In modern DDC programming, what is a function block and give an example?

• A. A hardware device used for data logging
• B. A software library for math operations
• C. A modular programming unit representing a control or logic operation; example: a PID block
• D. A graphical interface for editing programs

Answer: (C)

In modern DDC programming, a function block is a modular programming unit that represents a single control or logic operation, with defined inputs, outputs, and often internal state, which you can connect with other blocks to create a complete control strategy. The idea is to encapsulate a specific function so it can be reused and combined like building blocks.

A classic example is a PID block. It takes the process variable and a setpoint, applies proportional, integral, and derivative calculations with configurable gains, and outputs a control signal to the actuator. It may also include features like anti-windup and output limits, illustrating how a single block can implement a full control algorithm while remaining reusable and adjustable within the larger control network.

This concept differs from a hardware device used for data logging, a general-purpose math library, or a graphical editor. Those serve other roles, whereas a function block specifically encapsulates a controllable or logical function that can be wired into a broader control scheme.