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Galvanometer

A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. Galvanometers work by deflecting a pointer in response to an electric current flowing through a coil in a constant magnetic field. The mechanism is also used as an actuator in applications such as hard disks.

Galvanometers came from the observation, first noted by Hans Christian Ørsted in 1820, that a magnetic compass's needle deflects when near a wire having electric current. They were the first instruments used to detect and measure small amounts of current. André-Marie Ampère, who gave mathematical expression to Ørsted's discovery, named the instrument after the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk.

Galvanometers have been essential for the development of science and technology in many fields. For example, in the 1800s they enabled long-range communication through submarine cables, such as the earliest transatlantic telegraph cables, and were essential to discovering the electrical activity of the heart and brain, by their fine measurements of current.

Galvanometers have also been used as the display components of other kinds of analog meters (e.g., light meters and VU meters), capturing the outputs of these meters' sensors. Today, the main type of galvanometer still in use is the D'Arsonval/Weston type.

Operation

Modern galvanometers, of the D'Arsonval/Weston type, are constructed with a small pivoting coil of wire, called a spindle, in the field of a permanent magnet. The coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position.

When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. Careful design of the pole pieces ensures that the magnetic field is uniform so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains a provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation.

The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current). Such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude. The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents. A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full-scale current. A meter can be configured to read other voltages by putting it in a voltage divider circuit. This is generally done by placing a resistor in series with the meter coil. A meter can be used to read resistance by placing it in series with a known voltage (a battery) and an adjustable resistor. In a preparatory step, the circuit is completed and the resistor adjusted to produce full-scale deflection. When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously unknown resistor.

These capabilities to translate different kinds of electric quantities into pointer movements make the galvanometer ideal for turning the output of other sensors that output electricity (in some form or another), into something that can be read by a human.

Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along with the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by positioning one's head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator's eye must be directly above the pointer and any parallax error has been minimized.

Uses
Probably the largest use of galvanometers was of the D'Arsonval/Weston type used in analog meters in electronic equipment. Since the 1980s, galvanometer-type analog meter movements have been displaced by analog-to-digital converters (ADCs) for many uses. A digital panel meter (DPM) contains an ADC and numeric display. The advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favor the application of analog meter movements.

Modern uses
Most modern uses for the galvanometer mechanism are in positioning and control systems. Galvanometer mechanisms are divided into moving magnet and moving coil galvanometers; in addition, they are divided into closed-loop and open-loop - or resonant - types.

Mirror galvanometer systems are used as beam positioning or beam steering elements in laser scanning systems. For example, for material processing with high-power lasers, closed loop mirror galvanometer mechanisms are used with servo control systems. These are typically high power galvanometers and the newest galvanometers designed for beam steering applications can have frequency responses over 10 kHz with appropriate servo technology. Closed-loop mirror galvanometers are also used in similar ways in stereolithography, laser sintering, laser engraving, laser beam welding, laser TVs, laser displays and in imaging applications such as retinal scanning with Optical Coherence Tomography (OCT) and Scanning Laser Ophthalmoscopy (SLO). Almost all of these galvanometers are of the moving magnet type. The closed loop is obtained measuring the position of the rotating axis with an infrared emitter and 2 photodiodes. This feedback is an analog signal.

Open loop, or resonant mirror galvanometers, are mainly used in some types of laser-based bar-code scanners, printing machines, imaging applications, military applications and space systems. Their non-lubricated bearings are especially of interest in applications that require functioning in a high vacuum. Moving coil type galvanometer mechanisms (called 'voice coils' by hard disk manufacturers) are used for controlling the head positioning servos in hard disk drives and CD/DVD players, in order to keep mass (and thus access times), as low as possible.

Past uses
A major early use for galvanometers was for finding faults in telecommunications cables. They were superseded in this application late in the 20th century by time-domain reflectometers.

Galvanometer mechanisms were also used to get readings from photoresistors in the metering mechanisms of film cameras (as seen in the adjacent image).

In analog strip chart recorders such as used in electrocardiographs, electroencephalographs and polygraphs, galvanometer mechanisms were used to position the pen. Strip chart recorders with galvanometer driven pens may have a full-scale frequency response of 100 Hz and several centimeters of deflection.

Hans Christian Ørsted
The deflection of a magnetic compass needle by the current in a wire was first described by Hans Christian Ørsted in 1820. The phenomenon was studied both for its own sake and as a means of measuring electric current.

Schweigger and Ampère
The earliest galvanometer was reported by Johann Schweigger at the University of Halle on 16 September 1820. André-Marie Ampère also contributed to its development. Early designs increased the effect of the magnetic field generated by the current by using multiple turns of wire. The instruments were at first called "multipliers" due to this common design feature. The term "galvanometer," in common use by 1836, was derived from the surname of Italian electricity researcher Luigi Galvani, who in 1791 discovered that electric current would make a dead frog's leg jerk.

Poggendorff and Thomson

Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called "tangent" galvanometers and had to be oriented before use. Later instruments of the "astatic" type used opposing magnets to become independent of the Earth's field and would operate in any orientation.

An early mirror galvanometer was invented in 1826 by Johann Christian Poggendorff. An astatic galvanometer was invented by Hermann von Helmholtz in 1849; a more sensitive version of that device, the Thomson mirror galvanometer, was patented in 1858 by William Thomson (Lord Kelvin). Thomson's design was able to detect very rapid current changes by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.

Georg Ohm
The ability to measure voltage and current quantitatively allowed Georg Ohm, in 1827, to formulate Ohm's law – that the voltage across a conductor is directly proportional to the current through it.

D'Arsonval and Deprez

The early moving-magnet form of galvanometer had the disadvantage that it was affected by any magnets or iron masses near it, and its deflection was not linearly proportional to the current. In 1882 Jacques-Arsène d'Arsonval and Marcel Deprez developed a form with a stationary permanent magnet and a moving coil of wire, suspended by fine wires which provided both an electrical connection to the coil and the restoring torque to return to the zero position. An iron tube between the magnet's pole pieces defined a circular gap through which the coil rotated. This gap produced a consistent, radial magnetic field across the coil, giving a linear response throughout the instrument's range. A mirror attached to the coil deflected a beam of light to indicate the coil position. The concentrated magnetic field and delicate suspension made these instruments sensitive; d'Arsonval's initial instrument could detect ten microamperes.

Edward Weston
Edward Weston extensively improved the design of the galvanometer. He substituted the fine wire suspension with a pivot and provided restoring torque and electrical connections through spiral springs rather than through the traditional wristwatch balance wheel hairspring. He developed a method of stabilizing the magnetic field of the permanent magnet, so the instrument would have consistent accuracy over time. He replaced the light beam and mirror with a knife-edge pointer that could be read directly. A mirror under the pointer, in the same plane as the scale, eliminated parallax observation error. To maintain the field strength, Weston's design used a very narrow circumferential slot through which the coil moved, with a minimal air-gap. This improved linearity of pointer deflection with respect to coil current. Finally, the coil was wound on a light-weight form made of conductive metal, which acted as a damper. By 1888, Edward Weston had patented and brought out a commercial form of this instrument, which became a standard electrical equipment component. It was known as a "portable" instrument because it was affected very little by mounting position or by transporting it from place to place. This design is almost universally used in moving-coil meters today.

Initially, laboratory instruments relying on the Earth's own magnetic field to provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive portable instruments essential to the development of electro-technology.

Taut-band movement
The taut-band movement is a modern development of the D'Arsonval-Weston movement. The jewel pivots and hairsprings are replaced by tiny strips of metal under tension. Such a meter is more rugged for field use.

Types
There is broadly two types of galvanometers. Some galvanometers use a solid pointer on a scale to show measurements; other very sensitive types use a miniature mirror and a beam of light to provide mechanical amplification of low-level signals.

Tangent galvanometer
A tangent galvanometer is an early measuring instrument used for the measurement of electric current. It works by using a compass needle to compare a magnetic field generated by the unknown current to the magnetic field of the Earth. It gets its name from its operating principle, the tangent law of magnetism, which states that the tangent of the angle a compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields. It was first described by Johan Jakob Nervander in 1834.

A tangent galvanometer consists of a coil of insulated copper wire wound on a circular non-magnetic frame. The frame is mounted vertically on a horizontal base provided with levelling screws. The coil can be rotated on a vertical axis passing through its centre. A compass box is mounted horizontally at the centre of a circular scale. It consists of a tiny, powerful magnetic needle pivoted at the centre of the coil. The magnetic needle is free to rotate in the horizontal plane. The circular scale is divided into four quadrants. Each quadrant is graduated from 0° to 90°. A long thin aluminium pointer is attached to the needle at its centre and at right angle to it. To avoid errors due to parallax, a plane mirror is mounted below the compass needle.

In operation, the instrument is first rotated until the magnetic field of the Earth, indicated by the compass needle, is parallel with the plane of the coil. Then the unknown current is applied to the coil. This creates a second magnetic field on the axis of the coil, perpendicular to the Earth's magnetic field. The compass needle responds to the vector sum of the two fields and deflects to an angle equal to the tangent of the ratio of the two fields. From the angle read from the compass's scale, the current could be found from a table. The current supply wires have to be wound in a small helix, like a pig's tail, otherwise the field due to the wire will affect the compass needle and an incorrect reading will be obtained.

Theory
The galvanometer is oriented so that the plane of the coil is vertical and aligned along parallel to the horizontal component $B_{H}$ of the Earth's magnetic field (i.e. parallel to the local "magnetic meridian"). When an electric current flows through the galvanometer coil, a second magnetic field $B$ is created. At the center of the coil, where the compass needle is located, the coil's field is perpendicular to the plane of the coil. The magnitude of the coil's field is:
 * $$B={\mu_0 nI\over 2r}\,$$

where $I$ is the current in amperes, $n$ is the number of turns of the coil and $r$ is the radius of the coil. These two perpendicular magnetic fields add vectorially, and the compass needle points along the direction of their resultant $B_{H}+B$. The current in the coil causes the compass needle to rotate by an angle $θ$:
 * $$\theta = \tan^{-1} \frac{B}{B_H}\,$$

From tangent law, $B = B_{H }tan θ$, i.e.
 * $${\mu_0 nI\over 2r} = B_H \tan\theta\,$$

or
 * $$I=\left(\frac{2rB_H}{\mu_0 n}\right)\tan\theta\,$$

or $I = K tan θ$, where $K$ is called the Reduction Factor of the tangent galvanometer.

One problem with the tangent galvanometer is that its resolution degrades at both high currents and low currents. The maximum resolution is obtained when the value of $θ$ is 45°. When the value of $θ$ is close to 0° or 90°, a large percentage change in the current will only move the needle a few degrees.

Geomagnetic field measurement
A tangent galvanometer can also be used to measure the magnitude of the horizontal component of the geomagnetic field. When used in this way, a low-voltage power source, such as a battery, is connected in series with a rheostat, the galvanometer, and an ammeter. The galvanometer is first aligned so that the coil is parallel to the geomagnetic field, whose direction is indicated by the compass when there is no current through the coils. The battery is then connected and the rheostat is adjusted until the compass needle deflects 45 degrees from the geomagnetic field, indicating that the magnitude of the magnetic field at the center of the coil is the same as that of the horizontal component of the geomagnetic field. This field strength can be calculated from the current as measured by the ammeter, the number of turns of the coil, and the radius of the coils.

Astatic galvanometer
Unlike the tangent galvanometer, the astatic galvanometer does not use the Earth's magnetic field for measurement, so it does not need to be oriented with respect to the Earth's field, making it easier to use. Developed by Leopoldo Nobili in 1825, it consists of two magnetized needles parallel to each other but with the magnetic poles reversed. These needles are suspended by a single silk thread. The lower needle is inside a vertical current sensing coil of wire and is deflected by the magnetic field created by the passing current, as in the tangent galvanometer above. The purpose of the second needle is to cancel the dipole moment of the first needle, so the suspended armature has no net magnetic dipole moment, and thus is not affected by the earth's magnetic field. The needle's rotation is opposed by the torsional elasticity of the suspension thread, which is proportional to the angle.

Mirror galvanometer
To achieve higher sensitivity to detect extremely small currents, the mirror galvanometer substitutes a lightweight mirror for the pointer. It consists of horizontal magnets suspended from a fine fiber, inside a vertical coil of wire, with a mirror attached to the magnets. A beam of light reflected from the mirror falls on a graduated scale across the room, acting as a long mass-less pointer. The mirror galvanometer was used as the receiver in the first trans-Atlantic submarine telegraph cables in the 1850s, to detect the extremely faint pulses of current after their thousand-mile journey under the Atlantic. In a device called an oscillograph, the moving beam of light is used, to produce graphs of current versus time, by recording measurements on photographic film. The string galvanometer is a type of mirror galvanometer so sensitive that it was used to make the first electrocardiogram of the electrical activity of the human heart.

Ballistic galvanometer
A ballistic galvanometer is a type of sensitive galvanometer for measuring the quantity of charge discharged through it. It is an integrator, by virtue of the long time constant of its response, unlike a current-measuring galvanometer. The moving part has a large moment of inertia that gives it an oscillation period long enough to make the integrated measurement. It can be either of the moving coil or moving magnet type; commonly it is a mirror galvanometer.

title: Galvanometer


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ADC

ADC may refer to:

Science and medicine

 * ADC (gene), a human gene
 * AIDS dementia complex, neurological disorder associated with HIV and AIDS
 * Allyl diglycol carbonate or CR-39, a polymer
 * Antibody-drug conjugate, a type of anticancer treatment
 * Apparent diffusion coefficient, a derived value from a diffusion MRI
 * Automated dispensing cabinet, a computerized drug storage device for hospitals
 * Azodicarbonamide, a blowing agent

Arts

 * ADC Theatre, venue of the University of Cambridge Amateur Dramatic Club
 * Art Directors Club of New York, a professional association
 * Australian Dance Council, a national dance advocacy organisation
 * Hong Kong Arts Development Council, a statutory body in Hong Kong

Aviation

 * ADC Aircraft, a British firm established in 1920
 * ADC Airlines, based in Ikeja, Nigeria
 * Aerospace Defense Command, of the U.S. Air Force

Government and politics

 * Aboriginal Development Commission, an Australian statutory body that existed from 1980 to 1990
 * African Democratic Congress, a political party in Nigeria
 * Alliance for Democratic Change, a political party in Tanzania
 * American Deserters Committee, an anti-Vietnam War group
 * American-Arab Anti-Discrimination Committee, a civil rights organization
 * Arizona Department of Corrections, US
 * Arkansas Department of Correction, US
 * Ashfield District Council, Nottinghamshire, England
 * Asociación Democrática de Colima, a political party from the State of Colima, Mexico

Others

 * Acadia Divinity College, a seminary on the campus of Acadia University, Canada
 * Advanced Digital Corporation, a defunct computer company of Southern California
 * ADC Map, an American map publisher
 * ADC Telecommunications, in Eden Prairie, Minnesota
 * Australian Defence College, Weston Creek, Canberra

Technology

 * Advanced Data Connector, a Microsoft technology
 * Advanced Direct Connect, a peer-to-peer file sharing and chat protocol
 * Air data computer, an essential avionics component found in modern glass cockpits
 * Analog-to-digital converter, a type of electronic circuit
 * Android Developer Challenge, a competition
 * Apple Developer Connection, Apple Computer's developer network
 * Apple Display Connector, similar to the DVI connector
 * Application delivery controller, for accelerating website performance
 * Automatic Data Capture, for automatic identification, data collection and storage into computer systems

Other uses

 * New Zealand ADC class diesel multiple unit, a type of diesel railway vehicle used on Auckland's suburban network
 * Adlington (Cheshire) railway station, UK (National Rail code)
 * Aid to Dependent Children, an American government social program from 1935 to 1960
 * Aide-de-camp, assistant to a senior military or government person
 * Alternative Daily cover, material other than soil for containment in a landfill
 * Andakombe Airport, airport in Papua New Guinea (IATA: ADC)
 * Andrew Dice Clay (born 1957), American comedian
 * A.DC., taxonomic author abbreviation for Alphonse Pyramus de Candolle (1806–1893), French-Swiss botanist
 * Axiom of dependent choice

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: ADC


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Analog-to-digital converter

In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities.

There are several ADC architectures. Due to the complexity and the need for precisely matched components, all but the most specialized ADCs are implemented as integrated circuits (ICs). These typically take the form of metal–oxide–semiconductor (MOS) mixed-signal integrated circuit chips that integrate both analog and digital circuits.

A digital-to-analog converter (DAC) performs the reverse function; it converts a digital signal into an analog signal.

Explanation
An ADC converts a continuous-time and continuous-amplitude analog signal to a discrete-time and discrete-amplitude digital signal. The conversion involves quantization of the input, so it necessarily introduces a small amount of quantization error. Furthermore, instead of continuously performing the conversion, an ADC does the conversion periodically, sampling the input, and limiting the allowable bandwidth of the input signal.

The performance of an ADC is primarily characterized by its bandwidth and signal-to-noise ratio (SNR). The bandwidth of an ADC is characterized primarily by its sampling rate. The SNR of an ADC is influenced by many factors, including the resolution, linearity and accuracy (how well the quantization levels match the true analog signal), aliasing and jitter. The SNR of an ADC is often summarized in terms of its effective number of bits (ENOB), the number of bits of each measure it returns that are on average not noise. An ideal ADC has an ENOB equal to its resolution. ADCs are chosen to match the bandwidth and required SNR of the signal to be digitized. If an ADC operates at a sampling rate greater than twice the bandwidth of the signal, then per the Nyquist–Shannon sampling theorem, near-perfect reconstruction is possible. The presence of quantization error limits the SNR of even an ideal ADC. However, if the SNR of the ADC exceeds that of the input signal, then the effects of quantization error may be neglected, resulting in an essentially perfect digital representation of the bandlimited analog input signal.

Resolution
The resolution of the converter indicates the number of different, i.e. discrete, values it can produce over the allowed range of analog input values. Thus a particular resolution determines the magnitude of the quantization error and therefore determines the maximum possible signal-to-noise ratio for an ideal ADC without the use of oversampling. The input samples are usually stored electronically in binary form within the ADC, so the resolution is usually expressed as the audio bit depth. In consequence, the number of discrete values available is usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels (28 = 256). The values can represent the ranges from 0 to 255 (i.e. as unsigned integers) or from −128 to 127 (i.e. as signed integer), depending on the application.

Resolution can also be defined electrically, and expressed in volts. The change in voltage required to guarantee a change in the output code level is called the least significant bit (LSB) voltage. The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of intervals:

 * $$R = \dfrac{E_\mathrm {FSR}}{2^M - 1},$$

where M is the ADC's resolution in bits and EFSR is the full-scale voltage range (also called 'span'). EFSR is given by

 * $$E_ \mathrm {FSR} = V_\mathrm {RefHi} - V_ \mathrm {RefLow}, \,$$

where VRefHi and VRefLow are the upper and lower extremes, respectively, of the voltages that can be coded.

Normally, the number of voltage intervals is given by

 * $$N = 2^M -1, \,$$

where M is the ADC's resolution in bits.

That is, one voltage interval is assigned in between two consecutive code levels.

Example:
 * Coding scheme as in figure 1
 * Full scale measurement range = 0 to 1 volt
 * ADC resolution is 3 bits: 23 = 8 quantization levels (codes)
 * ADC voltage resolution, Q = 1 V / ( 23 - 1 ) = 0.143 V (intervals)

In many cases, the useful resolution of a converter is limited by the signal-to-noise ratio (SNR) and other errors in the overall system expressed as an ENOB.

Quantization error

Quantization error is introduced by the quantization inherent in an ideal ADC. It is a rounding error between the analog input voltage to the ADC and the output digitized value. The error is nonlinear and signal-dependent. In an ideal ADC, where the quantization error is uniformly distributed between −$1⁄2$ LSB and +$1⁄2$ LSB, and the signal has a uniform distribution covering all quantization levels, the signal-to-quantization-noise ratio (SQNR) is given by

 * $$\mathrm{SQNR} = 20 \log_{10}(2^Q) \approx 6.02 \cdot Q\ \mathrm{dB} \,\!$$

where Q is the number of quantization bits. For example, for a 16-bit ADC, the quantization error is 96.3 dB below the maximum level.

Quantization error is distributed from DC to the Nyquist frequency. Consequently, if part of the ADC's bandwidth is not used, as is the case with oversampling, some of the quantization error will occur out-of-band, effectively improving the SQNR for the bandwidth in use. In an oversampled system, noise shaping can be used to further increase SQNR by forcing more quantization error out of band.

Dither
In ADCs, performance can usually be improved using dither. This is a very small amount of random noise (e.g. white noise), which is added to the input before conversion. Its effect is to randomize the state of the LSB based on the signal. Rather than the signal simply getting cut off altogether at low levels, it extends the effective range of signals that the ADC can convert, at the expense of a slight increase in noise. Dither can only increase the resolution of a sampler. It cannot improve the linearity, and thus accuracy does not necessarily improve.

Quantization distortion in an audio signal of very low level with respect to the bit depth of the ADC is correlated with the signal and sounds distorted and unpleasant. With dithering, the distortion is transformed into noise. The undistorted signal may be recovered accurately by averaging over time. Dithering is also used in integrating systems such as electricity meters. Since the values are added together, the dithering produces results that are more exact than the LSB of the analog-to-digital converter.

Dither is often applied when quantizing photographic images to a fewer number of bits per pixel—the image becomes noisier but to the eye looks far more realistic than the quantized image, which otherwise becomes banded. This analogous process may help to visualize the effect of dither on an analog audio signal that is converted to digital.

Accuracy
An ADC has several sources of errors. Quantization error and (assuming the ADC is intended to be linear) non-linearity are intrinsic to any analog-to-digital conversion. These errors are measured in a unit called the least significant bit (LSB). In the above example of an eight-bit ADC, an error of one LSB is $1⁄256$ of the full signal range, or about 0.4%.

Nonlinearity
All ADCs suffer from nonlinearity errors caused by their physical imperfections, causing their output to deviate from a linear function (or some other function, in the case of a deliberately nonlinear ADC) of their input. These errors can sometimes be mitigated by calibration, or prevented by testing. Important parameters for linearity are integral nonlinearity and differential nonlinearity. These nonlinearities introduce distortion that can reduce the signal-to-noise ratio performance of the ADC and thus reduce its effective resolution.

Jitter
When digitizing a sine wave $$x(t)=A \sin{(2 \pi f_0 t)}$$, the use of a non-ideal sampling clock will result in some uncertainty in when samples are recorded. Provided that the actual sampling time uncertainty due to clock jitter is $$\Delta t$$, the error caused by this phenomenon can be estimated as $$E_{ap} \le |x'(t) \Delta t| \le 2A \pi f_0 \Delta t$$. This will result in additional recorded noise that will reduce the effective number of bits (ENOB) below that predicted by quantization error alone. The error is zero for DC, small at low frequencies, but significant with signals of high amplitude and high frequency. The effect of jitter on performance can be compared to quantization error: $$\Delta t < \frac{1}{2^q \pi f_0}$$, where q is the number of ADC bits.

Clock jitter is caused by phase noise. The resolution of ADCs with a digitization bandwidth between 1 MHz and 1 GHz is limited by jitter. For lower bandwidth conversions such as when sampling audio signals at 44.1 kHz, clock jitter has a less significant impact on performance.

Sampling rate
An analog signal is continuous in time and it is necessary to convert this to a flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter. A continuously varying bandlimited signal can be sampled and then the original signal can be reproduced from the discrete-time values by a reconstruction filter. The Nyquist–Shannon sampling theorem implies that a faithful reproduction of the original signal is only possible if the sampling rate is higher than twice the highest frequency of the signal.

Since a practical ADC cannot make an instantaneous conversion, the input value must necessarily be held constant during the time that the converter performs a conversion (called the conversion time). An input circuit called a sample and hold performs this task—in most cases by using a capacitor to store the analog voltage at the input, and using an electronic switch or gate to disconnect the capacitor from the input. Many ADC integrated circuits include the sample and hold subsystem internally.

Aliasing
An ADC works by sampling the value of the input at discrete intervals in time. Provided that the input is sampled above the Nyquist rate, defined as twice the highest frequency of interest, then all frequencies in the signal can be reconstructed. If frequencies above half the Nyquist rate are sampled, they are incorrectly detected as lower frequencies, a process referred to as aliasing. Aliasing occurs because instantaneously sampling a function at two or fewer times per cycle results in missed cycles, and therefore the appearance of an incorrectly lower frequency. For example, a 2 kHz sine wave being sampled at 1.5 kHz would be reconstructed as a 500 Hz sine wave.

To avoid aliasing, the input to an ADC must be low-pass filtered to remove frequencies above half the sampling rate. This filter is called an anti-aliasing filter, and is essential for a practical ADC system that is applied to analog signals with higher frequency content. In applications where protection against aliasing is essential, oversampling may be used to greatly reduce or even eliminate it.

Although aliasing in most systems is unwanted, it can be exploited to provide simultaneous down-mixing of a band-limited high-frequency signal (see undersampling and frequency mixer). The alias is effectively the lower heterodyne of the signal frequency and sampling frequency.

Oversampling
For economy, signals are often sampled at the minimum rate required with the result that the quantization error introduced is white noise spread over the whole passband of the converter. If a signal is sampled at a rate much higher than the Nyquist rate and then digitally filtered to limit it to the signal bandwidth produces the following advantages:
 * Oversampling can make it easier to realize analog anti-aliasing filters
 * Improved audio bit depth
 * Reduced noise, especially when noise shaping is employed in addition to oversampling.

Oversampling is typically used in audio frequency ADCs where the required sampling rate (typically 44.1 or 48 kHz) is very low compared to the clock speed of typical transistor circuits (>1 MHz). In this case, the performance of the ADC can be greatly increased at little or no cost. Furthermore, as any aliased signals are also typically out of band, aliasing can often be eliminated using very low cost filters.

Relative speed and precision
The speed of an ADC varies by type. The Wilkinson ADC is limited by the clock rate which is processable by current digital circuits. For a successive-approximation ADC, the conversion time scales with the logarithm of the resolution, i.e. the number of bits. Flash ADCs are certainly the fastest type of the three; The conversion is basically performed in a single parallel step.

There is a potential tradeoff between speed and precision. Flash ADCs have drifts and uncertainties associated with the comparator levels results in poor linearity. To a lesser extent, poor linearity can also be an issue for successive-approximation ADCs. Here, nonlinearity arises from accumulating errors from the subtraction processes. Wilkinson ADCs have the best linearity of the three.

Sliding scale principle
The sliding scale or randomizing method can be employed to greatly improve the linearity of any type of ADC, but especially flash and successive approximation types. For any ADC the mapping from input voltage to digital output value is not exactly a floor or ceiling function as it should be. Under normal conditions, a pulse of a particular amplitude is always converted to the same digital value. The problem lies in that the ranges of analog values for the digitized values are not all of the same widths, and the differential linearity decreases proportionally with the divergence from the average width. The sliding scale principle uses an averaging effect to overcome this phenomenon. A random, but known analog voltage is added to the sampled input voltage. It is then converted to digital form, and the equivalent digital amount is subtracted, thus restoring it to its original value. The advantage is that the conversion has taken place at a random point. The statistical distribution of the final levels is decided by a weighted average over a region of the range of the ADC. This in turn desensitizes it to the width of any specific level.

Types
These are several common ways of implementing an electronic ADC.

RC charge time
Resistor-capacitor (RC) circuits have a known voltage charging and discharging curve that can be used to solve for an unknown analog value.

Wilkinson
The Wilkinson ADC was designed by Denys Wilkinson in 1950. The Wilkinson ADC is based on the comparison of an input voltage with that produced by a charging capacitor. The capacitor is allowed to charge until a comparator determines it matches the input voltage. Then, the capacitor is discharged linearly by using a constant current source. The time required to discharge the capacitor is proportional to the amplitude of the input voltage. While the capacitor is discharging, pulses from a high-frequency oscillator clock are counted by a register. The number of clock pulses recorded in the register is also proportional to the input voltage.

Measuring analog resistance or capacitance
If the analog value to measure is represented by a resistance or capacitance, then by including that element in an RC circuit (with other resistances or capacitances fixed) and measuring the time to charge the capacitance from a known starting voltage to another known ending voltage through the resistance from a known voltage supply, the value of the unknown resistance or capacitance can be determined using the capacitor charging equation:

$$V_\text{capacitor}(t) = V_\text{supply}\left(1 - e^{-\frac{t}{RC}}\right)$$

and solving for the unknown resistance or capacitance using those starting and ending datapoints. This is similar but contrasts to the Wilkinson ADC which measures an unknown voltage with a known resistance and capacitance, by instead measuring an unknown resistance or capacitance with a known voltage.

For example, the positive (and/or negative) pulse width from a 555 Timer IC in monostable or astable mode represents the time it takes to charge (and/or discharge) its capacitor from $1/3$ Vsupply to $2/3$ Vsupply. By sending this pulse into a microcontroller with an accurate clock, the duration of the pulse can be measured and converted using the capacitor charging equation to produce the value of the unknown resistance or capacitance.

Larger resistances and capacitances will take a longer time to measure than smaller one. And the accuracy is limited by the accuracy of the microcontroller clock and the amount of time available to measure the value, which potentially might even change during measurement or be affected by external parasitics.

Direct-conversion
A direct-conversion or flash ADC has a bank of comparators sampling the input signal in parallel, each firing for a specific voltage range. The comparator bank feeds a digital encoder logic circuit that generates a binary number on the output lines for each voltage range.

ADCs of this type have a large die size and high power dissipation. They are often used for video, wideband communications, or other fast signals in optical and magnetic storage.

The circuit consists of a resistive divider network, a set of op-amp comparators and a priority encoder. A small amount of hysteresis is built into the comparator to resolve any problems at voltage boundaries. At each node of the resistive divider, a comparison voltage is available. The purpose of the circuit is to compare the analog input voltage with each of the node voltages.

The circuit has the advantage of high speed as the conversion takes place simultaneously rather than sequentially. Typical conversion time is 100 ns or less. Conversion time is limited only by the speed of the comparator and of the priority encoder. This type of ADC has the disadvantage that the number of comparators required almost doubles for each added bit. Also, the larger the value of n, the more complex is the priority encoder.

Successive approximation
A successive-approximation ADC uses a comparator and a binary search to successively narrow a range that contains the input voltage. At each successive step, the converter compares the input voltage to the output of an internal digital-to-analog converter (DAC) which initially represents the midpoint of the allowed input voltage range. At each step in this process, the approximation is stored in a successive approximation register (SAR) and the output of the digital-to-analog converter is updated for a comparison over a narrower range.

Ramp-compare
A ramp-compare ADC produces a saw-tooth signal that ramps up or down then quickly returns to zero. When the ramp starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters can be implemented economically, however, the ramp time may be sensitive to temperature because the circuit generating the ramp is often a simple analog integrator. A more accurate converter uses a clocked counter driving a DAC. A special advantage of the ramp-compare system is that converting a second signal just requires another comparator and another register to store the timer value. To reduce sensitivity to input changes during conversion, a sample and hold can charge a capacitor with the instantaneous input voltage and the converter can time the time required to discharge with a constant current.

Integrating
An integrating ADC (also dual-slope or multi-slope ADC) applies the unknown input voltage to the input of an integrator and allows the voltage to ramp for a fixed time period (the run-up period). Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero (the run-down period). The input voltage is computed as a function of the reference voltage, the constant run-up time period, and the measured run-down time period. The run-down time measurement is usually made in units of the converter's clock, so longer integration times allow for higher resolutions. Likewise, the speed of the converter can be improved by sacrificing resolution. Converters of this type (or variations on the concept) are used in most digital voltmeters for their linearity and flexibility.
 * Charge balancing ADC: The principle of charge balancing ADC is to first convert the input signal to a frequency using a voltage-to-frequency converter. This frequency is then measured by a counter and converted to an output code proportional to the analog input. The main advantage of these converters is that it is possible to transmit frequency even in a noisy environment or in isolated form. However, the limitation of this circuit is that the output of the voltage-to-frequency converter depends upon an RC product whose value cannot be accurately maintained over temperature and time.
 * Dual-slope ADC: The analog part of the circuit consists of a high input impedance buffer, precision integrator and a voltage comparator. The converter first integrates the analog input signal for a fixed duration and then it integrates an internal reference voltage of opposite polarity until the integrator output is zero. The main disadvantage of this circuit is the long duration time. They are particularly suitable for accurate measurement of slowly varying signals such as thermocouples and weighing scales.

Delta-encoded
A delta-encoded or counter-ramp ADC has an up-down counter that feeds a DAC. The input signal and the DAC both go to a comparator. The comparator controls the counter. The circuit uses negative feedback from the comparator to adjust the counter until the DAC's output matches the input signal and number is read from the counter. Delta converters have very wide ranges and high resolution, but the conversion time is dependent on the input signal behavior, though it will always have a guaranteed worst-case. Delta converters are often very good choices to read real-world signals as most signals from physical systems do not change abruptly. Some converters combine the delta and successive approximation approaches; this works especially well when high frequency components of the input signal are known to be small in magnitude.

Pipelined
A pipelined ADC (also called subranging quantizer) uses two or more conversion steps. First, a coarse conversion is done. In a second step, the difference to the input signal is determined with a DAC. This difference is then converted more precisely, and the results are combined in the last step. This can be considered a refinement of the successive-approximation ADC wherein the feedback reference signal consists of the interim conversion of a whole range of bits (for example, four bits) rather than just the next-most-significant bit. By combining the merits of the successive approximation and flash ADCs this type is fast, has a high resolution, and can be implemented efficiently.

Delta-sigma
A delta-sigma ADC (also known as a sigma-delta ADC) is based on a negative feedback loop with an analog filter and low resolution (often 1 bit) but high sampling rate ADC and DAC. The feedback loop continuously corrects accumulated quantization errors and performs noise shaping: quantization noise is reduced in the low frequencies of interest, but is increased in higher frequencies. Those higher frequencies may then be removed by a downsampling digital filter, which also converts the data stream from that high sampling rate with low bit depth to a lower rate with higher bit depth.

Time-interleaved
A time-interleaved ADC uses M parallel ADCs where each ADC samples data every M:th cycle of the effective sample clock. The result is that the sample rate is increased M times compared to what each individual ADC can manage. In practice, the individual differences between the M ADCs degrade the overall performance reducing the spurious-free dynamic range (SFDR). However, techniques exist to correct for these time-interleaving mismatch errors.

Intermediate FM stage
An ADC with an intermediate FM stage first uses a voltage-to-frequency converter to produce an oscillating signal with a frequency proportional to the voltage of the input signal, and then uses a frequency counter to convert that frequency into a digital count proportional to the desired signal voltage. Longer integration times allow for higher resolutions. Likewise, the speed of the converter can be improved by sacrificing resolution. The two parts of the ADC may be widely separated, with the frequency signal passed through an opto-isolator or transmitted wirelessly. Some such ADCs use sine wave or square wave frequency modulation; others use pulse-frequency modulation. Such ADCs were once the most popular way to show a digital display of the status of a remote analog sensor.

Time-stretch
A time-stretch analog-to-digital converter (TS-ADC) digitizes a very wide bandwidth analog signal, that cannot be digitized by a conventional electronic ADC, by time-stretching the signal prior to digitization. It commonly uses a photonic preprocessor to time-stretch the signal, which effectively slows the signal down in time and compresses its bandwidth. As a result, an electronic ADC, that would have been too slow to capture the original signal, can now capture this slowed-down signal. For continuous capture of the signal, the front end also divides the signal into multiple segments in addition to time-stretching. Each segment is individually digitized by a separate electronic ADC. Finally, a digital signal processor rearranges the samples and removes any distortions added by the preprocessor to yield the binary data that is the digital representation of the original analog signal.

Measuring physical values other than voltage
Although the term ADC is usually associated with measurement of an analog voltage, some partially-electronic devices that convert some measurable physical analog quantity into a digital number can also be considered ADCs, for instance:

 * Rotary encoders convert from an analog physical quantity that mechanically produces an amount of rotation into a stream of digital Gray code that a microcontroller can digitally interpret to derive the direction of rotation, angular position, and rotational speed.
 * Capacitive sensing converts from the analog physical quantity of a capacitance. That capacitance could be a proxy for some other physical quantity, such as the distance some metal object is from a metal sensing plate, or the amount of water in a tank, or the permittivity of a dielectric material.
 * Capacitive-to-digital (CDC) converters determine capacitance by applying a known excitation to a plate of a capacitor and measuring its charge.
 * Digital calipers convert from the analog physical quantity of an amount of displacement between two sliding rulers.
 * Inductive-to-digital converters measure a change of inductance by a conductive target moving in an inductor's AC magnetic field.
 * Time-to-digital converters recognize events and provide a digital representation of the analog time they occurred.
 * Time of flight measurements for instance can convert from some analog quantity that affects a propagation delay for an event.
 * Sensors in general that don't directly produce a voltage may indirectly produce a voltage or through other ways be converted into a digital value.
 * Resistive output (e.g. from a potentiometer or a force-sensing resistor) can be made into a voltage by sending a known current through it, or can be made into a RC charging time measurement, to produce a digital result.

Commercial
In many cases, the most expensive part of an integrated circuit is the pins, because they make the package larger, and each pin has to be connected to the integrated circuit's silicon. To save pins, it is common for ADCs to send their data one bit at a time over a serial interface to the computer, with each bit coming out when a clock signal changes state. This saves quite a few pins on the ADC package, and in many cases, does not make the overall design any more complex.

Commercial ADCs often have several inputs that feed the same converter, usually through an analog multiplexer. Different models of ADC may include sample and hold circuits, instrumentation amplifiers or differential inputs, where the quantity measured is the difference between two inputs.

Music recording
Analog-to-digital converters are integral to modern music reproduction technology and digital audio workstation-based sound recording. Music may be produced on computers using an analog recording and therefore analog-to-digital converters are needed to create the pulse-code modulation (PCM) data streams that go onto compact discs and digital music files. The current crop of analog-to-digital converters utilized in music can sample at rates up to 192 kilohertz. Many recording studios record in 24-bit 96 kHz pulse-code modulation (PCM) format and then downsample and dither the signal for Compact Disc Digital Audio production (44.1 kHz) or to 48 kHz for radio and television broadcast applications.

Digital signal processing
ADCs are required in digital signal processing systems that process, store, or transport virtually any analog signal in digital form. TV tuner cards, for example, use fast video analog-to-digital converters. Slow on-chip 8-, 10-, 12-, or 16-bit analog-to-digital converters are common in microcontrollers. Digital storage oscilloscopes need very fast analog-to-digital converters, also crucial for software-defined radio and their new applications.

Scientific instruments
Digital imaging systems commonly use analog-to-digital converters for digitizing pixels. Some radar systems use analog-to-digital converters to convert signal strength to digital values for subsequent signal processing. Many other in situ and remote sensing systems commonly use analogous technology.

Many sensors in scientific instruments produce an analog signal; temperature, pressure, pH, light intensity etc. All these signals can be amplified and fed to an ADC to produce a digital representation.

Displays
Flat-panel displays are inherently digital and need an ADC to process an analog signal such as composite or VGA.

Testing
Testing an analog-to-digital converter requires an analog input source and hardware to send control signals and capture digital data output. Some ADCs also require an accurate source of reference signal.

The key parameters to test an ADC are:
 * 1) DC offset error
 * 2) DC gain error
 * 3) signal-to-noise ratio (SNR)
 * 4) Total harmonic distortion (THD)
 * 5) Integral nonlinearity (INL)
 * 6) Differential nonlinearity (DNL)
 * 7) Spurious free dynamic range
 * 8) Power dissipation

title: Analog-to-digital converter


text:
Wikipedia talk:What Wikipedia is not

By-the-book approach against NOTBURO and IAR?
I've been thinking. If my way of enforcing rules is too "by the book", would this be against longstanding WP:NOTBURO and/or WP:IAR? What about following strictly WP:NFCC or WP:N, including WP:GNG, or whatever better example? George Ho (talk) 19:05, 20 June 2024 (UTC)

 * You have asked us to assume that your way of enforcing the rules is "too" by the book. Given that assumption, my answer to your first question is "yes."
 * With regard to your second question, IAR says to ignore rules when they prevent you from improving or maintaining Wikipedia. Can you suggest a situation in which, for example, it would improve or maintain Wikipedia to violate copyright laws and subject the Foundation to being sued (putting Wikipedia at financial risk)? - Butwhatdoiknow (talk) 15:22, 21 June 2024 (UTC)
 * Can you suggest a situation in which, for example, it would improve or maintain Wikipedia to violate copyright laws and subject the Foundation to being sued (putting Wikipedia at financial risk)? Hmm... (Assuming your question is rhetorical,) Good point. I shouldn't have mentioned NFCC broadly. What about "contextual significance" criterion? It's interpreted variously, especially in FFD discussions, yet WP:NFC is doing its best to clarify (the meaning and enforcement of) "contextual significance". —George Ho (talk) 16:00, 21 June 2024 (UTC)
 * I'm guessing that disputes over the contextual significance criterium are about whether proposed content will "significantly increase" or be "detrimental to" understanding. If the result of such a dispute is that copyrighted material is only marginally beneficial or, worse, detrimental then I don't see the "improving and maintaining Wikipedia" condition is present and IAR does not apply. - Butwhatdoiknow (talk) 23:39, 21 June 2024 (UTC)
 * be "detrimental to" understanding – Umm... I don't think "detrimental" means the content's presence would harm the project. Rather it refers to whether omitting, i.e. removing or deleting, the non-free content from an article or the whole project would harm readers' (contextual) understanding of a certain topic in question, i.e. article subject, like a person or a song. If omitting the NFC file or text doesn't harm what's already understood, then the said non-free content would automatically fail that criterion and fail to contextually signify the said topic. (BTW, I don't mean to make you feel bad, but "criterium" means bike race consisting of closed circuits. Criterion is a singular form of criteria; bacterium, bacteria.) George Ho (talk) 00:30, 22 June 2024 (UTC)
 * I submit that content that is detrimental to understanding an article does not improve or maintain that article. And, if it does not improve or maintain the article, it does not improve or maintain Wikipedia. (Thanks for the BTW. It's good to learn things.) - Butwhatdoiknow (talk) 02:09, 22 June 2024 (UTC)
 * There is no danger whatsoever that Wikipedia will violate copyright laws and subject the Foundation to being sued (putting Wikipedia at financial risk). This is because nearly everything we do falls under fair use. Our rules go well beyond what is legally required. What it would mean though is that someone could not appropriate all or part of the Wikipedia for commercial use. Hawkeye7   (discuss)  04:41, 22 June 2024 (UTC)

NOTNEWS
What's happened to the enforcement of WP:NOTNEWS? I look at a number of articles created in the wake of October 7 that pay no heed to this. The article is the Wikipedia version of a live blog of a news event. Is this not a main tenet of Wikipedia anymore? MaskedSinger (talk) 20:45, 26 June 2024 (UTC)

 * @MaskedSinger on top of that, several Philippine-related articles may run counter to WP:NOTNEWS, in particular 2013 Metro Manila Skyway bus accident and 2010 Balamban bus accident. JWilz12345 (Talk|Contrib's.) 03:06, 27 June 2024 (UTC)
 * Interesting. MaskedSinger (talk) 07:48, 27 June 2024 (UTC)
 * You may want to propose a change to NOTNEWS, so that it more clearly proscribes the types of articles that you are objecting to. As it stands, NOTNEWS has an overview and four bullets.
 * Overview: does not restrict what types of articles are forbidden, explicitly supports "stand-alone articles on significant current events"
 * Original reporting: not applicable here
 * News reports: the examples given are pretty limiting. Editors seeing "routine news coverage of announcements, events, sports, or celebrities" are not likely to count major news events as falling into that bucket. News event are "events", but the policy links to WP:ROUTINE, which makes it clear the events in question are things like "Wedding announcements, sports scores, crime logs", "sports matches, film premieres, press conferences", "Run-of-the-mill events—common, everyday, ordinary items that do not stand out", and "brief, often light and amusing (for example bear-in-a-tree or local-person-wins-award), stories". Deadly attacks or accidents would not appear to be included.
 * Who's who: not applicable here
 * Celebrity gossip and diary: not applicable here
 * I would be interested in expanding NOTNEWS, but we'd need a carefully written explanation of what new article types should be included. Firefangledfeathers (talk / contribs) 15:22, 28 June 2024 (UTC)
 * @Firefangledfeathers Sounds wonderful! How should we proceed? MaskedSinger (talk) 20:43, 29 June 2024 (UTC)
 * I don't have a bright idea. Maybe you could pull together a few articles you think should be proscribed by NOTNEWS and propose some language that would describe them narrowly? Firefangledfeathers (talk / contribs) 02:15, 30 June 2024 (UTC)
 * I'd say a lot of deadly attacks or accidents do fit into "routine" news coverage, as they get the usual brief spurt of coverage in the immediate aftermath and then disappear entirely, the same way an average film premiere or the like would. Obviously the amount of coverage shifts, generally with how exceptional the incident is or how many casualties, so there's no hard line, but I think you have to do more than just robotically look at a list of sources, say "GNG pass" and move on. The Gaza war is the latest example, but there's plenty more, such as the absolute train wreck that is the exhaustive day-by-day coverage of Covid. I don't think NOTNEWS is really what needs revision, though, beyond pointing people to WP:NEVENTS and specifically WP:PERSISTENCE, which have much more useful and detailed information on why news stories alone are not inherently notable. Der Wohltemperierte Fuchs  talk 11:25, 30 June 2024 (UTC)
 * NOTNEWS does link via a "See also" link to NEVENTS, but a more emphatic point might help. Firefangledfeathers (talk / contribs) 04:54, 1 July 2024 (UTC)
 * @David Fuchs@Firefangledfeathers@MaskedSinger one more possible example: 2020 Masbate earthquake. Is the article a breach of the policies y'all mentioned? JWilz12345 (Talk|Contrib's.) 07:58, 14 July 2024 (UTC)

WP:NOTFILESTORAGE and WP:Freedom of panorama 2nd
Second discussion; first discussion was at Wikipedia talk:What Wikipedia is not/Archive 59.

Is the "collection" of 12 Villa Savoye images" existing on English Wikipedia – at Category:Villa Savoye — still acceptable and do not breach WP:NOTFILESTORAGE? Only three of the images are in use; the rest unused. IMO, having more than 5 or 10 is already making enwiki comparable to a file storage service/site, which is against the said policy (WP:NOT is higher than WP:Freedom of panorama which is essentially just a guidance page that is not yet an established policy). Ping again the users that I pinged before in the prior discussion: . JWilz12345 (Talk|Contrib's.) 03:45, 5 July 2024 (UTC)

 * If they are decent-quality, freely-licensed photos of a thing with encyclopedic relevance, why should we care? How many kilobytes, or megabytes, of squabbling over whether images are "good enough" does it take before the arguments consume more space than the images in question? More importantly, how many hours of contributor time have to be spent arguing about this before it outstrips any conceivable cost of hosting the images? I would argue this point has already been reached, but I suppose it depends on how valuable editor-hours are. At any rate: it seems clear to me that having decent images is good, in general, for the purposes of writing an encyclopedia. For example, File:VillaSavoye3.jpg is currently not in use. But it is the only photo of this staircase that we have here (?) and deleting it would make it permanently impossible for us to use it for anything. Say someone is writing an article about trends in interior architecture, or about different types of spiral staircases. Should they be forbidden to use this image? What difference does it make? jp×g🗯 03:56, 5 July 2024 (UTC)
 * @JPxG if that is the case, then WP:NOTFILESTORAGE should be rewritten again, and WP:Freedom of panorama should be made into a policy needing consensus. As the boilerplate notice on the top of the latter page stands, it is not yet a policy. JWilz12345 (Talk|Contrib's.) 04:01, 5 July 2024 (UTC)
 * WP:NOTFILESTORAGE rather clearly says "Please upload only files that are used (or could be used) in encyclopedia articles or project pages" -- these files could be used in encyclopedia articles or project pages. I do not see any contradiction. jp×g🗯 04:03, 5 July 2024 (UTC)
 * Same here, especially given how recurrent various "which picture(s) should we use?" disputations get. "Not used right this instant" does not equate to "unusable".  — SMcCandlish ☏ ¢ 😼  05:58, 5 July 2024 (UTC)

Although we do have Don't worry about performance, it might be true years ago, but may not be in recent times, as seen in the case of proposed Wikidata split and alleged watchlist time-out on Commons, though I haven't seen any discussion (so far) relating to low server performance effect on English Wikipedia itself. JWilz12345 (Talk|Contrib's.) 03:56, 5 July 2024 (UTC)
 * If only we had hundreds of millions of dollars of donations coming in that could be spent on doing basic stuff like paying for hosting costs! jp×g🗯 03:57, 5 July 2024 (UTC)
 * @JWilz12345, would you have fewer concerns if a WMF employee directly told you that you genuinely do not need to worry at all about twelve possibly unnecessary photos, or even about twelve thousand of them?  WhatamIdoing (talk) 04:49, 5 July 2024 (UTC)
 * @WhatamIdoing in technical aspect, I may not need to worry. But on the possible conflict between WP:NOTFILESTORAGE and WP:Freedom of panorama, that needs to be addressed in a concrete manner, not just confined to the wording that is open to multiple interpretations ("or could be used"). I will only accept the situation if WP:Freedom of panorama is made as a policy page, not a guidance page that states that it reflects the varying degrees of consensus and vetting (as stated on the top of the page). JWilz12345 (Talk|Contrib's.) 05:28, 5 July 2024 (UTC)
 * Hmm. Since we run on a WP:Consensus basis, I don't think that any single editor actually has the ability to reject the situation.  If it upsets you enough, I suppose you could quit editing, but you can't force the community to do things your way.  The community can choose to leave the situation exactly like it is, even if you claim you "will only accept the situation" if it's done your way.  Sometimes the community wants its policies to be open to multiple interpretations.  I suspect that this is one of those times. WhatamIdoing (talk) 05:34, 5 July 2024 (UTC)
 * It's also too often the case than one particular editor gets it into their head that there's some kind of "policy conflict", but the community itself finds no such conflict, ergo there actually is not one. (That is, if the community's interpretation and implementation of policy doesn't result in a real problem, then the policy is not in fact broken, even if some particular individual can willfully misinterpret it in a way that for that specific person produces some kind of cognitive dissonance.) Ultimately it's simply not a community problem, but a personal matter. In my tenure, I've done a whole lot of policy-wording cleanup, but not every attempt to do so is successful, because sometimes the wording problem I think I see isn't one that others see. Such cases simply have to be let go, not clung to and recycled endlessly.  — SMcCandlish ☏ ¢ 😼  05:58, 5 July 2024 (UTC)
 * In this case, I don't think anyone is engaging in willful misinterpretation. I think it could be resolved by changing it from its current form:
 * File storage areas. Please upload only files that are used (or could be used) in encyclopedia articles or project pages; anything else (e.g., personal photos) will be deleted. Ideally, freely licensed files should be uploaded to Wikimedia Commons, where they can be linked from Wikipedia.
 * to something like:
 * File storage areas. Please upload only files that are used (or could be used) in encyclopedia articles or project pages; anything else (e.g., personal photos) will be deleted. Ideally, freely licensed files should be uploaded to Wikimedia Commons, where they can be linked from Wikipedia. So long as each individual file could be used in an article (even if it is extremely unlikely that it will ever be used in an article), editors may upload an unlimited number of files."
 * Alternatively, we could specify a limit, e.g., "up to 100,000 files without seeking permission in advance, and an unlimited number with permission". (There are about 920,000 local files at the moment, so 100K would add 10% 'locally', and less than 0.01% globally.)
 * But as there is only one editor who worries that five or ten files might be too many, it would probably be WP:CREEPY to add such a sentence, even though it's true. WhatamIdoing (talk) 15:43, 5 July 2024 (UTC)

2028 US presidential election is an "appropriate topic", but we keep deleting it
The WP:CRYSTAL section states that "Examples of appropriate topics include the 2028 U.S. presidential election"; however, this is currently a red link and even a draft of this article was rejected as recently as April 2024 because it's WP:TOOSOON, which links to WP:CRYSTAL. Which one is wrong, the policy or the implementation? Jpatokal (talk) 03:14, 9 July 2024 (UTC)

 * The year in CRYSTAL is determined using a formula, I wonder if it doesn't always generate the correct date. 2028 would be a valid topic in 2024, but by convention only after the 2024 election. However the formula jumped from 2024 to 2028 at the beginning of 2024. -- LCU A ctively D isinterested  «@» °∆t° 10:17, 9 July 2024 (UTC)

Discussion on application of NOTCATALOG criteria
there is currently a discussion on the application of WP:NOTCATALOG at Talk:Survival_Records around the exhaustive listing of album releases by a record label. Graywalls (talk) 21:23, 10 July 2024 (UTC)

With all due respect regarding Wikipedia policy
Ever since the Wikipedia Group "The Guerilla Skeptics" became a known mainstream subject it shows that Wikipedia does not have a neutral stance and this group has gone out of its way to make changes to ridicule individuals and subjects. The problem is not the evidence, but the tone of their message towards the person or subject matter which is unbecoming of this website.

if we're going to follow "wikipedia is not" then that group needs to put down their fists and try to be neutral, and if not they should have their privileges be revoked. My apologies if this is not the right talk page, but I do not know where to go to address this issue. 2606:A000:9FC0:57:6937:10A7:B067:6E7B (talk) 17:20, 18 July 2024 (UTC)

 * I hadn't heard of this group. Ridicule would have no place on WP, but would need to be addressed at the administrators' noticeboard (WP:AN/I). It's easier to address the neutrality of articles at their individual talk pages. But if it became systemic, it would help to provide multiple examples of articles, as evidence of a pattern. Shooterwalker (talk) 20:27, 18 July 2024 (UTC)
 * Mainstream? Because someone complains about the way UFO-related articles are handled here? Not to be taken serious. The Banner  talk 23:17, 18 July 2024 (UTC)

title: Wikipedia talk:What Wikipedia is not


text:
John Thaw

John Edward Thaw, (3 January 1942 – 21 February 2002) was an English actor in television, stage and cinema, best known for his starring role in the television series Inspector Morse as Detective Chief Inspector Endeavour Morse and The Sweeney as Detective Inspector Jack Regan.

Early life
Born in Gorton, Manchester, to John Edward ("Jack") Thaw, a tool-setter at the Fairey Aviation Company aircraft factory, later a long-distance lorry driver, and Dorothy (née Ablott). Dorothy left when he was seven years old. He and his younger brother, Raymond Stuart (Ray) had a difficult childhood due to their father's long absences. Thaw grew up in Gorton and Burnage, attending the Ducie Technical High School for Boys, gaining just one O level. He entered the Royal Academy of Dramatic Art (RADA) at the age of 16 (two years underage), and won the Academy's Vanburgh Award. Ray emigrated to Australia in the mid-1960s.

Career
In 1960, Thaw made his stage début in A Shred of Evidence at the Liverpool Playhouse and was awarded a contract with the theatre. His first film role was a bit part in The Loneliness of the Long Distance Runner (1962) starring Tom Courtenay and he also acted on-stage opposite Sir Laurence Olivier in Semi-Detached (1962). In 1963/64, he appeared in several episodes of the BBC series Z-Cars as a detective constable. Between 1964 and 1966, he starred in two series of the ABC Weekend Television/ITV production Redcap, playing the hard-nosed military policeman Sergeant John Mann. He was also a guest star in an early episode of The Avengers. In 1967 he appeared in Bat Out of Hell and in the Granada TV/ITV series, Inheritance, alongside James Bolam and Michael Goodliffe; TV plays including The Talking Head, and episodes of series such as Budgie, where he played against type as an effeminate failed playwright with a full beard and a Welsh accent.

Thaw was only 32 when he was cast in The Sweeney (1975–1978), although many viewers thought he was older. His role as the hard-bitten, tough-talking Flying Squad detective Jack Regan established him as a major star in the United Kingdom. He followed this dramatic series with the comedy series Home to Roost (1985–1990), which co-starred Reece Dinsdale, about a divorced father whose teenage son moves back in with him after choosing as a child to live with his mother. The show ran for four series.

It was his role as Detective Chief Inspector Endeavour Morse in Inspector Morse (1987–93, with later specials until 2000), which cemented his fame. Alongside his put-upon Detective Sergeant Robert "Robbie" Lewis (Kevin Whately), Morse became a high-profile character—"a cognitive curmudgeon with his love of classical music, his drinking, his classic Jaguar and spates of melancholy". According to The Guardian, "Thaw was the definitive Morse, grumpy, crossword-fixated, drunk, slightly anti-feminist, and pedantic about grammar." Inspector Morse became one of the UK's most loved TV series; at its peak in the mid-'90s, ratings hit 18 million people, about one third of the British population. He won "Most Popular Actor" at the 1999 National Television Awards and won two BAFTA awards for his role as Morse.

He subsequently played liberal working-class Lancastrian barrister James Kavanagh in Kavanagh QC (1995–99, and a special in 2001). Thaw also appeared in two sitcoms—Thick as Thieves (London Weekend/ITV, 1974) with Bob Hoskins and Home to Roost (Yorkshire/ITV, 1985–90). Thaw is mainly known in America for the Morse series, as well as the BBC series A Year in Provence (1993) with Lindsay Duncan.

He appeared in a number of films for director Richard Attenborough, including Cry Freedom, where he portrayed the conservative South African justice minister Jimmy Kruger (for which he received a BAFTA nomination for Best Supporting Actor), and Chaplin alongside Robert Downey Jr.

Thaw also appeared in the TV adaptation of the Michelle Magorian book Goodnight Mister Tom (Carlton Television/ITV). It won "Most Popular Drama" at the National Television Awards, 1999.

During the 1970s and 1980s, Thaw appeared in productions with the Royal Shakespeare Company and National Theatre.

He was the subject of This Is Your Life in 1981 when he was surprised by Eamonn Andrews in the foyer of the National Theatre in London.

Personal life
In 1964, Thaw married Sally Alexander, a feminist activist and stage manager, now professor of history at Goldsmiths, University of London. They divorced four years later. He met actress Sheila Hancock in 1969 on the set of So What About Love? She was married to fellow actor Alexander "Alec" Ross. They became friends, but she refused to have an affair as she did not want to disrupt her daughter's life. Following the death of her husband (from oesophageal cancer) in 1971, Thaw and Hancock married on 24 December 1973 in Cirencester,. They remained together until his death in 2002 (also from oesophageal cancer).

He had three daughters (all actresses): Abigail from his first marriage to Sally Alexander, Joanna from his second marriage to Sheila Hancock, and he also adopted Sheila Hancock's daughter Melanie Jane, from Hancock's first marriage to Alec Ross. His granddaughter Molly Whitmey made a cameo in the Endeavour episode Oracle (series 7, episode 1, broadcast 1 February 2020) as the younger version of her grandmother Sally Alexander.

Thaw was a committed socialist and a lifelong supporter of the Labour Party. He was appointed a Commander of the Most Excellent Order of the British Empire (CBE) in March 1993 by Queen Elizabeth II. In September 2006, Thaw was voted by the general public as number 3, after David Jason and Morecambe and Wise, in a poll of TV's 50 Greatest Stars for the past 50 years.

Illness and death
A heavy drinker until going teetotal in 1995, and a heavy smoker from the age of 12, Thaw was diagnosed with cancer of the oesophagus in June 2001. He underwent chemotherapy in hope of overcoming the illness, and at first had appeared to respond well to the treatment. However, just before Christmas 2001 he was informed that the cancer had spread and the prognosis was terminal.

He died on 21 February 2002, seven weeks after his 60th birthday, the day after he signed a new contract with ITV, and the day before his wife's birthday. At the time of his death he was living at his country home, near the villages of Luckington and Sherston in Wiltshire, and was cremated in Westerleigh, near Yate in South Gloucestershire, in a private service. A memorial service was held on 4 September 2002 at St Martin-in-the-Fields church in Trafalgar Square, attended by 800 people including Charles, Prince of Wales, Richard Attenborough, Tom Courtenay and Cherie Blair.

Honours and awards
A memorial bench is dedicated to Thaw within the grounds of St Paul's Covent Garden.

title: John Thaw


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Space technology

Space technology is technology for use in outer space. Space technology includes space vehicles such as spacecraft, satellites, space stations and orbital launch vehicles; deep-space communication; in-space propulsion; and a wide variety of other technologies including support infrastructure equipment, and procedures.

Many common everyday services for terrestrial use such as weather forecasting, remote sensing, satellite navigation systems, satellite television, and some long-distance communications systems critically rely on space infrastructure. Of the sciences, astronomy and Earth science benefit from space technology. New technologies originating with or accelerated by space-related endeavors are often subsequently exploited in other economic activities.

History of space technology
The first country on Earth to put any technology into space was the Soviet Union, formerly known as the "Union of Soviet Socialist Republics" (USSR). The USSR sent the Sputnik 1 satellite on October 4, 1957. It weighed about 83 kg, and is believed to have orbited around the globe. Analysis of the radio signals was used to gather information about the electron density of the ionosphere, while temperature and pressure data was encoded in the duration of radio beeps.

The first successful human spaceflight was Vostok 1, carrying 27-year-old Soviet cosmonaut Yuri Gagarin in April 1961. The entire mission was controlled by either automatic systems or by ground control. This was because medical staff and spacecraft engineers were unsure how a human might react to weightlessness, and therefore it was decided to lock the pilot's manual controls.

The first probe to impact the surface of the Moon was the Soviet probe Luna 2, which made a hard landing on September 14, 1959. The far side of the Moon was first photographed on October 7, 1959, by the Soviet probe Luna 3.s On December 24, 1968, the crew of Apollo 8, Frank Borman, James Lovell and William Anders, became the first human beings to enter lunar orbit and see the far side of the Moon in person. Humans first landed on the Moon on July 20, 1969. The first human to walk on the lunar surface was Neil Armstrong, commander of Apollo 11. The first space probe to land on moon South Pole of India.Chandrayaan-3 was launched aboard an LVM3-M4 rocket on 14 July 2023, at 09:05 UTC from Satish Dhawan Space Centre Second Launch Pad in Sriharikota, Andhra Pradesh, India, entering an Earth parking orbit with a perigee of 170 km (106 mi) and an apogee of 36,500 km (22,680 mi).

Apollo 11 was followed by Apollo 12, 14, 15, 16, and 17. Apollo 13 had a failure of the Apollo service module, but passed the far side of the Moon at an altitude of 254 km above the lunar surface, and 400,171 km (248,655 mi) from Earth, marking the record for the farthest humans traveled from Earth in 1970.

The first robotic lunar rover to land on the Moon was the Soviet vessel Lunokhod 1 on November 17, 1970, as part of the Lunokhod program. To date, the last human to stand on the Moon was Eugene Cernan, who, as part of the Apollo 17 mission, walked on the Moon in December 1972. Apollo 17 was followed by several uncrewed interplanetary missions operated by NASA.

One of the notable interplanetary missions is Voyager 1, the first artificial object to leave the Solar System into interstellar space on August 25, 2012. It is also the most distant artificial object from Earth. The probe passed the heliopause at 121 AU to enter interstellar space. Voyager 1 is currently at a distance of 145.11 AU (21.708 billion kilometers; 13.489 billion miles) from Earth as of January 1, 2019.

title: Space technology