Triple modular redundancy

Definition

Triple modular redundancy (TMR) is a fault-tolerant system design that uses three identical modules to perform the same task, with the outputs of these modules compared to determine the correct result. This technique helps enhance reliability by ensuring that if one module fails, the other two can still provide accurate data, thereby improving overall system robustness. TMR is particularly useful in critical applications where failures could lead to severe consequences, making it a key concept in the realm of combinational circuits and their applications.

5 Must Know Facts For Your Next Test

1. TMR requires three identical systems to operate simultaneously, which helps ensure that even if one fails, the overall function remains intact.
2. The voting mechanism in TMR typically involves majority voting, where the output from two out of three modules dictates the final output.
3. TMR is commonly used in aerospace and military applications, where system failures can have life-or-death consequences.
4. Implementing TMR can significantly increase the cost and complexity of a system due to the need for additional hardware.
5. While TMR improves reliability, it does not eliminate all types of failures, such as those caused by common-mode faults affecting all modules simultaneously.

Review Questions

• How does triple modular redundancy enhance the reliability of a system?
  • Triple modular redundancy enhances reliability by employing three identical modules that perform the same operation concurrently. If one module fails, the other two can still provide accurate results, ensuring that the system continues to function correctly. This redundancy allows for continuous operation even in the presence of faults, which is crucial in critical applications where failure is not an option.
• Discuss how voting logic functions within a triple modular redundancy setup and its importance.
  • In a triple modular redundancy setup, voting logic is employed to compare the outputs from the three modules. The logic selects the majority output as the correct one, typically assuming that at least two modules will provide valid data even if one fails. This voting mechanism is essential because it allows the system to determine accurate results despite potential module failures, thereby maintaining system integrity and reliability.
• Evaluate the trade-offs involved in implementing triple modular redundancy in critical systems.
  • Implementing triple modular redundancy involves significant trade-offs between reliability and cost-effectiveness. While TMR greatly enhances fault tolerance by ensuring continued operation despite individual component failures, it also requires additional hardware resources, increasing both costs and complexity. Moreover, while TMR can mitigate certain types of failures, it does not protect against common-mode failures that might affect all three modules simultaneously. Thus, careful consideration must be given to its application based on specific operational requirements and budget constraints.

Related terms

Fault Tolerance: The ability of a system to continue operating properly in the event of the failure of some of its components.

Voting Logic: A process used in TMR systems to determine the correct output by comparing the outputs of multiple modules and selecting the majority result.

Redundancy: The inclusion of extra components that are not strictly necessary to functioning, intended to increase reliability and availability.