Channels and Tasks

Physical Channels and Virtual Channels

A physical channel is a terminal or pin at which you can measure or generate an analog or digital signal. A virtual channel is a collection of settings such as a name, a physical channel, input terminal connections, the type of measurement or generation, and can include scaling information. In NI-DAQmx, virtual channels are integral to every measurement. In NI-DAQmx, use the DAQ Assistant, accessible from MAX or NI application software to configure channels and measurement tasks. Refer to the DAQ Assistant Help and Measurement & Automation Explorer Help for NI-DAQmx. You can also configure virtual channels with the NI-DAQmx API in your application program. In Traditional NI-DAQ (Legacy) and earlier versions, you can use MAX to configure virtual channels, an optional way to record which channels are being used for different measurements.

Tasks

A task, an important concept for NI-DAQmx, is a collection of one or more virtual channels with timing, triggering, and other properties. Conceptually, a task represents a measurement or generation you want to perform. You can set up and save all of the configuration information in a task and use the task in an application.

Global Virtual Channels and Local Virtual Channels

In NI-DAQmx, you can configure virtual channels as part of a task or separate from a task. Virtual channels created inside a task are local virtual channels. Virtual channels defined outside a task are global virtual channels. You can create global virtual channels in MAX or in your application software and save them in MAX. You can use global virtual channels in any application or add them to a number of different tasks. If you modify a global virtual channel, the change affects all tasks in which you reference that global virtual channel. In most cases, it is simpler to use local virtual channels.

Note  If you are using LabVIEW 8.0 and later, you can also create tasks and channels local to a LabVIEW Project.

Using the DAQ Assistant in Your Application

Using the DAQ Assistant, you can create, configure, and save virtual channels or tasks for use in your applications. If you are using NI application software, you also can generate code based on a task or virtual channel.

Refer to LabVIEW Help, LabWindows/CVI Help, Measurement Studio Help, or NI-DAQmx Key Concepts for more information about programming with your task or global channel.