# Measuring instrument

A measuring instrument is a device to measure 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. 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

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. Stopwatches are also used to measure time in some sports.

## Energy

Measuring instruments in fiction: Captain Nemo and Professor Aronnax contemplating thermometers, barometers, clocks, etc. in Jules Verne's 1869-1870 science fiction novel Twenty Thousand Leagues Under the Sea

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)

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.

• (see any measurement device for power below)

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

## Action

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.

## Geometry

### Dimensions (size)

#### 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

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)

## Mechanics

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

### Speed or velocity (flux of length)

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

### Mass

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

### Pressure (flux density of linear momentum)

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

### 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)

## 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 field.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 Covariant formulation of classical electromagnetism)

### Electric charge

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

### Magnetic field

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

### Combination instruments

• Multimeter, combines the functions of ammeter, voltmeter, and ohmmeter as a minimum.
• LCR meter, combines the functions of ohmmeter, capacitance meter, and inductance meter. Also called component bridge due to the bridge circuit method of measurement.

## 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 multiplying 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 Molar mass.) 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

This includes thermal mass 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.

### 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.

• calorimeter
• (any device for measuring the work which will or would eventually be converted to heat and the ambient temperature)

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

• calorimeter

### 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 terminology 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 capacity"

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)

## 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)

### Deformation of condensed matter

#### Plasticity of a solid

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

### Imaging technology

• Tomograph, device and method for non-destructive analysis of multiple measurements done on a geometric object, for producing 2- or 3-dimensional images, representing the inner structure of that geometric object.
• Wind tunnel

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

### 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.

### 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 into 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.

## 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.

### Light and radiation without a rest mass, non-ionizing

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

#### Pressure (current density of linear momentum)

The measure of the total power of light emitted.

#### Atom polarization and electron polarization

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.

## Identification and content

This could include chemical substances, rays of any kind, elementary particles, and 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, List of chemical analysis methods, and List of materials analysis methods.

## Human senses and human body

### 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

Synthetic Aperture Radar (SAR) instruments measure radar brightness, Radar Cross Section (RCS), which is a function of the reflectivity and moisture of imaged objects at wavelengths which are too long to be perceived by the human eye. Black pixels mean no reflectivity (e.g. water surfaces), white pixels mean high reflectivity (e.g. urban areas). Colored pixels can be obtained by combining three gray-scaled images which usually interpret the polarization of electromagnetic waves. The combination R-G-B = HH-HV-VV combines radar images of waves sent and received horizontally (HH), sent horizontally and received vertically (HV) and sent and received vertically (VV). The calibration of such instruments is done by imaging objects (calibration targets) whose radar brightness is known.

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

Blood-related parameters are listed in a blood test.

## 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

### Alphabetical listing

Instrument Quantity measured
alcoholmeter alcoholic strength of liquid
altimeter altitude
ammeter electric current
anemometer windspeed
astrolabe latitude and altitude of celestial bodies
audiometer hearing
barkometer tanning liquors used in tanning leather
barometer air pressure
bettsometer integrity of fabric coverings on aircraft
bevameter mechanical properties of soil
Brannock Device measuring shoe size
breathalyzer breath alcohol content
caliper length
calorimeter heat of chemical reactions
cathetometer vertical distances
ceilometer height of a cloud base
chronometer or clock time
clap-o-meter volume of applause
compass direction of North
Coulombmeter electrostatic charge of a material
colorimeter color
creepmeter slow surface displacement of an active geologic fault in the earth
corrator corrosion rate
declinometer magnetic declination
densimeter specific gravity of liquids
densitometer degree of darkness in photographic or semitransparent material
diffractometer structure of crystals
dilatometer volume changes caused by a physical or chemical process
disdrometer size, speed, and velocity of raindrops
drumometer amount of drum strokes over time
dumpy level horizontal levels, polar angle
dynamometer force, torque, or power
electricity meter electrical energy used
electrometer electric charge
electronic tuner pitch of musical notes
ellipsometer refractive index, dielectric function, thickness of thin films
eudiometer change in volume of a gas mixture following combustion
evaporimeter rate of evaporation
fathometer ocean depth
feeler gauge gap widths
forward looking infrared (FLIR) detects infrared energy (heat)converts it into an electronic signal, which is then processed to produce a thermal image on a video monitor and perform temperature calculations.
framing square right angles in construction
frequency counter frequency of alternating current
fuel gauge fuel levels
galvanometer electricity
gas pycnometer volume and density of solids
geiger counter ionizing radiation (alpha, beta, gamma, etc.)
glucometer blood glucose (diabetes)
graphometer angle
heliometer variation of the sun's diameter
hourmeter elapsed machine hours
hydrometer specific gravity of liquids (density of liquids)
hygrometer humidity
inclinometer angle of a slope
inkometer ink
interferometer wave interference
katharometer composition of gases
lactometer specific gravity of milk
light meter light (in photography)
linear position transducer speed of movement
lux meter intensity of light
magnetometer strength of magnetic fields
manometer pressure of gas
mass flow meter mass flow rate of a fluid travelling through a tube
mass spectrometer masses of ions, used to identify chemical substances through their mass spectra
measuring cup liquid and dry goods
measuring cylinder volume
measuring spoon a spoon used to measure an amount of an ingredient, either liquid or dry
megger electrical insulation
mercury barometer Atmospheric pressure
micrometer small distances
multimeter electrical potential, resistance, and current
nephoscope to measure the speed and direction of clouds
nephelometer particle in a liquid
odometer distance travelled
ohmmeter electrical resistance
opisometer lengths of arbitrary curved lines
orchidometer testicle size in male humans
oscilloscope oscillations
osmometer osmotic strength of a solution, colloid, or compound matter of an object
parking meter collects moneys for vehicle parking rights in a zone for a limited time
pedometer steps
pH meter pH (chemical acidity/basicity of a solution)
planometer area
polarimeter rotation of polarized light
potentiometer voltage (term is also used to refer to a variable resistor)
profilometer surface roughness
protractor angle
psychrometer humidity
pycnometer fluid density
pyrheliometer direct solar insolation
pyrometer high temperatures
quadrat percentage cover of a certain species
quartz crystal microbalance thickness of deposited thin films
rain gauge measuring of rain
refractometer index of refraction
rheometer response to applied forces
rotameter pressure of a liquid or gas in a closed tube
ruler for measuring length
saccharometer amount of sugar in a solution
seismometer seismic waves (for example, earthquakes)
sextant location on earth's surface (used in naval navigation)
spectrometer properties of light
spectrophotometer intensity of light as a function of wavelength
speedometer speed, velocity of a vehicle
spirometer the lung capacity
sphygmomanometer blood pressure
strainmeter seismic strain
SWR meter standing wave ratio
Synthetic Aperture Radar reflectivity and moisture
tacheometer distance
tachometer revolutions per minute, rate of blood flow, speed of aeroplanes
taximeter distance travelled, displacement
tensiometer surface tension of a liquid
theodolite angle, in the horizontal and vertical planes
thermometer temperature
tiltmeter minor changes to the Earth
tintometer colour
universal measuring machine geometric locations
vacuum gauge very low pressure
viscometer viscosity of a fluid
voltmeter electric potential, voltage
VU meter volume unit
wattmeter electrical power
weighing scale weight
wind vane wind direction
zymometer fermentation