Introduction
Diagnostic techniques are very much linked to the use of test equipment. In other words you must be able to interpret the results of tests. In most cases this involves comparing the result of a test to the reading given in a data book or other source of information. By way of an introduction, Table lists some of the basic words and descriptions relating to tools and equipment. shows a selection of basic tools.
Basic hand tools
You cannot learn to use tools from a book, it is clearly a very practical skill. However, you can follow the recommendations made here and, of course, by the manufacturers. Even the range of basic hand tools is now quite daunting and very expensive.
One thing to highlight, as an example, is the number of different types of screwdriver ends, as shown in These are worthy of mention because often using the wrong driver and damaging the screw head causes a lot of trouble. And of course, as well as all these different types they are all available in many different sizes!
It is worth repeating the general advice and instructions for the use of hand tools.
- Only use a tool for its intended purpose.
- Always use the correct size tool for the job you are doing.
- Pull a wrench rather than push it whenever possible.
- Do not use a file or similar, without a handle.
- Keep all tools clean and replace them in a suitable box or cabinet.
- Do not use a screwdriver as a pry bar.
- Always follow manufacturers’ recommendations (you cannot remember everything!).
- Look after your tools and they will look after you.
The first and second of these issues can be dispensed with by knowing how to read the test equipment correctly and also knowing the appropriate level of accuracy required. A micrometer for a plug gap? A ruler for valve clearances I think you get the idea.
The accuracy of the equipment itself is another issue. Accuracy is a term meaning how close the measured value of something is to its actual value. For example, if a length of about 30 cm is measured with an ordinary wooden ruler, then the error may be up to 1 mm too high or too low.
This is quoted as an accuracy of 1 mm. This may also be given as a percentage, which in this case would be 0.33%. The resolution, or in other words the ‘fineness’, with which a measurement can be made, is related to accuracy. If a steel ruler was made to a very high standard but only had markings of one graduation per centimetre it would have a very low resolution even though the graduations were very accurate.
Accuracy of test equipment
he loading effect is a consideration for any form of measurement. The question to ask is: ‘Does the instrument change the conditions, so making the reading incorrect ’With a multimeter this relates to the internal resistance of the meter.
Last word
It is recommended that the internal resistance of a meter should be a minimum of 10 M This not only ensures greater accuracy but also prevents the meter damaging sensitive circuits.
