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A/D Channel List Start

Signal used to start the A/D acquisition of channels in the channel list. The triggering edge of this signal (falling edge) enables the ADC Conversion Start signals

A/D Conversion

The process of converting a single analog input to a digital value

A/D Conversion Start

Signal used to start the conversion process of an analog input to a digital value. The source of this signal can be either an internal ADC synchronous clock or an external asynchronous signal. This signal causes the stepping in the Channel List.

AC – Alternating Current

Electric current that varies in amplitude and direction. The usual waveform of ac is a sine wave, but can be triangular, or square.

ADC – Analog-to-Digital Converter (a.k.a. simply an “A/D”)

An electrical circuit that converts analog voltage into a binary number. A/D converters perform the measurements in all data acquisition systems


A false lower frequency image of a high-frequency component that appears in sampled data acquired at too low a sampling rate. For more information about aliasing please visit this explanation at Analog Devices.


A brand name for a magnetic nickel alloy containing small amounts of manganese, aluminum, and silicon. Used in thermocouples and thermocouple extension wire.

Ampere (A)

SI unit of electric current.


A device for increasing the power of a signal by taking power from a power supply and controlling the output to match the input signal shape
but with a larger amplitude.


The size or magnitude of a signal.

Analog Input

An analog input is an infinitely variable signal. In most data acquisition systems this signal is connected to an input amplifier and then to an A/D converter.

Analog Output

A waveform or control signal generated as a continuous function of the measured parameter.

Analog Trigger

A trigger that occurs at a user-selected point on an incoming analog signal. Triggering can be set to occur at a specific level on either an increasing or a decreasing signal (positive or negative slope).

Anti-alias filter

A low pass filter that allows the desired low frequency component of the input waveform through, but stops the higher frequency components that can lead to aliasing errors (See Alias).


Application Programming Interface, a collection of high-level language function calls that provide access the functions in a driver or other utility.


An Input parameter to a program.


An avionics interface protocol which is the standard communications link in virtually all modern commercial aircraft.


American Standard Code for Information Interchange. Coding for text files.


A program that translates assembly language instructions into machine language instructions.

Assembly Language

A machine oriented language in which mnemonics are used to represent each machine language instruction for a particular CPU.


American Society for Testing and Materials.


(1) Hardware – A property of an event that occurs at an arbitrary time, without synchronization to a reference clock.

(2) Software – A property of a function that begins an operation and returns prior to the completion or termination of the operation.


B-Type Thermocouple

Platinum-rhodium thermocouple with a temperature range of 600 to >1700 °C


The primary-level of a hierarchical computer network connected to lower-level nodes in the hierarchy

Background Acquisition

Background Data Acquisition refers to data that is acquired while another program or processing routine is running in the foreground without apparent interruption

Background Noise

Interfering signals that can cause disturbance affecting a signal that may distort the intended signal

Base Address

A memory address that serves as the starting address for programmable registers. All other addresses are located by adding to the base address.

Batch process

Any process on which operations are carried out on a limited number of articles, as opposed to continuous process.


A signal range that includes both positive and negative values (for example, -5 V to +5 V).


One binary digit (either 0 or 1).

Block Mode

A high-speed data transfer in which the address of the data is sent followed by a specified number of back-to-back data words.

Burst Mode

A high-speed data transfer in which the address of the data is sent followed by back-to-back data words while a physical signal is asserted.


The group of conductors that interconnect individual circuitry in a computer. Typically, a bus is the expansion vehicle to which I/O or other devices are connected. Examples of PC buses are the ISA and PCI buses.

Bus Master

A type of a plug-in board or controller with the ability to read and write devices on the computer bus, without using the host CPU.


Eight related bits of data, an eight-bit binary number. Also used to denote the amount of memory required to store one byte of data. A byte may represent 256 unique numbers (typically from 0 to 255 in the decimal system)



High-speed processor memory that buffers commonly used instructions or data to increase processing throughput


The process of determining the relationship between the output of a measurement device, and the input data, and comparing it against a measurement standard. In most cases, the term calibration also includes the process of adjusting the output of the measurement device to comply with the measurement standard


The amount of a stored (or separated) electrical charge for a given electrical potential, measured in farads (F)


Conformite Europeene. A mark designating product’s compliance with all applicable European Union legal requirements

Channel List

A variable length list of channels and their associated gains specifying which analog input channels to convert to digital values. In continuous A/D acquisition mode, the list wraps around to the first channel after it reaches the end. The channels need not be in any particular order.


A 90% nickel alloy with about 10% chromium, used with Alumel in K-type thermocouples.


Common-Mode Rejection Ratio. A measure of an instrument’s ability to reject interference from a common-mode signal, usually expressed in decibels (dB).

Code Generator

A software program, controlled from an intuitive user interface, that creates syntactically correct high-level source code in languages such as C or Basic.

Cold-Junction Compensation

Compensation for ambient temperature when a thermocouple is used in a data acquisition system.

COM port

A serial device connectivity port on a PC, often RS-232.

Common-Mode Range

The input range over which a circuit can handle a common-mode signal.

Common-Mode Signal

The mathematical average voltage, relative to the computer’s ground,of the signals from a differential input. For more information on the Common-Mode Signal please visit Maxim/Dallas

Component Software

An application that contains one or more component objects that can freely interact with other component software. Examples include OLE enabled applications such as Microsoft Visual Basic and OLE Controls for virtual instrumentation in Component Works.

Control Register(s)

Registers containing bits that initiate control signals for various onboard subsystems.

Conversion Time

The time elapsed, in an analog input or output system, from the moment a channel is interrogated (such as with a read instruction) to the moment that accurate data is available.


A circuit such as the Intel 8254 device that counts external pulses or clock pulses (timing).


The manner in which a signal is connected from one location to another.


An unwanted signal on one channel induced by signal activity on another nearby channel.Current Drive


The amount of current a digital or analog output channel is capable of sourcing or sinking while still operating within voltage range specifications.

Current Sinking

The ability of a DAQ board to dissipate current for analog or digital output signals.

Current Sourcing

The ability of a DAQ board to supply current for analog or digital output signals.





Digital-to-analog converter. An integrated circuit that converts a digital number into a corresponding analog voltage or current.

DAC Conversion Start

Signal used to start the conversion process of digital value to an analog output. The source of this signal can be either an internal DAC synchronous clock or an external asynchronous signal. This is a common signal fed to both DACs.

Data Acquisition

(1) The process of automatically collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing; (2) Collecting and measuring the same kinds of electrical signals with A/D and/or DIO boards plugged into a PC, and possibly generating control signals with D/A and/or DIO boards in the same PC.

Data Logger

A stand alone data acquisition device that acquires data and stores it in local memory from which it may then be downloaded to a computer for subsequent analysis and display.

Data Recorder

Another name for a data logger, though data recorders are typically higher performance and offer higher sample rates than a typical data


An abbreviation for Data acquisition.


Decibel. The unit for expressing a logarithmic measure of the ratio of two signal levels: dB=20log10 V1/V2, for signals in volts.

Differential Input

An analog input consisting of two terminals, both of which are isolated from computer ground, whose difference is measured.


Digital input/output.


Dynamic Link Library. A software module in Microsoft Windows containing executable code and data that can be called or used by Windows applications or other DLLs. Functions and data in a DLL are loaded and linked at run time when they are referenced by a Windows application or other DLLs.


Direct memory access. A method by which data can be transferred to/from computer memory from/to a device or memory on the bus while the processor does something else. DMA is the fastest method of transferring data to/from computer memory.


Differential Non-linearity. A measure in LSB of the worst-case deviation of code widths from their ideal value of 1 LSB. For more information on Differential Non-Liniarity please visit the Computer Action Team


Software that controls a specific hardware device, such as DAQ boards.


Digital Signal Processor. A specialized microprocessor for digital signal processing.

Dual-Ported Memory

Memory that can be simultaneously accessed by more than one controller or processor.

Dynamic Range

The ratio of the largest signal level a circuit can handle to the smallest signal level it can handle (usually taken to be the noise level), normally expressed in dB.



Electrically erasable programmable read-only memory. ROM that can be erased with an electrical signal and reprogrammed.

Embedded Controller

A control device built into (embedded in) a host device. Monitoring and control are handled by the same CPU as general system operation.


A device that converts linear or rotary displacement into digital or pulse signals. The most popular type of encoder is the optical quadrature encoder, which uses a rotating disk with alternating opaque areas, a light source, and a photo detector to indicate a rotary position.


Erasable programmable read-only memory. ROM that can be erased (usually by ultraviolet light exposure) and reprogrammed.


Signals or interrupts generated by a device to notify another device of an asynchronous event. The contents of events are device-dependent.

External Trigger

A voltage pulse from an external source that triggers an event such as A/D conversion.



First-In First-Out Memory Buffer. The first data stored is the first data sent to the acceptor.


A device that allows certain parts of a signal to pass through while blocking others. In data acquisition systems, the most common type of filter used is a low pass, anti-aliasing filter. For more information on filters please visit this page at Texas Instruments


A format for processing or storing numbers as digital integers.


A format for processing or storing numbers in scientific notation (digits multiplied by a power of 10).


A set of software instructions executed by a single line of code that may have input and/or output parameters, that returns a value when executed.



The factor by which a signal is amplified, sometimes expressed in dB.

Gain Accuracy

A measure of deviation of the gain of an amplifier from the ideal gain.


General Purpose Interface Bus. Also known as IEEE-488, the GPIB was
originally developed by Hewlett Packard and called the HPIB. For more
information on GPIB please visit Radio-Electronics


Global Positioning System. A series of satellites is used to provide
accurate location and velocity information to both ground based and
land based devices. A powerful and often ignored benefit in data acquisition
applications is the ability of a GPS system to generate extremely
accurate timing information. One microsecond accuracy is available with
inexpensive units and much tighter specifcations are available from some
vendors. For more information on GPS please visit Trimble or Garmin.


In terms of data acquisition systems, a ground is typically where system current is returned. In single ended systems the negative terminal of the sensor is typically connected to ground.

Ground Loop

Many measurements are made between an input signal and ground.
However, ground is not an absolute reference point and current flowing
in wires between various ground connections can cause the potential at
different “ground” points in the system to be at different potentials.
These differences then manifest themselves as errors in the measurement.


Graphical User Interface. An intuitive, easy-to-use means of
communicating information to and from a computer program by means of
graphical screen displays. GUIs can resemble the front panels of
instruments or other objects associated with a computer program.



A device driver that is installed as part of the operating system of the computer.


The physical components of a computer system, such as the circuit boards, plug-in boards, chassis, enclosures, peripherals, cables, and so on.



Input/Output. The transfer of data to/from a computer system involving communications channels, operator interface devices, and/or data acquisition and control interfaces.

ICP® (piezoelectric vibration sensor)

A simple yet powerful 2-wire interface developed by PCB Piezo Electronics® to facilitate connection of Piezo Crystal based vibration sensors to data acquisition systems. Also referred to as IEPE.


Input/Output Module. This term is synonymous with the CPU board in the UEI chassis.


Intermodulation Distortion. The ratio, in dB, of the total rms signal level of harmonic sum and difference distortion products, to the overall rms signal level. The test signal is two sine waves added together according to the following standards:INLIntegral Non-linearity. A measure in LSB of the worst-case deviation from the ideal A/D or D/A transfer characteristic of the analog I/O circuitry. For more information about Integral Non-linearity please visit Maxim Integrated Products

Input Bias Current

The current that flows into the inputs of a circuit.Input Impedance The measured resistance and capacitance between the input terminals of a circuit.

Input Offset Current

The difference in the input bias currents of the two inputs of an instrumentation amplifier.

Instrumentation Amplifier

A circuit whose output voltage with respect to ground is proportional to the difference between the voltages at its two inputs.

Integral Control

A control action that eliminates the steady-state offset inherent in proportional control.Integrating ADC An ADC whose output code represents the average value of the input voltage over a given time interval.


A software utility that executes source code from a high-level language such as Basic, C, or Pascal, by reading one line at a time and executing the specified operation.


A computer signal indicating that the CPU should suspend its current task to service a designated activity.


Interprocess Communication. Protocol by which processes can pass messages. Messages can be either blocks of data and information packets, or instructions and requests for process to perform actions. A process can send messages to itself, other processes on the same machine, or processes located anywhere on the network.Isolation Voltage The voltage that an isolated circuit can normally withstand, usually specified from input to input and/or from any input to the amplifier output, or to the computer bus.



Kilo, the standard metric prefix for 1,000, or 103, used with units of measure such as volts, Hertz, and meters.

K (computer)

Kilo, the prefix for 1,024, or 210, used with byte in quantifying data or computer memory.


A unit for data transfer that means 1,000 or 103 bytes/s.



A popular data acquisition programming language developed by National Instruments®


(1) Generic term often used to refer to one of the 7 Layers of the Open Systems Interconnection Basic Reference Model or OSI Model a layered, abstract description for communications and computer network protocol design. (2) A term used throughout the UEI website, and literature to describe the printed circuit bords of the UEI Cubes, and the RACKtangle™, (ie. I/O layers, CPU/NIC layer, etc.)


The adherence of device response to the equation R = KS, where R = response, S = stimulus, and K = a constant.


Least significant bit. In terms of data acquisition and measurement systems, the LSB is the smallest change in input that can be detected by the system’s A/D converter.


Designed as the Successor to GPIB, LXI is a standard developed by the LXI Consortium, and is an abbreviation for LAN eXtensions for Instrumentation. More information can be found at the LXI Standard Website



(1) mega, the standard metric prefix for 1 million or 106, when used with units of measure such as volts and Hertz; (2) mega, the prefix for 1,048,576, or 220, when used with byte to quantify data or computer memory.


A unit for data transfer that means 1 million or 106 bytes/s.


Man-Machine Interface, also Human-Machine Interface(HMI): The means by which an operator interacts with an industrial automation system;
often a GUI.


A defacto standard communications protocol used in a wide variety of Industrial Control and DAQ (data acquisition) systems industrial control and monitoring equipment. Modbus was developed by Modicon in 1979 as a means to facilitate communication in their programmable controller products. For more information on Modbus, please visit Modbus-IDA


A property of an operating system in which several processes can be run simultaneously.


Multiplexer. A switching device with multiple inputs that sequentially connects each of its inputs to its output, typically at high speeds, in order to measure several signals with a single analog input channel. Most data acquisition systems utilize multplexers to allow a single A/D converter to measure or monitor multiple inputs.



An undesirable electrical signal. Noise comes from external sources such as the AC power line, motors, generators, transformers, fluorescent
lights, soldering irons, CRT displays, computers, electrical storms, welders, radio transmitters, and internal sources such as
semiconductors, resistors, and capacitors.

Nyquist Sampling

Sampling based on Harry Nyquist’s Bell System Technical Journal article of 1924 often called the Nyquist-Shannon Sampling Theorem
states, “Exact reconstruction of a continuous-time baseband signal from its samples is possible if the signal is bandlimited and the sampling
frequency is greater than twice the signal bandwidth.” For more information on Nyquist Sampling please visit this explanation at Wikipedia.



Object Linking and Embedding. A set of system services, developed by Microsoft, that provides a means for applications to interact by
linking and embedding document objects. Based on the underlying Component Object Model, OLE is object-enabling system software. Through
OLE Automation, an application can dynamically identify and use the services of other applications, to build powerful solutions using
packaged software. OLE also makes it possible to create compound documents consisting of multiple sources of information from different

Operating System

Base-level software that controls a computer, runs programs, interacts with users, and communicates with installed hardware or peripheral devices.

Optical Isolation

The technique of using an optoelectric transmitter and receiver to transfer data without electrical continuity to eliminate high-potential differences and transients.

Output Settling Time

The amount of time required for the analog output voltage to reach its final value within specified limits.

Output Slew Rate

The maximum rate of change of analog output voltage from one level to another.


The amount of computer processing resources, such as time and/or memory, required to accomplish a task.



Also see Programmable Automation Controller below.


A technique used for extending the address range of a device to point into a larger address space


Peripheral Component Interconnect. A high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA. It offers a theoretical maximum transfer rate of 132 Mbytes/s. More information can be found at the PCI-SIG Website

PID Control

A three-term control mechanism combining proportional, integral, andderivative control actions. Also see proportional control and integral control.


A high-performance processor structure in which the completion of an instruction is broken into its elements so that several elements can beprocessed simultaneously from different instructions.


See Programmable Logic Controller.

Plug and Play ISA

A specification prepared by Microsoft, Intel, and other PC-related companies intended to create PCs with plug-in boards that can be fully configured in software, without jumpers or switches on the boards.

Polled Mode

DAQ card operating mode whereby the user application queries the board about the status of various subsystems as needed.Port A communications connection on a computer or a remote controller.


The technique used on a DAQ board to acquire a programmed number of samples after trigger conditions are met.


An electrical device of which the resistance can be manually adjusted; used for adjustment of electrical circuits and as a transducer
for linear or rotary position.

Programmable Automation Controller

Also commonly referred to as a PAC, these are stand-alone controllers that perform a function similar to a Programmable Logic Controller, but are programmed in standard programming languages (e.g. C or Visual Basic) rather that the Ladder Logic programming language used by most PLCs.

Programmable Logic Controller

Also commonly referred to as a PLC, these are highly reliable special-purpose computer used in industrial monitoring and control applications. PLCs typically have proprietary programming and networking protocols, and special-purpose digital and analog I/O ports.


The technique used on a DAQ board to keep a continuous buffer filled with data, so that when the trigger conditions are met, the sample includes the data leading up to the trigger condition.

Programmed I/O

The standard method a CPU uses to access an I/O device– each byte of data is read or written by the CPU.

Propagation Delay

The amount of time required for a signal to pass through a circuit.

Proportional Control

A control action with an output that is to be proportional to the deviation of the controlled variable from a desired set point.


The exact sequence of bits, characters and control codes used to transfer data between computers and peripherals through a communications channel, such as the GPIB.


An analog-input configuration where all channels refer their inputs to a common ground—but this ground is not connected to the computer ground.


A modular instrumentation platform used for building test equipment and automation systems promoted by the PXI Systems Alliance (PXISA) and is an a abbreviation that stands for PCI eXtensions for Instrumentation


Quadrature Encoder

A device used to measure rotation. The most popular type of encoder is the optical quadrature encoder, which uses a rotating disk with alternating opaque areas, a light source, and a photo detector. Each time the photo detector crosses an bright (or dark) as signal is generated. These signals are then turned into rotational information by a quadrature encoder input devices.

Quantization Error

The inherent uncertainty in digitizing an analog value due to the finite resolution of the conversion process.


Real Time

A property of an event or system in which data is processed as it is acquired instead of being accumulated and processed at a later time.

Relative Accuracy

A measure in LSB of the accuracy of an ADC. It includes all non-linearity and quantization errors. It does not include offset and gain errors of the circuitry feeding the ADC.


The smallest signal increment that can be detected by a measurement system. Resolution can be expressed in bits, in proportions, or in percent of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244 percent of full scale.

Resource Locking

A technique whereby a device is signaled not to use its local memory while the memory is in use from the bus.

Ribbon Cable

A flat cable in which the conductors are side by side.


Resistance temperature detector. A metallic probe that measures temperature based upon its coefficient of resistivity. For more information on resistance temperature detectors, please download these documents from ITS-90 or NIST Technology Services.



Sample-and-Hold. A circuit that acquires and stores an analog voltage on a capacitor for a short period of time.


Samples per second. Used to express the rate at which a data acquisition system samples an analog signal.


One run through the presently configured Channel List


Software developer’s kit, a collection of drivers and utilities that allow engineers to write their own application programs.


Single-Ended. A term used to describe an analog input that is measured with respect to a common ground.


DAQ board that calibrates its own A/D and D/A circuits without external reference source.


A device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal.

Slow Bit

A control bit in the analog-input configuration word that instructs the A/D to wait a short while before actually digitizing the input voltage; it gives the input amplifier time to settle, and is very useful when working with very high gains.


Signal-to-Noise Ratio. The ratio of the overall rms signal level to the rms noise level, expressed in dB.

Software Trigger

A programmed event that triggers an event such as data acquisition.


Single-Pole Double Throw. A property of a switch in which one terminal can be connected to one of two other terminals.


Simultaneous Sampling and Hold. A property of a system in which each input or output channel is digitized or updated at the same instant.

Strain Gage (also Strain Gauge)

A sensor whose resistance is a function of the applied force. For more information on Strain Gages please visit the Vishay Technical notes


A set of software instructions executed by a single line of code that may have input and/or output parameters.

Successive-Approximation ADC

An ADC that sequentially compares a series of binary-weighted values with an analog input to produce an output digital word in n steps, where n is the bit resolution of the ADC.


A property of a function that begins an operation and returns only when the operation is complete.

System Noise

A measure of the amount of noise seen by an analog circuit or an ADC when the analog inputs are grounded.



A device on the General Purpose Interface Bus (GPIB) that sends data to the Listener on the GPIB.


A set of standard protocols for communicating across a single network or interconnected set of networks. The Internet Protocol (IP) for the low-level service of taking data and packaging of components, and Transmission Control Protocol (TCP) for high-reliability data transmissions.


Total harmonic distortion. The ratio of the total rms signal due to harmonic distortion to the overall rms signal, in dB or percent.


Plus Noise. The ratio in decibels of the overall rms signal to the rms signal of harmonic distortion plus noise introduced.


A semiconductor sensor that exhibits a repeatable change in electrical resistance as a function of temperature. Most thermistors exhibit a negative temperature coefficient.


A common type of temperature sensor used to convert thermal potential difference to electrical potential difference. More information on thermocouples can be found at the NIST ITS-90 Thermocouple Database

Throughput Rate

The data, measured in bytes/s, for a given continuous operation.


A device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal.

Transfer Rate

The rate, measured in bytes/s, at which data is moved from source to destination after software initialization and set up operations; the maximum rate at which the hardware can operate.



Universal Asynchronous Receiver/Transmitter. Used for translating data between parallel and serial interfaces by converting bytes of data to and from asynchronous start-stop bit streams.


A signal range that is always positive (for example, 0 to +10 V).


Uninterruptible Power Supply (or source). Designed to maintain electrical power to electronic devices in the event of utility power failure.


Universal Serial Bus. Developed as a serial communications standard to replace Serial and Parallel devices.



The symbol for Volt


Voltage AC (alternating current)


The unit of measure for electrical potential difference across a conductor.


The value of electrical potential difference across a conductor expressed in volts.

Voltage-to-Frequency Converter

A device that converts analog input voltage into a sequence of digital pulses at a frequency proportional to the analog input voltage.



Wide Area Network. A wide area network is typically made up of two or more Local area Networks, or LANs

Wheatstone Bridge

A network of four resistors that allows a data acquisition system to measure very small changes in the resistance of sensors such as strain gages, load cells, and similar measurement devices which change resistance in response to some external stimulus.


Wireles-Fidelity. Wi-Fi is a brand of high-frequency wireless local area network (WLAN) licensed by the Wi-Fi Alliance trade group, and is based on the IEEE 802.11 specifications.



The horizontal axis on a graph



The horizontal axis perpendicular to the x-axis on a graph



The third axis in a three-dimensional coordinate graph perpendicular to the plane defined by the x and y axes.


The difference between true zero and an indication given by a measuring instrument.

Zero-Overhead Looping

The ability of a high-performance processor to repeat instructions without requiring time to branch to the beginning of the instructions.

Zero-Wait-State Memory

Memory fast enough that the processor does not have to wait during any reads and writes to the memory.

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