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A chart recorder is an
electromechanical Electromechanics combine processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focus on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each ...
device that records an electrical or mechanical input trend onto a piece of paper (the chart). Chart recorders may record several inputs using different color pens and may record onto strip charts or circular charts. Chart recorders may be entirely mechanical with clockwork mechanisms, electro-mechanical with an electrical clockwork mechanism for driving the chart (with mechanical or pressure inputs), or entirely electronic with no mechanical components at all (a virtual chart recorder). Chart recorders are built in three primary formats. Strip chart recorders have a long strip of paper that is ejected out of the recorder. Circular chart recorders have a rotating disc of paper that must be replaced more often, but are more compact and amenable to being enclosed behind glass. Roll chart recorders are similar to strip chart recorders except that the recorded data is stored on a round roll, and the unit is usually fully enclosed. Chart recorders pre-dated electronic
data logger A data logger (also datalogger or data recorder) is an electronic device that records data over time or about location either with a built-in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they a ...
s which have replaced them in many applications.


Origins

Charles Babbage Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...
incorporated a chart recorder into the
dynamometer car A dynamometer car is a railroad maintenance of way car used for measuring various aspects of a locomotive's performance. Measurements include tractive effort (pulling force), power, top speed, etc. History The first dynamometer car was probably ...
that he built in 1838 or 1839. Here is how he described it: "A roll of paper a thousand feet in length was slowly unwinding itself upon the long table ... About a dozen pens connected with a bridge crossing the middle of the table were each marking its own independent curve gradually or by jumps ..." The paper advance was geared to the wheels of the railroad carriage, while pens recorded time, the drawbar pull of the locomotive, and numerous other variables. Part of
Samuel Morse Samuel Finley Breese Morse (April 27, 1791 – April 2, 1872) was an American inventor and painter. After establishing his reputation as a portrait painter, Morse, in his middle age, contributed to the invention of a Electrical telegraph#Morse ...
's telegraph system was an automatic recorder of the dots and dashes of the code, inscribed on a paper tape by a pen moved by an electromagnet, with a clockwork mechanism advancing the paper. In 1848-1850 a system of such registers was used by
John Locke John Locke (; 29 August 1632 (Old Style and New Style dates, O.S.) – 28 October 1704 (Old Style and New Style dates, O.S.)) was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thi ...
to improve the precision of astronomical observations of stars, providing timing precision much greater than previous methods. This method was adopted by astronomers in other countries as well.
William Thomson, 1st Baron Kelvin William Thomson, 1st Baron Kelvin (26 June 182417 December 1907), was a British mathematician, Mathematical physics, mathematical physicist and engineer. Born in Belfast, he was the Professor of Natural Philosophy (Glasgow), professor of Natur ...
's syphon recorder of 1858 was a sensitive instrument that provided a permanent record of telegraph signals through long underwater telegraph cables. These recorders came to be referred to as
pen register A pen register, or dialed number recorder (DNR), is a device that records all numbers called from a particular telephone line. The term has come to include any device or program that performs similar functions to an original pen register, includin ...
s, although this term later became part of law enforcement jargon referring to the use of such a register to record dialed telephone numbers. A patent for a 'Pressure Indicator and Recorder' was issued to William Henry Bristol, on September 18, 1888. Bristol went on to form the Bristol Manufacturing Company in 1889. The Bristol Company was acquired by Emerson Electric Company in March 2006, and continues to manufacture a number of different electro-mechanical chart recorders, as well as other instrumentation, measurement, and control products. The first chart recorder for
environmental monitoring Environmental monitoring is the processes and activities that are done to characterize and describe the state of the environment. It is used in the preparation of environmental impact assessments, and in many circumstances in which human activit ...
was designed by American inventor J.C. Stevens while working for Leupold & Stevens in Portland, Oregon and was issued a patent for this design in 1915. Chart recorders are still used in applications where instant visual feedback is required or where users do not have the need, opportunity or technical ability to download and view data on a computer or where no electrical power is available (such as in hazardous zones on an oil rig or in remote ecological studies). However, dataloggers' decreasing cost and power requirements allow them to increasingly replace chart recorders, even in situations where battery power is the only option.


Chart drive

The paper chart is driven past the pen at a steady rate by a clockwork or electrical drive mechanism. One common method is to use a miniature
synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integer number of AC cycles. Sync ...
which turns at a constant speed related to the power frequency; a gear-train is used to propel the paper. Industrial strip-chart recorders may have two-speed gear trains that allow a higher speed to be used for initial adjustments of a process or to follow process upsets. Medical and scientific recorders allow a wide range of accurately-controlled speeds to be set. An "X-Y" recorder drives the chart depending on the value of another process signal. For example, a
universal testing machine A universal testing machine (UTM), also known as a universal tester, universal tensile machine, materials testing machine, materials test frame, is used to test the tensile strength (pulling) and compressive strength (pushing), flexural stren ...
may plot the tension force on a specimen against its length. Depending on the particular recorder, either the paper chart is moved or else the pen carriage has two axes of motion. Examples of an x-y recorder date back to the 18th century in the form of the steam indicator diagrams used to record pressure and volume in steam engines.


Marking mechanisms

Many mechanisms have been adopted for marking paper. In the telegraphic
siphon recorder The syphon or siphon recorder is an obsolete electromechanical device used as a receiver for submarine telegraph cables invented by William Thomson, 1st Baron Kelvin in 1867. It automatically records an incoming telegraph message as a wiggling in ...
of 1858 a fine capillary tube is connected to an ink reservoir and is deflected by the process signal. In modern strip chart recorders, a disposable cartridge combining both a fiber-tipped pen and ink reservoir has been used. Other types of recorder use a heated stylus and thermally sensitive paper, an impact printer using a ribbon and an electrically operated hammer, an electric signal acting through a stylus onto electro-sensitive paper, or an electric spark that makes a visible spot on aluminized paper. One form of sensitive and high-speed recorder used beams of ultraviolet light reflected off mirror
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. Galvanomet ...
s, directed at light-sensitive paper. The earliest instruments derived power to move the pen directly from the sensed process signal, which limited their sensitivity and speed of response. Friction between the marking device and paper would reduce the accuracy of the measurements. Instruments with pneumatic, mechanical, or electromechanical amplifiers decoupled pen movement from process measurement, greatly increasing the sensitivity of the instrument and the flexibility of the recorder. Directly-driven pens often moved in the arc of a circle, making the scale difficult to read; pre-printed charts have curvilinear scales printed on them that compensated for the path of the marking pen.W. Bolton ''Industrial Control And Instrumentation ''Universities Press, 1991 , pages 138-144


Galvanometer instruments

Many types of chart recorders use a
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. Galvanomet ...
to drive the marking device. A light coil of wire suspended in the magnetic field of a permanent magnet deflects in proportion to the current through it; instead of the pointer and scale of a direct-reading meter, the recorder deflects a pen or other marking device. The writing mechanism may be a heated needle writing on heat-sensitive paper or a simple hollow ink-fed pen. If the pen is continuously pressed against the paper, the galvanometer must be strong enough to move the pen against the friction of the paper. To lessen the strain on the galvanometer the pen might instead only intermittently be pressed against the writing medium, to make an impression, and then move while pressure is released. Where greater sensitivity and speed of response is required a
mirror galvanometer A mirror galvanometer is an ammeter that indicates it has sensed an electric Current (electricity), current by deflecting a light beam with a mirror. The beam of light projected on a scale acts as a long massless pointer. In 1826, Johann Chri ...
, might be used instead, to deflected a beam of light which can be recorded photographically.


Light beam oscillograph

Another type of paper chart recorder was the ''light beam oscillograph''. It had a bandwidth of ~5 kHz full scale (approximately 100 times higher than the typical pen recorders of the day). The original models used a small mirror attached to a
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. Galvanomet ...
to aim a high-intensity beam of light at photosensitive paper. The combination of the mirror's tiny mass combined with a chart drive that could move the paper up to per second provided high bandwidth and impressive time axis resolution. Later models replaced the mirror with a stationary fiber-optic cathode ray tube that was in direct contact with the paper. These recorders had several flaws. The photo-sensitive paper was very expensive, and would quickly fade when exposed to ambient light. High chart speeds meant that test durations were extremely short. These instruments were intended to capture short-duration events such as
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
rocket launches in the 1960s and a broad range of ballistic events.


Potentiometric (servo) instruments

Analog chart recorders using a galvanometer movement to directly drive the pen have limited sensitivity. In a potentiometric type of recorder, the direct drive of the marking pen is replaced with a
servomechanism In mechanical and control engineering, a servomechanism (also called servo system, or simply servo) is a control system for the position and its time derivatives, such as velocity, of a mechanical system. It often includes a servomotor, and ...
where energy to move the pen is supplied by an amplifier. The motor-operated pen is arranged to move the sliding contact of a
potentiometer A potentiometer is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrum ...
to feed back the pen position to an error amplifier. The amplifier drives the motor in such a direct as to reduce the error between desired and actual pen position to zero. With a suitable signal processing amplifier, such instruments can record a wide range of process signals. However, the inertia of the servo system limits the speed of response, making these instruments most useful for signals changing over the span of a second or more.


Digital chart recorders

A modern chart recorder is an embedded computer system with an
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 (signal processing), digi ...
, a
microcontroller A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
, and a hard-copy printing device; such instruments allow great flexibility in signal processing, variable chart speed on process upsets, and can also communicate their measurements to remote points. One of the first digital units was designed by William (Bill) C. McElroy Jr. working for Dohrman Instrument Company in
Santa Clara, California Santa Clara ( ; Spanish language, Spanish for "Clare of Assisi, Saint Clare") is a city in Santa Clara County, California. The city's population was 127,647 at the 2020 United States census, 2020 census, making it the List of cities and towns i ...
. Up until this unit, most chart recorders were rack mounted and had one speed and one sensitivity range. McElroy's design was an instant loading paper roll 'table-top' unit using an Integrated Chopper Circuit for signal conversion. The unit had plug in circuit boards, plug in single or multi-range modules and plug in single or multi-speed modules. The recorder's sensitivity was 1 microvolt to 100 volts full-scale, which at the time was an industry first. McElroy also aided in the design and build of the Gas Chromatograph used for analysing dirt and rock samples from the 1969
Apollo 11 Apollo 11 was a spaceflight conducted from July 16 to 24, 1969, by the United States and launched by NASA. It marked the first time that humans Moon landing, landed on the Moon. Commander Neil Armstrong and Lunar Module pilot Buzz Aldrin l ...
Moon landing. William (Bill) C. McElroy jr engineering technician


See also

*
Barograph A barograph is a barometer that records the barometric pressure over time in graphical form. This instrument is also used to make a continuous recording of atmospheric pressure. The pressure-sensitive element, a partially evacuated metal cylinde ...
* Electrocardiograph *
Plotter A plotter is a machine that produces vector graphics drawings. Plotters draw lines on paper using a pen, or in some applications, use a knife to cut a material like Polyvinyl chloride, vinyl or leather. In the latter case, they are sometimes k ...
(operates in two dimensions) *
Polygraph A polygraph, often incorrectly referred to as a lie detector test, is a pseudoscientific device or procedure that measures and records several physiological indicators such as blood pressure, pulse, respiration, and skin conductivity while a ...
*
Seismograph A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The out ...
* Thermo-hygrograph


References

{{Commons Recording devices