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, common time measuring instrument were sundials, water clocks and hourglasses, measuring periods of time within a day. 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
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. A phototube provides a voltage measurement which permits the calculation of the quantized action (Planck constant) of light. (See also Photoelectric effect.)
Geometry
Dimensions (size)
Length (distance) Length, distance, or range meter
For the ranges of length-values see: Orders of magnitude (length)
Area Planimeter
For the ranges of area-values see: Orders of magnitude (area)
Volume
Buoyant weight (solids) Eudiometer, pneumatic trough (gases) Flow measurement devices (liquids) Graduated cylinder (liquids) Measuring cup (grained solids, liquids) Overflow trough (solids) Pipette (liquids)
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)
Angle
Circumferentor Cross staff Goniometer Graphometer Inclinometer Mural instrument Plurimeter Protractor Quadrant Reflecting instruments Octant Reflecting circles Sextant Theodolite and total station
Orientation in three-dimensional space See also the section about navigation below.
Level
Level (instrument) Laser line level Spirit level
Direction Gyroscope
Coordinates Coordinate-measuring machine
Mechanics This includes basic quantities found in classical- and continuum mechanics; but strives to exclude temperature-related questions or quantities.
Mass or volume flow measurement Gas meter Mass flow meter Metering pump Water meter
Speed or velocity (flux of length) Airspeed indicator LIDAR speed gun Radar speed gun, a Doppler radar device, using the Doppler effect for indirect measurement of velocity. Speedometer Tachometer (speed of rotation) Tachymeter Variometer (rate of climb or descent) Velocimetry (measurement of fluid velocity)
For the ranges of speed-values see: Orders of magnitude (speed)
Acceleration Accelerometer
Mass
Balance Check weigher measures precise weight of items in a conveyor line, rejecting underweight or overweight objects. Inertial balance Katharometer Mass spectrometers measure the mass-to-charge ratio, not the mass, of ionised particles. Weighing scale
For the ranges of mass-values see: Orders of magnitude (mass)
Linear momentum Ballistic pendulum
Force (flux of linear momentum) Force gauge Spring scale Strain gauge Torsion balance Tribometer
Pressure (flux density of linear momentum) Anemometer (measures wind speed) Barometer used to measure the atmospheric pressure. Manometer (see Pressure measurement and Pressure sensor) Pitot tube (measures airspeed) Tire-pressure gauge in industry and mobility
For the ranges of pressure-values see: Orders of magnitude (pressure)
Angular velocity or rotations per time unit Stroboscope Tachometer
For the value-ranges of angular velocity see: Orders of magnitude (angular velocity)
For the ranges of frequency see: Orders of magnitude (frequency)
Torque Dynamometer Prony brake Torque wrench
Energy carried by mechanical quantities, mechanical work Ballistic pendulum, indirectly by calculation and or gauging
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 Electrometer is often used to reconfirm the phenomenon of contact electricity leading to triboelectric sequences. Torsion balance used by Coulomb to establish a relation between charges and force, see above.
For the ranges of charge values see: Orders of magnitude (charge)
Electric current (current of charge) Ammeter Clamp meter d'Arsonval galvanometer Galvanometer
Voltage (electric potential difference) Oscilloscope allows quantifying time-dependent voltages Voltmeter
Electric resistance, conductance, and conductivity Ohmmeter Time-domain reflectometer characterizes and locates faults in metallic cables by runtime measurements of electric signals. Wheatstone bridge
Electric capacitance Capacitance meter
Electric inductance Inductance meter
Energy carried by electricity or electric energy Electricity meter
Power carried by electricity (current of energy) Wattmeter
Electric field (negative gradient of electric potential, voltage per length) Field mill
Magnetic field See also the relevant section in the article about the magnetic field. Compass Hall-effect sensor Magnetometer Proton magnetometer SQUID
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 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. Gas collecting tube gases
Temperature Electromagnetic spectroscopy Galileo thermometer Gas thermometer principle: relation between temperature and volume or pressure of a gas (gas laws). Constant pressure gas thermometer Constant volume gas thermometer Liquid crystal thermometer Liquid thermometer principle: relation between temperature and volume of a liquid (coefficient of thermal expansion). Alcohol thermometer Mercury-in-glass thermometer Pyranometer principle: solar radiation flux density relates to surface temperature (Stefan–Boltzmann law) Pyrometers principle: temperature dependence of spectral intensity of light (Planck's law), i.e. the color of the light relates to the temperature of its source, range: from about −50 °C to +4000 °C, note: measurement of thermal radiation (instead of thermal conduction, or thermal convection) means: no physical contact becomes necessary in temperature measurement (pyrometry). Also note: thermal space resolution (images) found in thermography. Resistance thermometer principle: relation between temperature and electrical resistance of metals (platinum) (electrical resistance), range: 10 to 1,000 kelvins, application in physics and industry Solid thermometer principle: relation between temperature and length of a solid (coefficient of thermal expansion). Bimetallic strip Thermistors principle: relation between temperature and electrical resistance of ceramics or polymers, range: from about 0.01 to 2,000 kelvins (−273.14 to 1,700 °C) Thermocouples principle: relation between temperature and voltage of metal junctions (Seebeck effect), range: from about −200 °C to +1350 °C Thermometer Thermopile is a set of connected thermocouples Triple point cell used for calibrating thermometers.
Imaging technology Thermographic camera uses a microbolometer for detection of heat radiation.
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. Actinometer heating power of radiation. Constant-temperature calorimeter, phase change calorimeter for example an ice calorimeter or any other calorimeter observing a phase change or using a gauged phase change for heat measurement. Constant-volume calorimeter, also called bomb calorimeter Constant-pressure calorimeter, enthalpy-meter, or coffee cup calorimeter Differential Scanning Calorimeter Reaction calorimeter
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. Constant-temperature calorimeter, phase change calorimeter Heat flux sensor uses thermopiles (which are connected thermocouples) to determine current density or flux of entropy.
Entropy content