User manual

POSCOPE4 AND MEGA1+ MANUAL
41
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PoScopeMega1+ sampling frequency (analog and digital DAQ mode)
If you change sampling frequency knob you will note that label under the knob is changing from Pipe
to Buffer. Pipe and Buffer are names for two different data transfer modes.
Data is transferred over full speed USB 2.0 which has speed limitations (1,5Mb/s theoretical). Mega1
can sample faster than we can transfer data over USB thus we introduced these two modes.
Pipe mode: sampling is slower than USB 2.0 “full speed” maximum transfer speed. Device can
transfer sampled data over USB 2.0 continuously and without any interrupts
Buffer Mode: sampling is faster than USB 2.0 “full speed” maximum transfer speed. Device is
transferring limited amount of data (data images) and there are interrupts between data.
Pipe Mode
Buffer Mode
Pipe mode limit is set dynamically, depending on resources used:
 f
s
– Sampling frequency [Samples / second)]
 N – Count of used channels [n] (is channel B on?)
 S – size of one sample in bytes [bytes] (8-bit / 12-bit)
 V
usb
– USB 2.0 ‘’full speed’’ maximum transfer rate (1,5 MB/s in theory)
f
s
x N x S < V
usb
PoScoppeMega1+ maximum pipe mode sampling frequency is:
 12 bit mode and two channels: 200kS/s,
 8 bit mode and two channels: 200kS/s,
 12 bit mode and single channel: 500kS/s,
 8 bit mode and single channel: 500kS/s.
When Channel B is turned off, the Mega1+ maximum buffer mode sampling frequency is 2,5MS/s
(single channel only).