating in block mode at speeds that are less than
maximum, it is possible to oversample. Oversampling is taking more than one
measurement during a time interval and returning an average. This reduces the
effects of noise, and increases the effective resolution of the oscilloscope.
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