Measure
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Measure
Fundamentals
Measurement is an experimental process based on one or more physical principles of action, through which a characteristic value is determined as a multiple of a unit or reference value, supplemented by the measurement uncertainty, and is not identical to testing (see: testing).
Types of measurement methods
The practical activity itself is referred to as measurement. A distinction is made between:
- direct measurement
- indirect measurement
- analogue measurement and
- incremental measurement.
Direct and indirect measurement
Direct measurement is a basic measurement method in which a measured variable is compared directly with a scale bearing the unit (e.g. measuring length with a ruler, determining mass with weights, determining temperature with a thermometer).
In indirect measurement, the quantity to be measured is determined from the measurement data of one or more other quantities that are related to the quantity being sought (task quantity) in a defined and calibratable manner (e.g. force measurement with electro-mechanical or piezoelectric force transducers; the operating principle is a mechanical-electrical signal conversion based on strain gauges or, in the case of the piezoelectric effect, the charge change caused by lattice expansion or compression).
Analogue and incremental measurement
Analogue measurement always involves a one-to-one correspondence between the signal parameter and the measured value, i.e. the signal can assume any value within the valid value or calibration range (e.g. in length measurement with capacitive or inductive sensors, there is a clear correlation between the signal voltage and the length). The accuracy of this type of measurement is defined by the resolution and measurement uncertainty.
An incremental measurement (counting measurement) is when the current value is determined from a reference point by adding or subtracting in increments (the smallest increase in a changed variable), for example for angle measurement or length measurement on machine tools. For this purpose, markings mounted at regular intervals on a carrier are scanned optically or electrically (e.g. 0.1 µm/digit). Further classification options for measurement are provided by the temporal assignment (continuous or discontinuous) of the measurement process.
See also
References
- Blumenauer, H. (Hrsg.): Werkstoffprüfung. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1994) (ISBN 3-342-00547-5; see AMK-Library under M 3)
- Hering, E.; Modler, K.-H. (Eds.): Grundrisse des Ingenieurs. Fachbuchverlag Leipzig im Carl Hanser Verlag, Munich Vienna (2007) 14th revised Edition, 831 images und 265 Tables (ISBN 978-3-446-22814-6; AMK-Library 13th Edition (2002) under L 37)