US2535978A - Pickup circuit - Google Patents

Description

Dec. 26, 1950 w. E. WINTERHALTER ETAL 2,535,978

PICKUP CIRCUIT Original Filed Sept. 26, 1945 INVENTQRS, WILLIAM E. WINTERHALTER y & EDWIN E. ,VONADA ATTORNEY Patented Dec. 26', 1950 PICKUP CIRCUIT William E. Winterhalter, Coshocton, and Edwin E. Vonada, Cleveland, Ohio Original application September 26, 1945, Serial No. 618,664. Divided and this application December 9, 1949, Serial No. 132,028

2 Claims.

. This invention, which is a division of our cpending application, Serial No. 618,654, filed September 26, 1945, now Patent No. 2,494,852, relates to a pick-up circuit for an electric control and primarily to the control of the low voltage high current system which is used in maintaining the ratio of plating current to speed necessary for producing uniform coating thicknesses in variable speed electroplating processes. Electrolytic tin strip is ordinarily produced in a continuous processing line where the speed of the strip varies and this makes it necessary to change the current density in synchronism with changes in speed of strip travel so that the weight of deposited tin can be held constant. During ,voltage proportional to the current or voltage to be controlled. Such circuits now in use have not proved satisfactory for all values of currents and voltages which are to be controlled.

It is an object of this invention to provide a pickup circuit which is adapted for use in controlling the current of high or low D. C. current and voltage systems.

This and other objects will be more apparent after referring to the following specification and attached drawings in which:

Figure 1 is a schematic view showing the control applied to the electrotinning apparatus; and

Figure 2 shows the wave form of the voltage across the voltage divider of Figure 1.

Referring more particularly to the drawings, the reference numeral 2 indicates a plating tank which contains a suitable electrolyte. The strip S passes from an uncoiler 4 over conductor roll 6 and thence into the tank 2, and passes out of the tank over a conductor roll 8 from which it is directed by means of a billy roll Hl' into the driven puller rolls I2. As the strip passes through the tank, it is directed between anodes I4 by means of sink rolls [6 and conductor rolls I8. Plating current is supplied to the plating tank from a top plating generator 20 and a bottom plating generator 22. The positive terminal of generator 20 is connected to a positive bus bar 24 which is connected to the anodes 14 which act upon the top of the strip. Generator 22 is connected in like manner to a positive bus bar 2% which is connected to the anodes I4 acting upon the bottom of the strip. lhe generators 2i] and 22 have common negative connections and are connected to the negative bus bar 28 which is connected to the conductor rolls 6, 8 and I8.

A shunt 32 is installed in the negative bus for measuring the total plating current and for the control purpose described hereinafter.

Field 34, of generator 20, and field 36 of generator 22, are connected in parallel across the armature of a plating exciter 38 and are provided with hand operated rheostats 4i] and 42 connected in series with the respective fields to provide top and bottom current density balance. The apparatus described above is standard equipment. Shunt 32 is used in the control of our invention to exercise supervision over the armature voltage of the plating exciter 38 by varying its field 44. The excitation circuit 46, 41 and 48 of the exciter 38 is connected across the 7 armature or output circuit of a single unit amplifying exciter 50 through a current limiting re-' mon pole pieces. The armature or output voltage of the exciter 50 is principally derived from and controlled by two of these fields 54 and 56.

Field '54 is in the basic control circuit 58 which is connected to produce a positive flux which increases the output voltage of exciter 58 and consequently the plating current as the line speed in creases. A tachometer generator til connected to be driven by rolls I2 is located in this circuit and the output voltage of the generator is applied to field 54 through a current limiting resistor 62 and a. manually operated rheostat 64. This rheostat is used to accommodate plating current requirements when changes in product schedule, electrode areas, and coating weight occur. The tachometer generator 60 has the usual straight line speed voltage relationship.

Field 56 produces a restraining flux which is proportional to the total plating current and is in opposition to that of the basic control field 54. The voltage drop across the plating current negative conductor shunt 32 is used for varying the excitation of field 56. The low shunt voltage is amplified to the desired regulating system voltage by means of an A. C. electronic amplifier 98. An A. C. amplifier is used because the inherent 3 instability of a D. C. electronic amplifier is objectionable. This pickup circuit will be described with reference to a special application in which a 110 volts, 60 cycle power supply is transformed to 2.5 volts by means of transformer I02. A full wave rectifier I04 converts the 60 cycle sine wave to 120 unidirectional impulses per second. Two circuits emanate from the positive-terminal of rectifier I04. The current of one circuit passes through the shunt 32, a half wave rectifier I06 through voltage divider I08 to the center tap I I0, and thence to the negative terminal of rectifier I04. The current of the other circuit passes through resistor II2, half wave rectifier II4 through voltage divider I08 to the center tap I I and thence to the negative terminal of rectifier I04. The half wave rectifiers I06 and H4 are constructed to afford very low resistance to current flow in the direction described above, but will provide the usual blocking of any current tending to flow in the opposite direction. This prevents the current caused by the shunt millivolts from flowing through the circuit comprising resistance II2, rectifier II4, voltage divider I08, rectifier I06 and back to the negative terminal of the shunt. The low impedance winding of a bridging input transformer I I6 is connected across voltage divider I08. Transformer H6 steps up and converts the pulsating unidirectional voltage to A. C. and couples the pickup circuit to amplifier 98. The'pickup circuit voltage is greatly amplified by amplifier 98 and is converted into a pulsating unidirectional voltage by-rectifier H8 before it is impressed on field 50. A current limiting resistance I2 is provided in the circuit 60 i leading from the rectifier I I8 to'field 56. With no plating current, resistor II2 is adjusted until the voltage between points I and 122 of voltage divider I08 is zero. In such case, the voltage wave form is that shown at A in Figure 2. When plating current through the shunt is raised to 50% of the shunt rating, the wave form of the voltage across I20 and I22 will be as shown at B in' Figure 2 with the polarity of the shunt leads as shown. The magnitude of this voltage will be equal to the millivolts and exists as pictured because the instantaneous voltage at'I20 at zero time is below that at I22 by "an amount equal to the shunt millivolts. The maximum voltage is reached when the instantaneous voltage at I22 reaches the zero axis. This maximum voltage is maintained until the instantaneous voltage at I22 again crosses the zero axis. The negative maximum voltage is again reached when the instantaneous voltage at I22 reaches zero. If the plating current is increased to 100% of the shunt rating, the wave form of the voltage between I20 and I22 assumes the shape shown at C in Figure 2. The increased magnitude of this wave causes a linear increase in the output voltage of amplifier 98.

Since this circuit initially depends only on millivolt variationsfor its operation, the regulating control system can be adapted to the current control of high or low D. C. current and voltage systems.

- When the line speed is increased or when other changes are taking place, the output voltage of exciter 50 increases rapidly due to increased excitation from field 54 which is not immediately restrained by field 56. Likewise, when the line speed is decreased, the output voltage of exciter 50 decreases rapidly due to thedecrease of excitation from field 54 which causes an immediate exd cess of current in field 56. These rapid changes cause a fluctuating of the control as it seeks to establish the desired relationship between line speed and plating current. In order to effect a smooth transition to steady conditions from the transient conditions in which high forcing power has been applied by the exciter 50 to the exciter 38, a stabilizing circuit 04 having field therein is connected across the exciter 50 through direct current impulse transformer 88. A resistance is employed in the line to adjust the magnitude of the secondary impulse from the transformer 88 to effect the stabilization desired. The polarity connections of field 86 are such that the rapid increase of the output voltage from exciter 50 induces a delayed D. C. impulse voltage in the secondary of transformer 88 which is applied to circuit 84 in opposition to the increased total excitation of exciter 50 and tapers the output voltage to the steady conditions after the desired ratio of line speed and plating current has been established. In like manner, a delayed D. C. impulse voltage having a polarity opposite to that associated with line acceleration is induced in the secondary of transformer 88 which is applied to circuit 84 when there is rapid deceleration and this brings the output voltage of exciter 50 back to the steady conditions after the desired ratio between line speed and plating current has been established.

In order to compensate for the small leakage excitation of circuit 06 when there is no excitation in circuit 58, circuit 92 having field 94 therein is provided for exciter 50. in circuit 06 overcompensates the normal residual voltage of exciter 00, exciter 38, and generators 20 and 22 and causes reverse plating current to flow. That is, the strip S will become anodic and will be subject to anodic corrosion. To prevent this anodic corrosion; field 94 is energized from a source of constant D. C. voltage and When the line is operating at aparticular speed with the plating current constant, the adjusted algebraic summation ratio of control fields 54,

5B and 94 determine the output of exciter 50. When the line speed increases, the speed of tachometer generator 60 is also increased, thus increasing its output voltage. This increases the flux of field 54 thus causing an unbalance of flux:

ratio produced byfields 54 and 56. This causes a rapid increase in output voltage of exciter 50 which is not immediately restrained by field 56.

This in turn induces a delayed'D. C. voltage in the secondary of transformer 88, which is applied to field 86 in opposition to the increased total excitation of exciter 50 and tapers the output voltage tosteady conditions after the de-.

sired ratio of line speed and platingcurrent has been established. The increased, output of ex-.

citer 50 is supplied to the field of exciter '38, thus increasing the output of generators 20 and 22.

This changes the current flowing-in shunt 32,,

which increases the flux of field 56 to establish a new relationship between fluxes produced by fields 54 and 50 to provide the necessary increase in total. flux.

When the line speed decreases, the fiux pro-- The leakage current duced by field 56 will be proportionately greater than that produced by field 54 and the output of exciter 50 will be decreased, thus changing the output of exciter 38 which in turn changes the output of generators 20 and 22. This changes the current flowing in shunt 32, which decreases the flux of field 58 to establish a new relationship between the fluxes produced by fields 54 and 56 to provide the necessary decrease in total fiux.

While electrodeposition of tin on steel strip has been employed to illustrate the control and circuits described, it is evident that they are applicable generally to accurate continuously supervised current regulation of direct current machines without use of mechanical or other contact devices, excepting for protection.

While one embodiment of our invention has been shown and described, it will be apparent that other adaptations and modifications may be made Without departing from the scope of the following claims.

We claim:

1. A pickup circuit comprising a full wave rectifier, means for connecting a low voltage source to said rectifier, means for connecting an alternating current source to said rectifier, a pair of circuits emanating from the positive terminal of said rectifier, one of said circuits passing through the low voltage source, a half wave rectifier, part of a voltage divider and back to the negative terminal of the rectifier, the other of said circuits passing through circuit balancing means, a second half wave rectifier, the remaining part of 6 said voltage divider and back to the negative terminal of the rectifier, and output terminals connected to the ends of said voltage divider,

2. A pickup circuit comprising a full wave rectifier, means for connecting a low voltage source to said rectifier, means for connecting an alternating current source to said rectifier, a pair of circuits emanating from the positive terminal of said rectifier, one of said circuits including the low voltage source, a half wave rectifier, part of a voltage divider and a, conductor leading from the center tap of the voltage divider to the negative terminal of the full wave rectifier, the other of said circuits including a circuit balancing means, a second half wave rectifier, the remaining part of said voltage divider, and a conductor leading from the center tap of the voltage divider to the negative terminal of the full wave rectifier, and output terminals connected to the ends of said voltage divider.

WILLIAM E. WINTERHALTER. EDWIN E. VONADA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,325,401 Hurlston July 27, 1943 2,404,948 Croco July 30, 1946 2,488,856 Few Nov. 22, 1949 2,494,852 Winterhalter et a1. Jan. 17, 1950

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