Chart recorder
Encyclopedia
They are built in three primary formats. Strip chart recorders have a long strip of paper that is ejected out the side 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. Dickson is the largest US manufacturer of circular chart recorders.
Chart recorders pre-dated electronic data logger
Data logger
A data logger is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they are based on a digital processor...
s which have replaced them in many applications.
Origins
A patent for a 'Pressure Indicator and Recorder' was issued to William Henry BristolWilliam Henry Bristol
William Henry Bristol, inventive genius, pioneering manufacturer, educator, and environmentalist, was born in Waterbury, Connecticut on July 5, 1859, the eldest of six children....
, on September 18, 1888. Bristol went on to form the Bristol Manufacturing Company in 1889. The Bristol Company was acquired by Emerson Electric Company
Emerson Electric Company
Emerson Electric Company is a major multinational corporation headquartered in Ferguson, Missouri, United States. This Fortune 500 company manufactures products and provides engineering services for a wide range of industrial, commercial, and consumer markets.Emerson is one of the largest...
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
Environmental monitoring describes the processes and activities that need to take place to characterise and monitor the quality of the environment...
was designed by American inventor J.C. Stevens while working for Leupold & Stevens
Leupold & Stevens
Leupold & Stevens, Inc. is a manufacturer of telescopic sights, red dot sights, spotting scopes, and binoculars located in Beaverton, Oregon, United States...
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 motorSynchronous motor
A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the power supply frequency and resulting rotating magnetic field which drives it....
which turns at a constant speed related to the power frequency
Utility frequency
The utility frequency, line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end-user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...
; 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
Universal Testing Machine
A universal testing machine, also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile stress and compressive strength of materials...
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.
Marking mechanisms
Many mechanisms have been adopted for marking paper. In the telegraphic siphon recorderSiphon recorder
The syphon or siphon recorder is an item of telecommunications equipment invented by William Thomson, 1st Baron Kelvin in 1858. It was used to automatically record the receipt of a telegraph message, as a wiggling ink line on a roll of paper tape...
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, 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
Galvanometer
A galvanometer is a type of ammeter: an instrument for detecting and measuring electric current. It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field. .Galvanometers were...
s, directed at light-sensitive paper.
The earliest instruments derived power to move the pen directly from the sensed process signal, which limited their senstivity and speed of response. Instruments with pneumatic, mechanical, or electromechanical amplifiers decoupled pen movement from process measurement, greatly increasing the senstivity 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.
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 servomechanismServomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
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
Potentiometer
A potentiometer , informally, a pot, is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used , it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on...
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 amplifer, 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 systemEmbedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
with an analog to digital converter, a microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
, 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 measurments to remote points.
See also
- BarographBarographA barograph is a recording aneroid barometer. It produces a paper or foil chart called a barogram that records the barometric pressure over time....
- Electrocardiograph
- PolygraphPolygraphA polygraph measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions...
- Seismograph
- Thermo-hygrographThermo-hygrographA Thermo-Hygrograph is a chart recorder that measures and records both temperature and humidity . Similar devices that record only one parameter are a thermograph for temperature and hygrograph for humidity....