Why Instruments are important while Testing

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Author: jenny Dsouza

Testing is a process of executing a program with the intent of finding errors. Tester never fixes the error rather find them and return to the programmer.

Different Instruments used while testing:

1) Micrometer

A micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shafts and depths of slots. Micrometers have several advantages over other types of measuring instruments like the Vernier calliper.

- External micrometer - Internal micrometer - Depth micrometer An external micrometer is typically used to measure wires, spheres, shafts and blocks. An internal micrometer is used to measure the opening of holes, and a depth micrometer typically to measure depths of slots and steps. The precision of a micrometer is achieved by a mechanical advantage of a fine pitch screw mechanism. The Micrometer is very exactitude and has a toleration of 0.001 mm. There are also with a toleration of 0.01mm. The most Micrometers can measure a length different of 25mm. You must read a micrometer the same as a Caliper.

2) Vernier Calliper:

Vernier calipers are the simplest of vernier instruments and they are very important in tool room, die-making , model-making , and similar applications. They provide long measurement ranges (6 to 80in.) and fare economical. One pair of verniier calipers can substitute for many outside and inside micrometers, but they cannot replace them.Vernier calipers are slide calipers with a vernier scale attaché. Because the vernier increases its discrimination to 0.02 mm(1 mil,0.001 in.) , we need a fine adjustment and a means for a zero setting.

3) Surface plate:

A surface plate is a definite advantage for speeding up marking out and improving accuracy. Moreover, for castings it is sometimes indispensable. To be useful the plate needs to be at least 12 inches square, mine is 18" x 12" and this gets a little cramped at times. Whilst it is possible to use a flat lathe bed for the odd marking job, rubbing rough cast iron castings across it is not a good idea. A serviceable plate can be made from a section of thick plate glass (about 3/8-1/2" thick) provided it is mounted at 3 points on a firm wooden base.

Advantages of plate method:

1. Unlike the ring method, no correction is required for measurement values obtained by the plate method. 2. With the plate method, the densities of the liquids don't have to be known as they have to be with the ring method. 3. In an interfacial tension measurement the surface is only touched and not pressed into/pulled out of the other phase. This avoids the phases becoming mixed.

4) Height Gauge:

A height gauge is a measuring device used either for determining the height of something, or for repetitious marking of items to be worked on.

These measuring tools are used in metalworking or metrology to either set or measure vertical distances; the pointer is sharpened to allow it to act as a scriber and assist in marking out work pieces.

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Technical Details:

• Single Beam Type • Stainless Steel Beam with Dark Markings • Horse Shoe base gives extra stability • With Driving Wheels for easier movement • Carbide Tipped Scriber with Lock and Clamp • Buttons: On/Off, Inch / MM, ABS