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Fault location and Diagnosis. Preparation for fault diagnosis Access: have all obstructions been removed? Inspection covers?, Clutter? Signs barriers.

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Presentation on theme: "Fault location and Diagnosis. Preparation for fault diagnosis Access: have all obstructions been removed? Inspection covers?, Clutter? Signs barriers."— Presentation transcript:

1 Fault location and Diagnosis

2 Preparation for fault diagnosis Access: have all obstructions been removed? Inspection covers?, Clutter? Signs barriers are in place Visibility: has dust, grease and dirt been cleaned to reveal as much as possible of the job in hand? Symptoms: do you understand the nature of the problem? What is that the equipment has failed to do? How is the performance abnormal?

3 Now eliminate the obvious

4 1.Collect the evidence Approach with an open mind Before disturbing or changing anything- Stop, Look, Listen and Learn Collect only relevant information, if in doubt about its validity include it and discard later if unrelated Question the user Check the system running if possible Use sources of information, manuals, maintenance records etc Use test equipment to verify calibration and settings 2.Analyse the evidence separate the various symptoms and work out the importance of each one Check if the evidence leads to a previously recorded fault 3. Locate the Fault Use all resources available- test equipment etc If possible locate fault to component level Never assume- always remove and check suspect components Method

5 4.Determine and Remove the Root cause The root cause of the fault must be located and removed otherwise the fault will eventually reoccur 5.Rectify the Fault Any adjustment, repair or replacement should only be carried after identifying and removing the root cause of the problem 6.Test the System Ensure the machine, equipment or system is functioning correctly before being put back into service- fine tune if required

6 Identify the cause Symptom - signs or indications that there is a deviation from the normal operating mode Fault – the particular defect or combination of defects that cause the symptom to occur Cause – the reason why a fault has occurred Symptom (overheating) Fault (worn bearing) Cause (poor lubrication)

7 Sensory (visual) fractures, surface cracks, corrosion, leaks, damage, contaminated oils, Loose fastenings, excessive wear, metallic particles, broken chains and belts, missing parts

8 Sensory (smell) Smell- hot oil, burnt out motor, burnt out belts, overheating

9 Sensory (Touch) Touch- vibration, wear, play, belt or chain tension, out of balance, excessive clearance

10 Sensory (Noise) Noise- unfamiliar noises, out of balance, vibration, worn bearings, air leaks

11 Six Point Technique - Used on complex faults with a history of data 1. Collect the Evidence Observe machine running (if safe to do so) Refer to manufacturers manual (look for fault finding aids) Use test equipment (built in or otherwise ) Consider machine history records Use sensory techniques Question the operator (use good social skills ) Consider Packaging materials Raw materials Services (air water etc) 2. Analyse the evidence (diagnosis)

12 3. Locate the Fault (based on analysis of evidence) 4. Determine and remove cause (to prevent reoccurrence) 5. Rectify the fault 6. Check the machine or system (before handing over to production)

13 Emergent Problem Sequence In any equipment failure there are factors that have caused a deviation from the normal mode of operation (changed factors) Sequence Analysis: determine the real problem or problems Prioritise: seriousness, urgency, the expected outcome Statement: write down the problem or variance Describe the problem Where – geographically or on the object Size- how big-how much-how many What- object or defect When- time or life cycle

14 Set Boundaries - use the description to narrow down the field of investigation Differences- look for factors that are unique to the problem Identify – changed factors Diagnose – list and categorise each changed factor in terms of which it explains the facts Ask yourself Is there a deviation from the standard or norm? Is the cause unknown? Do I need to know the cause? Do I need to be involved? If all points are answered ‘Yes’ then use the six point technique

15 Half Split Technique This is used to reduce diagnosis time in circumstances where a series of components are working together. It is based on the process of iteration. This simply means narrowing down and revisiting 1 st check signal ok 2 nd check no signal 3 rd check signal ok fault

16 Function Testing There is normally a specification for the operation of an electrical component, equipment or system. By ensuring the outputs are connected correctly and the correct input is applied, the operation or function of the electrical equipment can be measured against the specification. Does it do what it designed to do within the given parameters? If not then it is faulty Input (240v) ok Output (heater) not heating up – heater is at fault

17 Input to Output Technique If the required function is known, and the input and output can be measured, then the location of the fault is narrowed down or found Output x Output y Inputs A B C

18 Unit Substitution If the input and output from a functional component can not be measured, a method of fault location is to replace each component in turn, useful where components are easily substituted with a known functioning unit

19 Diagnostic Aids Equipment manuals Valuable source of information Most manuals will include a section that is dedicated to the tracing of faults. It will usually be in the format that describes the symptoms, the possible faults that have caused the symptoms and the appropriate remedial actions

20 Algorithms Action Question Direction Stop A step-by-step problem-solving procedure, for solving a problem in a finite number of steps.

21 Self Diagnostics Many Modern Machines especially production and processing equipment, are equipped with self-diagnosis panels. They come in a variety of forms but they usually have a visual representation of the system. The elements of the system that may fail have a sensor that checks for correct operation

22 Maintenance/Equipment Records/CMMS It is imperative that any information relating to the equipment or system is recorded so as aid future maintenance and continual improvement Records can be in: Technical Files or Maintenance logs – written or electronic Recent trends have seen the introduction of software packages that are designed to hold and access equipment history (Computer Maintenance Management Systems) All Records should include: Breakdowns (fault, cause and remedy) Planned Maintenance (work done) Condition monitoring results

23 Computer Maintenance Management Systems Using software packages will: Reduce maintenance cost Optimise inventory and purchasing Implement standards and compliance Store and retrieve records Improve maintenance management program reliability


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