No, Human-Machine Interface (HMI) systems do not inherently require Programmable Logic Controllers (PLCs), but they often work in conjunction with PLCs in industrial automation systems.

PLCs are specialized computers used to control machinery and processes in industrial environments. They execute a set of logic instructions based on inputs from sensors and other devices, and produce outputs that control machinery or processes. HMIs, on the other hand, provide a graphical interface that allows humans to monitor and interact with the industrial process.

While HMIs can operate independently of PLCs in some cases, they are often used together to create comprehensive industrial automation solutions. In such systems:

1. PLCs provide control: PLCs handle the control logic and execution of commands to control machinery and processes based on inputs from sensors and user commands. They manage the low-level control functions of the system.

2. HMIs provide visualization and interface: HMIs provide operators with a graphical interface to monitor the process, visualize real-time data, adjust setpoints, and send commands to the PLCs. They serve as the means through which humans interact with the industrial system.

The integration of HMIs with PLCs allows for seamless communication and coordination between the human operator and the automated control system. Operators can monitor the process in real-time, respond to alarms, adjust parameters, and control equipment directly from the HMI interface, while the PLC executes the necessary control logic to carry out these commands.

Overall, while HMIs do not require PLCs to function, they are often used together to create integrated industrial automation systems that optimize efficiency, improve productivity, and enhance operator control and monitoring capabilities.