Glossary

F

FIFO

First-In-First-Out memory buffer—A data buffering technique that

 

functions like a shift register where the oldest values (first in) come out

 

first. Many DAQ products and instruments use FIFOs to buffer digital data

 

from an A/D converter, or to buffer the data before or after bus

 

transmission.

 

The first data stored is the first data sent to the acceptor. FIFOs are often

 

used on DAQ devices to temporarily store incoming or outgoing data until

 

that data can be retrieved or output. For example, an analog input FIFO

 

stores the results of A/D conversions until the data can be retrieved into

 

system memory, a process that requires the servicing of interrupts and often

 

the programming of the DMA controller. This process can take several

 

milliseconds in some cases. During this time, data accumulates in the FIFO

 

for future retrieval. With a larger FIFO, longer latencies can be tolerated. In

 

the case of analog output, a FIFO permits faster update rates, because the

 

waveform data can be stored on the FIFO ahead of time. This again reduces

 

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 frequency ranges and de-emphasizes others.

 

Electronic filters include lowpass, band-pass, and highpass types. Digital

 

filters can operate on numeric data to perform equivalent operations on

 

digitized analog data or to enhance video images.

filtering

A type of signal conditioning that allows you to filter unwanted frequency

 

components from the signal you are trying to measure.

floating

The condition where a common mode voltage exists, or may exist, between

 

earth ground and the instrument or circuit of interest. Neither the high, nor

 

the low side of a circuit is at earth potential.

floating signal sources

Signal sources with voltage signals that are not connected to an absolute

 

reference of system ground. Also called non-referenced signal sources.

 

Some common examples of floating signal sources are batteries,

 

transformers, and thermocouples.

FREQ OUT

Frequency Output signal.

frequency

The number of alternating signals that occur per unit time.

ft

Feet.