SRS Labs SR430, Руководство пользователя

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INSTRUMENT OVERVIEW
record can only acquire 4 counts per bin maximum
(4 * 10 ns = 40 ns). If the bins width is 5 ns, then
the maximum number of counts per bin is 1. The
maximum count capacity of each bin is 32,767.
When the bin width is large and the count rate is
high, it is possible to exceed the count capacity of
a bin in a single record. In this case, the data will
overflow and be stored as the maximum count
(32,767).
A single record can capture a transient counting
signal if there are enough counts to be statistically
significant in a single shot. If the count rate is very
low but the signal is repetitive, then multiple
records may be accumulated. Accumulation of
records means simply taking each new record and
adding it to the sum of all previous records on a
bin by bin basis, i.e. data from T1 of each record is
summed together, data from T2 of each record is
summed together, etc. Accumulation reduces sta-
tistical noise since the accumulated counts in each
bin will be larger than the data from a single
record. Each bin can accumulate counts up to
32,767. Additional counts will cause an overflow
and the data will be stored as 32,767. If this limit is
reached, then the bin width should be reduced and
the bins per record increased (to keep the same
record time). This will divide the bins which over-
flowed, into 2 or more smaller bins, each capable
of 32,767 counts. Thus, more total counts may be
accumulated for the same record time.
A scan is an accumulation of a number of records.
The number of records in a scan may be pro-
grammed from 1 to 65,535.
SR430 OVERVIEW
The SR430 data acquisition timing is diagrammed
below. A trigger starts a record of up to 32,704
time bins (T1, T2, ... TN). Each time bin is of equal
duration and is programmable from 5 ns to 10 ms.
There is no dead time between time bins. During
each time bin, signal pulses are counted. At the
end of each time bin, the counter data is stored in
memory. The memory address is then increment-
ed and the counter is reset for the next time bin.
Thus, a record is a list of counter data points cor-
responding to counts received in successive time
bins. Counts which arrive at a bin boundary are
not missed but either fall in the bin just ending or
in the bin just starting.
The number of bins per record is set in 1k incre-
ments from 1k (1024) to 16k (16,384). This repre-
sents the maximum number of bins which can be
displayed and analyzed at one time. This limitation
is due to the data display buffer having a maxi-
mum capacity of 16k data points. The data acqui-
sition memory, however, can store up to 32k data
points. Up to 32,704 bins may actually be acquired
and accumulated, of which, up to 16k bins may be
displayed at a time. The Trigger Offset determines
how many bins are skipped at the beginning of the
total record before data is transferred to the dis-
play buffer.
The maximum count rate is 100 MHz or one count
every 10 ns. Thus, short bins can only acquire a
small number of counts per bin in a single record.
For example, if the bin width is 40 ns, then a single
TIMING DIAGRAM
TRIG
BIN CLK
T
T
1
SYNC/
BUSY
T
2
ACCUMULATION AND
PROCESSING TIME
TBUSY
N
T
3
20 ns
SIGNAL
INPUT
DISC
OUT
BIN WIDTH
45 ns
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