B11 LMSS Module 3

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Questions and Answers

What can lead to a loss of the switching function in output devices?

Incorrect actuator position

Short circuit of outputs (correct)

Inadequate power supply

External environmental conditions

Which of the following is NOT a mode of fluid power failure?

Spring Failure

Pilot Section Failure

Seal Failure

Input Noise (correct)

What is a common fault of safety devices?

Internal component failure (correct)

Temperature fluctuations

External contamination

Inadequate lubrication

Which factor can cause diminished response time in fluid power systems?

Moisture levels Signup and view all the answers

What is a critical factor affecting pneumatic systems?

Air contamination Signup and view all the answers

In hydraulic systems, what can increase the rate of component wear?

Closed system contamination Signup and view all the answers

Which type of failure is characterized by a complete loss of electrical power?

Coil failure Signup and view all the answers

Which condition does NOT typically affect pneumatic systems?

Spring Failure Signup and view all the answers

What does PL stand for in the context of performance levels in safety systems?

Performance Level Signup and view all the answers

Which of the following standards relates specifically to safety integrity levels?

IEC 62061 Signup and view all the answers

What is the primary focus of ANSI B11.26 - 2018?

Functional safety for equipment Signup and view all the answers

In the classification of control reliability, which performance levels are being assessed?

Performance Levels (PL) and Safety Integrity Levels (SIL) Signup and view all the answers

What is the relationship between ISO 13849-1:2015 and IEC 62061?

Both are standards for safety-related control systems. Signup and view all the answers

What does a reliability design specification evaluate in a circuit?

The overall circuit performance level Signup and view all the answers

Which standard is NOT mentioned as a methodology for selecting reliability design specifications?

ANSI Z10 Signup and view all the answers

What should not be used to determine the reliability achieved by a circuit?

Control reliability ratings Signup and view all the answers

Which of the following best describes 'acceptable risk'?

A risk level considered tolerable for a given situation Signup and view all the answers

Which methodology evaluates the design of the overall circuit?

Performance level as per ISO 13849-1 Signup and view all the answers

What type of risk reduction measures include inherently safe design measures?

Fixed guards Signup and view all the answers

Which of the following represents the maximum level of risk avoidance?

Zero risk Signup and view all the answers

In risk management, what do administrative controls primarily aim to do?

Modify risk by implementing procedures Signup and view all the answers

What describes an open crossover in fluid power systems?

There is a flow path between the supply, outlet, and exhaust/return port. Signup and view all the answers

What is a primary concern when designing hydraulic circuits?

Minimizing the impact of stored energy. Signup and view all the answers

What occurs when control voltage is removed from a directional control valve?

The SRP/CS will not function as intended. Signup and view all the answers

Which of the following is part of fault consideration in fluid power systems?

Evaluating failure modes impacting the safety function. Signup and view all the answers

What is a characteristic of a closed crossover in fluid power systems?

Fluid pressure is trapped at the outlet port. Signup and view all the answers

What is essential for SRP/CS integration into the control system?

Incorporating various disciplines including electrical and pneumatic systems. Signup and view all the answers

Which statement about energy removal in fluid power is correct?

It can create a protective stop when properly managed. Signup and view all the answers

What is NOT a consideration in hydraulic circuit design?

Maximizing energy transfer at all outlets. Signup and view all the answers

What is the primary characteristic of positive logic in circuit design?

Current sourcing inputs interpret wire breaks as off state. Signup and view all the answers

What is the consequence of dropping power to the PES/PLC output card?

It SHALL cause a Category 0 Stop. Signup and view all the answers

What should the current interrupted by contacts in a circuit be?

Above the recommended minimum and below the maximum. Signup and view all the answers

Which method is NOT a recommended way to perform protective stops in fluid power systems?

Increasing power to the directional control valves. Signup and view all the answers

Why is it important to NOT remove power from the non-safety PES/PLC in safety functions?

It allows for necessary diagnostics. Signup and view all the answers

What does the removal of control voltage from a directional control valve imply?

There is no assurance that the SRP/CS will perform as required. Signup and view all the answers

What is a characteristic of negative logic systems?

They utilize current sourcing inputs exclusively. Signup and view all the answers

Which of the following methods is used to maintain actuator position in fluid power systems?

Blocking the fluid power energy source. Signup and view all the answers

What should be the configuration of the supply line in a protective stop circuit?

Control the last electrically powered device or actuator. Signup and view all the answers

Which option is a method of exhausting energy in fluid power systems?

Removing electrical power from control valves. Signup and view all the answers

Study Notes

Electrical Failure Modes

Short circuits in outputs, external wiring, or devices can lead to loss of switching functions.
PES/PLC programs may face alteration due to programming errors or unsecured logic.
Loss of PES/PLC memory can result in operational failures.
Safety devices can fail or exhibit faults due to internal component issues.
False actuator/input signals may arise from noise, external errors, or internal shorts.

Fluid Power Failure Modes

Common failures include seal, spring, coil, and power losses.
Diminished response times and valve position failures can lead to operational inefficiencies.
Inadequate mounting orientation and inertial forces can cause system instability.
Conductor and connector failures can compromise system performance.

Pneumatic Failure Modes

Temperature variations, moisture presence, and lubrication issues can affect pneumatic systems.
Line blockages or muffler restrictions can impede airflow.
Ingress of contaminants poses a significant risk to performance.

Hydraulic Failure Modes

Temperature and moisture control are critical in hydraulic systems, which are closed systems.
Contamination from component wear can lead to increased wear rates and system failure.

Reliability Specifications

A circuit's reliability specification can be based on performance levels as per ISO 13849-1, categories from EN 954-1, or control reliability from OSHA.
ISO 13849-1:2015 outlines safety standards for machinery and control systems.
IEC 62061 focuses on functional safety for electrical and programmable systems.
ANSI B11.26-2018 provides guidance for the design principles of safety control systems.

Electrical Design Requirements

Circuits should minimize the impact of stored energy in time-dependent functions.
Positive logic is preferred; it interprets shorts or breaks as “off” states, while negative logic is less fault-tolerant.
Electro-mechanical contact requirements stress that interrupted current must remain within manufacturer specifications.

Interfacing with Non-Safety PES/PLC

Do not remove power from non-safety PES/PLC during safety functions to maintain diagnostic capabilities.
Protective stop circuits should control the supply to output circuits for hazardous motion.
Power removal from PES/PLC output cards should trigger a Category 0 Stop, ensuring safety.

Fluid Power Design Requirements

Protective stops can be achieved by blocking fluid energy sources, removing electrical power from valves, or using mechanical means to control motion.
Reapplying pressure should not create hazards, as losing control voltage does not ensure compliance of SRP/CS.

Fluid Power Valve Crossover

Open crossover allows fluid pressure between supply, outlet, and exhaust ports with flow.
Closed crossover traps fluid pressure at the outlet, preventing flow to other ports.

Key Concepts in Fault Consideration

Evaluating failure modes is crucial to ensure that circuits perform their safety functions effectively.
Understanding the interaction between electrical, pneumatic, and hydraulic systems is vital for overall safety and reliability in design.

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Description

This quiz covers various failure modes related to electrical, fluid power, and pneumatic systems. You'll explore issues like short circuits, programming errors, and the impact of environmental factors on system performance. Test your understanding of these crucial concepts in system reliability.