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Glossary
©
National Instruments Corporation
G-7
F
FIFO
First-In-First-O
u
t memory b
u
ffer—A data b
u
ffering techniq
u
e that
f
u
nctions like a shift register where the oldest val
u
es (first in) come o
u
t
first. Many DAQ prod
u
cts and instr
u
ments
u
se FIFOs to b
u
ffer digital data
from an A/D converter, or to b
u
ffer the data before or after b
u
s
transmission.
The first data stored is the first data sent to the acceptor. FIFOs are often
u
sed on DAQ devices to temporarily store incoming or o
u
tgoing data
u
ntil
that data can be retrieved or o
u
tp
u
t. For example, an analog inp
u
t FIFO
stores the res
u
lts of A/D conversions
u
ntil the data can be retrieved into
system memory, a process that req
u
ires the servicing of interr
u
pts and often
the programming of the DMA controller. This process can take several
milliseconds in some cases. D
u
ring this time, data acc
u
m
u
lates in the FIFO
for f
u
t
u
re retrieval. With a larger FIFO, longer latencies can be tolerated. In
the case of analog o
u
tp
u
t, a FIFO permits faster
u
pdate rates, beca
u
se the
waveform data can be stored on the FIFO ahead of time. This again red
u
ces
the effect of latencies associated with getting the data from system memory
to the DAQ device.
filter
A physical device or digital algorithm that selectively removes noise from
a signal, or emphasizes certain freq
u
ency ranges and de-emphasizes others.
Electronic filters incl
u
de lowpass, band-pass, and highpass types. Digital
filters can operate on n
u
meric data to perform eq
u
ivalent operations on
digitized analog data or to enhance video images.
filtering
A type of signal conditioning that allows yo
u
to filter
u
nwanted freq
u
ency
components from the signal yo
u
are trying to meas
u
re.
floating signal so
u
rces
Signal so
u
rces with voltage signals that are not connected to an absol
u
te
reference of system gro
u
nd. Also called non-referenced signal so
u
rces.
Some common examples of floating signal so
u
rces are batteries,
transformers, and thermoco
u
ples.
freq
u
ency
The n
u
mber of alternating signals that occ
u
r per
u
nit time.
ft
Feet.
f
u
nction
1. A b
u
ilt-in exec
u
tion element, comparable to an operator, f
u
nction, or
statement in a conventional lang
u
age.
2. A set of software instr
u
ctions exec
u
ted by a single line of code that may
have inp
u
t and/or o
u
tp
u
t parameters and ret
u
rns a val
u
e when exec
u
ted.