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Glossary

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accuracy

A determination of how close a measurement comes to the true value.

acquiring data

The process of inputting an analog signal from a sensor into an analog input subsystem, and then converting the signal into bits that the computer can read.

actuator

A device that converts data output from your computer into a physical variable.

adaptor

The interface between the data acquisition engine and the hardware driver. The adaptor's main purpose is to update the engine with properties that are unique to the hardware device.

A/D converter

An analog input subsystem.

analog input subsystem

Hardware that converts real-world analog input signals into bits that a computer can read. This is also referred to as an AI subsystem, an A/D converter, or an ADC.

analog output subsystem

Hardware that converts digital data to a real-world analog signal. This is also referred to as an AO subsystem, a D/A converter, or a DAC.

bandwidth

The range of frequencies present in the signal being measured. You can also think of bandwidth as being related to the rate of change of the signal. A slowly varying signal has a low bandwidth, while a rapidly varying signal has a high bandwidth.

base property

A property that applies to all supported hardware subsystems of a given type (analog input, analog output, etc.). For example, the SampleRate property is supported for all analog input subsystems regardless of the vendor.

callback function

A function that you construct to suit your specific data acquisition needs. If you supply the callback function as the value for a callback property, then the function is executed when the event associated with the callback property occurs.

callback property

A property associated with a specific event type. When an event occurs, the engine examines the associated callback property. If a callback function is given as the value for the callback property, then that function is executed. All event types have a callback property.

channel

A component of an analog input subsystem or an analog output subsystem that you read data from, or write data to.

channel group

The collection of channels contained by an analog input object or an analog output object. For scanning hardware, the channel group defines the scan order.

channel property

A property that applies to individual channels.

channel skew

The time gap between consecutively sampled channels. Channel skew exists only for scanning hardware.

common property

A property that applies to every channel or line contained by a device object.

configuration

The process of supplying the device object with the resources and information necessary to carry out the desired tasks. Configuration consists of two steps: adding channels or lines, and setting property values to establish the desired behavior.

counter/timer subsystem

Hardware that is used for event counting, frequency and period measurement, and pulse train generation. This subsystem is not supported by Data Acquisition Toolbox™ software.

D/A converter

A digital to analog subsystem.

data acquisition session

A process that encompasses all the steps you must take to acquire data using an analog input object, output data using an analog output object, or read values from or write values to digital I/O lines. These steps are broken down into initialization, configuration, execution, and termination.

data block

The smallest "slice" of memory that the data acquisition engine can usefully manipulate.

device object

A MATLAB® object that allows you to access a hardware device.

device-specific property

A property that applies only for specific hardware devices. For example, the BitsPerSample property is supported only for sound cards.

differential input

Input channel configuration where there are two signal wires associated with each input signal — one for the input signal and one for the reference (return) signal. The measurement is the difference in voltage between the two wires, which helps reduce noise and any voltage common to both wires.

digital I/O subsystem

Hardware that sends or receives digital values (logic levels). This is also referred to as a DIO subsystem.

DMA

Direct memory access (DMA) is a system of transferring data whereby samples are automatically stored in system memory while the processor does something else.

engine

A MEX-file (shared library) that stores the device objects and associated property values that control your data acquisition application, controls the synchronization of events, and controls the storage of acquired or queued data.

engineering units properties

Channel properties that allow you to linearly scale input or output data.

event

An event occurs at a particular time after a condition is met. Many event types are automatically generated by the toolbox, while others are generated only after you configure specific properties.

execution

The process of starting the device object and hardware device. While an analog input object is executing, you can acquire data. While an analog output object is executing, you can output data.

FIFO buffer

The first-in first-out (FIFO) memory buffer, which is used by data acquisition hardware to temporarily store data.

full duplex

A system that can send and receive information simultaneously. For sound cards, full duplex means that the device can acquire input data via an analog input subsystem while outputting data via an analog output subsystem at the same time.

input range

The span of input values for which an A/D conversion is valid.

interrupts

The slowest but most common method to move acquired data from the hardware to system memory. Interrupt signals can be generated when one sample is acquired or when multiple samples are acquired.

legacy interface

The interface available with Data Acquisition Toolbox works with all supported data acquisition hardware, except CompactDAQ devices and devices using the counter/timer subsystem. Using this interface you create data acquisition objects with these commands:

line

A component of a digital I/O subsystem that you can read digital values from, or write digital values to.

line group

The collection of lines contained by a digital I/O object.

line properties

Properties that are configured for individual lines.

logging

A state of Data Acquisition Toolbox software where an analog input object stores acquired data to memory or a log file.

noise

Any measurement that is not part of the phenomena of interest.

onboard clock

A timer chip on the hardware board which is programmed to generate a pulse train at the desired rate. In most cases, the onboard clock controls the sampling rate of the board.

output range

The span of output values for which a D/A conversion is valid.

posttrigger data

Data that is acquired and stored in the engine after the trigger event occurs.

precision

A determination of how exactly a result is determined without reference to what the result means.

pretrigger data

Data that is acquired and stored in the engine before the trigger event occurs.

properties

A characteristic of the toolbox or the hardware driver that you can configure to suit your needs. The property types supported by the toolbox include base properties, device-specific properties, common properties, and channel or line properties.

quantization

The process of converting an infinitely precise analog signal to a binary number. This process is performed by an A/D converter.

queuing data

The process of storing data in the engine for eventual output to an analog output subsystem.

running

A state of Data Acquisition Toolbox software where a device object is executing.

sample rate

The per-channel rate (in samples/second) that an analog input or analog output subsystem converts data.

sampling

The process whereby an A/D converter or a D/A converter takes a "snapshot" of the data at discrete times. For most applications, the time interval between samples is kept constant (e.g., sample every millisecond) unless externally clocked.

scan

A set of measurements from all input channels in a session at a specific point in time. For output channels, a scan is the values written to all output channels in a session at a specific point in time.

scanning hardware

Data acquisition hardware that samples a single input signal, converts that signal to a digital value, and then repeats the process for every input channel used.

sending

A state of Data Acquisition Toolbox software where an analog output object is outputting (sending) data from the engine to the hardware.

sensor

A device that converts a physical variable into a signal that you can input into your data acquisition hardware.

session-based interface

The session-based interface only works with National Instruments® CompactDAQ devices including Counter/Timer modules. You cannot use other devices with this interface. Using this interface you create a data acquisition session object with daq.createSession. You can then add channels to the session and operate all channels within the session together.

signal conditioning

The process of making a sensor signal compatible with the data acquisition hardware. Signal conditioning includes amplification, filtering, electrical isolation, and multiplexing.

single-ended input

Input channel configuration where there is one signal wire associated with each input signal, and all input signals are connected to the same ground. Single-ended measurements are more susceptible to noise than differential measurements due to differences in the signal paths.

SS/H hardware

Data acquisition hardware that simultaneously samples all input signals, and then holds the values until the A/D converter digitizes all the signals.

subsystem

A data acquisition hardware component that performs a specific task. Data Acquisition Toolbox software supports analog input, analog output, and digital I/O subsystems.

trigger event

An analog input trigger event initiates data logging to memory or a disk file. An analog output trigger event initiates the output of data from the engine to the hardware.

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