block diagram

A block diagram is the wiring map of a control system drawn in the language of signals: each box is something that transforms a signal (a controller, a motor, a sensor), each arrow is a signal flowing, and a circle with a minus sign is where you subtract the feedback to form the error. It's the engineer's circuit diagram for dynamics — instead of resistors and wires, it shows transfer functions and signal paths. One glance tells you what acts on what, and where the loop closes.

Block diagrams aren't just pictures; they obey algebra. Two blocks in series multiply their transfer functions; a feedback loop with forward gain G and feedback H collapses to the single famous formula G / (1 + GH). Using these reduction rules you can squash a sprawling diagram down to one input-output transfer function and then analyse its poles and stability. This is why before anyone writes control code, they draw the block diagram: it makes the structure of the loop — what's measured, what's commanded, where disturbances enter — visible and manipulable.