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

Fault location and Diagnosis

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?

Now eliminate the obvious

1. Collect the evidenceApproach with an open mindBefore disturbing or changing anything- Stop, Look, Listen and LearnCollect only relevant information, if in doubt about its validity include it and discard later if unrelatedQuestion the userCheck the system running if possibleUse sources of information, manuals, maintenance records etcUse test equipment to verify calibration and settings

2. Analyse the evidenceseparate the various symptoms and work out the importance of each oneCheck if the evidence leads to a previously recorded fault

3. Locate the FaultUse all resources available- test equipment etcIf possible locate fault to component levelNever assume- always remove and check suspect components

Method

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

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)

Sensory (visual)

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

Sensory (smell)

Smell- hot oil, burnt out motor, burnt out belts, overheating

Sensory (Touch)

Touch- vibration, wear, play, belt or chain tension, out of balance, excessive clearance

Sensory (Noise)

Noise- unfamiliar noises , out of balance, vibration, worn bearings, air leaks

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)

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)

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

• 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

Half Split TechniqueThis 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

1st check signal ok

2nd check no signal

3rd check signal ok

fault

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

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

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

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

Algorithms

Action

Question

Direction

Stop

A step-by-step problem-solving procedure, for solving a problem in a finite number of steps.

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

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

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