Which modules provide a high-speed counter external to the PLC processors?

High-speed counters are crucial for applications that require precise measurement and control of high-speed events, such as in motion control systems. The Encoder/Counter modules are designed specifically for this purpose. They can process input signals from encoders and other high-speed devices, allowing them to count pulses and provide feedback to the PLC regarding position, speed, and direction.

These modules can handle much faster input signals than the standard processing capabilities of many PLC processors, which is essential in scenarios where rapid events occur, such as counting the revolutions of a motor or monitoring fast-moving equipment. This capability enables the PLC system to operate more effectively, ensuring accurate data collection and response in real-time applications.

In contrast, the other options focus on different functions: Analog Input modules deal with continuous signals, Discrete Output modules handle binary on/off outputs, and Relay Modules are utilized for switching high-power devices rather than high-speed counting. Therefore, recognizing the specialized function of Encoder/Counter modules illustrates their critical role in managing high-speed input efficiently.