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What is a dimension? Units of measurement and measurement errors

People often face finding a physical quantity. In this case, they say about the measurement of something. This term comes from a science called metrology. What is a dimension?

Definition

A measurement is the process of determining a physical quantity by means of experimental means. The result of the measurement process is the value in the accepted units, which is called valid.

The measurement principle refers to a physical phenomenon or several of these phenomena that form the basis of measurements. For example, measuring the temperature with the help of a thermoelectric effect.

What is the measurement method? This is such a combination of methods of using measuring instruments and their principles. And what is a measuring tool? These are those technical means that have metrological properties that meet the standards.

Types of measurements

So, what is the dimension, the definition of which is given above, is understandable. But there are also types, the classification of which is carried out, based on how the measured value depends on the type of equation, time, conditions that determine the accuracy of the results of the measurement, as well as the ways in which these results are expressed.

Dependence on time

Drawing attention to the dependence of a quantity that is measured on time, two types of measurement can be distinguished:

  • Dynamic refers to such measurements, during which the value varies with time. An example is the measurement of temperature or pressure during the gas compression process in the engine cylinders.
  • Static refers to measurements in which the required quantity does not change over time. Examples: measurement of temperature, constant pressure, dimensions.

Dependence on equation

The method of obtaining the results, which is determined by the type of the equation for measurement, divides the measurements into direct and indirect measurements, as well as joint and cumulative measurements.

  • What is a direct measurement? This is a measurement in which the desired value of the physical quantity is directly from the data obtained as a result of the experiment. Examples of direct measurements can be: temperature measurement using a thermometer, measuring the diameter of a product using a micrometer or a caliper, measuring angles using a protractor.
  • What is an indirect measurement? This is a measurement in which the desired value is determined on the basis of the relationship between those quantities that are found by direct measurements and the desired quantity. Examples of such measurements: the measurement of the thread diameter by the method of three wires, the determination of the volume of the body with the use of direct measurements of its dimensions. Indirect measurements are very common when the value is too difficult or impossible to measure directly. It happens that the required value can be measured only indirectly. This includes measuring the size of astronomical bodies.
  • What is the aggregate measurement? This is a measurement in which the desired values are determined by the results of several measurements of the values for different combinations. The very value of the sought value is determined by solving a system of equations that are compiled from the results of a series of direct measurements. An example of cumulative measurements is the determination of the mass of each weight from a set, that is, it is a calibration from the known mass of one of the weights, as well as from the results of direct measurements and comparison of masses of combinations of weights.
  • A joint measurement is one that is produced simultaneously for two or several quantities with different names in order to find a functional relationship between them. An example can be the determination of the length of an object as a function of temperature.

Dependence on conditions

Under the conditions that determine the accuracy of the result, you can divide the measurements into three classes:

1. Measurement accuracy, which is the maximum. This includes measurements of high and standard accuracy.

2. Control-checking. Their error with some probability should not be higher than some given value.

3. Technical. These are measurements where the error in the final value is determined by the characteristics of the means used in the measurement process.

Dependence on the methods of expression of results

By the method of expressing the results of measurements, you can divide by absolute and relative.

  • What is the absolute dimension? This is a measurement that is based on direct measurements of quantities or on the application of the values of some physical constants. Examples: determination of amperage current, length in meters.
  • What is relative measurement? This is a measurement in which the desired value is compared to another quantity that plays the role of a unit or is accepted as the original one. An example of such measurements is the determination of the relative humidity of air, which is defined as the ratio of the number of water vapor in a cubic meter of air to the number of vapors that saturate a cubic meter of air at a given temperature.

Measurement system

Unity of measurements means the consistency of the sizes of all quantities. This is obvious if we pay attention to the fact that one and the same quantity can be measured both by direct and indirect methods. Such coherence can be achieved by creating a system of units. The first such system appeared in the late 18th century. It became the well-known metric system. And the first scientifically grounded system of units was the system proposed by Karl Gauss. It was based on three units: the second, millimeter and milligram. It was on the basis of such an absolute system that a modern system of units was built.

What is a unit of measure and what are they

The unit of measurement is the concrete value, which is defined and established by agreement. With it, other quantities of the same kind are compared to express their size relative to the specified value.

Each measured physical quantity must have its own unit of measurement. Thus, individual units are necessary for measuring speed, length, volume, weight, distance, and so on. Each unit can be determined by selecting a standard. The system of units becomes more convenient if it contains only a few units that are chosen basic, and the rest are determined already through them. The standard unit of length is the meter. Based on this, one square meter is considered a square meter, the unit of speed is a meter per second, and the unit of volume measurement is a meter in a cube.

Error

What is the measurement error? This term refers to the deviation of measurement results from the actual or true value of a quantity that is measured. The true value of the quantity is unknown. It is used only in theoretical studies.

Sometimes the answer to the question "what is the measurement error?" Is another definition - "measurement error". But it is better not to use it, because it is less successful.

Types of errors

The systematic error in measurement is the component part of the error in the final measurement result, which remains constant or changes regularly with repeated measurements of the physical quantity. The nature of the measurement divides the systematic errors of several kinds.

  • A constant error is an error that remains valid for a long time. This kind is found most often.
  • Progressive error is one that continuously increases or decreases. This can include errors due to the wear of measuring instruments or tips that come into contact with the details.
  • A periodic error is an error whose value is a periodic function of time or the movement of the indicator of the instrument used in the measurement.
  • The error that is measured by a complex law is one that occurs due to the conscientious action of several systematic errors at once.

Instrumental error is called the component of the measurement error, which is due to the error of the instrument used.

The error of the measurement method is the component, which is due to the imperfection of the method that is adopted for the measurement.

Measurement result

What is the result of the measurement? This is the value of the physical quantity, which is obtained by measuring it.

A non-corrected measurement result is the value of the value that was obtained in the measurement process before it was introduced corrections that take into account systematic errors.

The corrected result is the value of the value that was obtained during the measurement and refined by introducing the necessary corrections.

The convergence of the measurement results is the proximity of the results, which were carried out repeatedly using the same means, by the same method and under the same conditions.

What is the reproducibility of the results? This is the proximity to each other of the results that were obtained in different places, different means and operators using different methods, but which were brought to the same conditions.

A series of measurement results is a sequence of values of the same value that were obtained as a result of a series of measurements that follow one another.

Measuring Information

Today you can measure not only physical quantities. Since the era of computer technology has come, information is used everywhere in a digital form. It is also possible to measure it. What is the measurement of information? This is the definition of the number of data that is expressed in terms of its units. The reference unit for measuring information is a bit, which is the amount of information that arises in equiprobable events. For example, tossing a coin can lead to two equiprobable outcomes. The loss of one of the sides contains one-bit information.

The name of this unit of measurement comes from the abbreviation of the term "binary number". This is a number that can take only two values - one or zero. Such numbers I use in all kinds of computer technology to represent any information. Since a bit is a very small unit of information measurement, it is customary to use larger ones. These are bytes, kilobytes, megabytes, gigabytes, terabytes, and so on.

The volume that is occupied by any character entered from the keyboard is one byte. This is 8 bits.

Results

Thus, all concepts used in the measurement were considered. This is a system of measurements, error and its types, results. It was considered what a unit of measurement, and what these units are. All this is necessary for people who are dealing with science, computing, and just to expand their horizons. After all, in the age of information technology, the wisdom is that knowledge is power.

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