What is a dimension? Units of measurement and measurement errors
People often face the finding of aphysical quantity. In this case, they talk about measuring something. This term comes from a science called metrology. What is a dimension?
Definition
A measurement is a process of determiningof any physical quantity by means of measuring instruments by experimental means. The result of the measurement process is the value in the accepted units, which is called valid.
The measurement principle is a physical phenomenon or several such phenomena that are used as the basis for 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, corresponding to the norms.
Types of measurements
So, what is a dimension whose definitiongiven above, it 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
Paying attention to the dependence of a quantity that is measured on time, two types of measurement can be distinguished:
- Dynamic called such measurements, in the process of which the quantity varies with time. An example can be the measurement of temperature or pressure during the gas compression process in the engine cylinders.
- Static The measurements are called when the required quantity does not change with 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 the measurements, divides the measurements into direct and indirect, as well as joint and cumulative.
- What is a direct measurement? This is a measurement in which the desired valuephysical quantity is directly from the data obtained as a result of the experiment. Examples of direct measurements can be: temperature measurement with a thermometer, measuring the diameter of a product using a micrometer or caliper, measuring angles using a protractor.
- What is an indirect measurement? This is a measurement in which the desired quantityis determined on the basis of the relationship between those quantities that are found by means of 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 valuesare determined from the results of several measurements of the quantities for various combinations. The very value of the sought value is determined by solving a system of equations, which are compiled from the results of a series of direct measurements. An example of cumulative measurements: 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 the comparison of masses of combinations of weights.
- Joint measurement called the one that is produced simultaneouslyfor two or several quantities with different names in order to find a functional dependence 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 reference 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 of 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, it can be divided into 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 measurement means consistencysizes 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: 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 specific value,which is defined and established by agreement. With it, other quantities of the same kind are compared to express their size with respect to the indicated magnitude.
Each measured physical quantity mustcorrespond to 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 question "what is the measurement error?" Can be heard as a response by another definition - "measurement error". But it is better not to use it, because it is less successful.
Types of errors
The systematic error in measurements ispart of the error of 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.
- Constant error Is an error that retains its significance over a long period of time. This species 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.
- Periodic error Is an error whose value is a periodic function of time or the movement of the instrument pointer used in the measurement.
- The error, which is measured by a complex law - this is the one that occurs because of the conscientious action of several systematic biases.
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 defective measuring result is the value of the value that was obtained during the measurement before it was corrected to 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 measurement results is called the proximity of results that were performed again by the same means, by the same method and under the same conditions.
What is reproducible results? This is the proximity to each other of the results that were obtained in different places, by 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, following one after another.
Measuring information
Today, you can measure not only physicalquantities. Since the era of computer technology has arrived, digital information is used everywhere. It is also possible to measure. What is the measurement of information? This is the definition of the number of data that is expressed in its units. The reference unit for measuring information is a bit, which is the amount of information that occurs when equiprobable events occur. For example, tossing a coin can lead to two equally probable outcomes. The fallout of one of the sides contains information in the amount of one bit.
The name of this unit comes fromabbreviations of the term "binary number". This is a number that can take only two values - one or zero. Such numbers are used in all types of computing technology to represent any information. Since the 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 any character entered from the keyboard is equal to one byte. This is 8 bits.
Outcomes
Thus, all concepts were considered,used in measurement. This is a measurement system, the error and its types, results. It was considered that such a unit of measurement, and what these units are. All this needs to be known to people dealing with science, computing, and also just to expand their horizons. Indeed, in the age of information technology, the wisdom that knowledge is power is relevant.
