Measurement Techniques and Instruments in Metrology

Precision Measurement Techniques and Instruments

Action

This is the procedure of comparing a magnitude, known as drive power, with another of the same nature to find the relation between them.

Magnitude

Everything is likely to be measured, such as length, mass, or time.

Metrology

The science that studies the measurement of magnitudes. It is currently attempting to standardize so that it will be unique for everyone, and called the International System of Units (SI).

Accuracy of Measurement

Accuracy of measurement is determined by its degree of approximation to the actual value of the magnitude or conventional that is measured. Accuracy is the ability of a measuring instrument to give results with very high accuracy.

Weighing

1. A) Direct measurement: We can read the measurement value directly from the divisions of the instrument.

   B) Indirect measurement: We make some mathematical operation to obtain the measurement value.

2. Measurement by comparison: We can measure the differences between the dimensions of an unknown and one known piece called a pattern.
3. Measurement for verification: Checks that measures of a piece or a series of pieces fall within established measures.

Instruments for Measuring Length

• Tape: Used to measure long lengths, up to 50m. Assessment of 10mm (1cm).
• Meters: As long, medium with an appreciation of 1mm.
• Steel Rules: We use these in the garage when action must be taken without much accuracy. Long, graduated rules have small lengths (250mm to 1000mm).
• Caliper: The caliper has two parts:
  • A fixed ruler graduated in divisions that normally have a value of 1mm.
  • A Vernier scale, where you can read tenths of mm (performance).

  Integral measurement: The Vernier scale of 0 coincides with an integer number of the fixed ruler.

  Measurement with a decimal: First, look at what the two values are on the Vernier scale of 0 (we know the integer part). The fractional part is indicated by the lines between matching the fixed ruler and the Vernier scale.

  With the caliper, we can make three types of measurements: interior, exterior, and depth.

• Micrometer or Palmer: Measures parts that require very high accuracy (0.01 mm). This works with a spiral-female (becomes a rotating movement in a linear). Corresponds to the female tube is divided by fixed assessments of ½ mm and 1mm. The spiral is a sensor and incorporates a rotating drum divided into 50 divisions. This assessment depends on the turn of the screw and the number of divisions of the drum, so the appreciation of the relationship between the micrometer screw, the spiral step sensor, and the number of divisions of the Vernier scale drum.

Instruments for Comparison and Verification

• Gauge: Comparison instruments that measure a fixed pattern or serve as a reference. The notches will be used to measure (openings) very small, or see the game resulting from a two-piece assembly in which the area to be measured is difficult to access.
• Block Pattern: A piece of prismatic shape with a square or rectangular section, made of an alloy steel or ceramic material of high accuracy with a maximum error of +/- 0.05 x 10^-6m. With the combination pattern of blocks or varicose veins, we can get any length.
• Comparator: These instruments show the difference in length between two pieces but cannot measure the length of the piece.
• Calibrators: Used to verify the parts that occur in a system of mass production, and whether a dimension is within the margin of error allowed. These are classified into two groups:
  1. Calibrators for holes are two discs connected by a steel hexagonal bar section. One of these discs contains the minimum diameter, the other the maximum.
  2. Calibrators for axes, is the simplest of ring formed by two individual pieces, one not step and another step.

Measuring Instruments for Angles

• Goniometer: Is formed by a ruler (1), a supportive outer ring (2) which can rotate around a central disc where there is a Vernier scale (3). The disc (4) has an arm where you can fix a strip (5) that slides at the same time can be set.

Goniometer Reading

Reading is as simple as setting up the measure, taking the integer degree angle, and seeing if the measured Vernier scale of 0 coincides with a line of the graduated circle. If so, the measure will be integral. If not, we must look if zero falls on the Vernier scale of 0 to the right or left of the main staircase. Whenever necessary for the line matching, the lettering has been zero on the Vernier scale on the main scale.