US2069599A - Circuit controller - Google Patents

Description

Feb. 2, 1937. c BROWN 2,069,599

, CIRCUIT CONTROLLER Original Filed June 15, 1951 Patented Feb. 2,

UNITED STATES PATENT OFFICE sum cnrcm'r couraotma Glendon G. Brown, Milwaukee, Wis., assignmto Cutler-Hammer,

Inc, Milwaukee, Wis, a

corporation of Delaware v 7 Claims.

This invention relates to improvements in systems aiiording control of an electric circuit in in which application I have disclosed and claimed the present invention as applied to the speed control of an electric motor.

An object of the present invention is to provide for control of a gaseous electron tube whereby it will respond selectively to frequencies below and above a given value.

Another object is to provide a system of the aforementioned type whose response is substantially independent of the voltage of the current supplied.

Another object is to provide a system of the aforementioned type including an, electron tube and anenergy storage discharge circuit connect-r ed thereto whose impedance is varied in accordance with the discharge conditions of the tube;

Other objects and advantages will hereinafter appear.

The accompanying drawing illustrates one system embodying my invention but it will be readily understood that the invention is capable of various modifications, all within the scope of the specification and the appended claims.

In the drawing, Figure 1 is a diagrammatic view of the system embodying the invention, while Figs. 2 and 3 are diagrams of the voltages which determine the operation of the system.

Referring to Fig. 1, L ,-L, and I? are three supply lines of a polyphase alternating current system, i is a motor having a primary winding I and a secondary winding l One terminalof the primary winding is directly connected to the line L while the two other terminals may be reversibly connected to the lines L and U by the electromagnetic switches 2 or 3. The switch 2 has a magnet winding 2, normally open main contacts 2 and 2, normally open auxiliary contacts 2 and normally closed auxiliary contacts 2 and 2 Switch 3 has a magnet winding 3 normally open main. contacts 3 and 3. and normally closed auxiliary contacts 5! and 3 The controller also includes relays 4 and 5 having respectively magnet windings 4 and 5 and normally open triple contacts 4 and 5 The armature l of the motor is connected through slip rings S S and 8 respectively to 3 sets of resistances, the resistances connected to S being 5*, i and 8, the resistances connected to S being 6 1 and ,8 and the resistances connected to S being 6, 1, and 8. The free end of the resistances 8*, 8 and 8 are joined together thus forming a center point for the armature circuit. The contacts 4* when closed shortcircuit all resistances in the armature circuit except the resistances 6, 6 and 6, while the closure of the contactsi short-circuits only resistances 8, 8 and 8. I also provide a relay 9 having a magnet winding 9" and normally open contacts 9' and 8.. The winding 9 is connected to the anode lo of an electron tube III which also has a cathode Ill and a grid 10. The cathode i0 is connected to slip ring S while the other end of the winding 9 is connected to the slip ring S The system further includes a rectifier I I which is shown here as being of the thermionic type but which may be of any other suitable type. The rectifier has a"cathode ll and an anode H, the connections of which will be explained hereinafter. Connected to the grid ill is a condenser 12 having plates of opposite polarity l2 and II".

The condenser is paralleled by a preferably noninductive impedance I3. The plate i2 is connected to the cathode H through a non-inductive resistance ii, the cathode H in turn being connected through an inductance I 8 to the slip ring S The inductance I8 is paralleled by a condenser'l'l having plates of opposite polarity I1 and I1". An additional condenser l9 having plates of opposite polarity 19 and 19 is 'connected in parallel with the inductance I8, such connection being controlled by the normally closed contact 3'. A transiormer 20 has its primary winding 20 connected across the slip rings S and S while one end of its secondary winding is connected to the slip ring S and its other end through a non-inductive resistance 2| to the anode H 2| is connected in circuit with the winding! and in series therewith are normally closed contacts 22 of a push button switch 22, said normally closed contacts 22" in turn being connected to line L The switch 2! is short-circuited by contacts 2 when the magnetic switch 2 is energized.

The controller operates as follows:

If it is desired to start the motor -I from rest, push button switch 2| is depressedjthereby closing a circuit from line L through normaliy'closed contact 22, push button "switch ILcolI'E-Q- riori A normally open push button switch next half cycle when the tube l I is non-conductmains energized. The motor accelerates with all of the resistances inserted in the secondary circult-until it reaches a certain speed determined by the value of such resistances.

If it is desired to further accelerate the motor, the switch 23 is closed. This completes an energizing circuit for coils 4 and 5* and switches 4 and 5 short circuit resistances 1, l 1 and 8', 8 and 8 and thus cause the motorto attain a higher speed.

The action of the controller in'plugging shall now be explained. With the motor running in the forward direction a voltage is induced in the secondary circuit, the frequency and magnitude of which varies with the speed of the armature.

This voltage is impressed upon the primary winding 20 of the transformer 20 and a corresponding voltage is induced in the secondary winding 20", the latter winding being so connected that.

during the half cycle when the terminal S is negative with respect to the terminal 8' the anode ii is negative with respect to the cathode ll. As the tubes l0 and ii are uni-laterally conducting, current can flow through the tube ii only during the half cycle when the tube i0 is nonconducting. Therefore a charging current flows through the tube II to the condenser I! only during that half cycle when no current flows between the' main electrodes of tube charging current causing the condenser plate I'l to assume a charge which is positive with respect to the terminal S and cathode ill. During the ing the charge of the condenser i'i tends to leali off through the impedance l8 and the resistance vII, which are so proportioned that a continuousoscillating current of substantially constant frequency of oscillation is set up in the condenser circuit. The voltage impressed upon the tube i0 is designated as E in Figure 2 while the voltage induced in the secondary winding is designated as Bi and it will be understood that this voltage is of Figure 2 and the potential of i1- reaches zero at a time t from the moment when it was a maximum, which time is substantially constant' independent of the value of such maximum voltage or the frequency of the impressed voltage E. After having reached zero value the condenser charges in the opposite direction and the system consisting of condenser I! and impedance ll continues to oscillate with decreasing amplitude but at a constant frequency for a considerable time if not prevented from doing so, as will be explained presently. v

It will be observed that the cathode il has at any moment the same potential as the plate il The tube I I becomes conducting whenever the anode li is sumciently positive with respect to the cathode H. As the voltage induced in winding 20'' after the initial charge of the condenser I0, such' then increases again towards zero, the voltage of the anode Ii becomes ultimately positive with respect to the cathode ll. 50 that the charge of the condenser causes a current flow from plate l'l over winding 20", resistance 2| and tube Ii to plate l1, thus reducing the charge of the condenser and the negative potential of grid HF. By properly adjusting the 'impedances in this circuit the charge of the'condenser I] is again reduced to zero at approximately the moment when E and E pass through zero as indicated in Fig. 2.

The function of. the condenser l2 and parallel resistance II will now be described. Let us as-- sume that the condenser l2 was-omitted and the tube III- was conducting during the positive half cycle and that the instantaneous grid potential it reached the critical value at which it just prevents the tube from further conducting, while at'the same time the motor speed was slowly changing. Under these conditions the margin between the condition of current conduction and non-conduction through the tube for succeeding half cycles is very small and any sudden variation of the voltage of the supply circuit or minute temporary variations in the tube characteristic or other disturbing influences will alter the potential of the grid i0 sumciently to change from the condition of discharge to the condition of stoppage of the tube II and hence without the steadying effect of the condenser i! there would be a tendency for the relay 8 and with it for the accelerating switches l and i td flutter. The condenser i2 provides for a definite and predetermined margin in the operation of the controller in the manner that if the tube I 0 starts at a given frequency of the voltage between the terminals S and 8 conditions are set up which cause it to continue to start during succeeding working half cycles'until discharge is stopped at some other definite frequency, such starting andstopping frequencies being sufficiently far apart to prevent telegraphing due to the disturbances aforementioned.

This action may be explained as follows: When the tube in is non-conducting during a negative half cycle, the condenser I2 is charged, the plate I2 being negative with respect to plate if. The charging current flows from S through winding 20*, the resistance 2i, rectifier II, the resistance i5, condenser i2, gridl0, cathode lii' to line S During the next positive half cycle the condenser I 2 discharges through the resistance i3, the voltage of the plate I! and the grid HP at the beginning of the following negative half cycle, depending upon the discharge rate through resistance It The'condenser thus, during succeeding half cycles, raises the potential of the grid [0 until an equilibrium is reached. If, however, the discharge conditions of the oscillating circuit consisting of condenser l1 and inductance I8 and the charge of condenser I! are such as to permit starting of the tube III, that is the potential impressed upon the grid il by the oscillating circuit being sufiiciently positive with respect to the cathode I II, the condenser if can discharge not oniy through the resistance I! but since the tube It is glowing, discharge current can alsofiow from the grid l0 through condenser I 2 and impedances II and II to the cathode I0- so that the discharge rateof condenser I2 is increased and the voltage impressed upon the grid I 0 at the beginning of the positive half cycle is gradually lowered in the reverse sense from that described above. so that the critical instantaneous grid voltage at which the tube l3 responds is lowered: v

The resistance. II is made relatively high so that the voltage impressed upon the condenser I! at any time depends not only uponthe value of the charging voltage but also upon the amount of charge remaining on the condenser at the end of its discharge period with the result that when the tube I is conducting the voltage on the condenser II is lessthan it is for the corresponding moment in the cycle when I is non-conducting. Thus for a corresponding moment in the cycle when the tube III is conducting the negative bias on the grid HF due to the condenser 12 is reduced and the tendency for the tube M to start is thereby increased from that when the tube was non-conducting during the previous positive half cycle. The starting of a discharge thus produces conditions in the tube Ill tending to maintain the tubeconducting and vice versa, the stopping of the discharge decreases the tendency of the tube to restart. However, the condenser l2 and the parallel resistance [3 which are inserted in the connection between the grid 1 and the oscillating circuit may, under certain conditions, not be necessary.

The dotted line in Fig. 2 indicates the nega-.

tive voltage which must be impressed upon the grid of the tube Hi to prevent it from starting conduction of current during the positive half cycle of the alternating voltage impressed upon it, that is during that half cycle in which the anode is positive with respect to the cathode. If the grid potential is at any instant during the positive half cycle more positive than the values represented by the dotted lines, the tube It becomes conducting.

Fig. 2 may be considered to represent thecon- -ditions at a frequency above the critical frequency. It will be seen from the diagram that during the first part of the half cycle the grid voltage E is positive and therefore the tube Ill becomes and stays conducting during the posi- 'tive half cycle. It thereby energizes the relay winding 9' and the relay closes normally open contacts 9'' and 9. In closing normally opencontact 8 the relay connects coil 4' in circuit, the current flowing from line L through contact 9,

Y coil 4, through normally closed contact 3* to line 1?. Switch 4 therefore closes contact 4" and short-circuits some of the armature resistance of the ,motor thereby increasing its current and torque. On the other hand, when the armature frequency is equal to the critical frequency, the

. voltages are as represented by Fig. 3. It will be seen, that now the grid voltage E is always more negative than the critical voltage of tube It during the working half cycle, so that relay 9 does not receive any more current and is deenergized.-

thereby causing reinsertion of resistance in the armature circuit and decrease of the motor torque.

Kit is desired to stop the motor push button switch 22 is depressed thereby opening the current supply to the switch 2 and causing the latter to open the connections to the primary winding of the motor. Simultaneously contact 22 is closed, completing a circuit for the coil 3' of switch 3 from line L through contact 22", contact 2 through the coil 3 to line I This causes the switch 3 to reverse the connections between the motor and the lines L and L thus reversing its torque and causing it to slow down. when the switch 3 closes it also opens the normally closed contact 3 which opens the circuit of the switches l and I thereby reinserting all of the aceelerating resistance in the armature circuit of the motor and limiting the reverse torque and the current taken by the motor from the line. 1

The energization of switch 3 also opens contact 3' which disconnects the condenser is from the oscillating circuit so that the total capacitance of the circuit and its time constant is reduced, and the tube ll responds to a relatively higher frequency of the secondary circuit, which may be equal to the primary frequency. When deenergized the switch 2 also closes normally closed contacts 2 and completes a circuit from line L through contact 2 and through the coil 5 of switch 5 to line 18. This energizes switch 5, it-

being assumed that switch 23 is open and causes it to short-circuit-the resistances 8-, 8 and 8.

The oscillating circuit is adjustedsothatthe tube I is conducting during the positive half cycle as long as the motor has not come to a standstill, in the manner aforedescribed, but as the motor slows down the frequency and the voltage in the secondary circuit decrease while the frequency of the oscillating circuit remains constant, until ultimately the conditions are as represented by Fig. 3, wherein the grid voltage E during the entire working half cycle of the voltage E is less than the critical voltage required to cause the tube III to become conducting. When this condition obtains the relay 9 is deenergized and it opens contact 9 which deenergizes switch 3, the latter disconnecting the motor from the line. By proper adjustment of .the oscillating circuit, the time t can be made such that the motor is disconnected at the moment when its armature comes to a standstill, that is, when its frequency is just equal to the primary frequency. It will be understood, however, that the time constant of the oscillating circuit maybe adjusted to any other value, so that the motor is disconnected from the line either before or after it passes through zero speed.

The system may also be used for maintaining constant the speed of the motor at any desired valuein the forward direction rotation. As has been explained when only the condenser I1 is inserted the oscillating system is preferably adjusted to cause the tube In to respond when the motor is at standstill, that is, at a frequency equal to the primary frequency of the motor. When the motor operates in the forward direction, that is, when the switch 2 is energized and the switch 3 is deenergized the condenser i9 is connected in parallel with the condenser l1 thereby increasing the time constant of the oscillating system so that the tube Ill responds to a frequency of the secondary circuit of the motor corresponding to some definite speed in the forward direction. Below this speed the conditions which obtain are illustrated by Fig. 2, that is, the frequency of the secondary circuit is such that the relay 9 is energized during each positive half cycle and its normally open contacts 9' are closed thus also energizing switches I and 5 and short-circuiting the resistances 1*, l and 1; and 3, 8 and 8. As soon as the motor has reached the critical speed, however, the conditions are as illustrated in Fig. 3 and the relay 9 is deenergized. It therefore opens the circuit of the switches I and 5 and reinserts the resistances above-mentioned thereby slowing down the motor. This again increases the frequency of the "secondary circuit thereby causing energization of the relay 9 and the switches 4 and 5 and acceleration of the motor. This intermittent operation of the motor is continuedand the average speed of the motor is maintained at a desired value which is determined .by. the ad iustment of the oscillating circuit,

new'and desire to secure by ombination, i an alternating current variable frequency, a gaseous discharge tube? having a cathode, an anode and a grid,

means to connect-said cathode and anode in circuit with said source and to pass current therebetwee'nwhenthe frequency of said source is approximatelyequal to a given frequency and to terminate such passage when the frequency of said source is below said given frequency, said means including an oscillating circuit adapted to oscillate at said given frequency and connected to said source, and a connection between said oscillating circuit-and said grid to impress upon the latter an oscillating voltage induced in said latter circuit.

2. In combination, an alternating current source of variable frequency, a translating device, means to connect the latter to the former and to supply it with energy from said source when the frequency of said source is approxi mately equal to a given frequency and to ter minate such supply when the frequency of said source'is below said given frequency, said means including a gaseous discharge tube having a cathode and an anode connected in circuit with said source and said translating device and also having a grid, an oscillating circuit adapted to oscillate at said given frequency and connected to said source, and a connection between said oscillating circuit and said grid to impress upon the latter an oscillating voltage induced in said latter circuit."

3. In combination, an alternating current source of variable frequency, a translating device, means to supply the latter'with energy and to control such energy in response to the departure of the frequency of said source from a. given frequency, said means including a gaseous discharge tube having a cathode, an anode and a grid, means to connect said cathode and anode in circuit with said source and to pass current there between when the frequency of said source is approximately equal to a given frequency and to terminate such passage when the frequency of said source is below said given frequency, an oscillating circuit adapted to oscillate ;at said given freque'icy and connected to said source, and a connection between said oscillating circuit and said grid to impress upon the latter in oscillating voltage induced in said latter circuit.

4. An alternating current supply, a gaseous discharge tube having a cathode and an anode connected thereto and also having a grid, a source of variable voltage connected to said grid and controlling the initiation of discharge current between said cathode and'anode during alternate half cycles of said alternating current, and means of variable voltage and said grid and means to I vary the impedance of said energy storage discharge circuit in response to the discharge current of said tube.

6. An alternating current supply, a gaseous discharge tube having a cathode and an anode connected thereto and also having a grid, means for supplying said grid with a variable voltage from said supply for controlling the initiation of discharge current between said cathode and anode during alternate half cycles of said alternating current, an energy storage discharge circuit in series with said source of variable voltage supply means and said grid, and'means' to vary the impedance of said energy storage discharge circuit in response to the discharge current of said tube.

7. An alternating current supply, a gaseous discharge tube having a cathode and an anode con-- nected thereto and also having a grid, means for supplying said grid with a variable voltage from said supply for controlling the initiation of discharge current between said cathode and anode .during alternate half cycles of said alternating current, a resistance and a condenser in series with said source of variable voltage and said grid, a second resistance in parallel with said condenser; to afford discharge of the latter, the

rate of discharge being varied in response to the discharge current of said tube.

GLENDON C. BROWN.

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