Linear Measurement - Classification of Linear Measurement,

 Linear Measurement: - Linear measurement is when you measure things in a straight line using tools such as a ruler, yardstick or tape measure. 

The following table shows different types of linear measurement. Standard of Length: - 

The standard unit of length based on the metric system is a meter (m). According to the length that needs to be measured, we can convert a meter into various units like millimeters (mm), centimeter (cm), and kilometer (km). 

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Classification of Linear Measurement:- 

The Linear measurements are classified into Two types they are. 

1. Precision Instruments. 

2. Non – Precision instruments. 

Linear measurements of Precision Instruments The precision instruments are following to possess high degree of accuracy in measuring the dimensions. 

The instruments used for measuring the angles and  Types of Plain Limit gauges. 

1. Vernier Calipers 

2. Slip Gauges

 3. Micrometers

 4. Vernier Height gauge and Depth Gauge 

5. Vernier Micrometer 

6. Depth micrometer

 7. Inside Micrometer and Outside micrometers 

Linear measurements of Non – Precision instrument The Non precision measuring instruments are. 

a. Calipers 

b. Steel Rule

Vernier Callipers :- Vernier calipers are used for internal and external dimensional linear measurements. The combined type provides a means for Internal, external and height, depth measurements

 The vernier caliper consists of a.

 1. Beam with a graduated scale made integral with the fixed jaw 

2. A sliding jaw

•  3. Carrying a vernier scale slides on the beam and it is provided with some means of locking. The formula of Vernier calliper least counts is determined by dividing the smallest reading of the main scale with the total number of vernier scale divisions. The LC of vernier calliper is the difference between one smallest main scale reading and one smallest vernier scale reading of 0.1 mm or 0.01 cm. L.C. =  EMMP – Linear Measurement 

least count :-  The smallest reading which can be accurately measured with a vernier caliper is called its least count (L.C), it is also known as the vernier constant. It is the difference between one main scale division which is 1 mm and one vernier division which is (0.9). L.C = 1 mm – 0.9 mm =0.1 mm There is another method to find the least count which is given as:

Micrometer:- A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers. 

• A Vernier scale on a caliper may have a least count of 0.1 mm while a micrometer may have a least count of 0.01 mm.
•  Vernier Height Gauge: - Vernier height gauge is a special type of vernier instruments which is used to measure heights of different engineering objects up to high precision and accuracy during many of industrial jobs where measuring process is require. 
• Dial Vernier :- A Dial caliper is a calibrated precision measuring tool that is useful for taking accurate measurements. 
•  Dial Height Gauge :- Dial height gauges with dial and dual-digit counters decrease the time needed to lay out a part. Not only is the dial easier to read than a Vernier scale, but the dual-digit counters allow one counter to be set at the reference datum and the other to be used as a floating zero.
•  Slip Gauge: - A very accurately ground block of hardened steel used to measure a gap with close accuracy: used mainly in tool-making and inspection. 
• Classification of slip Gauges:- Use of slip gauges: - Slip gauges are important means of measurement in industries and laboratories. 
• Their uses are:

1. They universally accepted as a “Standard of length”. 

 2. They used for direct precise measurement where accuracy of work piece being measure is high.

 3. They used with high-magnification comparators, to establish the size of the gauge blocks. 

4. They are used for checking the accuracy of measuring instruments. 

5. They are used to setting up a comparator to specific dimension. 

6. They are used to check a batch of components quickly and accurately. 

Wringing Process in slip gauges: - Wringing is the process of sliding two blocks together so that their faces bond. Because of their ultra flat surfaces, when wrung, gauge blocks adhere to each other tightly. 

 Comparator: - A comparator is an electronic circuit, which compares the two inputs that are applied to it and produces an output. The output value of the comparator indicates which of the inputs is greater or lesser. 

Classification of comparator:- 

 Mechanical Comparator 

 Mechanical-Optical Comparator 

 Reed Type Comparator 

 Electrical-Electronic Comparator 

 Pneumatic Comparator 

 Mechanical comparator: - A measuring instrument whose mechanism is in the form of a tape spring twisted in the middle part, which rotates through a definite angle upon tension (Figure 1). 

It is used for linear measurements by the relative contact method. Linear Measurement 

  Electrical comparator: - A comparator is a precision instrument used to compare the Dimensions of a given working component with the actual working standard. 

There are different types of comparators are available. In this article, we are going to discuss. 

 Electrical comparators convert the linear movement of the plunger into electrical signals and these signals further calibrated with the help of Galvanometer on to the graduated scale. Electrical comparators and Electronic Comparators. 

Advantages of Electrical and electronic Comparators :- 

1. Very high magnification possible with these electrical comparators. 

2. Less number of moving parts. 

3. More sensitive towards vibrations.

 4. The instrument is very compact in design.

Disadvantages of Electrical and electronic Comparators :- 

1. Quite expensive compared to the mechanical comparator

 2. An external source of energy is required 

3. Due to the heating coils, the accuracy will be affected. 

 Optical comparator: - Mechanical-Optical Comparators are same as the Optical comparators but the Plunger in mechanical-Optical comparator will be replaced with the Pivoted levers. See the following diagram of a Mechanical -Optical Comparator

 Working Principle of Mechanical-Optical Comparator :- 

1. The lever acts as the plunger. 

2. The mirror is connected to the lever mechanism. 

3. The lever is held by the pivot point. 

4. The lengths L1 and L2 make the Magnification The L2 should be greater than the L1 so the more magnification is achieved.

 5. When the measuring tip is contacted the workpiece, then the lever starts rotates about the pivot.

 6. The mirror will tilts accordingly about the Pivot point. 

7. The reflected ray will be projected on the graduated scale and shown as the reading.

 Advantages of Optical Comparators:- 

 1. High accuracy will be achieved since it is having very less moving parts.

 2. Parallax error will be avoided.

 3. Less weight compared to other comparators due to fewer parts. 

4. Very Suitable for precession measurements due to high magnification can be achieved. Disadvantages of Optical Comparators:- 

1. Need a separate electrical source. 

2. Optical means are expensive.