Recording, Automatic

the automatic processing and recording for preservation of quantities that characterize technological processes, the operation of machines, or investigated phenomena. The information being recorded is fixed on a physical medium, which may be, for example, paper, a photographic material, or a ferromagnetic film. Various marking devices are used, depending on the recording medium. Examples of marking devices are pencils, pens, styli, light beams, electron beams, magnetic recording heads, and metallic electrodes. The result of the recording process is usually visible and permanent; ink, for example, is often used. Less common are recording methods in which the recorded results are not visible and must be processed to be read, as in magnetic and some electrical recording processes. Also less common are methods where the results gradually disappear with time, as in processes involving luminescence. All known methods of automatic recording can be subdivided into three classes: recording by applying a layer of a material, recording by removing a layer of a material, and recording by deforming or otherwise changing the state of the recording-medium material (seeRECORDING AND REPRODUCTION OF INFORMATION).

Automatic recording is performed by automatic recording, or self-recording, instruments. Such an instrument consists of the recording medium, the marking device, and a system for moving the medium and marking device. There exist multichannel recorders that use several marking devices and drive mechanisms. Drive units often used include clockwork mechanisms, automatic controllers, servomechanisms, relays, and electric motors (for example, pulse-controlled and synchronous motors). Such units, which are controlled by outside influences, are called actuating transducers. In measuring systems, the recording instruments may be connected with various sensors, measuring instruments, command devices, computing devices, telemetry equipment, remote-control apparatus, and control computers.

The first automatic recorders were based on common monitoring instruments; writing devices that made marks on paper—pencils or pens—were attached to the instruments. For this reason, the term “autographic” has been sometimes applied to such recording instruments. Such recorders are used to record, for example, mechanical shifts and fluctuations, the pressure and flow rate of liquids and gases, temperature, humidity, voltage, and current. The division of recording instruments according to the type of quantity recorded is the basic classification for users who are interested primarily in the purpose of the device. This principle of division is reflected in the common names of recording devices, for example, the vibro-graph, barograph, thermograph, hygrograph, and chronograph. Other classifications used include those based on the structure and operating principle of the recorder, the type of information, and the methods used to process the information. According to the type of energy that is transformed, recording instruments are classified as mechanical, optical, electrical, or magnetic recorders. When recording instruments are classified according to area of use, such types as industrial, laboratory, accounting, navigation, and meteorological recorders are distinguished.

The recorders that automatically record the occurrence of a particular event are the simplest in structure. Such an event may be, for example, the starting or stopping of a machine or the occurrence of an emergency situation. The chronograph is one such instrument. It has actuating transducers of time (a clockwork mechanism or synchronous motor that moves the medium) and the event (for example, a relay element that deflects the pen when a signal arrives) (Figure 1,a). Such instruments are encountered comparatively rarely. The largest group of self-recording instruments consists of devices that record the change in different parameters over time (Figure 1,b) or the change in one parameter as a function of another parameter but not over time (Figure 1,c). The record is made in the form of a continuous curve on flat media by means of point marking devices that have two degrees of freedom of movement relative to the recording medium. Figure 1,d shows the structure of instruments for the simultaneous recording of changes in several parameters over time in the form of different-colored lines or lines labeled with different symbols.

Automatic recording instruments can be subdivided into four groups according to the methods of processing the information: direct-acting instruments, servo systems, scanning systems, and digital systems. The first group includes recording voltmeters, recording ammeters, bifilar oscillographs, cathode-ray oscillographs, and various mechanical devices. The servo systems are used in self-balancing potentiometers, balanced bridges, and electroacoustic recorders. Examples of instruments using scanning systems includes stroboscopic indicating and recording instruments, various graph-plotting devices, and photographic recorders with pulsed value markers (pulse recorders). Digital systems include instruments in which data are recorded in the form of complex-shaped marks or certain combinations of points; printers, some photographic recorders, and digital synthesizers also fall into this group.

The speed of recording is defined as the highest frequency of oscillation that can be recorded for a given recording accuracy. For example, for cathode-ray oscillographs it is about 10 megahertz, for light beam (bifilar) oscillographs about 10 kilo-hertz, for electronic pulsed and digital instruments about 10 hertz, for bridges and potentiometers about 1 hertz, and for electromechanical direct-acting devices about 1 hertz. The accuracy of data recording and reproduction is characterized by the permissible error, which is given in percent of the scale span. Thus, the accuracy is about 10 percent for oscillographs, about 1 percent for electromechanical devices, about 0.1 percent for bridges and potentiometers, and about 0.1 percent for pulsed and digital instruments.