Which component is essential in a digital data acquisition system?

In a digital data acquisition system, the data acquisition card is a critical component because it is responsible for converting analog signals into digital data. This process involves sampling the analog signal, quantizing it, and then digitizing it so that it can be processed by a computer or digital system. The data acquisition card interfaces with other components, allowing for the capture and manipulation of data from various sensors and devices.

The other options, while they may be useful or necessary in certain contexts, do not play the same essential role as the data acquisition card. An analog processor is often used for processing signals before digitization but is not required in every digital system. A display monitor is important for visual output but does not contribute to the acquisition of data itself. A power supply unit is needed to provide energy to the system but is not responsible for the data acquisition process. Therefore, the data acquisition card is fundamental to the functioning of a digital data acquisition system, making it the essential component in this context.