Understanding Measurement: Magnitudes, Units, and Errors
Magnitudes and Metrology
5 Magnitudes: Length, mass, time, volume, luminous intensity.
Metrology: The science that studies everything concerning measurement.
- Dimensional: From the measurements.
- Ponderal: Attempts to measure weights.
- Study: Quantities, unit systems, measurement instruments, norms, standards, and instructions.
Systems of Units
International System, CGS system, metric system…
Measurement Instruments
Rule, calipers, angle gauge, scale, protractor, Palmer, stopwatch, and micrometer.
Metrotechnics
Establishes and regulates the use of a set of techniques, skills, methods, and processes on which we rely to apply technical metrology.
Measurement and Measure
- Measurement: When we determine numerically the value of a length, mass, time, etc.
- Measure: Results obtained from the measurement.
Developing Measurement
Tools, precision and appreciation, skill of operator, and environmental conditions.
Environmental Conditions
Temperature, humidity, lighting.
Direct and Indirect Measurement
- Direct Measurement: When the value of the quantity is obtained immediately by reading on the scale of the instrument.
- Indirect Measurement: When the value of the quantity is not obtained directly with the measuring instrument, but requires a previous calculation.
Table Measurements
Length, volume, capacity, mass, intensity, power…
Components
Dial gauge, dial, needle, needle probe, small field, and indexes.
Verification
Verify that items meet certain characteristics: dimensions, shape, material…
Fundamentals of Measurement
Magnitude
Anything that can be measured.
Fundamental Magnitude
One that can be fully defined without resorting to any other.
Derived Magnitude
One that is defined by a combination of one or more fundamental quantities.
Measure
To compare quantities of the same nature.
Unit of Measure
The amount taken as reference to compare magnitudes of the same species.
Measuring Standard
The realization of a unit of measure so that its value is unchanged.
Meter
The length equal to 1,650,763.73 times the wavelength in a vacuum, corresponding radiation.
System of Units
An ordered set of fundamental and derived units that are each defined and have simple relationships.
Length
The magnitude that indicates the distance or separation between bodies.
Plane Angle
The magnitude that indicates the opening between two concurrent lines belonging to the same plane.
Radian
The angle corresponding to an arc that has the same length as the radius of the circle that contains it.
Accuracy and Error in Measurement
Objective Measurement
To obtain a piece’s dimensions as accurately as possible.
Reading vs. Measured Value
This expression indicates that the reading done on the scale of the measuring instrument does not necessarily coincide with the actual value of the dimension of the piece.
Accuracy
The greater or lesser extent to the approximation of the actual value of the magnitude.
Precision
The ability of a measuring instrument to provide results with a minimum error.
Estimation
A slight variation of the magnitude that we can read on its scale.
Measurement Error
The difference between the reading obtained on measurement and the actual value of the magnitude.
True Value
The measure asymmetric.
Systematic Errors
Those that occur consistently in all actions.
Parallax Error
Occurs when the scale and pointer are not coplanar and the visual is not perpendicular to them.
Absolute Error
The difference between the value of the measure and the value of the magnitude.
Relative Error
The ratio of the absolute error and the actual measurement of the quantity.
Nominal Measure
The value of the size indicated on the map.