• What is INTERLOCKS?
• What are the benefits of using INTERLOCKS?
• Who should use INTERLOCKS?
• Where has INTERLOCKS been used?
• Why the name INTERLOCKS?
• How is INTERLOCKS used?
• What is an INTERLOCKS event?
• How do events interact?

What is INTERLOCKS?

INTERLOCKS is a process modeling and simulation tool that can represent any system as a simple network of binary events whose relationships are expressed by AND and OR logic. Using INTERLOCKS software, a system developer, trainer, or maintainer can gain understanding of the system, test proposed changes before they are implemented (rapid prototype), and insert faults to see how the system reacts.

INTERLOCKS software applications are not your typical Computer Aided-Design (CAD) or simulation tool. INTERLOCKS is:

• Focused on events and their logical relationship;
• Applicable to diverse components (e.g. hardware, software, or operator events);
• Graphical (employing symbols and color to represent event relationships, event types, and event states); and
• Requires no programming knowledge to use

What are the benefits of using INTERLOCKS?

INTERLOCKS modeling and simulation tool reduces cost and time to perform engineering and training tasks throughout the system lifecycle. There are multiple benefits to using modeling and simulation including:

• Improved communication and understanding
• Increased engineering efficiency
• Reduced development time and cost
• Reduce schoolhouse training
• Reduce system downtime
• Reduce maintenance costs

Who should use INTERLOCKS?

INTERLOCKS is a powerful modeling and simulation tool for anyone involved in system demonstration, marketing, management, analysis, training, maintenance, or troubleshooting - regardless of the system on which they work.

Where has INTERLOCKS been used?

Over the past 20 years, INTERLOCKS modeling and simulation tool has been used by project managers, systems and safety engineers, analysts, control boards, software developers, maintenance technicians and operators for:

• Marketing
• Concept Demonstration
• System Demonstration
• Prototype Development
• Trade-off analysis
• Nuclear safety analysis
• Conventional safety analysis
• Hardware analysis
• Software analysis
• Requirements analysis
• Requirements specification
• Requirements tracing
• Systems engineering
• Interface Management
• Maintainability analysis
• Ambiguity analysis
• What-if analysis
• Proficiency training
• Schoolhouse training
• Troubleshooting
• Distance Support
• Performance Support
• Software Development
• Validation and verification
• System certification

Why the name INTERLOCKS?

INTERLOCKS was initially designed in the 1980's to provide a much-needed modeling and simulation tool for safety analysis practices. Its foundation is the graphics-based logic diagrams that describe the controls, or “interlocks”, of a system. These “interlocks” ensure that critical sequences of events can only occur in a safe, deliberate manner. These events—hardware controls, software controls, and operator actions— when combined, represent a defined system. INTERLOCKS modeling and simulation tool uses these events and their critical sequences to develop its model and simulate operation.

How is INTERLOCKS used?

The INTERLOCKS software application and associated models are used to describe a system and to simulate operation for analysis and demonstration. The model is built by identifying system events and the logic that describes their interaction. These logical relationships provide discrete event simulation that demonstrates how, what, and why a system operates.

What is an INTERLOCKS event?

An event is a system occurrence—such as a hardware relay closing, software passing data, or an operator pushing a button. An event has either happened (occurred) or not happened (not occurred), so that at any given time, the event occurrence state can be on or off. Normally, a system event occurs because one or more other events cause it to happen. However, in some cases the event may occur when it should not, or it may not occur when it should. These erroneous events are said to have failed. A failed event remains in its current state (Failed On or Failed Off), regardless of the state of any other events in the model.

How do events interact?

An event's state depends on its relationship with other events and their corresponding states. INTERLOCKS uses three logic operators—AND, OR, and NOT—to represent the relationships among system events. The network into which the event relationships are combined describes the system.

• AND

   - An AND relationship specifies that an event occurs only when all related input events have occurred.
  

• OR

   - An OR relationship specifies that an event occurs if one or more of its related events have occurred.
  

• NOT

   - A NOT inverts the state of an input event.