Measuring instrument

Captain Nemo and Professor Aronnax contemplating measuring instruments in Twenty Thousand Leagues Under the Sea
A Love Meter and Strength tester machine at a Framingham, Massachusetts rest stop.

A measuring instrument is a device for measuring a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument's use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty.

Scientists, engineers and other humans use a vast range of instruments to perform their measurements. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments.

Time

Watch, a time measurement device
Main article: Time

In the past, a common time measuring instrument was the sundial. Today, the usual measuring instruments for time are clocks and watches. For highly accurate measurement of time an atomic clock is used. Stop watches are also used to measure time in some sports.

Energy

Main article: Energy

Energy is measured by an energy meter. Examples of energy meters include:

Electricity meter

An electricity meter measures energy directly in kilowatt hours.

Gas meter

A gas meter measures energy indirectly by recording the volume of gas used. This figure can then be converted to a measure of energy by multiplying it by the calorific value of the gas.

Power (flux of energy)

Main article: Power (physics)

A physical system that exchanges energy may be described by the amount of energy exchanged per time-interval, also called power or flux of energy.

For the ranges of power-values see: Orders of magnitude (power).

Action

Main article: Action (physics)

Action describes energy summed up over the time a process lasts (time integral over energy). Its dimension is the same as that of an angular momentum.

Mechanics

This includes basic quantities found in classical- and continuum mechanics; but strives to exclude temperature-related questions or quantities.

Length (distance)

For the ranges of length-values see: Orders of magnitude (length)

Area

For the ranges of area-values see: Orders of magnitude (area)

Volume

A measuring cup, a common instrument used to measure volume.

If the mass density of a solid is known, weighing allows to calculate the volume.

For the ranges of volume-values see: Orders of magnitude (volume)

Mass- or volume flow measurement

Speed (flux of length)

For the ranges of speed-values see: Orders of magnitude (speed)

Acceleration

Mass

A pair of scales: An instrument for measuring mass in a force field by balancing forces.

For the ranges of mass-values see: Orders of magnitude (mass)

Linear momentum

Force (flux of linear momentum)

Measuring absolute pressure in an accelerated reference frame: The principle of a mercury (Hg) barometer in the gravitational field of the earth.

Pressure (flux density of linear momentum)

For the ranges of pressure-values see: Orders of magnitude (pressure)

Angle

Angular velocity or rotations per time unit

For the value-ranges of angular velocity see: Orders of magnitude (angular velocity)

For the ranges of frequency see: Orders of magnitude (frequency)

Torque

Orientation in three-dimensional space

See also the section about navigation below.

Level

Direction

Energy carried by mechanical quantities, mechanical work

Electricity, electronics and electrical engineering

Considerations related to electric charge dominate electricity and electronics. Electrical charges interact via a field. That field is called electric if the charge doesn't move. If the charge moves, thus realizing an electric current, especially in an electrically neutral conductor, that field is called magnetic. Electricity can be given a quality — a potential. And electricity has a substance-like property, the electric charge. Energy (or power) in elementary electrodynamics is calculated by multiplying the potential by the amount of charge (or current) found at that potential: potential times charge (or current). (See Classical electromagnetism and its Covariant formulation of classical electromagnetism)

An instrument for detecting net charges, the electroscope.

Electric charge

For the ranges of charge values see: Orders of magnitude (charge)

Electric current (current of charge)

Voltage (electric potential difference)

Electric resistance, electrical conductance (and electrical conductivity)

Electric capacitance

Electric inductance

Energy carried by electricity or electric energy

Power carried by electricity (current of energy)

These are instruments used for measuring electrical properties. Also see meter (disambiguation).

Electric field (negative gradient of electric potential, voltage per length)

Magnetic field

See also the relevant section in the article about the magnetic field.

For the ranges of magnetic field see: Orders of magnitude (magnetic field)

Combination instruments

Thermodynamics

Temperature-related considerations dominate thermodynamics. There are two distinct thermal properties: A thermal potential — the temperature. For example: A glowing coal has a different thermal quality than a non-glowing one.

And a substance-like property, — the entropy; for example: One glowing coal won't heat a pot of water, but a hundred will.

Energy in thermodynamics is calculated by multipying the thermal potential by the amount of entropy found at that potential: temperature times entropy.

Entropy can be created by friction but not annihilated.

Amount of substance (or mole number)

A physical quantity introduced in chemistry; usually determined indirectly. If mass and substance type of the sample are known, then atomic- or molecular masses (taken from a periodic table, masses measured by mass spectrometry) give direct access to the value of the amount of substance. See also the article about molar masses. If specific molar values are given, then the amount of substance of a given sample may be determined by measuring volume, mass or concentration. See also the subsection below about the measurement of the boiling point.

Temperature

Imaging technology

See also Temperature measurement and Category:Thermometers. More technically related may be seen thermal analysis methods in materials science.

For the ranges of temperature-values see: Orders of magnitude (temperature)

Energy carried by entropy or thermal energy

An active calorimeter lacking a temperature measurement device.

This includes thermal capacitance or temperature coefficient of energy, reaction energy, heat flow ... Calorimeters are called passive if gauged to measure emerging energy carried by entropy, for example from chemical reactions. Calorimeters are called active or heated if they heat the sample, or reformulated: if they are gauged to fill the sample with a defined amount of entropy.

see also Calorimeter or Calorimetry

Entropy

Entropy is accessible indirectly by measurement of energy and temperature.

Entropy transfer

Phase change calorimeter's energy value divided by absolute temperature give the entropy exchanged. Phase changes produce no entropy and therefore offer themselves as an entropy measurement concept. Thus entropy values occur indirectly by processing energy measurements at defined temperatures, without producing entropy.

Entropy content

The given sample is cooled down to (almost) absolute zero (for example by submerging the sample in liquid helium). At absolute zero temperature any sample is assumed to contain no entropy (see Third law of thermodynamics for further information). Then the following two active calorimeter types can be used to fill the sample with entropy until the desired temperature has been reached: (see also Thermodynamic databases for pure substances)

Entropy production

Processes transferring energy from a non-thermal carrier to heat as a carrier do produce entropy (Example: mechanical/electrical friction, established by Count Rumford). Either the produced entropy or heat are measured (calorimetry) or the transferred energy of the non-thermal carrier may be measured.

Entropy lowering its temperature—without losing energy—produces entropy (Example: Heat conduction in an isolated rod; "thermal friction").

temperature coefficient of energy or "heat capacity"

Concerning a given sample, a proportionality factor relating temperature change and energy carried by heat. If the sample is a gas, then this coefficient depends significantly on being measured at constant volume or at constant pressure. (The terminiology preference in the heading indicates that the classical use of heat bars it from having substance-like properties.)

specific temperature coefficient of energy or "specific heat"

The temperature coefficient of energy divided by a substance-like quantity (amount of substance, mass, volume) describing the sample. Usually calculated from measurements by a division or could be measured directly using a unit amount of that sample.

For the ranges of specific heat capacities see: Orders of magnitude (specific heat capacity)

Coefficient of thermal expansion

Melting temperature (of a solid)

Boiling temperature (of a liquid)

See also thermal analysis, Heat.

More on continuum mechanics

This includes mostly instruments which measure macroscopic properties of matter: In the fields of solid state physics; in condensed matter physics which considers solids, liquids and in-betweens exhibiting for example viscoelastic behavior. Furthermore, fluid mechanics, where liquids, gases, plasmas and in-betweens like supercritical fluids are studied.

Density

This refers to particle density of fluids and compact(ed) solids like crystals, in contrast to bulk density of grainy or porous solids.

For the ranges of density-values see: Orders of magnitude (density)

Hardness of a solid

Shape and surface of a solid

Deformation of condensed matter

Elasticity of a solid (elastic moduli)

Plasticity of a solid

Measurement results (a) brittle (b) ductile with breaking point (c) ductile without breaking point.

Tensile strength, ductility or malleability of a solid

Granularity of a solid or of a suspension

Viscosity of a fluid

Optical activity

Surface tension of liquids

Imaging technology

This section and the following sections include instruments from the wide field of Category:Materials science, materials science.

More on electric properties of condensed matter, gas

The electrochemical cell: A device for measuring substance potentials.

Permittivity, relative static permittivity, (dielectric constant) or electric susceptibility

Such measurements also allow to access values of molecular dipoles.

Magnetic susceptibility or magnetization

For other methods see the section in the article about magnetic susceptibility.

See also the Category:Electric and magnetic fields in matter

Substance potential or chemical potential or molar Gibbs energy

Phase conversions like changes of aggregate state, chemical reactions or nuclear reactions transmuting substances, from reactants to products, or diffusion through membranes have an overall energy balance. Especially at constant pressure and constant temperature molar energy balances define the notion of a substance potential or chemical potential or molar Gibbs energy, which gives the energetic information about whether the process is possible or not - in a closed system.

Energy balances that include entropy consist of two parts: A balance that accounts for the changed entropy content of the substances. And another one that accounts for the energy freed or taken by that reaction itself, the Gibbs energy change. The sum of reaction energy and energy associated to the change of entropy content is also called enthalpy. Often the whole enthalpy is carried by entropy and thus measurable calorimetrically.

For standard conditions in chemical reactions either molar entropy content and molar Gibbs energy with respect to some chosen zero point are tabulated. Or molar entropy content and molar enthalpy with respect to some chosen zero are tabulated. (See Standard enthalpy change of formation and Standard molar entropy)

The substance potential of a redox reaction is usually determined electrochemically current-free using reversible cells.

Other values may be determined indirectly by calorimetry. Also by analyzing phase-diagrams.

See also the article on electrochemistry.

Sub-microstructural properties of condensed matter, gas

Crystal structure

Imaging technology, Microscope

See also the article on spectroscopy and the list of materials analysis methods.

Rays ("waves" and "particles")

Sound, compression waves in matter

Microphones in general, sometimes their sensitivity is increased by the reflection- and concentration principle realized in acoustic mirrors.

Sound pressure

A device for unmixing sun-light: the prism.
The electromagnetic spectrum

Light and radiation without a rest mass, non-ionizing

(for lux meter see the section about human senses and human body)

See also Category:Optical devices

Photon polarization

Pressure (current density of linear momentum)

Radiant flux

The measure of the total power of light emitted.

A Cathode ray tube.

Radiation with a rest mass, particle radiation

Cathode ray

Atom polarization and electron polarization

Another visualization of the electromagnetic spectrum.

Ionizing radiation

Ionizing radiation includes rays of "particles" as well as rays of "waves". Especially X-rays and Gamma rays transfer enough energy in non-thermal, (single) collision processes to separate electron(s) from an atom.

A cloud chamber detecting alpha-rays.

Particle and ray flux

Identification and content

This could include chemical substances, rays of any kind, elementary particles, quasiparticles. Many measurement devices outside this section may be used or at least become part of an identification process. For identification and content concerning chemical substances see also analytical chemistry especially its List of chemical analysis methods and the List of materials analysis methods.

Substance content in mixtures, substance identification

pH: Concentration of protons in a solution

Humidity

Human senses and human body

Vitruvian Man by Leonardo da Vinci, Gallerie dell'Accademia, Venice (1485-90)

Sight

Brightness: photometry

Photometry is the measurement of light in terms of its perceived brightness to the human eye. Photometric quantities derive from analogous radiometric quantities by weighting the contribution of each wavelength by a luminosity function that models the eye's spectral sensitivity. For the ranges of possible values, see the orders of magnitude in: illuminance, luminance, and luminous flux.

Color: colorimetry

Hearing

Loudness in phon

Smell

Temperature (sense and body)

Body temperature or core temperature

Circulatory system (mainly heart and blood vessels for distributing substances fast)

Blood-related parameters are listed in a blood test.

Respiratory system (lung and airways controlling the breathing process)

A spirometer, inhaling into pipe a fills volume b, the rest balances forces.

Concentration or partial pressure of carbon dioxide in the respiratory gases

Nervous system (nerves transmitting and processing information electrically)

Musculoskeletal system (muscles and bones for movement)

power, work of muscles

metabolic system

Medical imaging

An echocardiogram processed into a three dimensional representation.

See also: Category:Physiological instruments and Category:Medical testing equipment.

Meteorology

See also Category:Meteorological instrumentation and equipment.

Navigation and surveying

See also Category:Navigational equipment and Category:Navigation. See also Surveying instruments.

Astronomy

See also Astronomical instruments and Category:Astronomical observatories.

Military

Some instruments, such as telescopes and sea navigation instruments, have had military applications for many centuries. However, the role of instruments in military affairs rose exponentially with the development of technology via applied science, which began in the mid-19th century and has continued through the present day. Military instruments as a class draw on most of the categories of instrument described throughout this article, such as navigation, astronomy, optics and imaging, and the kinetics of moving objects. Common abstract themes that unite military instruments are seeing into the distance, seeing in the dark, knowing an object's geographic location, and knowing and controlling a moving object's path and destination. Special features of these instruments may include ease of use, speed, reliability and accuracy.

Uncategorized, specialized, or generalized application

Fictional devices

See also

Notes

Note that the alternate spelling "-metre" is never used when referring to a measuring device.

References

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