Measuring Techniques:
Using what's in
the PQ bag

So, the next step is,

know your instruments !!

This may appear as a daft statement but many measurements have been done by very competent engineers with useless results, all because they did not know their instruments. What appears to be missing is the understanding of the use of basic instruments, such as oscilloscopes. There are very few people who know how to connect up an oscilloscope, and even less who can interpret what is displayed!

This section covers everything a power quality investigator should consider as part of his PQ bag. We'll also run through a list of instruments that have impressed us, either through introduction or, better still, through use. This is by no means a complete list of what is available, and there will be many manufacturers of effectively the same type of instrument.

Knowing the instruments, their availability and capability is only half the story. The need to understand the subtle, but all important difference between a Survey and an Investigation becomes paramount. The difference is:

This is done to obtain trend data for the planning and implementation of further loads or the upgrading of a Network. Such data could also include the monitoring for potential faults appearing (but not yet present) on a system.

This is the study of a Network's quality to ascertain the potential impact on, or the cause of a client's already present annoyance, loss of productivity, and/or damage to equipment.

The reason to understanding the difference is that it will ensure the correct instrument is taken to site. It is useless taking an oscilloscope to site when a long term recording of over-voltage is being assessed. Conversely, taking a long term recorder to site to trace a possible arc tracking fault is just as much a waste of time (and then people wonder why we wrote a whole section on "Using Ears"!).

We start with the obvious being the Multimeter and cover the advantages and pitfalls made by many.

We then bring in an instrument that still has many engineers scratching their heads - the Oscilloscope. This is such a handy instrument, and so incredibly versatile, that it makes one wonder why there is not a shortage of them in the world - but then watch an engineer operate one and you quickly find out!

Recorders are all very well and all three levels of Simple, Semi Complex, and Complex are covered. These should not be viewed as the only way to tackle a power quality issue, in fact they should not be viewed as anything more than "keeping a watch on things while I wasn't looking".

Even the power recorders can fail to indicate faults and there are "tricks of the trade" one can rely on. The Audio Amplifier and Portable Radio are two such tricks, their applications are dealt with in the relevant sections.

Using Multimeters  >>

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