General-Purpose DAQ

A general-purpose DAQ device is a device that acquires or generates data and can contain multiple channels. You also can use general-purpose DAQ devices to generate analog signals, such as a sine wave, and digital signals, such as a pulse. Typically, you connect these devices directly to the internal bus of a computer through a plug-in slot.

A general-purpose DAQ measurement system is different from other measurement systems because the software installed on the computer performs the actual measurements. The DAQ device only converts the incoming signal into a digital signal the computer can use. This means that the same DAQ device can perform a multitude of measurements simply by changing the software application that reads the data. In addition to acquiring the data, the application for a DAQ measurement system also uses the software that processes the data and displays the results. Although this flexibility allows you to have one hardware device for many types of measurements, you must spend more time developing the different applications for the different types of measurements. LabVIEW includes many acquisition and analysis functions to help you develop different applications.

How Computers Communicate with DAQ Devices

Before a computer-based measurement system can measure a physical signal, such as temperature, a sensor or transducer must convert the physical signal into an electrical one, such as voltage or current. The plug-in DAQ device is only one system component of the entire measurement system. You cannot always directly connect signals to a plug-in DAQ device. In these cases, you must use signal conditioning accessories to condition the signals before the plug-in DAQ device converts them to digital information. The software controls the DAQ system by acquiring the raw data, analyzing, and presenting the results.

A DAQ system has the following options:

• The plug-in DAQ device resides in the computer. You can plug the device into the PCI slot of a desktop computer or the PCMCIA slot of a laptop computer for a portable DAQ measurement system.
• The DAQ device is external and connects to the computer through an existing port, such as the serial port or Ethernet port, which means you can quickly and easily place measurement nodes near sensors.

Software and DAQ Devices

The computer receives raw data through the DAQ device. The application software you write presents and manipulates the raw data in a form you can understand. The software also controls the DAQ system by commanding the DAQ device when to acquire data from channels, and from which channels to acquire the data.

Typically, DAQ software includes drivers and application software. Drivers are unique to the device or type of device and include the set of commands the device accepts. Application software, such as LabVIEW, sends the drivers commands, such as a command to acquire and return a thermocouple reading. The application software also displays and analyzes the acquired data.

NI measurement devices include NI-DAQ driver software and NI Measurements VIs and functions that you can use to configure, acquire data from, and send data to the measurement devices.

NI-DAQ

NI-DAQ 7.x contains two NI-DAQ drivers�Traditional NI-DAQ (Legacy) and NI-DAQmx�each with its own application programming interface (API), hardware configuration, and software configuration. NI-DAQ 8.0 and later come with only NI-DAQmx, the replacement for Traditional NI-DAQ (Legacy).

• Traditional NI-DAQ (Legacy) is an upgrade to NI-DAQ 6.9.x, the earlier version of NI-DAQ. Traditional NI-DAQ (Legacy) has the same VIs and functions and works the same way as NI-DAQ 6.9.x. You can use Traditional NI-DAQ (Legacy) on the same computer as NI-DAQmx, which you cannot do with NI-DAQ 6.9.x. However, you cannot use Traditional NI-DAQ (Legacy) on Windows Vista.
• NI-DAQmx is the latest NI-DAQ driver with new VIs, functions, and development tools for controlling measurement devices. The advantages of NI-DAQmx over previous versions of NI-DAQ include the DAQ Assistant for configuring channels and measurement tasks for a device; increased performance, including faster single-point analog I/O and multithreading; and a simpler API for creating DAQ applications using fewer functions and VIs than earlier versions of NI-DAQ.

  Note��(Windows) LabVIEW supports NI-DAQmx and the DAQ Assistant. (Mac OS X) LabVIEW supports NI-DAQmx Base but not the DAQ Assistant. (Linux) LabVIEW supports NI-DAQmx but not the DAQ Assistant.

Traditional NI-DAQ (Legacy) and NI-DAQmx support different sets of devices. Refer to Data Acquisition (DAQ) Hardware on the National Instruments Web site for the list of supported devices.