Term 1 Week 7

This week we learnt about some measuring instruments - calipers, vernier calipers, and the micrometer screw gauge.

Firstly, what are calipers? There are two types of calipers - external and internal. The calipers are used to measure the inside and outside diameters of round objects. So... this is a picture of an external caliper.

To use the external caliper, move the jaws of the caliper such that that touch the outer surface of the round object. Then, remove the caliper from the object and measure the distance between the jaws with a ruler. That is the outer diameter of the object.










Now, this is a picture of an internal caliper.

The internal caliper is used to measure the internal diameter of a hollow round object (such as a pipe). To use this, move the jaws such that they touch the inner surface of the object. Then, again, remove the caliper from the object and measure the distance between the jaws with a ruler.








Now, what are vernier calipers? Vernier calipers are a type of measuring instrument which is accurate up to 0.01cm. However, rulers are only accurate up to 0.1cm, or 1mm. This is a picture of the vernier caliper.

The outside jaws are used to measure the external diameter of objects, while the inside jaws are, of course, to measure the internal diameter of round objects. Firstly, let's talk about how we measure the external diameter of objects. To measure the external diameter of objects, move the vernier scale such that the outside jaws touch the external surface of the object. Then, look at the vernier scale. The mark on the main scale that is to the left of or on the '0' on the vernier scale would be the diameter of the object up to 0.1cm. Then, check the vernier scale again. Check for the mark on the main scale which is directly on the mark on the vernier scale. For example, if the mark on the vernier scale which is directly below the mark on the main scale is '5', add 0.05cm to the measurement you got before this (the mark on the main scale to the left of the '0' on the vernier scale). If the mark on the vernier scale which is directly below the mark on the main scale is zero, take the mark on the main scale and add nothing. For the internal diameter, the only different step is that the inside jaws should touch the internal surface of the object.

However, there is more to the vernier caliper. Before we start any of the measurements, we have to check for a 'zero error'. Firstly, close the outside jaws such that they touch each other. If the main scale's '0' is in line with the vernier scale's '0', there is no zero error. However, if the vernier scale zero is not in line, there is a problem.

So, there are 2 types of zero error - positive and negative. Firstly, let's talk about the positive zero error. If the vernier scale's '0' is to the right of the main scale's zero, the zero error is positive. to measure the zero error, take the mark on the vernier scale which is in line with the mark on the main scale. So, if the mark on the vernier scale in line is '3', we deduct 0.03cm off the measurements with the vernier caliper.

For negative zero errors, the '0' on the vernier scale is to the left of the '0' on the main scale. To find out the negative zero error, check the mark on the vernier scale in line with the mark on the main scale. If the mark on the vernier scale in line is '7', take (0cm - (0.1cm - 0.07cm)) = -0.03cm. For future measurements with this vernier caliper, take away -0.03cm, or rather, add 0.03cm to the measurements.

Now, for the micrometer screw gauge. The micrometer screw gauge measures the length of objects up to an accuracy of 0.01mm. Note that the vernier caliper only measures up to 0.01cm, or 0.1mm. However, this is slightly harder to explain in words so I'll show a video instead.



However, the video does not explain on the zero error so I will do that instead. When the micrometer screw gauge is close, check if the '0' on the thimble scale is aligned to the line. If they are not, then there is a zero error. For the positive zero error, check the mark on the thimble scale which is aligned. If the mark is 5, for future measurements, deduct 0.05mm from the measurements.

For the negative zero error, the '0' is above the line. Check the mark on the thimble scale which is aligned to the line. If the mark is 46, the zero error is (0mm - (0.50mm - 0.46mm) = -0.04mm. For future readings with this micrometer screw gauge, deduct -0.04mm, or add 0.04mm, to the measurements.