Caliper, measurement tool

Manufacturers often check the parts with a variety of precision measuring tools. When accuracies of 0.001-0.0001 of an inch are needed, part inspection may be done by hand with micrometers or calipers (Figure 16-33). When accuracy greater than 0.0001 of an inch is required, very sophisticated machines take measurements. These measuring machines may use lasers for very precise measuring. 

External Dimensions. The external dimensions of a PCB are usually measured by calipers and micrometers. They can also be measured with a CMM or comparison gauges and templates. Tolerances for these dimensions should be reflected on the PCB procurement documentation. It is important to ensure that the measurement tools being used have sufficient accuracy to perform the intended measurements. 

Precision measurement is an important part of any maintenance procedure. Without micrometers, telescopic gauges, dial calipers, edge finders, and other precision measuring tools, the job cannot be done correctly. The areas covered in this chapter are ... 

Permeable intervals can be identified from a number of logging tool measurements, the most basic of which is the caliper tool. The caliper tool is used to measure the borehole diameter which, in a gauge hole, is a function of the bit size and the mudcake thickness. Mudcake will only build up across permeable sections of the borehole where mud filtrate has invaded the formation and mud solids (which are too big to enter the formation pore system) plate out on the borehole wall. Therefore the presence of mudcake implies permeability. 

There are two categories of equipment which determine the selection of equipment general-purpose and special-to-type equipment. It should not be necessary to specify all the general-purpose equipment needed to perform basic measurements, which would be expected to be known by appropriately trained personnel. You should not need to tell an inspector or tester which micrometer, vernier caliper, voltmeter, or oscilloscope to use. These are the tools of the trade and they should select the tool which is capable of measuring the particular parameters with the accuracy and precision required. However, you will need to tell them which device to use if the measurement requires unusual equipment or the environmental conditions prevailing require that only equipment be selected that will operate in such an environment. In such cases the particular devices to be used should be specified in the test or inspection procedures. In order to demonstrate that you selected the appropriate device at some later date, you should consider recording the actual device used in the record of results. With mechanical devices this is not normally necessary because wear should be detected well in advance of there being a problem by periodic calibration. 

Statistical methods are used to measure the density variation as the tool rotates, the stand-off can be estimated and the density corrected. A density caliper can be computed that works for cavings of 2 in. (5 cm) or less when the tool rotates at a speed ranging from 6 to 150 rpm. 

A dial caliper (see Fig. 2.9) is easier to read than a vernier caliper, but this ease comes at a price. An acceptable vernier caliper can be purchased for 30 - 50, and it can be found with metric and English measurements on the same tool. A good-quality dial caliper may cost between 75 and 150, and it shows only metric or English measurements. On the dial caliper, the 10th place is read on the numbers of the dial itself, and the 100th place is read on the lines between the numbers. 

Another common tool for length measurement is the micrometer. Like the vernier caliper, in the United States, it is typically made with English measurements. Whereas the caliper can provide precision measurement (to 0.002 in.), you need a micrometer for greater precision ( 0.0001 in.). 

Skinfold caliper— A curved, hinged claw-shaped tool used to measure the thickness of skinfolds containing subcutaneous fat deposits. Skinfold thickness is correlated to percent body fat, thus skinfold calipers are used to estimate percent body fat. 

The condition of the machine tool and the necessity of its repair are defined through block 5 in Fig. 4. With TTPl are measured co-ordinates (Xm,...,Cm) on the reference surfaces of the work caliper TPC (Fig. 1, position 4). The measured data are compared with the corresponding data in the database of geometric accuracy of the machine tool. When the deviation is out of tolerance (exit NO ) the possibility of corrections by altering the machine co-ordinate system is checked. If such corrections are not possible the possibility of compensating the deviation by altering the CNC programme is checked (exit YES ). If this correction is also not available (exit NO ) then the machine tool needs to be repaired. 

A tape measure can be used to measure distances from about 20 cm up to several meters. Dial calipers are useful for closely measuring extruded products, dimensions of the extruder screws, extrusion tooling, etc. A stopwatch is an indispensable tool for measuring screw speed, line speed, blender calibration, etc. A scale can be used to measure the output of an extruder. A small voltmeter is very useful in making sure that voltage and resistance levels of various components are at their required values. A millivolt source can be used for verifying thermocouple inputs and to check controller response and line continuity. 

A separate incident on an Olympic pipeline led, on September 17, 1996, to the Washington Department of Ecology ordering Olympic to carry out further remote inspection work, including the use of a diverse (mechanical) measurement technique called caliper tools . This led, on January 15, 1997, to another inspection of the pipeline done by a different company, Enduro, using the caliper tool inspection... 

Another tool that is widely used is the dial caliper. The dial caliper can take inside, outside, and depth measurements. The only drawback is that it is not as accurate as the micrometer (measurements to within. 001"). See Figure 20.9. 

---