Data acquisition (DAQ) is the process of measuring an electrical or physical phenomenon such as voltage, current, temperature, pressure, or sound. PLCs are independent CPU systems with their own proprietary additions for measuring or controlling different types of sensors and their difference signals generated. DAQ systems tend to be PC based using the PC CPU as the brains with the DAQ device ( internal board or external USB connected ) as the electrical interface with a computer. A DAQ system consists of sensors, DAQ measurement hardware, and a computer with programmable software. Compared to traditional measurement systems, PC-based DAQ systems exploit the processing power, productivity, display, and connectivity capabilities of industry-standard computers providing a more powerful, flexible, and cost-effective measurement solution.
This means the DAQ card are more interchangeable and the software is more rapidly modified along with the PC based technologies behind then. ( Unfortunately a PC based system also invites novice PC users and their issues, along with the never ending Operating System upgrades, issues, & obsolescence. )
Where robustness and critical process operation are required, a more expensive PLC based system is preferred.
When fast change and easy implementation is needed ( such as prototyping or QC measurement systems linked to a plant database ) a Daq system is preferred.