PC-based Data Acquisition selection.

Selecting the right PC-based data acquisition system to perform mechanical testing is a complex challenge.

A basic understanding of the types of systems available goes a long way towards clearing up the confusion before committing to a specific type of data acquisition system, it must include the necessary signal conditioning for the application.

For example, plug-in board and PC-card systems typically read only voltages. To measure temperature, strain and vibration, additional external signal conditioning hardware would be required to convert the transducers output to a voltage suitable for the data acquisition systems input.

Suppliers work closely with systems integrators, specialists in finding solutions to the customers hardware and software applications. Choosing the right system depends on the articular needs of the application.

The very first thing to consider is whether the application is portable, requiring a notebook PC, or whether a desktop PC can be used.

Plug-in boards
Data acquisition plug-in boards are a popular solution for desktop test applications. One advantage is high acquisition speeds because of direct data-bus connections. Boards with sampling speeds of up to 200kHz are commonly available.

On-board processing has the advantage of speeding up the data analysis by processing the raw data prior to transferring it to the PC.

PC-card systems
Because of their compact size, most portable PCs cannot accept plug-in boards. For PCs with a PC-card (PCMCIA) slot, PC-card data acquisition systems are available. Although they are more convenient to install than plug-in boards, PC-cards generally have a more limited capability due to their small form factor.

However, for many portable applications where the size of the system is of prime importance they are an ideal solution. In most cases the PC card can be connected to signal conditioning modules in a similar fashion to the plug-in boards.

Externally connected
Where channel expansion, convenient connections, a quiet environment and signal conditioning are required, externally connected data acquisition systems may be a better solution.

These systems make use of the PC's existing ports for communication, such as the serial port, parallel port, or the USB (Universal Serial Bus) port. Because they are external to the PC, external data acquisition systems offer a number of advantages...

They can be installed without opening the desk-top PC,
They can be easily used with notebook PCs,
They have room for built-in signal connections
They can be easily expanded by adding modules or boards that contain signal conditioning hardware.

Some external systems can achieve sampling rates up to 1MHz, making them suitable for dynamic signal measurement. However, speed is not always of importance in data acquisition.

USB-based systems are best suited to medium-speed acquisition and offer true plug-and-play, hot-swapping capability.

Other PC-based data acquisition systems are also available for measuring slow-changing phenomena such as temperature and voltage.

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