||Analog-to-digital converter—an electronic device, often an
integrated circuit, that converts an analog signal to a digital
||Application development environment—some examples include
LabVIEW and LabWindows/CVI.
||Analog input—acquisition of data.
||A type of signal conditioning that improves accuracy in the
resulting digitized signal by increasing signal amplitude relative
||Data represented by continuously variable physical
||Analog output—generation of data.
||Application programming interface—A library of functions,
classes or VIs, attributes, and properties for creating
applications for your device.
- Hardware—A signal that occurs or is acted upon at an arbitrary
time, without synchronization to another signal, such as a
- Software—A function that begins an operation and returns prior
to the completion or termination of the operation.
||The reduction of a voltage or acoustical pressure. Measured
referenced to the original voltage.
||The range of frequencies present in a signal, or the range of
frequencies to which a measuring device can respond.
||A signal range that includes both positive and negative values
(for example, –5 V to +5 V).
||The smallest unit of data used in a digital operation. Bits are
binary, so they can be either a 1 or a 0.
||In software, temporary storage for acquired or to-be-generated
- Physical—a terminal or pin at which you can measure or generate
an analog or digital signal. A single physical channel can include
more than one terminal, as in the case of a differential analog
input channel or a digital port of eight lines. The name used for a
counter physical channel is an exception because that physical
channel name is not the name of the terminal where the counter
measures or generates the digital signal.
- Virtual—a collection of property settings that can include a
name, a physical channel, input terminal connections, the type of
measurement or generation, and scaling information. You can define
NI-DAQmx virtual channels outside a task (global) or inside a task
(local). Configuring virtual channels is optional in Traditional
NI-DAQ and earlier versions, but is integral to every measurement
you take in NI-DAQmx. In Traditional NI-DAQ, you configure virtual
channels in MAX. In NI-DAQmx, you can configure virtual channels
either in MAX or in a program, and you can configure channels as
part of a task or separately.
- Switch—a switch channel represents any connection point on a
switch. It may be made up of one or more signal wires (commonly
one, two, or four), depending on the switch topology. A virtual
channel cannot be created with a switch channel. Switch channels
may be used only in the NI-DAQmx Switch functions and VIs.
||A periodic digital signal.
||Common-mode rejection ratio—a measure of the ability of an
instrument to reject interference from a common-mode signal,
usually expressed in decibels (dB).
||The smallest detectable change in an input voltage of a DAQ
||A method of compensating for inaccuracies in thermocouple
||A circuit that counts digital edges. Counters and timers
usually have from 16 bits to 48 bits (sometimes more) counting
capability. The total number of counts possible equals
2N, where N is the number of bits in the
counter. When the edges counted are produced by a clock, elapsed
time can be computed from the number of edges counted if the clock
frequency is known.
||A method of instructing NI-DAQmx to apply additional scaling to
your data. Refer to the Create Scale function in your reference
||Digital-to-analog converter—an electronic device, often an
integrated circuit, that converts a digital number into a
corresponding analog voltage or current.
||Refer to data acquisition.
||A graphical interface for configuring measurement tasks,
channels, and scales.
||A device that acquires or generates data and can contain
multiple channels and conversion devices. DAQ devices include
plug-in devices, PCMCIA cards, and DAQPad devices, which connect to
a computer USB or 1394 (FireWire) port. SCXI modules are considered
- Acquiring and measuring analog or digital electrical signals
from sensors, acquisition transducers, and test probes or
- Generating analog or digital electrical signals.
||Decibel—the unit for expressing a logarithmic measure of the
ratio of two signal levels: dB=20log10 V1/V2, for signals in
|delay from sample
||The amount of time to wait after receiving a sample clock edge
before beginning the acquisition of a sample.
|delay from start
||The amount of time to wait after receiving a start trigger
before beginning the operation.
- An instrument or controller you can access as a single entity
that controls or monitors real-world I/O points. A device often is
connected to a host computer through some type of communication
- See also DAQ device and measurement device.
||A TTL signal. Refer to edge.
||Direct Memory Access—A method of transferring data between a
buffer and a device that is used most often for high-speed
||Software unique to the device or type of device, and includes
the set of commands the device accepts.
||A standard architecture for instrumentation-class, multichannel
data acquisition devices.
||A digital edge is a single rising or falling TTL transition. An
analog edge is defined by the slope, level, and hysteresis
||A digital signal produced from a device or circuit.
||Supplying a voltage or current source to energize an active
sensor or circuit.
||The time for a signal to transition from 90% to 10% of the
maximum signal amplitude.
||A type of signal conditioning that you can use to remove
unwanted frequency components from the signal you are
||A type of memory that implements a First In First Out strategy
in which samples are removed in the order they were written. FIFOs
are typically used as intermediate buffers between an ADC or DAC
and the memory buffer.
|floating signal sources
||Signal sources with voltage signals that are not connected to
an absolute reference or system ground.
||The factor by which a signal is amplified, often expressed in
dB. Gain as a function of frequency is commonly referred to as the
magnitude of the frequency response function.
|grounded signal sources
||Signal sources with voltage signals that are referenced to a
system ground, such as the earth or a building ground. Grounded
signal sources are also called referenced signal sources.
||A form of triggering in which the source of the trigger is an
analog or digital signal. Refer to Software Triggering.
||A window around a trigger level that is often used to reduce
false triggering due to noise or jitter in the signal.
||Hertz—cycles per second of a periodic signal.
||Refer to driver.
||A method whereby a device notifies the computer of some
condition on the device that requires the computer's attention.
When this condition is a request for data or a notification of
available data, interrupts are used as a data transfer
||Input/output—the transfer of data to/from a computer system
involving communications channels, operator interface devices,
and/or data acquisition and control interfaces.
||A type of signal conditioning in which you isolate the
transducer signals from the computer. Isolation makes sure the
measurements from the measurement device are not affected by
differences in ground potentials.
||Light-emitting diode—a semiconductor light source.
||An individual signal in a digital port. The difference between
a bit and a line is that the bit refers to the actual data
transferred, and the line refers to the hardware the bit is
transferred on. However, the terms line and bit are fairly
interchangeable. For example, an 8-bit port is the same as a port
with eight lines.
||A type of signal conditioning in which software linearizes the
voltage levels from transducers, so the voltages can be scaled to
measure physical phenomena.
||Least significant bit—often used to refer to the smallest
voltage change detectable by an A/D converter or the smallest
voltage change that can be generated by a D/A converter.
|Measurement & Automation Explorer (MAX)
||A centralized configuration environment that allows you to
configure all of your National Instruments devices.
||DAQ devices such as the E Series multifunction I/O (MIO)
devices, SCXI signal conditioning modules, and switch modules.
||Refer to buffer.
||A technique for reading and writing to a device directly from
your program, which avoids the overhead of delegating the reads and
writes to kernel-level software. Delegation to the kernel is safer,
but slower. Memory mapping is less safe because an entire 4 KB page
of memory must be exposed to your program for this to work, but it
||Multifunction I/O—Designates a family of data acquisition
devices that have multiple analog input channels, digital I/O
channels, timing, and optionally, analog output channels. An MIO
product can be considered a miniature mixed signal tester, due to
its broad range of signal types and flexibility. It is also known
as multifunction DAQ. An E Series device is an example of an MIO
||A board assembly and its associated mechanical parts, front
panel, optional shields, and so on. A module contains everything
required to occupy one or more slots in a mainframe. SCXI and PXI
devices are modules.
||A switching device with multiple terminals that sequentially
connects each of its terminals to a single terminal, typically at
high speeds. Often used to measure several signals with a single
analog input channel.
||Driver software included with all NI measurement devices.
NI-DAQ is an extensive library of functions you can call from an
application development environment (ADE), such as LabVIEW, to
program all the features of an NI measurement device, such as
configuring, acquiring and generating data from, and sending data
to the device.
||The latest NI-DAQ driver with new functions and development
tools for controlling measurement devices. The advantages of
NI-DAQmx over earlier versions of NI-DAQ include the DAQ Assistant
for configuring channels and measurement tasks for your device for
use in LabVIEW, LabWindows/CVI, and Measurement Studio; increased
performance such as faster single-point analog I/O; and a simpler
API for creating DAQ applications using fewer functions than
earlier versions of NI-DAQ.
||A measure in percentage of full-scale range (FSR) of the
worst-case deviation from the ideal transfer function—a straight
||This specification is included only for DAQ products, such as
signal conditioning products, that do not have an ADC. Because a
product with this specification can also be used with a DAQ product
with an ADC, this nonlinearity specification must be added to the
relative accuracy specification of the DAQ product with the
||Nonreferenced single-ended mode—all measurements are made with
respect to a common (NRSE) measurement system reference, but the
voltage at this reference can vary with respect to the measurement
||Provided by the data acquisition device.
||Channels provided by the plug-in data acquisition device.
||The default source for a particular clock. Usually, the device
has dedicated a circuit for producing this signal and its only
purpose is to act as the source for a certain clock.
||Memory provided by a device for temporary storage of input or
output data. Typically, onboard memory is a FIFO, which is distinct
from computer memory.
||A type of SCXI operating mode in which the module sends each of
its input channels directly to a separate analog input channel of
the device connected to the module.
||Pattern input and output—a digital I/O operation on which a
clock signal initiates a digital transfer. Because the clock signal
is a constant frequency, you can generate and receive patterns at a
||Peripheral Component Interconnect—a high-performance expansion
bus architecture originally developed by Intel to replace ISA and
EISA. PCI has achieved widespread acceptance as a standard for PCs
and work stations, and it offers a theoretical maximum transfer
rate of 132 Mbytes/s.
||Programmable Function Interface—general purpose input
terminals, fixed purpose output terminals. The name of the fixed
output signal is often placed on the I/O connector next to the
terminal as a hint.
||Refer to channel.
||Refer to terminal.
||The negative ratio of the strain in the transverse direction
(perpendicular to the force) to the strain in the axial direction
(parallel to the force).
||A collection of digital lines. Usually the lines are grouped
into either a 8-bit or 32-bit port. Most E Series devices have one
||The number of lines in a port. For example, most E Series
devices have one port with eight lines; therefore, the port width
||If there is no reference trigger, posttrigger samples are the
data acquired after the task is started. If there is a reference
trigger, this is the data acquired after the reference
||Data acquired before the occurrence of the reference
||The technique used on a measurement device to keep a circular
buffer filled with samples, so that when the reference trigger
conditions are met, the buffer includes samples leading up to the
trigger condition as well as samples acquired immediately after the
||A data transfer mechanism in which a buffer is not used and
instead, the computer reads and writes directly to the device.
||The amount of time required for a signal to pass through a
||A form of counter signal generation by which a pulse is
generated when a counter reaches a certain value.
||PCI eXtensions for Instrumentation—a rugged, open system for
modular instrumentation based on CompactPCI, with special
mechanical, electrical, and software features. The PXI standard was
originally developed by National Instruments in 1997 and is now
managed by the PXI Systems Alliance.
|PXI trigger bus
||The timing bus that connects PXI DAQ devices directly, by means
of connectors built into the backplane of the PXI chassis, for
precise synchronization of functions. This bus is functionally
equivalent to the RTSI bus for PCI DAQ devices.
||The minimum and maximum analog signal levels that the ADC can
||Data that has not been changed in any way. For input, data is
returned exactly as received from the device. For output, data is
written as is to the device. Refer to unscaled and scaled.
|referenced signal source
||Signal sources with voltage signals that are referenced to a
system ground, such as the earth or a building ground. Also called
grounded signal sources.
||The smallest amount of input signal change that a device or
sensor can detect. The term discrimination is also used
||The time for a signal to transition from 10% to 90% of the
maximum signal amplitude.
||A connection between a pair of terminals. Any time the source
or destination terminal of a signal is specified, a route is
||Referenced single-ended mode—all measurements are made with
respect to a common reference measurement system or a ground. Also
called a grounded measurement system.
||Resistance temperature detector—a metallic probe that measures
temperature based on its coefficient of resistivity.
||Real-time system integration bus—the NI timing bus that
connects DAQ devices directly, by means of connectors on top of the
devices, for precise synchronization of functions. This bus is
functionally equivalent to the PXI Trigger bus for PXI DAQ
||Samples. Refer to sample.
||Samples per second—used to express the rate at which a
measurement device samples an analog signal.
||A sample is a single measurement from a single channel or, for
output, a single generation to a single channel. A device may
produce more than one sample per channel upon receiving a single
digital edge of a sample clock. An E Series device, for example,
produces one sample from each analog input channel in its task for
every sample clock edge.
||The clock controlling the time interval between samples. Each
time the Sample Clock ticks (produces a pulse) one sample per
channel is acquired or generated.
|sample clock rate
||The number of samples per channel per second. For example, a
sample clock rate of 10 S/s means sampling each channel 10 times
||Data that has been mathematically transformed into engineering
units. Other manipulations also can be done such as reordering to
match the channel order.
||Method of sequentially connecting channels.
||Signal Conditioning eXtensions for Instrumentation—the NI
product line for conditioning low-level signals within an external
chassis near sensors so that only high-level signals are sent to
measurement devices in the noisy PC environment. SCXI is an open
standard available for all vendors.
||A device that responds to a physical stimulus (heat, light,
sound, pressure, motion, flow, and so on) and produces a
corresponding electrical signal.
||A means of conveying information. An analog waveform, a clock,
and a single digital (TTL) edge are all examples of signals.
||The manipulation of signals to prepare them for
||A function that, when it executes, triggers an action such as
starting an acquisition.
||A parameter of signal sources that reflects current-driving
ability of voltage sources (lower is better) and the
voltage-driving ability of current sources (higher is better).
||System timing controller.
- Hardware—a signal that occurs or is acted upon in synchrony
with another signal, such as a reference clock.
- Software—a function that begins an operation and returns only
when the operation is complete.
||A collection of one or more channels, timing, and triggering
and other properties that apply to the task itself. Conceptually, a
task represents a measurement or generation you want to
||Refer to buffer.
||A named location on a DAQ device where a signal is either
generated (output or produced) or acquired (input or
||When counting up, an N bit counter reaches its
terminal count at 2N -1. An N bit
counter counting down reaches its terminal count at 0.
||A semiconductor sensor that produces a repeatable change in
electrical resistance as a function of temperature. Most
thermistors have a negative temperature coefficient.
||A temperature sensor created by joining two dissimilar metals.
The junction produces a small voltage as a function of the
||The voltage level a signal must reach for a trigger to
||A digital edge of a clock.
||A clock that is divided down to produce another clock or a
clock provided to a counter for measuring elapsed time.
||Refer to sensor.
|Traditional NI-DAQ (Legacy)
||An upgrade of the earlier version of NI-DAQ. Traditional NI-DAQ
(Legacy) has the same VIs and functions and works the same way as
NI-DAQ 6.9.x, except you can use both Traditional NI-DAQ
(Legacy) and NI-DAQmx on the same computer, and some hardware is no
||A type of signal conditioning that uses external voltages and
currents to excite the circuitry of a signal conditioning system
into measuring physical phenomena.
||Any signal that causes a device to perform an action, such as
starting an acquisition.
||Transistor-transistor logic—a signal having two discrete
levels, a high and a low level.
||A signal range that is always positive (for example, 0 to +10
||Samples in the integer form that the hardware produces or
requires. Although no mathematical transformations are applied to
unscaled data, other manipulations may be done such as reordering
to match the channel order.
||Refer to channel.