CLASSIFICATION OF S I G N V.

AND

BRIEF

CHARACTERISTIC

DISPLAYS S.

Govorov

UDC 681.2.085(012)

A sign display is the most convenient form for representing the quantitative indexes of the tested parameters of various devices, mechanisms, and controlled members as a whole. In reading the data off the screens of such displays, operators produce a m i n i m u m number of errors (reduced by a factor of 22-71) [1, 2, 3]. The speed and precision in reading indications off the screens of sign displays is higher than that of any other type of displays [4, 8]. Instruments with sign displays are b e c o m i n g more and more widely used. At present there does not exist an a c c e p t a b l e scheme for classifying these instruments. Thus, in [6-8] a l l the displays are divided into three groups, one of which contains sign displays. In [9] the displays are classified according to their reproduced signals. In [10] the sign displays are divided only according to the method of shaping their visual symbols. The most expedient approach to the classification of sign displays should be based on the principle of their t e c h n i c a l i m p l e m e n t a t i o n . In [11] the a p p l i c a t i o n of this principle is suggested for unfamiliar displays, and in [12] for d i g i t a l displays whose screen or board consists of a set of separate elemen:s. According to the amount of reproduced data the sign displays (SD) can be divided into the following two groups: 1) sign displays whose visual part carries one parameter of a single test point; 2) sign displays whose visual part carries parameters of several test points. By the methods of presenting their visual information the sign displays can be classified into those with a simultaneous reproduction of a l l the tested data and parameters, with the reproduction on demand, and with the reproduction of only the data which are close to their boundary or c r i t i c a l values. The design principles of sign displays are affected by the coordinate characteristics of their visual part (screen or board), the methods of reproducing and fixing the visual symbols, the methods of displaying the location of the visual alphabet letters on a screen or a board, and the principle of forming or segregating visual symbols from the components of anSD visual part. By the structure of their visual parts the sign displays (see Table 1) can be divided into those with t w o - c o o r dinate (two-dimensional) screens and those with three-coordinates ( t h r e e - d i m e n s i o n a l or solid) screens. By the method of producing their projected i m a g e [13] the displays can be divided into those of the e l e c t r o m e c h a n i c a l type whose rotating disc is either solid and carries a system of symbols which are selected on receiving a given instruction, or it is m a d e of a semitransparent m a t e r i a l and inscribed in symbols i l l u m i n a t e d with a beam of light; those consisting of transparencies or displays with i n t e r m e d i a t e information carriers whose images are projected onto a screen [14]; and those of the refracting type whose s o - c a l l e d "schlieren" have deformation or ripple marks on their o p t i c a l surface produced by electron bombardment from an ordinary electron gun. Those d e f o r m a tions produce refractions and the beam of light is transmitted to the screen through an optical grating or a system of diffracting strips. The system of dark and light areas thus formed is used for displaying visual symbols. It is necessary to supplement these three groups by the e l e c t r o o p t i c a l [18] and e l e c t r o n - o p t i c a l [16] displays. The former displays consist of a stationary digital stencil, a set of incandescent lamps and light condensers. The stencil is projected through objectives onto a c o m m o n frosted glass. All the light beams are directed to the center of the glass. The e l e c t r i c a l circuit of these displays is arranged in such a manner that only a single l a m p can be lit at a time. In the e l e c t r o n - o p t i c a l displays the sign images are projected onto a common screen. By the method of forming their 3-D i m a g e the t h r e e - c o o r d i n a t e sign displays are divided into axonometric, stereoscopic, and natural displays [17]. The axonometric method consists of projecting in parallel the display data Translated from i z m e r i t e l ' n a y a Tekhnika, No. 5, pp. 49-53, May, 1969~ Original article submitted October 28, 1967. 663

and the coordinates to which they are referred in space onto a plane surface which in this case consists of the display screen. According to the data of [18, 19] the image can be displayed either on a 4%cm-diameter screen of a direct-vision cathode-ray tube, or by projecting it onto a 1.8-m square screen. In stereoscopic sign displays the data is reproduced on one or two screens. In order to produce a 3-D effect it is necessary to provide the two sign images in the same manner as they would have been received on the retinas of the left and the right eye (such a combination of images is known as a stereoscopic pair). This pair is divided in such a manner that each eye "sees" only a single picture which is intended for it. By the method of dividing the stereoscopic pair such displays are classified into those of the individual and group types. The former are suitable for observing the 3-D image by a single person at a time, and the latterby a number of people in given places of the premises in which the screen is located [17, 20, 21]. The natural t h r e e - c o o r d i n a t e displays are provided with volumetric screens. By the principle of designing their screens, or, more precisely, by the method of reproducing their symbols in space, such displays can be divided into those of the e l e c t r o m e c h a n i c a l [22], e l e c t r o n - m e c h a n i c a l [16, 22, 23], and electronic [24] types. In the latter case the display does not contain any m e c h a n i c a l components, however, the luminance of the displayed signs is rather low. The two-coordinate sign displays can be classified by the method of retaining their visual symbols on the screen into those with a single and cyclic recording. In the former case the symbol is "stored" on the screen and is displayed until it is deleted by the observer. The screens of such sign displays consist mainly of those belonging to "storage" CRTs [28], or special electroluminescent screens [26]. Sign displays with a single recording of symbols can be divided, according to the method of their renewal, into devices with a c o m m o n and a selective erasing. In the former displays all the data on the screen is erased before replacing a single obsolete visual symbol by a new one. Such displays use CRTs whose principle of operation is similar to a typotron [25]. The data produced on the screens of such displays can be retained for more than three hours [27]. Sign displays with selective erasing have plane multielement electroluminescent screens which serve to delete, according to certain criteria, only the data whose values have changed. CRTs are now being developed with selective erasing [28]. In sign displays with cyclic data recording the visual signals are registered at given time intervals which are determined by the critical flicker frequency. The visual part of such displays consists of C R T screens with a m e d i u m afterglow, or electroluminescent screens without "storage." In order to raise the amount of displayed data, the frequency of symbol reproduction is sometimes reduced, i.e., the duration of the cycle is increased. For stabilizing luminance with time the effect of the prolonged afterglow of phosphors or electr0phosphors is then used. Such two-coordinate sign displays are known as displays with a long afterglow. By the method of displaying the position of the symbol the two-coordinate displays are divided into those of the discrete and analog types. The former consist of only discrete components: The registered visual symbols consist of a set of c o m p l e t e elements which are displayed in a given manner on a screen or a board. Such displays are classified into those with s i n g l e - s y m b o l cells and those with m u l t i e l e m e n t (raster) screens [17, 29]. In the former displays the screen consists of components of different shapes assembled in autonomous cells. In the latter ones the screen consists of c o m ponents which are the same in their shape and dimensions, According to the principle of their design the single-symbol display cells can be either of the electroluminescent or the l a m p type. T h e latter can be with [1] or without signs, In the l a t t e r case the visual symbol is reproduced by i l l u m i n a t i n g transparent plates at their edges, by using light-guide optics, etc. [7]. The discrete sign displays with electroluminescent screens have a long life (up to40,O00 h) [29]. However, they have drawbacks which consists of a c o m p l i c a t e d e l e m e n t switching system, an insufficient contrast in the reproduced symbols, and a nonuniform distribution of luminance over the screen areas. This is due to the excitation voltage attenuation along the strip electrodes which form the visual part of the display. The analog sign displays comprise CRTs or other components, for instance, special electroluminescent screens [30] whose reproduced information is controlled by means of continuously generated and variable in rime voltages or currents. 664

ISighdisplays I

TABLE 1

1

1

1

Three -coordinate

Two-coordinate

Projection

_,[ Electromecti'~nical

i' i

With selective crazing ]

--, Refraction type

]

1 With a long [afterglow

- ~lectro anT--- 1 ~leet ron-optical!

1

l

IAxonometric I "Stereoscopic __1

1

Direct vision 1

I 1

I

"

1

Witha single

Natural

[

tWith cyclic !

recording . . . . .recording I....... . . . f

-

I

Individual

-With common lerazing

_Groupl Electronmechanical

1

Electro9 mechafiical

1 With a medium 9 afterglow ]

Electronic,

Discrete 1 With single- - symbol cells

--,

1

I

1-

l

Raster type

1

Profiling

1

]Functional

I

Raster type I

I With a fixed

-+tIluminescent[ W--~ts~

visual alphabet

With a variable visual alphabet ]

Open type

With negative feedback ]

With signs

L

Itype

__l

[

1

l With representation " ~ h approx, o f ~ With a corn ~.y_means of Lissajous }and~b(t)by means I| .mon raster .ngures , JofFourier series--I[

(t) and O(t) by step-law

Combined - - =

i.__

t t Without intermediate, energy convei~lon

1 Without signs.

1

[

l ] W i t h inter[ mediate energY conversion J 1

Eleetr~

Analog

lb

r and r pieeewise= Y linear law

raster type

l

With a minia. ture raster

Raster and functional type ___ 1

With a point raster

With a ! lined ras.ter

The displays are classified by the method of forming the symbol on their visual part into those of the profiling, functional, raster, and combined types, Displays of the first category consist of special sign-type CRTs (charactrons, typotrons, printoscopes, and indicating coders [25]) in which the electronic beam in passing through one of the matrix openings assumes in its cross section a shape corresponding to a visual symbol, By the composition of the visual alphabet the profiling displays can be classified as those with a constant and variable alphabet. The latter include signal displays with a compositron. The sign-display tubes "with the best characteristics include in the first place the charactron" [16]. It has

the following basic characteristics: a diameter of 75 cm [311, a life upto4000 h[28], smoothly changing registered symbols of a size of 0.5-8 mm [32], with their matrix comprising either 64 [25] or 96 [33] of them, all illuminating pulse duration of 50 gsec during which the electron beam reproduces the visual symbol [16].

665

The raster displays produce a strictly determined sequence of pulses which direct the electron beam to certain points of the television raster thus producing the required visual symbol. According to the principle of the formation of their symbols these displays can be divided into those with a c o m m o n and independent visual alphabet raster for each letter [38, 86]. In the first instance the electron beam is displaced along the lines of a raster whose size corresponds to that of the effective part of the CRT screen. I n t h e second instance the dimensions of the raster are equal to those of the visual alphabet's reproduced letters and, therefore, it is known as a miniature raster. There exist two methods for shaping the visual signals from component elements of a miniature raster consisting of the point and the line methods. In the first case the letters of the visual alphabet are made up of sets of points, and in the second case out of straight line segments of various sizes. Different designers choose different numbers of composite e l e m e n t s for the miniature point television raster, which possesses greater potentialities than the line raster. The numbers of these points amount to 3 x 5 [aT], 8 x 6 [38], 5 x 7 [39], 6 x 6 [40], 6 x 8 [41], 8 x 8 [42], and 7 x 15 [42]. Certain data on raster sign displays with component elements amounting from 480 to 11,000 are provided in [43]. In the latter case the t i m e required to form a single symbol amounts to 5 gsec. In the m a j o r ity of the a b o v e - m e n t i o n e d rasters this t i m e is equal to 20-80 gsec [44]. Functional sign displays produce voltages or currents whose variation with t i m e generates in the deflecting systems of an ordinary CRT (television picture tube) appropriate fields for writing on the screen with the electron b e a m , as with a pencil, the required letters of the visual alphabet. The line which forms the visual signal and is reproduced on the plane screen can be represented a n a l y t i c a l l y in Cartesian coordinates as an i m p l i c i t equation F (x, y) = 0

(1)

Y = fil (X'), X = f$ ( y ) .

(~)

or an e x p l i c i t equation

The l a t t e r equation can be represented in the parametric form as

x=~

(t), y = ~

(~),

(3)

where ~0(t) and ~(t) are s i n g l e - v a l u e d and continuous functions of t. In ordinary or projection picture tubes the relationship between the displacement vector ~(t) of the electron beam trace in the plane of the screen and the vector of the deflecting vpltage ~ ( t ) of current I(t) can be represented as:

~ ( t ) -= kB (t),

(4)

J E(t) I = V *," (t) + y" (t) ,

(5)

where k is a constant coefficient

l u (t) l= i f ..~ u)

u).

(6)

Thus, if the deflecting system of a CRT is fed with a voltage U(t) or a current I (t), then under the effect of the variations of the deflecting system's field the electron beam will draw on the screen a symbol whose generating line is represented b y (3). Since the generating line of the m a j o r i t y of signals is not a closed curve and function (1 m a y have a finite number of discontinuities of the first kind, an e l e c t r o n - b e a m b i a s - l i g h t i n g voltage is used for producing the required segments which combine to form letters of the visual alphabet [48]. To obtain voltages and currents which change strictly according to (3) is often difficult, and sometimes i m possible. At present t h e following methods are used for shaping the voltages and currents under whose effect the electron b e a m trace is displaced along the generating lines of visual symbols: 1) sinusoidal voltages and currents are used whose amplitudes, frequencies and phases differ from each other [46]; 2) the voltages and currents a r e m a d e up of a sum of components whose amplitude and frequencies are determined by expanding the functional relationships

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(3) into Fourier series [47]; 3) the voltages and currents are varied in time according to the law of stepped approximation; 4) the voltages and currents are varied in time with respect to the law of piecewise-Iinear approximations. A symbol which is reproduced under the effect of two mutually perpendicular sinusoidal oscillations cormsponds to the classical determination of a Lissajous figure, therefore, this method is known as reproduction, by means of Lissajous figures of their segments. In approximating ~o(t) and ,I,(t) by means of Fourier series it was found that for reproducing digits from O to 9 it is sufficient to use five-seven harmonics [44]. The time required for the formation of a single symbol amounts to 33 psec [47]. The number of segments for representing Arabic figures and letters of the Latin alphabet by means of stepfunction approximations of ~0(t) and ~(t) is selected by different designers in different ways as 16 [46], 10 [48], and 8 [48]. The time required for reproducing a single segment amounts to 0.25 psec [48]. In approximating the shape of the voltages or currents by curves which follow the piecewise-linear law, the generating line of symbols is represented by parametric equations provided in [45]. This approximation method can be used for representing in addition to letters and figures, also various kinds of conventional notations of objects, trajectories, as well as their displacements and vectors. The combined signal displays use combinations of the above-mentioned shaping principles, including the profiling and raster, the profiling and functional, as well as the raster and functional methods. In the first two methods, the letters, figures, and conventional notations are obtained by using a charactron matrix, and lines by using the raster of futlctional method. It is asserted in [59] that a combination of a profiling and raster methods is expedient. In the raster-functional sign displays, the raster method is used for reproducing directionally orientated conventional notations of objects, and the functional method for indicating symbols with a constant orientation, as well as vectors and various types of curves [51]. The light-biasing control voltages or pulse sequences are produced either directly by logical elements, or by means of intermediate transformation of energy of a given type. In the latter case the electrical energy is transformed into luminons energy and then retransformed into electrical and back to Iuminous energy. These devices comprise as a rule auxiliary CRTs with screens whose profiles or optical density are varied strictly according to (3) [52, 53]. According to the application of feedback, such sign displays are divided into those of an open type and those with a negative feedback [53]. In conclusion it should be noted that raster-functional sign displays are the most flexible and universal [51]. Regarding the three coordinate displays it should be stated that the eiectromechanicaI method is the most suitable for producing a 3-D image. The design principles of the "recorders" and "registers" of electromechanical and mechanical printing methods are described in [14, 54, 55, 56]. LITERATURE 1. 2. 3, 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

CITED

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