18 Human-Machine Interface

18.1 Introduction

• Historical Context:

  • The traditional user interface for control systems included large panels with physical switches, buttons, and indicators.

  • These were gradually replaced by computer systems with graphical interfaces due to cost efficiency and functionality.

  • Modern interfaces typically use color graphic touch screens but sometimes retain simpler hard-wired panels for redundancy.

• HMI Terminology: HMI is often referred to by various names, such as:

  • Operator Interface (OI)

  • Man-Machine Interface (MMI)

  • Human-Machine Interface (HMI)

18.2 HMI Types

• Mechanical Buttons/Switches: Used for simple applications.

• Text and Graphic Displays:

  • Range from small one-line displays to large scrolling text displays.

  • Proprietary graphic displays may use LCD or CRT screens with specific functionalities.

• PC-Based HMIs: More complex and capable of interfacing with databases and other applications.

Scenario 1: Operator-Initiated Start with Permissives

• The process cannot start if not all permissives (conditions) are met, leading to operational delays until issues are resolved.

18.3 HMI Panel Design

• Good Design Practices:

  • Pushbuttons should reflect intuitive functionality: start buttons above/left of stop buttons.

  • Color coding: Red for danger; Amber for caution; Green for operational status.

• Operator Feedback: Critical for operators to have feedback from their actions to avoid accidents or delays.

Scenario 2: Hydrofluoric Acid Spill

• Cause of Incident: Lack of proper switch functionality and operator errors initiated an acid fill.

• Solution: Implement confirmation prompts for actions initiated via the HMI to prevent future incidents.

• Faults Identified: Inoperable high-high switch, unclosed lockout valve, and operator-initiated fills without proper authorization.

18.4 Graphical HMI Design

• General Guidelines:

  • Simplify displays to contain necessary information without clutter.

  • Layout: Important elements positioned at the top and right for easy scanning.

  • Use of colors should be minimal, focusing on contrast for readability.

• Animations and Interactivity:

  • Operators should easily navigate through multiple screens and displays.

• Controls and Indicators:

  • Must be clearly labeled with intuitive designs to facilitate ease of use during operations.

18.5 Graphical HMI Development

• HMI Lifecycle: Development includes establishing standards, designing, implementing, and continually improving the HMI.

• Display Components: Setting up communication with PLCs, building tag databases, and establishing proper graphical elements.

• Security: Login systems to prevent unauthorized access to sensitive controls and data.

18.6 Chapter Summary

• Reviewed the structure and functions of HMI. Guidelines for effective design, color use, operator feedback, and security measures.

  • Regular re-evaluation of HMIs is essential to address issues and incorporate improvements.