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LabVIEW 2011 Help

Edition Date: June 2011

Part Number: 371361H-01

»View Product Info

Control Design and Simulation Module Glossary

Datalogging and Supervisory Control Module Glossary

Sound and Vibration Measurement Suite Glossary

Unit Test Framework Toolkit Glossary


Symbol Prefix Value
y yocto 10–24
z zepto 10–21
a atto 10–18
f femto 10–15
p pico 10–12
n nano 10–9
µ micro 10–6
m milli 10–3
c centi 10–2
d deci 10–1
da deka 101
h hecto 102
k kilo 103
M mega 106
G giga 109
T tera 1012
P peta 1015
E exa 1018
Z zetta 1021
Y yotta 1024


Δ delta; difference—x denotes the value by which x changes from one index to the next.

1D One-dimensional
2D Two-dimensional
3D Three-dimensional


A amperes
A/D analog-to-digital; analog/digital
absolute coordinates Picture coordinates relative to the origin (0,0) of the 2D picture control.
absolute path File or directory path that describes the location relative to the top level of the file system.
AC alternating current
access level Determines access privileges a user has for certain LabVIEW utilities. Access level values range from 0 to 255.
active cell Cell of a listbox, multicolumn listbox, table, digital data, or tree control to which you can apply property changes.
active row Row of a listbox to which you can apply property changes.
active window Window that is currently set to accept user input, usually the frontmost window. The title bar of an active window is highlighted. Make a window active by clicking it or by selecting it from the Windows menu.
ADC analog-to-digital converter—An electronic device, often an integrated circuit, that converts an analog voltage to a digital number.
ADC resolution Resolution of the ADC, measured in bits. An ADC with 16 bits has a higher resolution and thus a higher degree of accuracy than a 12-bit ADC.
AI analog input
AI device Analog input device that has AI in its name, such as the NEC-AI-16E-4.
AIGND Analog input ground pin on a DAQ device.
alias A false lower frequency component that appears in sampled data acquired at too low a sampling rate compared to the Nyquist frequency.
Am9513-based devices These MIO devices do not have an E- in their names. These devices include the NB-MIO-16, NB-MIO-16X, NB-TIO-10, and NB-DMA2800 on Mac OS X; and the AT-MIO-16, AT-MIO-16F-5, AT-MIO-16X, AT-MIO-16D, and AT-MIO-64F-5 on Windows.
amplification Type of signal conditioning that improves accuracy in the resulting digitized signal and reduces noise.
analog trigger Trigger that occurs at a user-selected level and slope on an incoming analog signal. You can set triggering to occur at a specified voltage on either an increasing or a decreasing signal (positive or negative slope).
ancestor class Any LabVIEW class that is the parent, grandparent, and so on, of another LabVIEW class. The LabVIEW Object may be the ultimate ancestor.
ANSI American National Standards Institute
AO analog output
application Application created using the LabVIEW Development System and executed in the LabVIEW Run-Time System environment.
application instance Instance of LabVIEW created for each target you create in a LabVIEW project. When you open a VI from the Project Explorer window, the VI opens in the application instance for the target. There is a separate instance of LabVIEW running for each target you create. Every time you create a new target in a project, you create a new application instance. For example, with multiple projects, there is an application instance for My Computer in each project. LabVIEW also creates a main application instance, which contains open VIs that are not part of a project and VIs that you did not open from a project. See also target.
Application Programming Interface (API) Programming interface for controlling some software packages, such as Microsoft Visual SourceSafe.
array Ordered, indexed list of data elements of the same type.
array shell Front panel object that houses an array. An array shell consists of an index display, a data object window, and an optional label. It can accept various data types.
artificial data dependency Condition in a dataflow programming language in which the arrival of data, rather than its value, triggers execution of a node.
ASCII American Standard Code for Information Interchange—ASCII is a standard for assigning numeric values to characters.
asynchronous execution Mode in which multiple processes share processor time. For example, one process executes while others wait for interrupts during device I/O or while waiting for a clock tick.
auto-indexing Capability of loop structures to disassemble and assemble arrays at their borders. As an array enters a loop with auto-indexing enabled, the loop automatically disassembles it extracting scalars from 1D arrays, 1D arrays extracted from 2D arrays, and so on. Loops assemble data values into arrays as data values exit the loop in the reverse order.
autoscaling Ability of scales to adjust to the range of plotted values. On graph scales, autoscaling determines maximum and minimum scale values.
autosizing Automatic resizing of labels to accommodate text you enter.


BDF backwards difference formula—Also known as Gear’s Method.
Bessel filters These filters have a maximally flat response in both magnitude and phase. The phase response in the passband, which is usually the region of interest, is nearly linear. Use Bessel filters to reduce nonlinear phase distortion inherent in all IIR filters.
Bessel function The Bessel function of the first kind of order n

is defined by

with n = 0, 1, ...

The Bessel function of the second kind of order n, is defined by

with n = 0, 1, ...
Bessel polynomial The Bessel polynomial of order n is defined by a recurrence relation

for n = 2, 3, ... where and
beta function An integral defined by

or, in terms of the gamma function

bin The interval or component that represents the values at a point in a range.
binary point The binary equivalent of the decimal point. The binary point indicates the transition point from integer bits to fractional bits in a binary number.
binomial coefficient The binomial coefficient is given by

bit array tag Multi-bit value representation of a connection to a real-world I/O point or memory variable. In LabVIEW, this type of tag can be comprised of up to 32 discrete values.
block diagram Pictorial description or representation of a program or algorithm. The block diagram consists of executable icons called nodes and wires that carry data between the nodes. The block diagram is the source code for the VI. The block diagram resides in the block diagram window of the VI.
block diagram terminal Terminal on the block diagram that represents a control or indicator on the front panel. Every front panel control or indicator has a corresponding block diagram terminal. You can view the terminal as an icon terminal or a data type terminal.
BNF Backus-Naur Form—A common representation for language grammars in computer science.
Boolean controls and indicators Front panel objects to manipulate and display Boolean (TRUE or FALSE) data.
bracketing interval A bracketing triplet (a, b, c) of a continuous 1D function f is a combination of three points with f(a) > f(b) and f(c) > f(b). This guarantees the existence of a local minimum of f in the interval (a, c).
bracketing of a minimum A root of a continuous function is said to be bracketed by a pair of points, a < b, when f(a) and f(b) are of opposite signs. A minimum is bracketed when there are three points, a < b < c, with f(a) > f(b) and f(c) > f(b).
breakpoint Pause in execution used for debugging.
Breakpoint tool Tool to set a breakpoint on a VI, node, wire, or (MathScript RT Module) line of script in a MathScript Node.
Brent Method For solving nonlinear equations, methods that converge rapidly to the solution are unreliable because convergence may not occur unless started close enough to the actual solution. On the other hand, the more reliable methods are slower. The Brent method is a hybrid method that combines both the safety of the bisection method and the rapid convergence of inverse quadratic interpolation.
broken Run button Button that replaces the Run button when a VI cannot run because of errors.
broken VI VI that cannot run because of errors; signified by a broken arrow in the broken Run button.
buffer Temporary storage for acquired or generated data.
Bundle function Function that creates clusters from various types of elements.
Butterworth filter A filter with low ripple.
byte stream file File that stores data as a sequence of ASCII characters or bytes.


C string (CStr) A series of zero or more unsigned characters, terminated by a zero, used in the C programming language.
caption label Label on a front panel object used to name the object in the user interface. You can translate this label to other languages without affecting the block diagram source code. See also Name Label.
case One subdiagram of a Case structure.
Case structure Conditional branching control structure that executes one of its subdiagrams based on the input to the Case structure. It is the combination of the IF, THEN, ELSE, and CASE statements in control flow languages.
Cash Karp method Numerical method for solving ordinary differential equations with start conditions. The Cash Karp method is an embedded Runge Kutta formula and is based on a fifth order strategy with six steps. The Cash Karp method works with an adaptive step rate and is computationally more efficient than the Euler method or the Runge Kutta method.
cast To change the type descriptor of a data element without altering the memory image of the data.
  1. 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. A counter also can be a physical channel, although the counter name is not the name of the terminal where the counter measures or generates the digital signal.
  2. 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 (Legacy) and earlier versions, but is integral to every measurement you take in NI-DAQmx. In Traditional NI-DAQ (Legacy), you configure virtual channels in MAX. In NI-DAQmx, you can configure virtual channels either in MAX or in your program, and you can configure channels as part of a task or separately.
  3. Switch—a switch channel represents any connection point on a switch. It can 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.

channel clock Clock that controls the time interval between individual channel sampling within a scan. Products with simultaneous sampling do not have this clock.
chart 2D display of one or more plots in which the display retains a history of previous data, up to a maximum that you define. The chart receives the data and updates the display point by point or array by array, retaining a certain number of past points in a buffer for display purposes. See also scope chart, strip chart, and sweep chart.
Chebyshev polynomial The Chebyshev polynomial, for real numbers x, is given by . This results in and so on.
checkbox Small square box in a dialog box you can select or clear. Checkboxes generally are associated with multiple options that you can set. You can select more than one checkbox.
child class A LabVIEW class that inherits data and member VIs from an ancestor LabVIEW class.
chi-squared An error function given by

In this equation, are the input data points, and is the nonlinear function where are coefficients. If the measurement errors are independent and normally distributed with constant, standard deviation , this is also the least-square estimation.
class A category containing properties, methods, and events. Classes are arranged in a hierarchy with each class inheriting the properties and methods associated with the class in the preceding level.
class library The group of VIs that define a LabVIEW class. The class library also stores the data of the LabVIEW class.
clock Hardware component that controls timing for reading from or writing to groups.
cloning To make a copy of a control or another object by clicking it while pressing the <Ctrl> key and dragging the copy to its new location. (Mac OS X) Press the <Option> key. (Linux) Press the <Alt> key.

(Linux) You also can clone an object by clicking the object with the middle mouse button and then dragging the copy to its new location.
cluster A set of ordered, unindexed data elements of any data type, including numeric, Boolean, string, array, or cluster. The elements must be all controls or all indicators.
cluster shell Front panel object that contains the elements of a cluster.
CMRR common-mode rejection ratio—The measure of the capability of an instrument to reject a signal that is common to both input leads. For example, if you measure a thermocouple in a noisy environment, the noise from the environment appears on both input leads. Therefore, this noise is a common-mode voltage signal that is rejected by an amount equal to the CMRR of the instrument. The CMRR is defined by the following equation:

CMRR = 20 log(Differential Gain/Common Mode Gain)

The ratio is important because it indicates how much of the common mode signal appears in your measurement. The value of the CMRR depends on signal frequency as well and must be specified as a function of frequency. An equivalent equation to represent CMRR is as follows:

20 Log(Measured Common Voltage/Applied Common Voltage)
CODATA Committee on Data for Science and Technology—An international committee that promotes the compilation of reliable numerical data that is important to all fields of science and technology.
coercion Automatic conversion LabVIEW performs to change the numeric representation of a data element.
coercion dot Appears on a block diagram node to alert you that you have wired data of two different numeric data types together. Also appears when you wire any data type to a variant data type, or when LabVIEW discards bits of a fixed-point number.
cold-junction compensation
  1. A method of compensating for inaccuracies in thermocouple circuits.
  2. An artificial reference level that compensates for ambient temperature variations in thermocouple measurement circuits. IC temperature sensors are linear and their output is expressed as mV/°C. A 10 mV/°C sensor, for example, outputs 250 mV at 25 °C. Thermistor outputs, however, are nonlinear. Therefore, thermistor output is specified as the voltage range over a defined temperature range (x volts at 50 °C to y volts at 0 °C).

Coloring tool Tool to set foreground and background colors.
common-mode voltage Any voltage present at the instrumentation amplifier inputs with respect to amplifier ground.
compile Process that converts high-level code to machine-executable code. LabVIEW compiles VIs automatically before they run for the first time after you create or edit alteration.
concatenated Pascal string (CPStr) A list of Pascal-type strings concatenated into a single block of memory.
conditional terminal Terminal of a While Loop that contains a Boolean value that determines if the VI performs another iteration. A conditional terminal also can be added to a For Loop to stop execution early when a condition occurs.
confidence interval The interval within which a function is expected to fall. The narrower the confidence interval, the more likely a fitted model is close to the actual function.
configuration utility Refers to Measurement & Automation Explorer on Windows and configuration utilities for the instrument on Mac OS X and Linux.
conjugate gradient method This method can be used for multidimensional unconstrained minimization. It determines the local minimum of a function of n independent variables. The direction of the gradient is modified at each iteration. This is done by forming a sequence of conjugate (the inner product being orthogonal) search directions and tends to avoid slow convergence, which may result by repeated searching in the same direction. To minimize the function f(x), given an initial guess first calculate . The rest of the algorithm consists of following a sequence of steps until convergence. One of these steps consists of solving for a quantity where

(Fletcher & Reeves) or

(Polak & Ribiere).
connector Part of the VI or function node that contains input and output terminals. Data values pass to and from the node through a connector.
connector pane Region in the upper right corner of a front panel or block diagram window that displays the VI terminal pattern. It defines the inputs and outputs you can wire to a VI.
constant A terminal on the block diagram that supplies fixed data values to the block diagram. See also universal constant and user-defined constant.
container object An object that contains other objects, such as a block diagram, case structure, or array.
content rectangle Region of a listbox, table, digital data, or tree control that contains all headers and cells. The content rectangle does not include scroll bars.
Context Help window Window that displays basic information about LabVIEW objects when you move the cursor over each object. Objects with context help information include VIs, functions, constants, structures, palettes, properties, methods, events, dialog box components, and items in the Project Explorer window.
continued fraction The continued fraction of two sequences (a0, a1, ... , an) and (b0, b1, ... , bn) is defined by the following term

Continued fractions are valuable tools for calculating special functions.
continuous run Execution mode in which a VI runs repeatedly until the operator stops it. Click the Continuous Run button to run a VI repeatedly.
Continuous Run button Icon that indicates a VI is set to execute repeatedly until the user stops it.
contour plot Plot where contour lines are used to connect points of equal value.
control Front panel object for entering data to a VI interactively or to a subVI programmatically, such as a knob, push button, or dial.
control flow Programming system in which the sequential order of instructions determines execution order. Most text-based programming languages are control flow languages.
Controls palette Palette that contains front panel controls, indicators, and decorative objects.
conversion Changing the type of a data element.
Coordinated Universal Time (UTC) Time scale that is determined using highly precise atomic clocks. LabVIEW uses UTC as the standard for the internal representation of dates and times.
cosine integral The cosine integral is defined by

with the Euler constant and x as any real non-negative number.
count terminal Terminal of a For Loop whose value determines the number of times the For Loop executes its subdiagram.
counter A circuit that counts pulses or clock cycles (timing). 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 events counted are the number of clock cycles from a clock source, the amount of time can be computed if the clock frequency is known.
counter/timer group Collection of counter/timer channels. Use this type of group for simultaneous operation of multiple counter/timers.
coupling Manner in which a signal connects from one location to another.
current VI VI whose front panel, block diagram, or Icon Editor is the active window.
curve fitting A technique for extracting a set of curve parameters or coefficients from the data set to obtain a functional description of the data set.
curve in 3D Special parametric plot (x(t), y(t), z(t)), where the parameter t runs over a given interval.


D/A digital-to-analog
DAC digital-to-analog converter—An electronic device, often an integrated circuit, that converts a digital number to a corresponding analog voltage or current.
DAQ See data acquisition (DAQ) and NI-DAQ.
DAQ Assistant A graphical interface for configuring measurement tasks, channels, and scales. The DAQ Assistant is available on Windows only.
DAQ device A device that acquires or generates data and can contain multiple channels and conversion devices. DAQ devices include plug-in drivers, PCMCIA cards, and DAQPad devices, which connect to a computer USB or 1394 (FireWire®) port. SCXI modules are considered DAQ devices.
DAQ-STC Data Acquisition System Timing Controller
data acquisition (DAQ) 1. Acquiring and measuring analog or digital electrical signals from sensors, acquisition transducers, and test probes or fixtures.
2. Generating analog or digital electrical signals.
data dependency Condition in a dataflow programming language in which a node cannot execute until it receives data from another node. See also artificial data dependency.
data flow Programming system involving the creation of block diagrams having executable nodes connected by wires, where the wires between nodes indicate that data produced by one node is used by another node. Nodes may execute when they have received all necessary input data and may produce output data to other nodes in the diagram. G is a dataflow system.
data storage formats Arrangement and representation of data stored in memory.
data type Format for information. In LabVIEW, acceptable data types for most VIs and functions are numeric, array, string, Boolean, path, refnum, enumerated type, waveform, and cluster.
data type descriptor Code that identifies data types; used in data storage and representation.
datalog To acquire data and simultaneously store it in a disk file. LabVIEW File I/O VIs and functions can log data.
datalog file File that stores data as a sequence of records of a single, arbitrary data type that you specify when you create the file. Although all the records in a datalog file must be a single type, that type can be complex. For example, you can specify that each record is a cluster that contains a string, a number, and an array.
Daubechies4 Function Daubechies wavelet with 4 coefficients.
dB decibels—A logarithmic unit for measuring ratios of levels. If the levels are specified in terms of power, then 1 dB = 10*log10 (P/Pr) where P is the measured power and Pr is the reference power. If the levels are specified in terms of amplitude, then 1 dB = 20*log10 (A/Ar) where A is the measured amplitude and Ar is the reference amplitude.
DC direct current
deadband In process instrumentation, the range through which an input signal can vary, upon reversal of direction, without initiating an observable change in output signal. Deadband is usually expressed in percent of range.
default Preset value. Many VI inputs use a default value if you do not specify a value.
default input Default value of a front panel control.
default setting Default parameter value recorded in the driver. In many cases, the default input of a control is a certain value (often 0) that means use the current default setting. For example, the default input for a parameter can be do not change current setting, and the default setting can be no AMUX-64T boards. If you change the value of such a parameter, the new value becomes the new setting. You can set default settings for some parameters in the configuration utility.
deploy To download items or apply settings to a target in the Project Explorer window.
descendant class A child, grandchild, and so on, of another LabVIEW class.
device 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 network. See also DAQ device and measurement device.
device number Slot number or board ID number assigned to the device when you configured it.
DFT See discrete Fourier transform.
dialog box Window that appears when an application needs further information to carry out a command.
differential measurement system A way to configure a device to read signals in which you do not need to connect either input to a fixed reference, such as a building ground.
digital trigger TTL signal that you can use to start or stop a buffered data acquisition operation, such as buffered analog input or buffered analog output.
dimension Size and structure of an array.
directory Structure for organizing files into convenient groups. A directory is like an address that shows the location of files. A directory can contain files or subdirectories of files.
discrete Having discontinuous values of the independent variable, usually time.
discrete Fourier transform A digital technique for computing the Fourier transform. The discrete Fourier transform determines the amplitude and phase of frequency components present in a time domain digital signal.
dithering Addition of Gaussian noise to an analog input signal. By applying dithering and then averaging the input data, you can effectively increase the resolution by another one-half bit.
DLL Dynamic Link Library. See also shared library.
DMA direct memory access—A method by which you can transfer data to computer memory from a device or memory on the bus, (or from computer memory to a device), while the processor does something else. DMA is the fastest method of transferring data to or from computer memory.
Document Object Model (DOM) An application programming interface for well-formed XML documents. The DOM defines the manner in which you can access and manipulate the structure of a document.
Document Type Definition (DTD) A list of elements and attributes allowed in XML document.
DOM See Document Object Model.
domain A network that contains user and group accounts.
downhill simplex method Determines a local minimum of a function of n independent variables. The Downhill Simplex algorithm, also called the Nelder and Mead method, works without partial derivatives. The algorithm consists of catching the minimum of the function, f(X), with the help of simple geometrical bodies, namely with a simplex. A simplex in 2D is a triangle, a simplex in 3D is a tetrahedron, and so on. You must have n + 1 starting points, each of dimension n, forming the initial simplex. The user must enter only one point of these (n+1). The (n+1) dimensional simplex is automatically constructed. The algorithm generates a new simplex by some elementary operations like reflections, expansions, and contractions. In the end, the minimum is concentrated in a very small simplex.
drag To use the cursor on the screen to select, move, copy, or delete objects.
drive Letter in the range a-z followed by a colon (:), to indicate a logical disk drive.
driver Software that controls a specific hardware device, such as a DAQ device.
DS (data space) Memory allocation section that holds all data in a VI except execution data.
DSP digital signal processing or digital signal processor
DTbl digital table
DTD See Document Type Definition.
duty cycle The ratio of the duration, or time, that a signal is on to the total period of the signal.
DWDT digital waveform data type
dynamic data type Data type used by Express VIs that includes the data associated with a signal and attributes that provide information about the signal, such as the name of the signal or the date and time the data was acquired. Attributes specify how the signal appears on a graph or chart.
dynamic dispatch A VI that defines a method of a LabVIEW class. Dynamic dispatch member VIs are VIs with the same name that occur throughout the class hierarchy. Similar to polymorphic VIs, LabVIEW determines at run time which member VI to call.


edit mode When you can make changes to a VI.
EEPROM electrically erased programmable read-only memory—Read-only memory that you can erase with an electrical signal and reprogram.
eigenvalues Values of l for which the matrix equation Ax = lx has a nontrivial solution (x ≠ 0) are known as eigenvalues or characteristic values.
eigenvectors Solutions of x for which the matrix equation Ax = lx has a nontrivial solution (x ≠ 0) are known as eigenvectors or characteristic vectors.
empty array Array that has zero elements but has a defined data type. For example, an array that has a numeric control in its data display window but has no defined values for any element is an empty numeric array.
encapsulation The consolidation of data and methods into a LabVIEW class, where the data is accessible only through class member VIs.
end of file (EOF) Character offset of the end of file relative to the beginning of the file. The EOF is the size of the file.
Engineering Unit (EU) Term of data measurement, as degrees Celsius, pounds, grams, and so on.
error cluster Consists of a Boolean status indicator, a numeric code indicator, and a string source indicator.
error in Error cluster that enters a VI.
Error list window Window that displays errors and warnings occurring in a VI and in some cases recommends how to correct the errors.
error message Indication of a software or hardware malfunction or of an unacceptable data entry attempt.
error out The error cluster that leaves a VI.
Euler method Numerical method for solving ordinary differential equations with start conditions. This is a single-step method because it depends on information at only one point in time to advance to the next point.
event Condition or state of an analog or digital signal.
Event Data Node Node attached to the left and right sides of an Event structure indicating the available data for the event you configured that case to handle. If you configure a single case to handle multiple events, only the data that is common to all handled event types is available.
event driven programming Method of programming whereby the program waits on an event to occur before executing one or more functions.
EXE See stand-alone application.
execution buffer Memory allocation for data on the block diagram.
execution highlighting Debugging technique that animates VI execution to illustrate the data flow in the VI.
exponential window The shape of the exponential window is that of a decaying exponential. The following equation defines the exponential window.

for n = 0, 1, 2, …, N – 1

where N is the length of the window, w is the window value, and f is the final value.

The initial value of the window is one and gradually decays toward zero. You can adjust the final value of the exponential window to between 0 and 1. The exponential window is useful for analyzing transient response signals whose duration is longer than the length of the window. The exponential window damps the end of the signal, ensuring that the signal fully decays by the end of the sample block. You can apply the exponential window to signals that decay exponentially, such as the response of structures with light damping that are excited by an impact, such as the impact of a hammer.
Express VI A subVI designed to aid in common measurement tasks. You configure an Express VI using a configuration dialog box.
external trigger Voltage pulse from an external source that triggers an event, such as A/D conversion.
extrema Maxima and minima.


fall time The time for a signal to move from 90% to 10% of the signal value.
fast Fourier transform An efficient mathematical algorithm for calculating the discrete Fourier transform. The number of samples is usually constrained to be a power of two. The fast Fourier transform determines the amplitude and phase of frequency components present in a time domain digital signal.
FFFT fast fractional Fourier transform
FFT See fast Fourier transform.
FieldPoint A family of industrial I/O modules from National Instruments.
FIFO First-in-first-out memory buffer—The first data stored is the first data sent to the acceptor.
file refnum See refnum.
filter events Allow control over how the user interface behaves.
filtering Type of signal conditioning that allows you to filter unwanted signals from the signal you are trying to measure.
fixed step-size ODE solver ODE solver that does not adjust the step size during simulation.
Flat Sequence structure Program control structure that executes its subdiagrams in numeric order. Use this structure to force nodes that are not data dependent to execute in the order you want if flow-through parameters are not available. The Flat Sequence structure displays all the frames at once and executes the frames from left to right until the last frame executes.
flat top window The flat top window has the best amplitude accuracy of all the smoothing windows at ±0.02 dB for signals exactly between integral cycles. Because the flat top window has a wide main lobe, it has poor frequency resolution. The following equation defines the flat top window.

where ω = (2πn)/N

a0 = 0.215578948
a1 = 0.416631580
a2 = 0.277263158
a3 = 0.083578947
a4 = 0.006947368

The flat top window is most useful in accurately measuring the amplitude of single frequency components with little nearby spectral energy in the signal.
flattened data Data of any type that has been converted to a string, usually for writing the data to a file.
Fletcher & Reeves See conjugate gradient method.
floating signal sources Signal sources with voltage signals that are not connected to an absolute reference or system ground. Some common examples of floating signal sources are batteries, transformers, or thermocouples. Also called nonreferenced signal sources.
For Loop Iterative loop structure that executes its subdiagram a set number of times with the option of stopping execution early when a condition occurs. Equivalent to text-based code: For i = 0 to n — 1, do...
Formula Node Node that executes equations you enter as text. Especially useful for lengthy equations too cumbersome to build in block diagram form.
Fourier transform A mathematical technique that resolves a given signal into the sum of sines and cosines. Widely used as the FFT (fast Fourier transform), which is the basis for spectrum analysis.
frame Subdiagram of a Flat or Stacked Sequence structure.
free label Label on the front panel or block diagram that does not belong to any other object.
frequency f, the basic unit of rate, measured in events or oscillations per second using a frequency counter or spectrum analyzer. Frequency is the reciprocal of the period of a signal.
frequency bin The interval or component that represents the values at a point in a frequency domain. Also called a frequency line or FFT bin.
frequency response The gain and phase response of a circuit or other unit under test at all frequencies of interest. Although the formal definition of frequency response includes both the gain and phase, in common usage, the frequency response often only implies the magnitude (gain). The frequency response is defined as the Fourier transform of the Impulse Response of a system.
front panel Interactive user interface of a VI. Front panel appearance imitates physical instruments, such as oscilloscopes and multimeters.
function Built-in execution element, comparable to an operator, function, or statement in a text-based programming language.
Functions palette Palette that contains VIs, functions, block diagram structures, and constants.


G Graphical programming language LabVIEW uses.
gain Amplification or attenuation of a signal.
gamma function The gamma function of x is the generalization of the common factorial function n!. The relation between these two functions is for all natural numbers n. The gamma function is defined by

for real and complex x and has the property .
GATE input pin Counter input pin that controls when counting in the application occurs.
Gear's Method See BDF.
General Purpose Interface Bus GPIB. Synonymous with HP-IB. The standard bus used for controlling electronic instruments with a computer. Also called IEEE 488 bus because it is defined by ANSI/IEEE Standards 488-1978, 488.1-1987, and 488.2-1992.
Get Color tool Copies colors for pasting with the Coloring tool.
global error Maximum difference between the solution the function computes and the exact solution.
global property A VISA property whose value is the same for all sessions to the specified resource.
global variable Accesses and passes data among several VIs on a block diagram.
glyph Small picture or icon.
GPIB See General Purpose Interface Bus.
graph A display of one or more plots. A graph receives and plots data as a block.
graph control Front panel object that displays data in a Cartesian plane.
grounded signal sources Signal sources with voltage signals that are referenced to a system ground, such as a building ground. Also called referenced signal sources.
group Collection of input or output channels or ports that you define. Groups can contain analog input, analog output, digital input, digital output, or counter/timer channels. A group can contain only one type of channel. Use a task ID number to refer to a group after you create it. You can define up to 16 groups at one time.

To erase a group, pass an empty channel array and the group number to the group configuration VI. You do not need to erase a group to change its membership. If you reconfigure a group whose task is active, LabVIEW clears the task and returns a warning. LabVIEW does not restart the task after you reconfigure the group.


Hamming window The Hamming window is a modified version of the Hanning window. The shape of the Hamming window is similar to that of a cosine wave. The following equation defines the Hamming window.

for n = 0, 1, 2, …, N – 1

where N is the length of the window and w is the window value.

handle Pointer to a pointer to a block of memory that manages reference arrays and strings. An array of strings is a handle to a block of memory that contains handles to strings.
handshaking A type of protocol that makes it possible for two devices to synchronize operations.
Hanning window A Hanning window has a shape similar to that of half a cycle of a cosine wave. The following equation defines the Hanning window.

for n = 0, 1, 2, …, N – 1

where N is the length of the window and w is the window value. Also called a Hann window.

hardware triggering Form of triggering where you set the start time of an acquisition and gather data at a known position in time relative to a trigger signal.
hex Hexadecimal. Base-16 number system.
Hierarchy window See VI Hierarchy window.
housing Non-moving part of front panel controls and indicators that contains sliders, scales, or scroll boxes.
Hz hertz—Cycles per second.


I/O input/output—The transfer of data to or from a computer system involving communications channels, operator input devices, and/or data acquisition and control interfaces.
IAC interapplication communication
icon Graphical representation of a node on a block diagram.
Icon Editor Interface similar to that of a graphics program for creating VI icons.
IDE integrated development environment—A software application that serves as a comprehensive human interface for computer programming, typically dedicated to a specific programming language.
IEEE Institute for Electrical and Electronic Engineers
immediate digital I/O Type of digital acquisition/generation where LabVIEW updates the digital lines or port states immediately or returns the digital value of an input line. Also called nonlatched digital I/O.
incomplete beta function The incomplete beta function is defined by

with a, b > 0 and where B(a, b) denotes the beta function of a and b
incomplete gamma function The incomplete gamma function is defined by

for a > 0
indicator Front panel object that displays output, such as a graph or LED.
Inf Digital display value for a floating-point representation of infinity.
inheritance The use of one LabVIEW class as the initial definition of a new LabVIEW class. The inheriting class has the same data and member VIs as the ancestor class initially, but you can modify or add to the existing data and methods as you need.
initializer terminal Terminal that sets the initial value of a Feedback Node.
inplace The condition in which two or more terminals, such as error I/O terminals or shift registers, use the same memory space.
input range Difference between the maximum and minimum voltages an analog input channel can measure at a gain of 1. The input range is a scalar value, not a pair of numbers. By itself, the input range does not uniquely determine the upper and lower voltage limits. An input range of 10 V could mean an upper limit of +10 V and a lower limit of 0 V or an upper limit of +5 V and a lower limit of -5 V.

The combination of input range, polarity, and gain determines the input limits of an analog input channel. For some products, jumpers set the input range and polarity, although you can program them for other products. Most products have programmable gains. When you use SCXI modules, you also need their gains to determine the input limits.
instrument driver A set of high-level functions that control and communicate with instrument hardware in a system.
Instrument I/O Assistant Add-on launched from the Instrument I/O Assistant Express VI that communicates with message-based instruments and graphically parses the response.
integer Any of the natural numbers, their negatives, or zero.
integer word length The number of integer bits in a binary number, or, given an initial position to the left or right of the most significant bit, the number of bits to shift the binary point to reach the most significant bit. If the integer word length is positive, shift the binary point to the left. If the integer word length is negative, shift the binary point to the right.
intensity map/plot Method of displaying three dimensions of data in a 2D plot with the use of color.
interrupt Signal that indicates that the central processing unit should suspend its current task to service a designated activity.
interval scanning Scanning method where there is a longer interval between scans than there is between individual channels that comprises a scan.
Invoke Node Invokes a method or action on a reference.
IP Internet protocol
IrDA Infrared Data Association
isolation Type of signal conditioning in which you isolate the transducer signals from the computer for safety purposes. This protects you and the computer from large voltage spikes and makes sure the measurements from the DAQ device are not affected by differences in ground potentials.
iteration terminal Terminal of a For Loop or While Loop that contains the current number of completed iterations.
IVI Interchangeable Virtual Instruments—A software standard for creating a common interface (API) to common test and measurement instruments.
IVI driver A driver written according to the IVI specification. The generic driver for a class of instruments (such as voltmeters) is called a class driver, whereas the driver for a specific instrument from a specific manufacturer is called a device-specific driver.


Jacobian elliptic function The value of sn (Jacobian Elliptic Function) is determined by the relation

where u and k are given real numbers. The other Jacobian Elliptic functions have the following definitions


Kaiser-Bessel window A Kaiser-Bessel window is a flexible smoothing window whose shape you can modify by adjusting the inputs. Thus, depending on your application, you can change the shape of the window to control the amount of spectral leakage. The Kaiser-Bessel window is useful for detecting two signals of almost the same frequency but with significantly different amplitudes.
kH kilohertz
Kwords 1,024 words (16 bits) of memory.


Lab/1200 device Devices, such as the Lab-PC-1200 and the DAQCard-1200, that use the 8253 type counter/timer chip.
label Text object used to name or describe objects or regions on the front panel or block diagram.
Labeling tool Tool to create labels and enter text into text windows.
LabVIEW Laboratory Virtual Instrument Engineering Workbench—LabVIEW is a graphical programming language that uses icons instead of lines of text to create programs.
LabVIEW class A user-defined data type in LabVIEW. A LabVIEW class defines the data and methods associated with an object of the class.
LabVIEW class hierarchy The inheritance relationship of LabVIEW classes.
LabVIEW Object The root of the LabVIEW class inheritance tree.
LabVIEW string (LStr) The string data type that LabVIEW block diagrams use.
LabVIEW system time The date and time that LabVIEW uses as a reference for absolute time. LabVIEW system time is defined as 12:00 a.m., Friday, January 1, 1904, Universal Time [01-01-1904 00:00:00]. See also Coordinated Universal Time (UTC).
LED light-emitting diode
Legacy MIO device Devices, such as the AT-MIO-16, that typically are configured with jumpers and switches and are not Plug and Play compatible. They also use the 9513 type counter/timer chip.
legend Object a graph or chart owns to display the names and plot styles of plots on that graph or chart.
Legendre elliptic integral The Legendre Elliptic Integral of the 1st kind is defined by the following equation

library See LLB or project library.
limit settings Maximum and minimum voltages of the analog signals you are measuring or generating.
linear programming Suppose that we are given f, a linear function of the variables x1, x2, x3,.....xn, and a set of constraints on these variables in terms of linear inequalities. Linear programming consists of methods for maximizing or minimizing f. Such problems usually are found in the areas of economics, distribution of goods, production, and approximation theory.
linearization Type of signal conditioning in which LabVIEW linearizes the voltage levels from transducers so the voltages can be scaled to measure physical phenomena.
listbox Box within a dialog box that lists all available choices for a command. For example, a list of filenames on a disk.
LLB LabVIEW file that contains a collection of related VIs for a specific use.
local error Error introduced into the solution per time step.
local property A VISA property whose value is unique to the session.
local variable Variable that enables you to read or write to one of the controls or indicators on the front panel of a VI.
logic gate An electronic circuit designed to act as boolean logic.
logical processor A processing unit of a computer or target. For example, a single hyperthreaded processor can have two or more logical processors, and a machine with two quad-core processors has eight logical processors.
lowpass filter A circuit that attenuates the high-frequency components in an analog signal and only passes low frequencies. For imaging, a lowpass filter removes detail and blurs the image.
LSB Least Significant Bit


mA milliamp
main lobe window The center of the main lobe of a smoothing window occurs at each frequency component of the time-domain signal. By convention, to characterize the shape of the main lobe, the widths of the main lobe at approximately 3 dB and 6 dB below the main lobe peak describe the width of the main lobe. The unit of measure for the main lobe width is FFT bins or frequency lines. The width of the main lobe of the smoothing window spectrum limits the frequency resolution of the windowed signal. Therefore, the ability to distinguish two closely spaced frequency components increases as the main lobe of the smoothing window narrows. As the main lobe narrows and spectral resolution improves, the window energy spreads into its side lobes, increasing spectral leakage and decreasing amplitude accuracy. A trade-off occurs between amplitude accuracy and spectral resolution.
major time step A time step at which the ODE solver produces an approximate solution to the differential equation.
marquee Moving, dashed border that surrounds selected objects.
matrix A rectangular array of numbers or mathematical elements that represent the coefficients in a system of linear equations.
MAX See Measurement & Automation Explorer.
maxima Maximum value(s) of a function.
MB Megabytes of memory. 1 MB is equal to 1,024 KB.
Measurement & Automation Explorer The standard National Instruments hardware configuration and diagnostic environment on Windows.
measurement device A DAQ device such as the E Series multifunction I/O (MIO) device, the SCXI signal conditioning module, and the switch module.
member VI A VI that a LabVIEW class owns. A member VI can access the private data of a LabVIEW class.
memory buffer See buffer.
menu bar Horizontal bar that lists the names of the main menus of an application. The menu bar appears below the title bar of a window. Each application has a menu bar that is distinct for that application, although some menus and commands are common to many applications.
method A procedure that is executed when an object receives a message. A method is always associated with a class.
MHz megahertz
minima Minimum value(s) of a function.
minor time step A time step evaluated between major time steps. Typically taken in order to improve the accuracy of the major time step.
model Code designed to mimic the behavior of a particular hardware configuration or software application for the purposes of debugging and simulation.
module 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.
MSB Most Significant Bit
multicore programming See multi-core programming.
multi-core programming Two or more processors in one computer, each of which can simultaneously run a separate thread.
multiplexed mode SCXI operating mode in which analog input channels are multiplexed into one module output so that the cabled DAQ device can access the module's multiplexed output and the outputs on all other multiplexed modules in the chassis through the SCXI bus. Also called serial mode.
multi-step ODE solver ODE solver that approximates the behavior of a model at time t + dt by taking into account the behavior of the model at a number of previous time steps.
multithreaded application Application that runs several different threads of execution independently. On a multiple processor computer, the different threads might be running on different processors simultaneously.
multithreading A technique for an operating system to handle multiple small tasks at one time, known as threads.


Name Label Label of a front panel object used to name the object and as distinguish it from other objects. The label also appears on the block diagram terminal, local variables, and property nodes that are part of the object. See also caption label.
NaN Digital display value for a floating-point representation of <Not A Number>. Typically the result of an undefined operation, such as log(–1).
Network Address Translating (NAT) routers Routers that allow multiple host machines to use a single IP address.
Newton Raphson method Determines a zero of a 1D function close to two points with the help of the derivative of this 1D function. The two values form a search limit for the unknown zero of the 1D function. The Newton Raphson method, or Newton method, is an iterative method for solving equations of the form f(x) = 0 where the derivative of f, f', is continuous. Given two values, x1 and x2, with f(x1)×f(x2) < 0, first use the midpoint method to calculate


Then use the Newton method to calculate


Replace x(n) by x(n+1) and repeat equation 2 until a certain termination condition occurs. This termination condition could be either after a given number of repetitions or if . This is a fast and simple method.
NI-DAQ Driver software included with all NI-DAQ devices and signal conditioning components. NI-DAQ is an extensive library of VIs and functions you can call from an application development environment (ADE), such as LabVIEW, to program an NI measurement device, such as the M Series multifunction I/O (MIO) DAQ devices, signal conditioning modules, and switch modules.
NI-DAQ 7.x Includes two NI-DAQ drivers—NI-DAQmx and Traditional NI-DAQ (Legacy)—each with its own APIs, hardware configuration, and software configuration.
NI-DAQ 8.x and later Includes the latest version of the software driver, NI-DAQmx. NI-DAQmx replaces Traditional NI-DAQ (Legacy). NI-DAQmx and Traditional NI-DAQ (Legacy) have their own APIs, hardware configurations, and software configurations.
NI-DAQmx The latest NI-DAQ driver with new VIs, 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 a device for use in LabVIEW, LabWindows™/CVI™, and Measurement Studio; increased performance such as faster single-point analog I/O; NI-DAQmx simulation for most supported devices for testing and modifying applications without plugging in hardware; and a simpler, more intuitive API for creating DAQ applications using fewer functions and VIs than earlier versions of NI-DAQ. LabVIEW supports NI-DAQmx on Windows and Linux only.
NI-PSP NI Publish-Subscribe Protocol—A data transfer protocol to write and allow users to read live data. NI-PSP is a proprietary technology that provides fast and reliable data transmission for large and small applications and is installed as a service on the computer when you install LabVIEW.
NIST National Institute of Standards and Technology—A federal technology agency that develops and promotes measurement, standards, and technology.
node Program execution element. Nodes are analogous to statements, operators, functions, and subroutines in text-based programming languages. On a block diagram, nodes include functions, structures, and subVIs. See also XML node.
non-displayable characters ASCII characters that cannot be displayed, such as null, backspace, tab, and so on.
Non-referenced single-ended (NRSE) measurement system All measurements are made with respect to a common reference, but the voltage at this reference can vary with respect to the measurement system ground.
nonsingular matrix Matrix in which no row or column is a linear combination of the other rows or columns, respectively. In other words, the rows or columns are linearly independent. This matrix has a unique inverse, and it has a nonzero determinant.
not-a-refnum Predefined value that indicates the refnum is invalid.
notify events Tell LabVIEW that a user action has already occurred, such as when a user changes the value of a control.
ns nanoseconds
numeric controls and indicators Front panel objects to manipulate and display numeric data.
Nyquist criterion 0 f1< 0.5fs, where f1 is the cutoff frequency and fs is the sampling frequency.
Nyquist frequency When an analog signal is sampled at a rate more than twice that of its highest frequency component, it can be properly reconstructed when reconverted back to the analog domain. The required sampling rate is called the Nyquist frequency.
Nyquist Theorem A law of sampling theory stating that if a continuous bandwidth-limited signal contains no frequency components higher than half the frequency at which it is sampled, then the original signal can be recovered without distortion. If the signal is not sampled fast enough, aliasing will occur.


object Generic term for any item on the front panel or block diagram, including controls, indicators, nodes, wires, and imported pictures.
object code Compiled version of source code. Object code is not standalone because you must load it into LabVIEW to run it.
Object Shortcut Menu tool Tool to access a shortcut menu for an object.
ODE ordinary differential equation
ODE solver Algorithm that solves an ordinary differential equation.
OLE Object Linking and Embedding
OLE for Process Control (OPC) See OPC.
one-dimensional Having one dimension, as in the case of an array that has only one row of elements.
OPC OLE for Process Control—A set of standard interfaces developed by the OPC Foundation to ensure interoperability among control devices from different manufacturers for the transfer of real-time plant data.
Operating tool Tool to enter data into controls or to operate them.
operation buffer Memory allocation for data at each front panel control.
  1. Person who initiates and monitors the operation of a process.
  2. A symbol that represents a mathematical operation, such as +, −, ÷, and so on.
  3. In the case of a logical operator, operator refers to the logical constants AND, OR, or NOT.

optimal step For a function that has many maxima, minima, or singularities, the standard method (using equidistant points) may yield incorrect results. In such cases, the optimal step method is better. This method starts off with taking equidistant points but also checks the steepness of the curve between these points. In very steep portions (determined by the value of epsilon on the front panel) of the graph, a new point is generated in between. As a rule, the smaller the value of epsilon, the more the points that are generated and the better the graph.
  1. ODE solver characteristic that determines how much the error amount changes when you vary the step size.
  2. Harmonic of the rotational speed of rotating machinery. For example, in the case of a shaft rotating at 6,000 rpm, the first order component occurs at a frequency of 100 Hz (6000/60), whereas the third order component occurs at a frequency of 300 Hz.

OUT output pin Counter output pin where the counter can generate various TTL pulse waveforms.
overflow A condition in which the result of an operation exceeds the range of values that the output type can represent.
override VI Allows you to override an member VI of an ancestor LabVIEW class.
owning pane The pane of the front panel in which an object resides.


package The physical processor, or chip, in a computer or target.
Pade approximation Determines the coefficients of a rational polynomial to best suit a given set of first derivatives. Let f be a given function with known values

A unique rational polynomial exists


The rational polynomial can be determined by solving a special linear equation.
palette Displays objects or tools you can use to build the front panel or block diagram.
panel window VI window that contains the front panel, the toolbar, and the icon and connector panes.
parametric plot Plot of the variables (such as x and y) that are given in terms of another variable t (called a parameter), resulting in the parametric equations x = f(t) and y = g(t). Each value of t determines a point (x,y). As t is varied, the point (x,y) = (f(t), g(t)) varies and traces a curve, to plot.
parent class An existing LabVIEW class from which another class inherits.
parser VI that scans a string to determine the function of each of the elements in the string.
partial derivative Derivative taken with respect to one of two or more independent variables, with the others treated as constants.
Pascal string (PStr) A series of unsigned characters, with the value of the first character indicating the length of the string. Used in the Pascal programming language.
PCI Peripheral Component Interconnect—An industry-standard, high-speed databus.
period The period of a signal, most often measured from one zero crossing to the next zero crossing of the same slope. The period of a signal is the reciprocal of its frequency (in Hz). Period is designated by the symbol T.
picture Series of graphics instructions that a 2D picture control uses to create a picture.
PID control See Proportional Integral Derivative (PID) control.
pixel Smallest unit of a digitized picture.
pixmap Standard format for storing pictures in which a color value represents each pixel. A bitmap is a black and white version of a pixmap.
PLC See Programmable Logic Control (PLC).
plot Graphical representation of an array of data shown either on a graph or a chart.
point Cluster that contains two 16-bit integers that represent horizontal and vertical coordinates.
Poisson's Ratio The negative ratio of the transverse strain to the longitudinal strain.
Polak & Ribiere See conjugate gradient method.
polling Method of sequentially observing each I/O point or user interface control to determine if it is ready to receive data or request computer action.
polymorphism Ability of a node to automatically adjust to data of different representation, type, or structure.
Positioning tool Tool to move and resize objects.
power spectrum fractional FFT Magnitude of the FFFT.
prediction interval The interval within which values of a function are expected to fall.
pretty print To make the contents of a document, such as XML data, easier to read. Pretty printing makes content easier to read by adding white space and end-of-line (EOL) characters to the content.
prime FFT Special case of the FFT where the signal length is prime. The prime FFT VI is computationally more efficient than the classical FFT algorithms.
private data The data of a LabVIEW class. Only member VIs of a class can access the private data of a class.
private data control Defines the data of the LabVIEW class.
private scope Only VIs within the same LabVIEW class can call the member VI. Private member VIs display a red key glyph in the Project Explorer window.
probe Debugging feature for checking intermediate values in a VI.
Probe tool Tool to create probes on wires or (MathScript RT Module) MathScript Nodes.
Programmable Logic Control (PLC) Device with multiple inputs and outputs that contains a program you can alter. LabVIEW Device Servers establish communication with PLCs.
project A collection of LabVIEW files and files not specific to LabVIEW that you can use to create build specifications and deploy or download files to targets.
Project Explorer window Window in which you can create and edit LabVIEW projects.
project library A collection of VIs, type definitions, shared variables, palette menu files, and other files, including other project libraries.
Properties dialog boxes Dialog boxes accessed from the shortcut menu of a control or indicator that you can use to configure how the control or indicator appears in the front panel window.
Property Node Sets or finds the properties of a VI or application.
Proportional Integral Derivative (PID) control Combination of proportional, integral, and derivative control actions. Refers to a control method in which the controller output is proportional to the error, its time history, and the rate at which it is changing. The error is the difference between the observed and desired values of a variable that is under control action.
protected scope Only VIs within the same LabVIEW class or a descendant class can call the member VI. Protected member VIs display a dark yellow key glyph in the Project Explorer window.
prototype Simple, quick implementation of a particular task to demonstrate that the design has the potential to work. The prototype usually has missing features and might have design flaws. In general, prototypes should be thrown away, and the feature should be reimplemented for the final version.
pseudocode Simplified language-independent representation of programming code.
public scope Any VI can call the member VI of the LabVIEW class as a subVI.
pull-down menus Menus accessed from a menu bar. Pull-down menu items are usually general in nature.
pulse A signal whose amplitude deviates from zero for a short period of time.
pulse train Multiple pulses.
pulse width The time from the rising to the falling slope of a pulse (at 50% amplitude).
PXI PCI eXtensions for Instrumentation—A modular, computer-based instrumentation platform.


quantization error The inherent uncertainty in digitizing an analog value due to the finite resolution of the conversion process. The quantization error depends on the number of bits in the converter, along with its errors, noise, and nonlinearities.


R resistance
race condition Occurs when two or more pieces of code that execute in parallel change the value of the same shared resource, typically a global or local variable.
range Region between the limits within which a quantity is measured, received, or transmitted. Expressed by stating the lower and upper range values.
rational polynomial Quotient of polynomials. The advantage they have over polynomials for approximating functions is that they can be used to model functions with poles.
read mark Points to the scan at which a read operation begins. Analogous to a file I/O pointer, the read mark moves every time you read data from an input buffer. After the read is finished, the read mark points to the next unread scan. Because multiple buffers are possible, you need both the buffer number and the scan number to express the position of the read mark.
real Laplace transform Laplace transform for real s.
real-time Pertaining to the performance of a computation during the actual time that the related physical process transpires so results of the computation can be used in guiding the physical process.
rectangle Cluster that contains four 16-bit integers. The first two values describe the vertical and horizontal coordinates of the top left corner. The last two values describe the vertical and horizontal coordinates of the bottom right corner.
rectangular window A rectangular window has a value of one over its length. The following equation defines the rectangular window. w(n) = 1.0

for n = 0, 1, 2, …, N – 1

where N is the length of the window and w is the window value.

Applying a rectangular window is equivalent to not using any window because the rectangular function just truncates the signal to within a finite time interval. The rectangular window has the highest amount of spectral leakage.
recursion The ability of a VI to call itself on its own block diagram including the block diagram of any subVIs. Use recursion to operate many times on the output of the same process.
reentrant execution Mode in which calls to multiple instances of a subVI can execute in parallel with distinct and separate data storage.
referenced single-ended (RSE) measurement system All measurements are made with respect to a common reference or a ground. Also called a grounded measurement system.
refnum Reference number. An identifier that LabVIEW uses as reference to an object such as a VI, application, or an ActiveX or .NET object. Use a refnum as an input parameter for a function or VI to perform an operation on the object.
relative coordinates Picture coordinates relative to the current location of the pen.
relocatable Able to be moved by the memory manager to a new memory location.
representation Subtype of the numeric data type, of which there are 8-, 16-, 32-, and 64-bit signed and unsigned integers, as well as single-, double-, fixed-point, and extended-precision, floating-point numbers.
resizing handles Squares or circles that appear on the borders of an object to indicate the points where you can resize the object.
ring control Special numeric control that associates 32-bit integers, starting at 0 and increasing sequentially, with a series of text labels or graphics.
rise time The time for the signal to transition from 10% to 90% of the maximum signal of amplitude.
RMS root mean square
roots Zeros of a function. In other words, values of the variable(s) for which the function is equal to zero.
row-major order Way to organize the data in a 2D array by rows.
RSE referenced single-ended
RTD resistance temperature detector—A temperature-sensing device whose resistance increases with increases in temperature.
RTSI Real-Time System Integration bus—The National Instruments timing bus that interconnects data acquisition devices directly by means of connectors on top of the devices for precise synchronization of functions.
run mode When a VI is running or reserved to run. A VI enters run mode when you click the Run or Run Continuously buttons on the front panel toolbar, the single-stepping buttons on the block diagram toolbar, or select Operate»Change to Run Mode. In run mode, all front panel objects have an abridged set of shortcut menu items. You cannot edit a VI while the VI runs.
Runge Kutta method Numerical method for solving ordinary differential equations with start conditions. The Runge Kutta method works with a fixed step rate but with a higher degree of accuracy than the common Euler method.


s seconds
S sample
sample Single analog or digital input or output data point.
sampling period Time interval between observations in a periodic sampling control system.
scalar Number that a point on a scale can represent. A single value as opposed to an array. Scalar Boolean values and clusters are explicitly singular instances of their respective data types.
scale Part of graph, chart, and some numeric controls and indicators that contains a series of marks or points at known intervals to denote units of measure.
scan One or more analog or digital input samples. Typically, the number of input samples in a scan equals the number of channels in the input group. For example, one pulse from the scan clock produces one scan that acquires one new sample from every analog input channel in the group.
scan clock Clock that controls the time interval between scans in Traditional NI-DAQ (Legacy). On products with interval scanning support (for example, E Series devices), this clock gates the channel clock on and off. On products with simultaneous sampling (for example, S Series devices), this clock determines the rate at which conversions are made across all channels.
scan rate Number of times, (or scans), per second that LabVIEW acquires data from channels. For example, at a scan rate of 10 Hz, LabVIEW samples each channel in a group 10 times per second.
schema An XML-based alternative to a DTD. A schema defines the elements of an XML document.
scope chart Numeric indicator modeled on the operation of an oscilloscope.
SCPI Standard Commands for Programmable Instruments—An extension of the IEEE 488.2 standard that defines a standard programming command set and syntax for device-specific operations.
Scrolling tool Tool to move through windows.
SCXI Signal Conditioning eXtensions for Instrumentation—The National Instruments product line for conditional low-level signals within an external chassis near sensors, so only high-level signals in a noisy environment are sent to DAQ devices.
sec Seconds.
sensor Device that produces a voltage or current output representative of a physical property being measured, such as speed, temperature, or flow.
sequence local Terminal to pass data between the frames of a Stacked Sequence structure.
sequence structure See Flat Sequence structure or Stacked Sequence structure.
serialized When you convert an object into a sequence of bits that you can store or transfer and revert back to the original object.
service name Name associated with a port number.
settling time Amount of time required for a voltage to reach its final value within specified limits.
shared library A file containing executable program modules that any number of different programs can use to perform some function. Shared libraries are useful when you want to share the functionality of the VIs you build with other developers.
shared variable Variable that enables you to read or write live data among several VIs in a project or across a network.
shift register Optional mechanism in loop structures to pass the value of a variable from one iteration of a loop to a subsequent iteration. Shift registers are similar to static variables in text-based programming languages.
shortcut menu Menu accessed by right-clicking an object. Menu items pertain to that object specifically.
sibling class Any LabVIEW class that has the same parent class.
side lobe window Side lobes occur on each side of the main lobe and approach zero at multiples of fs/n from the main lobe. The side lobe characteristics of the smoothing window directly affect the extent to which adjacent frequency components leak into adjacent frequency bins. The side lobe response of a strong sinusoidal signal can overpower the main lobe response of a nearby weak sinusoidal signal. Maximum side lobe level and side lobe roll-off rate characterize the side lobes of a smoothing window. The maximum side lobe level is the largest side lobe level in decibels relative to the main lobe peak gain. The side lobe roll-off rate is the asymptotic decay rate in decibels per decade of frequency of the peaks of the side lobes.
signal conditioning Manipulation of signals to prepare them for digitizing.
signal-to-noise ratio The ratio of total signal to noise expressed in decibels (dB). The larger the number, the better. SNR is calculated by SNR = 20 log (SignalRMS/NoiseRMS). This can be a peak, RMS, or other amplitude that appropriately characterizes the data.
sign-extend To use an arithmetic operation to increase the number of bits of a number without changing the sign or value of the original number.
simplex Simple geometrical body. A simplex in 2D is a triangle, a simplex in 3D is a tetrahedron, and so on. Used in finding the minimum of a function.
sine integral The sine integral is defined by

si(x) = –si(x) where x is any real number.
single-step ODE solver ODE solver that approximates the behavior of a model at time t + dt by taking into account only the behavior of the model between time t and time t + dt.
singular matrix Square matrix in which a row or column is a linear combination of the other rows or columns, respectively. The rows or columns are linearly dependent. This matrix does not have an inverse, and its determinant is equal to zero.
slider Moveable part of slide controls and indicators.
SNR See signal-to-noise ratio.
software configuration management (SCM) Mechanism for controlling changes to source code, documents, and other material that make up a product. During software development, source code control is a form of configuration management. Changes occur only through the source code control mechanism. It is also common to implement release configuration management to ensure you can rebuild a particular release of software, if necessary. Configuration management implies archival development of tools, source code, and so on.
software trigger Programmed event that triggers an event, such as data acquisition.
software triggering Method of triggering in which you simulate an analog trigger using software. Also called conditional retrieval.
source control A solution to the problem of sharing VIs and controlling access to avoid accidental loss of data. You can use a source control provider to share files among multiple users, improve security and quality, and track changes to shared projects. Also called source code control.
SOURCE input pin Counter input pin where the counter counts the signal transitions.
source lines of code (SLOC) Measure of the number of lines of code that make up a text-based project. It is used in some organizations to measure the complexity and cost of a project. How the lines are counted depends on the organization. For example, some organizations do not count blank lines and comment lines. Some count C lines, and some count only the final assembly language lines.
sparse signals Signals with a large number of zero values.
spectrogram Particular representation of a signal that describes the distribution of the energy of the time waveform in the joint time-frequency domain.
spike function The spike function is defined by

square function The square function is defined as

where x is any real number.
Stacked Sequence structure Program control structure that executes its subdiagrams in numeric order. Use this structure to force nodes that are not data dependent to execute in the order you want if flow-through parameters are not available. The Stacked Sequence structure displays each frame so you see only one frame at a time and executes the frames in order until the last frame executes.
stand-alone application A file that provides other users with executable versions of VIs. Stand-alone applications are useful when you want users to run VIs without installing the LabVIEW development system.
static dispatch A method of a LabVIEW class. You define a static dispatch member VI in only one level of the LabVIEW class hierarchy.
STC System Timing Controller
step function The step function is defined by

where x is any real number.
step size Size of the interval of one time step.
STFT short-time Fourier transform
stiff ODE solver ODE solver used to evaluate a stiff model.
stiff problem Problem whose dynamics are described by widely varying time constants.
STL Stereolithography—STL is a file format for representing 3D object models.
strain gage Thin conductor, which is attached to a material, that detects stress or vibrations in that material.
string Representation of a value as text.
string controls and indicators Front panel objects to manipulate and display text.
string tag ASCII character representation of a connection to a real-world I/O point.
strip chart Numeric plotting indicator modeled after a paper strip chart recorder, which scrolls as it plots data.
structure Program control element, such as a Flat Sequence structure, Stacked Sequence structure, Case structure, For Loop, or While Loop.
subdiagram Block diagram within the border of a structure.
subpalette Palette that you access from another palette that is above the subpalette in the hierarchy.
substitution of variables Method commonly used in calculus for finding solutions to equations, where a variable is substituted in terms of another variable to make the equation tractable or solvable. It is also a good method to simplify complex terms.
subVI VI used on the block diagram of another VI. Comparable to a subroutine.
supervisory control Control in which the control loops operate independently subject to intermittent corrective action.
sweep chart Numeric indicator modeled on the operation of an oscilloscope. It is similar to a scope chart, except that a line sweeps across the display to separate old data from new data.
syntax Set of rules to which statements must conform in a particular programming language.


target A device or machine on which a VI runs. You must use a LabVIEW project to work with an RT, FPGA, or Mobile target.
task A collection of one or more channels, timing, triggering, and other properties in NI-DAQmx. A task represents a measurement or generation you want to perform. See also task ID.
task ID Number LabVIEW generates to identify the task at hand for the NI-DAQ drive. The following table gives the function code definitions.

Function Code I/O Operation
1 analog input
2 analog output
3 digital port I/O
4 digital group I/O
5 counter/timer I/O

TCP/IP Transmission Control Protocol/Internet Protocol—A standard format for transmitting data in packets from one computer to another. The two parts of TCP/IP are TCP, which deals with the construction of data packets, and IP, which routes them from computer to computer.
template VI VI that contains common controls and indicators from which you can build multiple VIs that perform similar functions. Access template VIs from the New dialog box.
terminal Object or region on a node through which data values pass.
ticks Time in milliseconds required for the entire calculation.
time step Interval from t to t + dt.
timed digital I/O Type of digital acquisition/generation where LabVIEW updates the digital lines or port states at a fixed rate. The timing is controlled either by a clock or by detection of a change in the pattern. Timed digital I/O is either finite or continuous. Also called pattern generation or pattern digital I/O.
tip strip Small yellow text banners that identify the terminal name and make it easier to identify terminals for wiring.
tool Special cursor to perform specific operations.
toolbar Bar that contains command buttons to run and debug VIs.
Tools palette Palette that contains tools you can use to edit and debug front panel and block diagram objects.
top-level VI VI at the top of the VI hierarchy. This term distinguishes the VI from its subVIs.
Traditional NI-DAQ (Legacy) An older driver with outdated APIs for developing data acquisition, instrumentation, and control applications for older National Instruments DAQ devices. You should use Traditional NI-DAQ (Legacy) only in certain circumstances. Refer to the NI-DAQ Readme for more information about when to use Traditional NI-DAQ (Legacy), including a complete list of supported devices, operating systems, and application software and language versions.
transducer excitation Type of signal conditioning that uses external voltages and currents to excite the circuitry of a signal conditioning system into measuring physical phenomena.
transfer buffer Buffer of memory that carries the operation buffer to the execution buffer.
triangle window The shape of the triangle window is that of a triangle. The following equation defines the triangle window.

for n = 0, 1, 2, …, N – 1

where N is the length of the window and w is the window value.
trigger Any event that causes or starts some form of data capture.
TTL Transistor-Transistor Logic—A digital circuit composed of bipolar transistors wired in a certain manner.
tunnel Data entry or exit terminal on a structure.
two-dimensional Having two dimensions, as in the case of an array that has several rows and columns.
two's complement Method of representing negative integers in binary by converting the number to binary, inverting the bits, and adding 1 to the result.
type definition Master copy of a custom object that several VIs can use.
type descriptor See data type descriptor.


UDP User Datagram Protocol
UNC Universal Naming Convention—UNC filenames provide the primary means for specifying the location of a file or directory in a networked environment.
underflow A condition in which the result of an operation is smaller than the smallest value that the output type can represent.
unevenly sampled data Data that has been sampled with non-equal sampling intervals.
universal constant Block diagram object you cannot edit that emits a particular ASCII character or standard numeric constant, for example, π.
update One or more analog or digital output samples. Typically, the number of output samples in an update equals to the number of channels in the output group. For example, one pulse from the update clock produces one update that sends one new sample to every analog output channel in the group.
update rate Number of output updates per second.
URL uniform resource locator—A logical address that identifies a resource on a server, usually on the Web. For example, is the URL for the National Instruments Web site.
user See operator.
user-defined constant Block diagram object that emits a value you set.
UUT unit under test


V volts
VAC volts, alternating current
variable step-size ODE solver ODE solver that adjusts the step size throughout the simulation to ensure that the per-step error remains at a given relative and absolute tolerance.
variant data Variant data do not conform to a specific data type and they contain attributes, such as channel names and channel units. LabVIEW represents variant data with the variant data type.
VDC volts, direct current
vector 1D array.
VI See virtual instrument (VI).
VI application class Reference to an application capable of loading VIs that allow access to the application properties and methods.
VI class A reference to a virtual instrument that allows access to VI properties and methods.
VI Hierarchy window Window that graphically displays all open LabVIEW projects and targets, as well as the calling hierarchy for all VIs in memory. The window displays type definitions, global variables, shared variables, LabVIEW classes, XControls, Statecharts, Project libraries (.lvlib), Express VIs, static VI references, and (MathScript RT Module) .m files you reference from MathScript Nodes.
VI library See LLB.
VI Server Mechanism for controlling VIs and LabVIEW applications programmatically, locally and remotely.
VI string file Tagged text file that contains all localization strings found on the front panel of a VI.
virtual instrument (VI) Program in LabVIEW that models the appearance and function of a physical instrument.
Virtual Instrument Software Architecture VISA. Single interface library for controlling GPIB, VXI, RS232, and other types of instruments.
VISA See Virtual Instrument Software Architecture.
VRML Virtual Reality Modeling Language—VRML is a file format for representing 3D object models. VRML files commonly appear with a .wrl file extension.
VXI VME eXtensions for Instrumentation (bus)


Walsh Hadamard transform Transform based on an orthogonal system that consists of functions of only two elements 1 and 1. Its properties are similar to the more well-known Fourier transform, but the computational effort is considerably smaller.
waveform Multiple voltage readings taken at a specific sampling rate.
waveform chart Indicator that plots data points at a certain rate.
wavelet transform Transform used to represent a signal in the time-scale domain.
WDT waveform data type
Wheatstone bridge A technique for measuring voltage or resistance changes. The voltage between the midpoints of two parallel voltage dividers is measured, and the value of one of the resistors in the bridge is adjusted to give a balance voltage of zero. Changes in the bridge voltage, resulting from a resistive transducer as one of the elements in the bridge, are then measured. If a parallel resistor in the bridge is part of the transducer, temperature sensitivities are cancelled out.
While Loop Loop structure that repeats a section of code until a condition occurs.
wire Data path between nodes.
wire bend Point where two wire segments join.
wire branch Section of wire that contains all the wire segments from junction to junction, terminal to junction, or terminal to terminal if there are no junctions between.
wire junction Point where three or more wire segments join.
wire segment Single horizontal or vertical piece of wire.
wire stubs Truncated wires that appear next to unwired terminals when you move the Wiring tool over a VI or function node.
Wiring tool Tool to define data paths between terminals.
wizard A dialog box with multiple dynamic pages through which you can move as you fill in information.
word length The total number of bits a system uses to store a particular piece of data, such as a number. LabVIEW accepts a maximum word length of 64 bits.
write mark Points to the update at which a write operation begins. Analogous to a file I/O pointer, the write mark moves every time you write data into an output buffer. After the write finishes, the write mark points to the next update to write. Because multiple buffers are possible, you need both the buffer number and the update number to express the position of the write mark.
WVD Wigner-Ville distribution—A form of time-frequency distribution used to represent a signal in the time-frequency domain.


X0 Vector of start (initial) conditions.
XML node An object in an XML document. An XML node can refer to an element, attribute, text, comment, or other node type defined by the World Wide Web Consortium (W3C).
XML Path Language (XPath) See XPath.
XPath Language for locating parts of an XML document. XPath syntax is defined by the World Wide Web Consortium (W3C).


zeros See roots.
z-value Standardization of a random variable by subtracting the mean and dividing by the standard deviation.


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