Measuring principle

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A sender emits a wave which is scattered by an object. The backscattered part of the wave reaches a receiver: The measurement principle of sonar and radar devices.

Another visualization of the principle described by the caption of the previous diagram. The farther away the object, the longer the (backscattered) wave has to travel until it reaches the receiver.

To actually get a number describing the distance of the object, one has to know the velocity of the wave and the time it needs to travel from sender to receiver.

Concepts for describing aspects of nature by numbers are called physical quantities. Examples may range from counting fruit to reading a thermometer gauge to determine temperature.

Aquiring such a number, a set of such numbers or related numbers directly from a natural system is called measurement. Examples include counting fruit or using a ruler to measure length.

Often the concepts or ideas that define physical quantities offer themselves straightforward (time, length, ...). To directly assess the value or number of a physical quantity usually proves difficult when very small or very large values are to be measured or when one indends to obtain a high precision measurement. Again examples indicate actual proceedings: In practice, larger amounts of fruit won't be counted but sold by weight. Distances between villages may be measured by counting the rotations of a Surveyor's wheel. Thus this instrument has to be gauged to yield the proper number indicating the distance with respect to some reference.

Furthermore, there may exist innate properties of the natural phenomena that require special attention: Within the thermodynamics-related view on nature, the measurement of entropy could produce entropy itself. Measurements in domains of quantum theory are said to influence the measured quantity significantly.

Skilled devising of measurement methods and measurement instruments allows to circumvent these problems and nevertheless acquire useful data.

A measuring principle condenses the essentials of a method or an instrument for gaining the desired numbers.

[edit] Counting integers

An elementary measurement method. Used by humans without any device. And realized by mechanical and electronic automatons.

[edit] Dividing/multiplying integers -- Relating to a standard

Also an elementary measurement method. Multiples and fractions of a given standard value are related to an unknown value until its number of relation to the standard value is found.

[edit] Runtime measurement

This method uses the timing of reflected signals of a known velocity for measuring lengths. See also the images above.

[edit] Integration -- Summation

When rates of a physical quantity are readily accessible along some time-interval, integration over time becomes feasable to get the value of the physical quantity.

[edit] See also

• Measurement
• Measurement instruments