Instruments, measuring dial caliper

FIGURE 16-33 (a) A dial caliper and (b) a micrometer are precision measuring instruments. 

The dial caliper can accurately measure objects to thousandths of an inch. It takes practice to read this instrument. This is a versatile measuring device because it can measure either outside or inside dimensions. The long jaws at the top measure the outside dimension of an object. On the opposite side are two shorter jaws that are designed to measure inside a hole or a piece of tubing. 

In the contacting measurement techniques, the micrometer caliper is a common instrument. The micrometer, however, can only be used for pot measurements and this is done manually. A spring-loaded dial gauge can be moved over the extrudate if the thickness variations are small. Thus, the dial gauge can be used to monitor the variation of thickness with time, i. e., in the extrusion direction. If an accurate traversing mechanism is constructed, the dial gauge can also measure the thickness variation perpendicular to the extrusion direction. At the point of measurement, the opposite side of the extrudate has to be firmly supported to avoid measurement errors. 

Many of the electronic measuring instruments outlined in this chapter, e.g. vernier calipers, micrometers and dial test indicators, can be equipped to output data either through available data cables or by wireless transmitters/receivers. This data can be printed out or sent to a computer and collected and used by quality control to provide statistical information or for the generation of inspection certificates. 

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