How useful are multi-meter and oscilloscope in diagnising intermittent faults, multiple faults and faults which may cause system interaction.

 

I'm not sure what you mean by intermittent faults/multiple faults?

 

Multiple faults= one affecting more than one.

Intermittent faults= on and off ie, once in a while( seconds, minute or hour).

Thanks B)

 

I used to do a lot of worth on Strain Gauges which were particularly succeptable to what we called "raising"; the arms that constitute the strain gauge sometimes didn't take properly to the test surface we were working on and as a result occasionally didn't produce the desired outputs when functioned. Funny thing was that the strain gauge worked perfectly well most of the time. It was an intermittent fault. The test rig wouldn't tell us what the problem was, just that there was a problem occasionally.

The only way we could test for this "raising" was by hooking up the DMM to the strain gauge and by testing the individual arms on strain gauge to look for variations in the resistances that were not consistant with Engineering Standards. Although we never tried it, an oscilloscope would have probably shown the same result as the test rig because it is analysing continuous data, changes in the operation of a component would show up on the screen occasionally, but it wouldn't pin-point where the problem lied.

Oscilloscopes have the advantage that they can look at multiple parameters, and plot the results against each other, for example Lissalious figures. The interpretation of such data is considerably more difficult, but to analyse multiple, concurrent parameters with a DMM would be extremely difficult and very prone to human error. This obviously relates to multiple faults.

Could you elaborate on what 'faults which may cause system interaction' is?

 

Thanks Dave.

System interaction, hem :unsure: yeh like, Car radio getting feed back from the engine when in motion. Kind of whistling noise from engine to radio.

More feed-back from earlier 2 will be appreciated.

 

Originally posted by lanre olutola@Feb 26 2004, 07:21 AM
Thanks Dave.

System interaction, hem :unsure: yeh like, Car radio getting feed back from the engine when in motion. Kind of whistling noise from engine to radio.

More feed-back from earlier 2 will be appreciated.

So you mean the act of something working affects the operation of the system. This is more of a continous type fault. Using your example of noise, noise would be unnoticed when using a DMM, so its use in such for such tasks is pointless. However, the oscilloscope would allow to see the magnitude and form of the noise on a continous cycle. If you ever do a laboratory experiment looking at microelcetronic components (transistors, photodiodes etce) they will always exhibit some suscepability to noise, when you plot this on the oscilloscope you can see exactly how the noise disturbs the waveform, for example causing fluctuations in ampitude and 'flattening' the waveforms peaks and troughs. As the system becomes more complex the effects of noise will change and the oscilloscope will allow the user to observe such changes, so the user is observing the fault alterations caused by system interaction.

To pick up on what was mentioned earlier, I worked as part of a test instrumentation team who commisioned instrumentation for aircraft. A lot of our work was 'in-the-field', we didn't have access to test rigs and high-tech data aquisition units all the time so a lot of our work included using a DMM and a book of engineering standards - you'd be amazed what you can work out by measuring voltages and currents and comparing them against standards! The point I'm trying to make is that DMMs are very useful pieces of equipemnt and can be used to diagnose a wide range of faults both continous and intermittent provided the user is competant and knows what they are doing. The DMM unit is very small and therefore is ideal for use 'in-the-field', plus the display does not require a vast amount of interpretation. This compares against oscilloscopes which tend to be rather bulky by their nature and are really suited to laboratories. Also the set-up, use and display can often confuse the user making interpretation of the data difficult. You can see whats going on, on an oscilloscope, but this is not always of an advantage as I explained before in a previous example.

I can't think of any further examples off the top of my head at the moment, long day! :wacko: Post back if you have any more questions.

 

You may also find the following two links useful:

Introduction to test equipment

Test methods and practices

Both links have an abundance of information, much of which will not be of much use to you, but have a look anyway (particularly the second one)

 

Thanks Dave.

Those sites were great, to say the least. Very usefull. US navy is it, l'll be frequient.

Standing on the shoulder of a giant. A relieve, catch U later man.

 

Originally posted by lanre olutola@Mar 4 2004, 09:01 PM
Thanks Dave.

Those sites were great, to say the least. Very usefull. US navy is it, l'll be frequient.

Standing on the shoulder of a giant. A relieve, catch U later man.

No probs, glad to be of help.