E20-10
User Manual
5.2.4. FIFO buffer and its overloading elimination logic
E20-10
has on board 8 Mbyte memory where FIFO buffer is organized. Such depth of
buffer is enough to, for example, compensate 400 ms of spooling delay via USB by operating
system at maximum acquisition frequency of 10 MHz (with zero interframe delay). Experiments
show, that this time interval is fair enough even in operation under Windows (under operating
system of
un
real time) at average load of operating system with rest applications, in the absence of
explicit computer resource exhaustion (see details in
Programmer's manual
). Thereof,
maximum spooling delay time will increase proportionally to decreasing of data transmission traffic
in computer during data acquisition frequency decreasing and when setting to non-zero interframe
delay. We referred in detail on buffer overflow situation processing inside
E20-10
.
In
E20-10
of revision А FIFO buffer overflow occurrence causes data acquisition stopping
and upper-level program necessity to restart
E20-10
, that leads to time-consuming "freezing" of
E20-10 out of data acquisition process. This problem has been strongly taken into account in
E20-
10
of revision B. Here, the specific hardware logic for FIFO buffer overflow elimination against
continuous acquisition has been entered.
Overflow elimination logic
will spool from FIFO data
with volume multiple of minimum required one to eliminate FIFO overflow capability at the
approach to edge of 8 megabit of data collected in FIFO. These emergency spooled data are thrown
from data flow but, in principle, data acquisition without channel number accounting failure at
upper level can be continued due to thrown data volume multiple always of frame size. So, in
E20-
10
of revision В FIFO buffer overflow will always leads to unavoidable (in this case) data flow
break but unlike revision А, you may not restart data acquisition
E20-10
.
It is noteworthy, that all revisions of E20-10 have upper software level tools to alarm FIFO
overflow occurrence which indicate the user data flow from
E20-10
breakage (details see in
Programmer's manual
[1]).
5.2.5. Readings adjustment (calibration)
Module
E20-10
is delivered with calibrations recorded in
L-Card
.
Relevant calibration
factors (product serial number and other additional details as well) are recorded in Flash-memory of
AVR controller.
Using calibration factors
stored in Flash-memory of AVR controller you may account offset
and scale errors (of gain factor) of analog path at each range.
In revision А of module E20-10
the data calibration procedure is implemented with upper
level tools (in computer), and in revision В – with tools of E20-10
itself
.
Working with pure
uncalibrated data in both revisions, on demand, the calibration mechanism may not be used, but you
should take into account, that in this case dispersion in readings of different instances of modules
E20-10
can reach 5% of scale.
It also important to note, that in
E20-10
or rev
ision В the linear calibration arithmetic
– is
integer of ADC data within the range –8192…8191. Calibration factors under calibrating of
E20-
10
at manufacturer are set in such a way that extreme points of each ADC input subrange
correspond to calibrated code values ±8000.
5.2.6. ADC word size overflow warning
ADC word size overflow signal is available at ADC chip output LTC2245, it is generated for each
ADC sample and this signal is used in
E20-10
for this overflow warning
.
In overflow case ADC
uncalibrated code takes one of extreme value -8192 or 8191 – depending on sign of input voltage supplied
to ADC input.
