Control systems may be pneumatic, analog, digital, or a combination of the three. Older designs utilized pneumatic control for local control loops. Analog control systems were an industry standard for a short time before quickly being replaced by digital control systems. The present industry standard is for a distributed control system (DCS), a programmable logic controller (PLC), or a direct digital controller (DDC) to provide digital control logic based on information gathered from electronic sensor inputs and responding with electronic control of pneumatic or electric powered valves and dampers.