Everything about Vernier Scale totally explained
A
vernier scale lets one read more precisely from an evenly divided straight or circular measurement scale. It is fitted with a sliding secondary scale that's used to indicate where the measurement lies when it's in between two of the marks on the main scale.
Verniers are common on
sextants used in
navigation, scientific instruments and
machinists' measuring tools (all sorts, but especially
calipers and
micrometers) and on
theodolites used in
surveying.
When a measurement is taken by mechanical means using one of the above mentioned instruments, the measure is read off a finely marked data scale (the "fixed" scale, in the diagram). The measure taken will usually be between two of the smallest graduations on this scale. The indicating scale ("vernier" in the diagram) is used to provide an even finer additional level of precision without resorting to estimation.
History
It was invented in its modern form in
1631 by the
French mathematician
Pierre Vernier (
1580–
1637). In some languages, this device is called a
nonius. It was also commonly called a nonius in English until the end of the 18
th century.
Construction
In the following, N is the number of divisions the maker wishes to show at a finer level of measure.
Direct vernier:Direct verniers are the most common. The indicating scale is constructed so that when its zero point is coincident with the start of the data scale, its graduations are at a slightly smaller spacing than those on the data scale and so none but the last graduation coincide with any graduations on the data scale. N graduations of the indicating scale would cover N-1 graduations of the data scale.
Retrograde vernier:Retrograde verniers are found on some devices, including surveying instruments. A retrograde vernier is similar to the direct vernier except its graduations are at a slightly larger spacing. N graduations of the indicating scale would cover N+1 graduations of the data scale. The retrograde vernier also extends backwards along the data scale.
Direct and retrograde verniers are read in the same manner.
Use
When a length is measured the zero point on the indicating scale is the actual point of measurement, however this is likely to be between two data scale points. The indicator scale measurement which corresponds to the best-aligned pair of indicator and data graduations yields the value of the finer additional precision digit.
Examples
On instruments using decimal measure, as shown in the diagram below, the indicating scale would have 10 graduations covering the same length as 9 on the data scale. Note that the vernier's 10th graduation is omitted.
On an instrument providing angular measure, the data scale could be in half-degrees with an indicator scale providing 30 1-minute graduations (spanning 29 of the half-degree graduations).
Why a vernier scale works
The vernier scale is constructed so that it's spaced at a constant fraction of the fixed main scale. So for a decimal measuring device each mark on the vernier would be spaced nine tenths of those on the main scale. If you put the two scales together with zero points aligned then the first mark on the vernier scale will be one tenth short of the first main scale mark, the second two tenths short and so on up to the ninth mark which would be misaligned by nine tenths. Only when a full ten marks have been counted would there be an alignment because the tenth mark would be ten tenths, that's a whole main scale unit, short and will therefore align with the ninth mark on the main scale.
Now if you move the vernier by a small amount, say, one tenth of its fixed main scale, the only pair of marks which come into alignment will be the first pair since these were the only ones originally misaligned by one tenth. If we'd moved it 2 tenths then the second pair and only the second would be in alignment since these are the only ones which were originally misaligned by that amount. If we'd moved it 5 tenths then the fifth pair and only the fifth would be in alignment. And so on for any movement, only one pair of marks will be in alignment and that pair will show what is the value of the small displacement.
Vernier Acuity
Vernier acuity is the ability by a person to detect the proper alignment of two line segments. In most persons, Vernier acuity is particularly acute. This allows one to differentiate the aligned and misaligned marks on a Vernier scale.
Further Information
Get more info on 'Vernier Scale'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://vernier_scale.totallyexplained.com">Vernier scale Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
