History of Measurement
The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction, and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.
The History of Electric Measuring Instruments
Precision electric meters are indispensable to the development of technology in this age. The first
electric measuring instruments, however, were physically impossible to transport, and were functionally
inadequate for use in a laboratory. The measuring instruments of today have evolved into sturdy, easy-to-use instruments with higher performance, adopting new active components which have appeared one after another. Expanding in functionality, measuring instruments that have adopted such new technology have enabled even more precise measurement. The users have also expanded from research organizations and educational facilities, to the manufacturers of electrical equipment and electronic parts. The measuring instrument manufacturers were able to supply more convenient measuring instruments to the user, and conversely, the user, the manufacturers of electrical equipment and electronic parts, needed more easy-to-use and highly precise measuring instruments in order to respond to a rapidly increasing demand. Consequently, cheap and high quality electronic parts were supplied to the market, and the measuring instrument manufacturers were also able to develop new measuring instruments using those parts. In fact, it can be said that they have been mutually complementary. It should not be forgotten that the demand for electronic components for consumer use has also driven the whole in the meantime.
Electric Current:
Instruments used for measuring electric current is ammeter, there are various techniques that can be used to measure current: Shunt resistors, Hall effect, Transformer, Magnetoresistive
An electric current is a flow of electric charge. In electric circuitsthis charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas (plasma). The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.
Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators. The moving charged particles in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors.
Symbol: The conventional symbol for current is I, which originates from the French phrase intensité de courant, (current intensity). Current intensity is often referred to simply as current. The Isymbol was used by André-Marie Ampère, after whom the unit of electric current is named, in formulating Ampère's force law (1820). The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using C to I until 1896.
Current Measurement: Current can be measured using an ammeter.
At the circuit level, there are various techniques that can be used to measure current:
⚫ Shunt resistors
⚫ Hall effect current sensor transducers
⚫ Transformers (however DC cannot be measured)
⚫ Magnetoresistive field sensors
Electrical Resistance and conductance:
An Instrument for measuring resistance is called an ohmmeter.
The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
The resistance (R) of an object is defined as the ratio of voltage across it (V) to current through it (I), while the conductance (G) is the inverse:
R = V/I , G = I/V = 1/R
Measuring Resistance: An instrument for measuring resistance is called an ohmmeter. Simple ohmmeters cannot measure low resistances accurately because the resistance of their measuring leads causes a voltage drop that interferes with the measurement, so more accurate devices use four-terminal sensing.
Electric Charge:
Instrument used for measuring electric charge is electrometer, or indirectly measured with a ballistic galvanometer.
The electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces.
Units: The SI unit of quantity of electric chargeis the coulomb, which is equivalent to about 6.242×1018 e.
Instrument used for measuring electric charge directly is electrometer, or indirectly measured with a ballistic galvanometer.
Magnetic Field:
Instrument for measuring magnetic field is magnetometer.
A magnetic field is a force field that is created by moving electric charges (electric currents) and magnetic dipoles, and exerts a force on other nearby moving charges and magnetic dipoles. At any given point, it has a direction and a magnitude (or strength), so it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols Band H, where, in the International System of Units, H is measured in units of amperes per meter and B is measured in teslas or newtons per meter per ampere.
Measurement: Instrument for measuring magnetic field is magnetometer. Important classes of magnetometers include using induction magnetometer (or search-coil magnetometer) which measure only varying magnetic field, rotating coil magnetometer, Hall effectmagnetometers, NMR magnetometers, SQUID magnetometers, and fluxgate magnetometers. The magnetic fields of distant astronomical objects are measured through their effects on local charged particles. For instance, electrons spiraling around a field line produce synchrotron radiation that is detectable in radio waves.
Electrical Conductivity:
Instrument used for measuring electrical conductivity is Ohmmeter, Time - domain reflectometer, Wheatstone bridge.
1. Ohmmeter: An ohmmeter is an electrical instrumentthat measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters (also a trademarked device Megger) measure large values of resistance. The unit of measurement for resistance is ohms (Ω).
Working Principle: An ohmmeter measures resistance by applying a current and a voltage to a resistance (sometimes also called a "load"), and feeding the response of that current and voltage to something that we can visualize. This visualization can be an inductor as seen in galvanometers or can be a display driven by an analog digital converter (adc) as seen in digital multimeters.
This approach gives us the resistance derived from Ohm's Law, which states that the value of the resistance (R) is given by:
R = V / I
2. Time - domain Reflectometer: A time-domain reflectometer (TDR) is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables (for example, twisted pair wire or coaxial cable).[1] It can also be used to locate discontinuities in a connector, printed circuit board, or any other electrical path. The equivalent device for optical fiber is an optical time-domain reflectometer.
3. Wheatstone bridge: A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of a wheatstone bridge is its ability to provide extremely accurate measurements (in contrast with something like a simple voltage divider). Its operation is similar to the original potentiometer.
The Wheatstone bridge was invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for the purpose of soils analysis and comparison.
Electrical Capacitance:
Instrument used to measure electric capacitance is Capacitance meter.
Capacitance Meter: A capacitance meter is a piece of electronic test equipment used to measure capacitance, mainly of discrete capacitors. Depending on the sophistication of the meter, it may display the capacitance only, or it may also measure a number of other parameters such as leakage, equivalent series resistance (ESR), and inductance. For most purposes and in most cases the capacitor must be disconnected from circuit; ESR can usually be measured in circuit.
Electrical Inductance:
Instrument used to measure electrical inductance is inductance meter / LCR meter.
LCR meter: An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic components. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components.
Energy carried by electricity or Electric Energy:
Instrument used to measure electric energy is Electric Energy Meter or Electricity Meter.
Electricity Meter: An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device.
Electric utilities use electric meters installed at customers' premises to measure electric energy delivered to their customers for billing purposes. They are typically calibrated in billing units, the most common one being the kilowatt hour [kWh]. They are usually read once each billing period. When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for demand response load shedding during peak load periods.
Power carried by electricity / Current of Energy:
Instrument used to measure power carried by electricity is wattmeter.
Wattmeter: The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in wattsof any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.
Electric Field (negative gradient of electric potential, voltage per length):
Instrument for measuring electric field is Field Mill.
Field Mill: A field mill is a specialized instrument used for measuring the strength of electrical fields in the atmosphere near thunderstorm clouds. They are used in the launch criteria for rockets bound for orbit, as well as the now-retired Space Shuttle, to avoid lightning strikes. They are also used in outdoor laboratories for lightning protection equipment to determine favorable experiment conditions.
The "mill" is a typical rotating shutter design in the instrument. It is usually deployed airborne and flown through anvil head clouds to make measurements.
Mangnetic Field:
Instruments for measuring magnetic field are compass, Hall effect sensor, Magnetometer, Proton magnetometer, SQUID.
(i) Compass: A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (or points). Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials. When the compass is used, the rose can be aligned with the corresponding geographic directions; for example, the "N" mark on the rose really points northward. Compasses often display markings for angles in degrees in addition to (or sometimes instead of) the rose. North corresponds to 0°, and the angles increase clockwise, so east is 90° degrees, south is 180°, and west is 270°. These numbers allow the compass to show azimuths or bearings, which are commonly stated in this notation.
(ii) Hall Effect Sensor: A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications.
In a Hall effect sensor a thin strip of metal has a current applied along it, in the presence of a magnetic field the electrons are deflected towards one edge of the metal strip, producing a voltage gradient across the short-side of the strip (perpendicular to the feed current). Inductive sensors are just a coil of wire, in the presence of a changing magnetic field a current will be induced in the coil, producing a voltage at its output. Hall effect sensors have the advantage that they can detect static (non-changing) magnetic fields.
(iii) Magnetometer: A magnetometer is an instrument that measures magnetism—either the magnetization of a magnetic material like a ferromagnet, or the direction, strength, or relative change of a magnetic field at a particular location. A compass is a simple type of magnetometer, one that measures the direction of an ambient magnetic field. Magnetometers have a very diverse range of applications, including locating objects such as submarines, sunken ships, hazards for tunnel boring machines, hazards in coal mines, unexploded ordnance, toxic waste drums, as well as a wide range of mineral deposits and geological structures. They also have applications in heart beat monitors, weapon systems positioning, sensors in anti-locking brakes, weather prediction (via solar cycles), steel pylons, drill guidance systems, archaeology, plate tectonics and radio wave propagation and planetary exploration.
(iv) SQUID: A SQUID (for superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely subtle magnetic fields, based on superconducting loops containing Josephson junctions.
The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction, and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.
The History of Electric Measuring Instruments
Precision electric meters are indispensable to the development of technology in this age. The first
electric measuring instruments, however, were physically impossible to transport, and were functionally
inadequate for use in a laboratory. The measuring instruments of today have evolved into sturdy, easy-to-use instruments with higher performance, adopting new active components which have appeared one after another. Expanding in functionality, measuring instruments that have adopted such new technology have enabled even more precise measurement. The users have also expanded from research organizations and educational facilities, to the manufacturers of electrical equipment and electronic parts. The measuring instrument manufacturers were able to supply more convenient measuring instruments to the user, and conversely, the user, the manufacturers of electrical equipment and electronic parts, needed more easy-to-use and highly precise measuring instruments in order to respond to a rapidly increasing demand. Consequently, cheap and high quality electronic parts were supplied to the market, and the measuring instrument manufacturers were also able to develop new measuring instruments using those parts. In fact, it can be said that they have been mutually complementary. It should not be forgotten that the demand for electronic components for consumer use has also driven the whole in the meantime.
Electric Current:
Instruments used for measuring electric current is ammeter, there are various techniques that can be used to measure current: Shunt resistors, Hall effect, Transformer, Magnetoresistive
An electric current is a flow of electric charge. In electric circuitsthis charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas (plasma). The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.
Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators. The moving charged particles in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors.
Symbol: The conventional symbol for current is I, which originates from the French phrase intensité de courant, (current intensity). Current intensity is often referred to simply as current. The Isymbol was used by André-Marie Ampère, after whom the unit of electric current is named, in formulating Ampère's force law (1820). The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using C to I until 1896.
Current Measurement: Current can be measured using an ammeter.
At the circuit level, there are various techniques that can be used to measure current:
⚫ Shunt resistors
⚫ Hall effect current sensor transducers
⚫ Transformers (however DC cannot be measured)
⚫ Magnetoresistive field sensors
Electrical Resistance and conductance:
An Instrument for measuring resistance is called an ohmmeter.
The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
The resistance (R) of an object is defined as the ratio of voltage across it (V) to current through it (I), while the conductance (G) is the inverse:
R = V/I , G = I/V = 1/R
Measuring Resistance: An instrument for measuring resistance is called an ohmmeter. Simple ohmmeters cannot measure low resistances accurately because the resistance of their measuring leads causes a voltage drop that interferes with the measurement, so more accurate devices use four-terminal sensing.
Electric Charge:
Instrument used for measuring electric charge is electrometer, or indirectly measured with a ballistic galvanometer.
The electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces.
Units: The SI unit of quantity of electric chargeis the coulomb, which is equivalent to about 6.242×1018 e.
Instrument used for measuring electric charge directly is electrometer, or indirectly measured with a ballistic galvanometer.
Magnetic Field:
Instrument for measuring magnetic field is magnetometer.
A magnetic field is a force field that is created by moving electric charges (electric currents) and magnetic dipoles, and exerts a force on other nearby moving charges and magnetic dipoles. At any given point, it has a direction and a magnitude (or strength), so it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols Band H, where, in the International System of Units, H is measured in units of amperes per meter and B is measured in teslas or newtons per meter per ampere.
Measurement: Instrument for measuring magnetic field is magnetometer. Important classes of magnetometers include using induction magnetometer (or search-coil magnetometer) which measure only varying magnetic field, rotating coil magnetometer, Hall effectmagnetometers, NMR magnetometers, SQUID magnetometers, and fluxgate magnetometers. The magnetic fields of distant astronomical objects are measured through their effects on local charged particles. For instance, electrons spiraling around a field line produce synchrotron radiation that is detectable in radio waves.
Electrical Conductivity:
Instrument used for measuring electrical conductivity is Ohmmeter, Time - domain reflectometer, Wheatstone bridge.
1. Ohmmeter: An ohmmeter is an electrical instrumentthat measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters (also a trademarked device Megger) measure large values of resistance. The unit of measurement for resistance is ohms (Ω).
Working Principle: An ohmmeter measures resistance by applying a current and a voltage to a resistance (sometimes also called a "load"), and feeding the response of that current and voltage to something that we can visualize. This visualization can be an inductor as seen in galvanometers or can be a display driven by an analog digital converter (adc) as seen in digital multimeters.
This approach gives us the resistance derived from Ohm's Law, which states that the value of the resistance (R) is given by:
R = V / I
2. Time - domain Reflectometer: A time-domain reflectometer (TDR) is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables (for example, twisted pair wire or coaxial cable).[1] It can also be used to locate discontinuities in a connector, printed circuit board, or any other electrical path. The equivalent device for optical fiber is an optical time-domain reflectometer.
3. Wheatstone bridge: A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of a wheatstone bridge is its ability to provide extremely accurate measurements (in contrast with something like a simple voltage divider). Its operation is similar to the original potentiometer.
The Wheatstone bridge was invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for the purpose of soils analysis and comparison.
Electrical Capacitance:
Instrument used to measure electric capacitance is Capacitance meter.
Capacitance Meter: A capacitance meter is a piece of electronic test equipment used to measure capacitance, mainly of discrete capacitors. Depending on the sophistication of the meter, it may display the capacitance only, or it may also measure a number of other parameters such as leakage, equivalent series resistance (ESR), and inductance. For most purposes and in most cases the capacitor must be disconnected from circuit; ESR can usually be measured in circuit.
Electrical Inductance:
Instrument used to measure electrical inductance is inductance meter / LCR meter.
LCR meter: An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic components. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components.
Energy carried by electricity or Electric Energy:
Instrument used to measure electric energy is Electric Energy Meter or Electricity Meter.
Electricity Meter: An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device.
Electric utilities use electric meters installed at customers' premises to measure electric energy delivered to their customers for billing purposes. They are typically calibrated in billing units, the most common one being the kilowatt hour [kWh]. They are usually read once each billing period. When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for demand response load shedding during peak load periods.
Power carried by electricity / Current of Energy:
Instrument used to measure power carried by electricity is wattmeter.
Wattmeter: The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in wattsof any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.
Electric Field (negative gradient of electric potential, voltage per length):
Instrument for measuring electric field is Field Mill.
Field Mill: A field mill is a specialized instrument used for measuring the strength of electrical fields in the atmosphere near thunderstorm clouds. They are used in the launch criteria for rockets bound for orbit, as well as the now-retired Space Shuttle, to avoid lightning strikes. They are also used in outdoor laboratories for lightning protection equipment to determine favorable experiment conditions.
The "mill" is a typical rotating shutter design in the instrument. It is usually deployed airborne and flown through anvil head clouds to make measurements.
Mangnetic Field:
Instruments for measuring magnetic field are compass, Hall effect sensor, Magnetometer, Proton magnetometer, SQUID.
(i) Compass: A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (or points). Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials. When the compass is used, the rose can be aligned with the corresponding geographic directions; for example, the "N" mark on the rose really points northward. Compasses often display markings for angles in degrees in addition to (or sometimes instead of) the rose. North corresponds to 0°, and the angles increase clockwise, so east is 90° degrees, south is 180°, and west is 270°. These numbers allow the compass to show azimuths or bearings, which are commonly stated in this notation.
(ii) Hall Effect Sensor: A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications.
In a Hall effect sensor a thin strip of metal has a current applied along it, in the presence of a magnetic field the electrons are deflected towards one edge of the metal strip, producing a voltage gradient across the short-side of the strip (perpendicular to the feed current). Inductive sensors are just a coil of wire, in the presence of a changing magnetic field a current will be induced in the coil, producing a voltage at its output. Hall effect sensors have the advantage that they can detect static (non-changing) magnetic fields.
(iii) Magnetometer: A magnetometer is an instrument that measures magnetism—either the magnetization of a magnetic material like a ferromagnet, or the direction, strength, or relative change of a magnetic field at a particular location. A compass is a simple type of magnetometer, one that measures the direction of an ambient magnetic field. Magnetometers have a very diverse range of applications, including locating objects such as submarines, sunken ships, hazards for tunnel boring machines, hazards in coal mines, unexploded ordnance, toxic waste drums, as well as a wide range of mineral deposits and geological structures. They also have applications in heart beat monitors, weapon systems positioning, sensors in anti-locking brakes, weather prediction (via solar cycles), steel pylons, drill guidance systems, archaeology, plate tectonics and radio wave propagation and planetary exploration.
(iv) SQUID: A SQUID (for superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely subtle magnetic fields, based on superconducting loops containing Josephson junctions.
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