US2876060A - Recording paper - Google Patents

Description

March 3, 1959 H. l. CHAMBERS 2,376,060

RECORDING PAPER Filed Jan. 22, 1957 2 Sheets-Sheet 1 F/Gl.

Pl GME N 7' I3 P/GMEN T l3 1:76. 2. 2 CARBON l2? v v A IN VENTOR. HERBERT CHAMBERS A TTORNEVS March 3, 1959 H. l. CHAMBERS RECORDING PAPER Filed Jan. 22, 1957 2 Sheets-Sheet 2 WR/T/NG CURRENT GENERATOR RECORD/N6 'AMPL/F/ER FIG. 4.

INVENTORL HERBERT CHAMBERS RECORDING PAPER Herbert I. Chambers, Pasadena, Calif., assignor to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Application January 22, 1957, Serial No. 635,484

1 Claim. (Cl. 34674) This invention relates to coated recording paper, and more particularly, to electrosensitive paper which is used in direct simultaneous recording of a plurality of signals.

The paper of this invention is particularly suitable for recording the output of multi-channel string galvanometers.

In a typical string galvanometer, the writing element is a string, i. e., a movable conductor. The string is supported at its two ends so that its central portion can be deflected transversely a relatively large distance in a fixed plane to provide the large amplitudes of motion which are required for recording directly.

The conductive string is located in a magnetic field perpendicular to the direction of the magnetic field, so that the string moves transversely with respect to the magnetic flux in accordance with the magnitude of the electric current which flows through the string in response to an applied signal. Preferably, the string is supported at each end by springs so that as the string is deflected in either direction, the springs permit the ends of the string to move closer together.

For direct writing on electrosensitive recording paper, an anvil having an edge located at the central portion of the string is employed to guide a strip of recording paper adjacent the center of the string. The edge of the anvil is perpendicular to the string, and the electrosensitive paper is moved over the edge ofthe anvil so that it passes between the anvil and the string. Suitable means are provided for urging the string against the paper Where the paper passes over the edge of the anvil, and a source of electrical writing voltage is applied across the paper and the string so that an electric current passes between the paper and the string at the intersection of the string and the line formed where the recording paper passes over the edge of the anvil. The current density at the point of contact between the paper and the string is sufiiciently high to visibly affect the paper at that point. Thus, as the strip of paper is pulled over the edge of the anvil, a trace is formed on the paper which provides a record of the deflections of the string in response to an applied signal.

In many types of measurements it is desirable to record the traces of two or more signals simultaneously on a common piece of electrosensitive direct recording paper. In such cases, a multi-channel oscillograph is used. Such a device employs as many strings as necessary to record the various signals, each string being adapted to receive a respective signal. The strings are usually placed side by side, parallel and in a common plane. Each string is adapted to travel over a separate given width or channel of the paper in recording its respective measurement.

One of the difiiculties presented by multi-channel direct recording oscillographs with presently available electrosensitive paper is that of obtaining satisfactory traces when signals of different frequencies are recorded simultaneously. A relatively high writing voltage is required for satisfactory recording of a high frequency signal, because of the relatively high velocity of the string across the 2,876,060 Patented Mar. 3, 1959 surface of the paper. On the other hand, less writing voltage is required for recording a low frequency signal because of better contact between the paper and the slower moving string. The presently available electrosensitive direct recording paper has a common electroconductive surface, and the use of a writing voltage sufiicint to record a high frequency trace in one channel sometimes burns the paper in another channel being used to record a lower frequency.

This invention overcomes this difiiculty by providing an electrosensitive direct recording paper for multi-channel recording, which has a series of elongated and laterally spaced recording channels which are electrically insulated from each other. Thus, the proper writing voltage can be applied to each respective recording channel in accordance with the frequency which is to be recorded on the particular channel.

Briefly, the invention contemplates an electrosensitive recording paper for multi-channel recording in which the paper comprises a base of electrically insulating material having elongated and laterally spaced longitudinal strips of conductive material to establish laterally spaced conductive channels. Each conductive channel is electrically insulated from adjacent channels and has a surface coating of such character to be visibly altered by the application to it of an electrical marking current.

In the presently preferred form of the invention, the strip of conductive material is a layer of carbon applied to the surface of the base material and is covered by the electrosensitive surface coating.

In an alternate form of the invention, the conductive strips are formed by impregnating laterally spaced channels of the base material with a conductive material such as carbon.

Electrosensitive direct recording paper is well known, and such paper is described in U. S. Patents 2,554,017 and 2,555,321. However, as stated above, all electro sensitive paper now available is made with a common electroconductive layer which covers the entire area of the paper, and therefore is not suitable for multi-channel recording where different writing voltages are required for the various channels. This invention provides a plurality of insulated recording channels on a common sheet of electrosensitive direct recording paper on which a plurality of traces can be recorded simultaneously, even though difierent writing voltages are required for the various channels. The advantages of multi-channel recording on a single strip of paper are that a single roll of paper is easy to handle and process, and the information recorded in each channel is automatically mounted on a common base so that the output from the various channels may easily be visually inspected and compared with each other.

These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a fragmentary plan view of the presently preferred form of multi-channel direct recording paper according to the invention;

Fig. 2 is a view taken on line 22 of Fig. 1;

Fig. 3 is a schematic side elevation of a direct recording string galvanometer;

Fig. 4 is a perspective view of an anvil of a direct recording string galvanometer of the type shown in Fig. 2, the anvil being adapted for use in a galvanometer in which two channels are recorded simultaneously; and

Fig. 5 is a transverse cross-sectional view of an alternate form of the paper of this invention in which the conductive strip is embedded directly in the base material of the paper.

Referring to Figs. 1 and 2, the direct recording paper includes an elongated base or carrier 10 which may be made of paper or other suitable pliable material, such as fabric, photographic transparencies, or the like. A pair of elongated, longitudinal and laterally spaced recording channels 11 are formed on one surface of the base of the carrier. Each recording channel includes an elongated conductive layer 12 of a suitable material, such as carbon, laid down on the surface of the carrier. An electrosensitive coating 13, preferably which is of a color substantially different from that of the conductive layer, is deposited on the surface of each conductive layer.

The conductive layers 12 may be of any suitable material which will adhere to the base. For example, carbon black may be mixed with any suitable adhesive, such as gelatin, starch, cellulose ester, etc. It is desirable to use as little binder as possible, and in general, the amount of binder may vary from to 30% of the dry weight of carbon black.

As an example of the proportions of carbon black and binder which may be utilized in forming conductive coatings for the paper, the following is given:

Example I 20 grams of carbon black 6 grams Methocel, or methyl cellulose (400 C. P. S.) 200 cc. water The Methocel is dissolved in cold water and the carbon black added while stirring. The mixture is then passed through a colloid mill and applied to the paper base by any of the normal coating methods, such as spraying, dipping, brushing, or knife coating, care being taken to confine the deposition of the mixture to the area of the recording channels on the paper, and leaving an insulating space 14 between adjacent channels. After coating the paper, the liquid contained in the binder is evaporated off by heating or any other suitable method. The paper is thereafter calendered to provide a smooth surface.

After the paper has been coated with the strips of conductive material, it is further processed with the electrosensitive coating, which consists of a white or light colored pigment and a binder. The binder utilized for the electrosensitive coating may be any one of those mentioned in connection with the conductive coating, but it is preferable to use a binder soluble in organic solvents for the electrosensitive coating and one soluble in water for the conductive coating.

Zinc oxide, zinc sulphide, and barium sulphate are examples of pigments which may be used satisfactorily in the electrosensitive coating.

The amount of electrosensitive coating necessary to produce a satisfactory recording paper is very small. The exact amount cannot be stated since variation in weight of the paper and variation in thickness of the black conducting coating will cause variations. It may be said, however, that as little coating as possible should be applied; just suflieient to cover the black conducting coating uniformly and to give the finished surface a light gray appearance. It is necessary to apply the electrosensitive coating in such a manner as to retain the pigment on the surface of the black coating and to guard against having the white pigment penetrate below the surface or between the black conducting particles. In order that this may be done it is necessary that the coating mixture be dried quite rapidly, since if it is dried too slowly, the penetration mentioned above occurs.

An example of a satisfactory electrosensitive coating is set forth below:

Example 11 -40 grams of zinc oxide 2.5 grams Methocel (400 C. P. S.) 100 cc. water The Methocel is dissolved in cold water and the zinc a colloid mill and applied to the paper by any of the methods mentioned hereinabove. The mixture of electrosensitive coating may be applied only to the exposed surface of the conductive strips, or it may be applied to the entire surface of the base material and conductive strips. In either case, the result is an electrosensitive paper for multi-channel direct recording in which a plurality of strips are provided on a common carrier and are covered with an electrosensitive coating such as would be visibly aifected by the application of an electric current.

The advantage of the multi-channel recording paper of this invention can be more fully appreciated when considered in use with the apparatus shown in Figs. 3 and 4.

Referring to Fig. 3, the string element of the galvanometer comprises a flexible conductor or string 16 which is supported at its ends by a pair of leaf springs 17 and 18. A conductive bearing sleeve 19 of a suitable ferromagnetic material is disposed around and pinched to secure it to the center of the string. The springs are arranged to provide resilient support for the string element along the direction of the string, and they serve to restrain movement in all other directions, so that the deflection of the string is not adversely affected by the end supports.

A lower magnetic pole piece 24) and a pair of spaced members 21, 22 forming an upper pole piece are located on opposite sides of the string element, and they provide a magnetic field which is perpendicular to the longitu dinal direction of the string. The outer end of each of the upper pole pieces is connected by a suitable yoke (not shown) to the lower pole piece to complete the magnetic circuit. A conductive guide or anvil 23 of suitable ferromagnetic material is located in the space between the two upper pole pieces and spaced from them. The anvil has a lower edge 24 which is perpendicular to the string and the direction of the magnetic field. The anvil edge is equidistant from the ends of the sleeves around the string. An electrosensitive recording paper 25 moves over the edge of the anvil so that it extends between the conductive anvil and the sleeve on the string element of the galvanometer in the plane of motion of the string. The two upper pole pieces induce magnetic poles of opposite polarity on the anvil, so that a magnetic field is established in the gaps between the anvil and the two pole pieces. The magnetic sleeve is attracted toward each of the gaps between the anvil and upper pole pieces with a resultant attraction toward the anvil in a direction perpendicular to the longitudinal axis of the sleeve. Thus, the sleeve bears firmly against the surface of the paper along the line defined by the lower edge of the anvil.

The ends of the string element are connected to receive a signal from a source 26 through a recording amplifier 27. The electric current which fiows through the string as the result of the applied signal causes the central portion of the string to be deflected in accordance with the magnitude of the signals provided by the signal source.

A writing current generator 28 has one terminal grounded and another terminal connected through a current limiting resistor 30 to ground. A movable tap 31 adapted to slide along resistor 30 is connected by a lead 32 to the anvil. Thus, a current discharge occurs in the electrosensitive recording paper at the intersection between the sleeve and the edge of the conductive anvil. This discharge renders the surface coating partially conducting, and at the same time discolors the coating or cats it away, causing a trace to be recorded on the electrosensitive recording paper in accordance with the movements of the string. The bearing sleeve takes any wear which may tend to occur as the string is deflected, and thereby greatly increases the useful life of the string without unduly increasing the effective mass of the string.

Fig. 4 shows an anvil and writing set-up for a direct recording oscillograph of the type shown in Fig. 2 which oxide added while stirring. The mixture is passed through is adapted for two channel recording. An anvil 40 is formed with conducting portions 41, 42 at each end. The central portion 43 of the anvil is an electric insulator. Conducting portions 41, 42 are respectively connected by leads 44, 45 to potentiomcters 46, 47 which permit the opposite ends of the anvil to be independently supplied adjustable amounts of current and voltage from separate writing current generators (not shown). Separate conductors or strings 48, 49 are supported as described above to extend perpendicularly over the edge of the anvil, and a strip of two channel direct recording paper, such as that shown in Fig. 1, is arranged to pass between the strings and the anvils as described above.

With the arrangement of Fig. 3, each conductive portion of the anvil spans a channel on the paper and maintains the desired voltage for its respective channel, independent of the voltage used on the adjacent channel.

Thus, with the paper of this invention, diflerent writing currents and voltages may be applied to adjacent recording channels without interference or burning, as occurs with presently available direct recording paper.

Fig. 5 shows an alternate form of the multi-channel recording paper of this invention in which a base or carriage strip 50 of paper is provided with spaced, elongated and longitudinal portions 51 impregnated with a carbon mixture of the type described above, and a surface layer of white pigment 52 is deposited on the conductive portions of the carriage. The white pigment may be of the same type described above, and may be applied either to the entire area of the recording paper, or limited to only the conductive portions of the recording paper. It will be apparent that the multi-channel paper of this invention may be formed with as many channels as is desired or required.

Iclaim:

A recording oscillograph comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, electrosensitive paper located between the anvil and the conductors, the paper having two separate elongated and laterally spaced longitudinal strips of conductive material on an electrically insulating base to establish laterally spaced and electrically insulated conductive channels, each channel having a surface coating of such character to be visibly altered by the application of electrical marking currents, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, means for imposing one voltage across the portion of the paper adjacent the first conductor, and means for imposing another voltage across the portion of the paper adjacent the second conductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,806,756 Van Der Wcrfl Sept. 17, 1957 FOREIGN PATENTS 161,559 Australia Mar. 1, 1955

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