Measurement

A measured value is the value of a measured variable, which is supplied by a measuring instrument or a measuring device.

Indication of a measured value

The measured value is determined for a quantitative assessment of a measure, which is that physical size, the measurement is valid ( DIN 1319 ). The special value of the measured quantity is expressed by the product of numerical value and unit ( also DIN 1313 ).

Unit

Units, often referred to differentiate units are agreed upon internationally, nationally established by law and in DIN 1301 recorded in the standardization values ​​of physical quantities with the purpose that all other values ​​of this size should be expressed as multiples of the unit.

Value

According to DIN 1301 numerical values ​​between 0.1 and 1000 should fall. Instead of larger or smaller values ​​Resolutions for units to be used, which are also listed in the standard.

Examples

This is the most significant digit, (see below ) is affected by error limit or measurement uncertainty, the units digit or a decimal (DIN 1333); thus only significant digits are given.

Examples

Obtaining a measured value

The measured value is supplied for direct output of the measuring instrument or measuring device

• With analog measuring method preferably by a scale display; of a continuum of (real) values, a numerical value is read, the supplies together with the particulars to be provided on the scale unit of the measured value,
• In digital measurement method preferably by a digital display; from a range of values ​​of integers a number is used (eg meter reading), which along with the smallest increment the value. For example, at the time of measurement can be considered: 1 scale interval 0.1 ms. Then, from a count in 1234, the measured value of 123.4 ms.

With indirect output of the measured value is determined by a

Provided, preferably as

For further processing in a measurement chain, management, control or data processing system. Then the measured value is the people do not even notified, or after transformation or conversion it is brought into readable form.

Quality of a measured value

Readings are always fraught with measurement errors. DIN 1319 distinguishes between random and systematic measurement error.

• Primarily, it will be a deviation measuring instruments, ie, a deviation which is caused solely by the meter. It is predominantly a systematic nature. With a known margin of error ( eg due to a character class ) you will provide it together with the measured value.
• Random variations that are included in the test configuration and the measuring apparatus ( for example noise in amplifiers) that can be reduced in their influence by repeated measurement and error analysis. You used instead of a single measured value of the arithmetic mean. Meanwhile, uncertainty can also calculate and must be specified.
• Systematic deviations that are included in the test configuration and the measuring equipment must be subtracted from the measured value, if they - though difficult - are be specified. Such deviations are, for example, incorrect adjustment ( if not included in the margin of error ), the change of the measured value by feedback of the measuring device on the experimental setup (voltage meter with insufficient instruments internal resistance in relation to the source internal resistance of the voltage source ), or if a test set-up. Since these measurement errors are calculate out, they do not appear as a quality feature.
• Not known, only in estimating the systematic errors lead to a further component of the measurement uncertainty shall be stated.

Thus, a measurement that determines the acceleration due to ( 9.8 ± 1.0 ) m / s ², quite inaccurate, as can only be inferred from the measurement that the " true value " with a certain confidence level in the range of 8, 8 m / s ² to 10.8 m / s ². The true value is unknown. The fact that the value of 9.8 m / s ² with the value from the literature surprisingly good agreement, can not be seen from the given result. (If you would know the value of the literature, the measurement would indeed be superfluous. )

Boundary conditions

Depending on the circumstances, the measured value includes additional information such as the nature of the instrument or the environmental conditions, the position of the measuring point and date / time.