Modular PLCs can have their capability expanded by adding what?

Modular PLCs (Programmable Logic Controllers) are designed with a flexible architecture that allows for expansion in capabilities. By adding input and output cards, the system can increase the number of devices it can control and monitor, which enhances its functionality. Input cards accept signals from sensors, switches, and other input devices, while output cards send commands to actuators, motors, and other output devices. This modular design is essential for tailoring the PLC system to specific industrial automation needs, allowing for scalability and customization based on the project requirements.

In contrast, memory upgrades and additions of hard drives might improve processing speed or storage capacity, but they do not directly enhance the interaction with external devices. Similarly, while transmitters and receivers can be important for communication purposes, they do not fundamentally increase the controlling capabilities of the PLC like input and output cards do. Hence, the correct answer reflects how PLCs can practically and effectively be expanded to meet diversified industrial demands.