Tools – DTI’s, inductive sensors and stands – links
There are all sorts of ways of measuring distances. A very common method is to have a known length and then compare another length against the known one. Very often we are only interested in variations from a standard. For example, if a round shape is fitted in a chuck we might need to know how eccentric it is. In fact we are not really interested in this but rather we want to reduce it to zero.
The solution to this is an indicator. The most common sort of this is the “dial test indicator”. This is usually abbreviated to “DTI”. These are purely mechanical devices. They can detect differences of about 0.01mm. Some are designed to detected just 0.001mm. This is the limit of a mechanical indicator.
It is traditional for all metric DTI’s to be calibrated in millimetres. The amount of 0.01mm is 10 micrometers, 0.001mm is 1 micrometer. When differences get smaller than this it is easier to think in terms of micrometers.
To measures smaller differences it is necessary to use electronic methods. The most common of these is the inductive sensor. These can measure down to 0.1 micrometers, which is 100 nanometers.
Both of these types of device require some means of holding them. They can either be held using special attachments designed for special application or stands designed specially for making comparisons.