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COHTROL SYSTEM
Filed July 25, > 1941
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TORQUE ourpur
OF POWER MOTOR
l
I
.
1
I
POSITION OF FOLLOV-UP
RELATIVE TO copesspomozmcs
Inven’mor:
John L’. Emwer“,
2,467,866
Patented Sept. 17, 1946
UNlTED STATES PATENT OFFICE
2,407,866
CONTROL SYSTENI
John L. Bower, Schenectady, N. Y., assignor to
General Electric Company, a corporation of
New York
Application July 23,
7 Claims.
194 1, Serial No. 403.5199
(Cl. 172-439)
2
1
This invention relates to control systems, more
particularly to follow-up control systems for driv
ing an object into positional agreement with a
pilot device, and it has for an object'the provi
sion of a simple, reliable and improved control
system or" this character.
In the operation of follow-up systems, it fre~=
use
quently
and occurs
is disconnected
that when
from
thethe
system
poweri" system,
not
the pilot device is moved out of positional corre
spondence with the driven object by a large
amount. When the follow~up system is recon»
nected with the power system for the purpose of
resuming operation, a very large syrchronizing
torque is developed in a direction to restore the
system to synchronism, i. e., to return the driven
object toward correspondence with the pilot de
vice. The initial positional disagreement may be
so large that the’ synchronizing torque will be of
su?icient magnitude to cause the driven object
to be driven toward positional agreement at such
a high velocity as to result in overshooting and
a subsequent condition of hunting or oscilla
torque amplifying system in which the driven ob
ject is driven by an electric motor under the con
trol of suitable means for producing a signal
Voltage dependent upon the positional disagree
ment of the pilot device and. driven object. For
better and more complete understanding of
the invention, reference should. now be had to
the following speci?cation and to the accom»
panying drawing of which Fig. 1 is a simple, dia
gra'mmatical representation of an embodiment of
the invention, and Fig. 2 is a chart of character
istic curves which serve to facilitate an under
standing of the operation of the invention.
Referring now to the drawing, a massive ob
ject M which may be a Searchlight, a gun, a gun
director or other object is to be driven in posi
tional agreement with a pilot or control device‘ l i
by suitable driving means such, for example, as
represented by the direct current electric motor
!2 to the drive shaft of which the driven object
if} is connected by imeans of suitable reduction
gearing (not shown). Direct current is supplied
positional disagreement of the pilot device and
to the armature of the motor 52 by means of a
suitable power ampli?er i3 and is under the con
trol of a pair of electric valves l4, 55.
The power ampli?er I?» may be of any suit
able type. For example, it may be an electric
valve type ampli?er, or it may be a dynamoelec~
driven object in excess of a predetermined value
tric machine ampli?er such as an armature reac
for reducing the synchronizing torque substan~
tially below the Value that would otherwise be
developed for such positional disagreement.
Follow-up systems of the character described
tion excited dynamoelectric machine. Since the
speci?c structure of the power ampli?er per se
does not constitute a part of this invention, it is
tion about the position or" correspondence. Such
a condition is of curse highly undesirable.
In order to minimize this undesirable condi~
tion, means are provided which are responsive to
represented conventionally in the drawing. If
the power ampli?er it should be of the electric
preventing hunting during normal operation of
valve type, it would preferably have two separate
the system. One form of such antihunting
conducting paths each controlled by a separate
means utilizes a capacitor for modifying the ccn~
grid and these control grids would be connected
trol of the driving means during the normal oper
by means of conductors it and H to the anodes
of the electric Valves M and I5. On the other
ation of the system. However, during the oper
ation of synchronizing the system from a large 40 hand, if the ampli?er is of the dynamoelectric
initial positional disagreement, the ability of the
machine type, it would preferably be provided
with a pair of control ?eld windings and these
capacitor to prevent hunting leaves much to be
?eld windings would be connected by means of
desired. For the purpose of providing an im
proved control during such synchronizing opera
conductors l6 and ii to the anodes of the elec
tion, means are provided which are responsive 45 tric valves l4 and lb. The electric valves iii and
55 may be of any suitable type but they are pref~
to speeds of the driving means in excess of a
predetermined value for by-passing the capacitor
erably vacuum triodes of the “hard” tube type.
and supplying a control voltage to the controlling
The cathodes of the valves iii. and it have a
common connection iii to an intermediate point
means for the driving means for modifying the
of an adjustable voltage. divider 59 which is con
control of the driving means in accordance with
nected across a suitable source of alternating
the speed of the driving means during the period
are provided with suitable antihunting means for
that the speed of the driving means exceeds a
voltage represented by the two supply lines ‘it.
A. pair of resistors 2i and 22 is connected across
the anodes of the valves ill and I5, and the junc
In illustrating the invention in one form there
of, it is shown as embodied in a follow-up or 55 tion point of these two resistors is connected by
predetermined value.
.
2,407,866
3
means of conductor 23 to one side of the source
4
clear that the rotation of the rotor of the trans
of alternating voltage 20. The cathode grid cir
mitter or of the receiver regulator will vary the
magnitude of the component voltage supplied to
cuit of the electric valve ill extends from the
cathode through conductor 58 and the right-hand
the grid circuit of the electric valves M
i5
portion of voltage divider l9 through conductor Cl which, in turn, will result in a variation in the
24, stabilizing resistor 25, and the right-hand sec—
relationship of the current flowing in the valves
ondary winding of input transformer 25 to the
14 and 15. This will ultimately result in causing
grid of the valve l4. Similarly, the cathode grid
the ampli?er l3 to supply current in one direc
circuit of the electric valve I5 extends from the
tion or the other to the armature of the driving
cathode to the conductor 24 by the circuit pre 10 motor l2. The grid connections to the electric
viously traced and thence through stabilizing re
valves M and 15 are so made, as explained in the
sistor 21 and the left-hand secondary winding of
foregoing, that when the signal voltage supplied
the input transformer 26 to the grid of valve 15.
to the primary winding of the input transformer
The voltages of the grids Ma and ‘5a with respect
is varied, the voltage applied to the grid of one
to the cathodes Mb and I511, respectively, as a re 15 of the valves is increased, and the voltage ap
sult of the inclusion of a portion of the volt
plied to the grid of the other valve is simultane
age divider IS in the anode-cathode circuit of the
ously decreased. Consequently, when the cur
valves are such that both valves normally conduct
rent through one of the valves is increased, the
equal amounts of current. This condition of
current through the other valve is simultane
equal conduction in both valves l4 and it occurs 20 ously decreased. As a result of the increase in
when the follow-up system is in correspondence,
current flowing through one of the valves and
1. e., when the driven object in is in positional
the decrease in current flowing in the other valve,
agreement with the- pilot device i I, and the veloce
the ampli?er i3 is caused to supply direct cur
ity of the driven object I!) is unchanging.
rent to the armature of motor I2 in one direction
In order to vary the bias voltages of the grids
or the other depending upon whether the cur
Ida and 15a of the valves I4 and I5, respectively,
rent is increased in the valve M or the valve H5.
a component voltage of variable magnitude is
The rotor member of the receiver regulator 28
supplied to the grid circuit substantally in phase
is connected through suitable gearing 33 to the
with the anode voltages of these valves through
shaft of the driving motor 12.
the input transformer 26 whose secondary wind
For the purpose of preventing hunting during
ings 26a and 25s are connected in the cathode
the normal follow-up operation of the system,
grid circuits of the electric valves l4 and I5, as
that is to say, during operation other than syn
explained in the foregoing, and whose primary
chronizing the system from a condition of large
winding is connected to the single phase alter
nating current source 20 through suitable rotary 35 angular disagreement between the pilot device
and driven object, a suitable electrical energy
induction apparatus illustrated as comprising the,
storage device such, for example, as a capacitor
pilot device H which is referred to as a trans
3| is connected in series relationship with the
mitter and the rotary induction device 28 re
stabilizing resistors 2'5 and 2'! across the terminals
ferred to as the receiver regulator. The rotary
induction device ll comprises a rotor member 40 of a tachometer generator 32 which is driven by
the driving motor [2 and generates a voltage
Ila provided with a single phase winding (not
substantially linearly proportional to the speed
shown) connected across the single phase source
of the motor 12. As a practical alternative, the
20, and a stator member lib provided with a
capacitor 3! might be connected in series with
distributed three-element winding (not shown)
the stabilizing resistors 25 and 21 across the ar
that is physically similar to the polyphase wind
mature terminals of the drive motor l2, since
ing of a wound rotor induction motor. The stator
the countervoltage of the drive motor i2 is ap
and rotor windings are arranged in inductive
proximately proportional to its speed under most
relationship with each other so that the
normal operating conditions. It is preferred,
alternating magnetic ?eld owing to the cur
rent ?owing in the primary winding induces 50 however, to utilize the tachometer generator 32.
This generator may either be provided with a
voltages in the winding element of the second
?eld winding 322, as shown, or it may be of the
ary winding. The receiver regulator 28 is in all
permanent magnet type. The charge on the
respects identical with the transmitter II, and
capacitor 3! varies as the voltage of the generator
the terminals of its stator winding are con
32 varies, which is to say that the charge on the
nected to the terminals of the stator winding of
capacitor varies as the speed of the driving mo
the transmitter by means of conductors 29 so
tor I2 varies. When the speed of the driving
that the voltages induced in the stator winding
motor l2 and the voltage of the generator 32 are
of the transmitter cause current to ?ow in the
constant, the charge on the capacitor is constant
stator winding of the receiver regulator, there
and when the voltage of the tachometer gen
by producing a magnetic ?eld similar to the mag
erator is varying at a high rate, the charge on
netic ?eld produced by the current ?owing in the
the capacitor is likewise varying at a high rate.
rotor winding of the transmitter. Rotation of
When the charge on the capacitor is varying, a
the rotor member of the transmitter causes a
current is caused to ?ow through the resistors 2'5
voltage to be induced in the rotor winding of
the receiver owing to the shift in the position
and 27 which is proportional to the rate at which
the charge on the capacitor is varying. In other
of the axis of the magnetic ?eld of the receiver
regulator relative to the axis of the coil of the
words, the current caused to flow in the stabiliz
rotor member, and the magnitude of this in
ing resistors is proportional to the rate of change
duced voltage depends upon the relationship of
of the charge on the capacitor which, in turn,
the axis of this winding to the axis of the mag 70 varies in accordance with the rate of change of
netic ?eld, e. g., when the axes of the magnetic
the voltage of the tachometer generator, and
?elds and of the rotor winding are parallel, the
therefore, to the rate of change of speed of the
induced voltage is maximum, whereas when these
motor I 2. Thus, the capacitor 31 introduces a
axes are at right angles with each other, the
correcting influence or voltage in the grid cir
induced voltage is zero. It will therefore be 75 Quit Of the electric valves it‘ and i5 which is
2,407,866
5
6
proportional to the rate of change of speed of
the driving motor‘ l2.
of the. capacitor 31 and the stabilizing resistors
25 and 21.
The voltage drop device 34 may be of any suit
able type. An ordinary incandescent lamp has
been found to give very good results.
With the foregoing understanding. of the ele
ments and their organization in the completed
system, the operation of the system itself will
readily be understood from the following detailed
The polarity of the. connections of the ca
pacitor 3! is such that the variations in the
current flowing through the stabilizing re
sistors 25 and Z'l' are out of phase and leading
with respect to any incipient hunting of the
driven object about the position of corre
spondence. The e?ect is of transiently varying
the current supplied to the driving motor it '10
description;
Assuming that the switch 39 is closed to con
ally supplied to the motor 12 is di?erent from
nect the follow-up system to the power source 20
the amount that would be supplied for any
and that the driven object Ill is in correspondence
positional disagreement of the pilot device and
with the pilot device II, the system will be in the
driven object in the absence of the capacitor 35. 15 synchronized condition in which it is illustrated.
general, when the system is approaching cor~
As previously pointed out, when in this condi
respondence, the effect produced by the capacitor
tion, both valves M and i5 are conducting equal
is to reduce the current supplied to the motor
amounts of current so that the net output of
the power ampli?er l3 to the driving motor [2 is
below the value of current that would otherwise
be supplied to the motor for any given error. 20 zero. Manual rotation of the pilot device II ef
However, if the system is approaching corre
fects a corresponding rotation of the magnetic
spondence at a very high velocity, the current
?eld of the stator of the receiver regulator 28
supplied to the motor l2 may even be reversed
so that a voltage is induced in the rotor winding
and braking torque thereby produced to prevent
of the receiver regulator approximately propor~
overshooting.
25 tional to the amount of rotation of the pilot de
vice ll. This induced voltage is applied to the
For the purpose of effectively controlling the
grid circuit of the electric valves is and I5 and
operation of the system when synchronizing from
results in increasing the current ?owing in one
condition of large initial error, additional syn
of the valves, e. g. the valve I4 and in decreasing
chronizing means is provided which comprises
the current flowing in the valve It. This results
electric valve apparatus 33 and a variable voltage
in causing a current to be supplied to the motor
drop device 35'. The electric valve apparatus 33
[2 in such a direction that the motor is caused
comprises a pair of electric valves 85 and 35 of
to rotate in a direction to drive the object IE! to
the gas containing triode type. Electric valve 35
ward correspondence with the pilot device 5 I. As
has a cathode 35a and a starting anode 35b con~
nected across one of the secondary windings of ‘v the object Iii approaches correspondence with the
pilot device, the signal voltage supplied through
the synchronizing transformer 31 whose primary
the input transformer 2% to the grid circuit of
winding 3'53 is connected across the primary wind
the electric valves l4 and it decreases and be
ing of the input transformer 26 so as to be re
comes zero when the condition of correspondence
sponsive to the signal voltage that is supplied
is reached, thereby cutting off the supply of cur
from the receiver regulator 23 to the input trans
rent to the driving motor l2. The operation just
former. The valve 35 also has a main anode 3%
described may be considered to be the normal
which together with the cathode 35a is connected
follow-up operation of the system.
across the capacitor 35. The electric valve 35 is
If the switch 33 should be opened to disconnect
in all respects identical with the electric valve 35
and, as shown, it has a cathode 35a and a start 45 the follow-up system from the power source 2d,
the synchronizing force between the driven object
ing anode 2555s which are connected across the
terminals of the other secondary winding of the
and pilot device H would disappear. While in
this condition the rotor of the pilot device I I may
transformer 31s. The main anode 35c and the
cathode 3311 are also connected across the capaci
coast or easily be moved to a new position such
that a large positional disagreement exists be
tor 3!. A potentiometer 38 is connected across
the terminals of the tachometer generator 32.
tween the driven object and pilot device. This
condition may and frequently does arise during
The electric valves 35 and 36 are so designed
normal use of the system.
that when the voltage between the cathodes and
so that the amount of current that is actu
the starting anodes reaches or exceeds a prede
termined value, such for example as 90 volts, con
duction takes place between the cathodes and
If new the switch 39 should be reclosed to re
sume normal operation, a large signal voltage
would be induced in the secondary winding of the
receiver regulator 28 and supplied through the
the starting anodes. This conduction will con
tinue until the voltage across the cathodes and
transformer 26 to the grid circuit of the electric
starting anodes is reduced to some considerably
valves Ill and I5, and a large current would be
lower predetermined value, such for example as (ill supplied to the driving motor 52. This current
60 volts. If at the same time there is a positive
would produce an excessively large synchronizing
torque which would not only restore the driven
voltage on the main anodes 350 or 36c, conduction
object Ill to a position of correspondence with the
will also take place between the main anode and
the cathode. The triode valves 35 and 35 are so
pilot device I i but would actually cause the driven
designed that conduction does not take place be
object to overshoot the position of correspond
tween the main anodes and the cathodes unless
the voltage supplied from the tachometer gener
ator 32 equals or exceeds a predetermined value
corresponding to a predetermined speed of the
ence and initiate a series of oscillations.
If the synchronizing means 3d and 35 were
omitted, the relationship between the torque of
the driving motor and error of the system, i. e.,
driving motor E2.
70 position of the driven object ill away from cor
The cathode of each of the valves 35 and 3c is
respondence, would be as indicated on curve ill
connected to the main anode of the other valve,
in Fig. 2 in which ordinates represent torque out
so that regardless of the direction of operation
put of the driving motor and abscissae represent
of the system, there will be a conducting path
the error or amount out of correspondence.
from the potentiometer 38 to the junction point 75
With the connections from the main anodes of
2,407,866
7
8
the gas triode valves 35 and 33 to the capacitor
3| removed, the voltage drop in the incandescent
lamp 34 is su?icient to reduce the torque of the
synchronizing circuit ceases to operate and the
follow-up system then returns to normal oper
ation. The remaining operation of the system
as the driven object I0 approaches the position
of correspondence with the pilot device is in ac
cordance with the curve 43.
During normal follow-up operation, the system
is una?ected by the synchronizing circuit as long
as the speed of the driving motor does not rise to
a value such that the adjustment of the poten
tiometer 33 causes conduction to take place be
driving motor for each value of error as repre
sented by the broken curve 4 I. In describing this
operating condition it is assumed that the error is
of such magnitude as to cause voltages to be in
duced in the secondary windings of the synchro
nizing transformer 31 of suf?cient magnitude to
cause conduction to take place between the cath- .
odes and the starting anodes of the valves 35 and
36. In Fig. 2 the amount of error existing at the
time of closing the switch 39 is represented by the
abscissa of vertical line 42.
tween tho cathodes and main anodes of the gas
triode valves 35 and 36, or as long as the error
does not exceed the critical value at which con
With the connections. between the main an
odes 35c and 360 of the valves 35 and 33 to the
capacitor 3! intact, which is the condition illus
trated in the drawing, the torque of the driving
duction is initiated between the starting anodes
and cathodes of these valves.
Although in accordance with the provisions of
the patent statutes this invention is described as
motor ii for each value of error is represented
embodied in concrete form and the principle
by the dotted curve 43. This further modi?ca 20 thereof has been explained together with the best
tion of the torque results from the variation in
mode in which it is now contemplated applying
grid voltage oi‘ valves hi and i5 produced by
that principle, it will be understood that the ele
conduction between the main anodes and cath
ments and apparatus shown are merely illustra
odes of valves 35 and 36 in response to the volt~
tive and that the invention is not limited there
age of tachometer generator 32. Since the volt 25 to, since alterations and modi?cations will read
age of tachometer generator 32 is zero at the
ily suggest themselves to persons skilled in the
instant of the closing of switch 33, zero current
art without departing from the true spirit of this
is conducted between the main anodes and cath
invention or from the scope of the annexed
odes of valves 35 and 33 and therefore the curves
claims.
iii and 43 coincide at the point of intersection
What I claim as new and desire to secure by
with the vertical line 42. Consequently at the
Letters Patent of the United States is:
instant of closing the switch 39, the motor it
1. A follow-up control system comprising in
develops a synchronizing torque proportional to
combination a pilot device, a driven object, an
the ordinate of the intersection of the curve Iii
electric motor for driving said object, means re
with the vertical line 42. In other words, at the 35 sponsive to positional disagreement of said pilot
instant of closing the switch 39, only the volt
device and driven object for producing a con
age drop across the incandescent lamp 34 is in
trol voltage proportional to said disagreement,
strumental in reducing the torque of the driving
means responsive to said control voltage for sup
motor.
plying a variable voltage to said motor thereby
However, the motor I?! comes up to speed 40 to cause said motor to develop a torque propor
quickly and the tachometer generator 32 gener
tional to said voltage to drive said object toward
ates a voltage which is suf?cient to cause con
correspondence with said pilot device, and means
duction between the main anode and cathode of
responsive only to positional disagreement of said
one of the valves 35 or 36, and the magnitude of
the current so conducted increases as the speed
of the motor l2 increases. As the voltage of the
tachometer generator 32 increases, the increas~
ing current through the stabilizing resistors 25
and 2'! resulting from the conduction through
one or
oe other of the valves 35 and 33 causes '
pilot device and driven object in excess of a pre
determined amount for reducing said control
voltage thereby to reduce the synchronizing
torque of said motor.
2. A follow-up control system for a pilot de_
vice and driven object comprising in combina~
tion driving means for said object, a control cir
the torque of the driving motor 12 to be de
cult operatively connected to said driving means,
means responsive to positional disagreement of
other words, during this operating condition, the
said pilot device and driven object for supplying
torque of the driving motor is reduced by two
to said control circuit a signal voltage varying
e?ects: (1) The reduction of the torque as a re 55 with said positional disagreement thereby to
sult of the voltage drop in the incandescent lamp,
cause said driving means to produce a torque
and (2) the voltage from the tachometer gener
corresponding in magnitude to the amount of
ator applied through one or the other of the gas
said disagreement to drive said object toward
triode valves to the stabilizing resistors '25 and
correspondence with said pilot device, a voltage
21.
60 drop device in said control circuit, an electric
As the driven object 15 approaches correspond
discharge device connected to said circuit and
ence with the pilot device H, the signal voltage
responsive only to a control voltage in excess of
supplied from the receiver regulator 28 to the
a predetermined value for completing a current
input transformer 25 decreases until ?nally at an
conducting path to produce a voltage drop across
error E the signal voltage decreases below the 65 said voltage drop device thereby to decrease said
critical value which is required to support con
signal voltage and reduce the synchronizing
duction between the starting anodes of the valves
torque of said driving means.
35 and 36 and the cathodes. By this time the
3. A iollow~up control system for a pilot device
speed of the driving motor has been so reduced
and driven object comprising in combination
that the voltage generated by the tachometer 70 driving means for said object, a control circuit
generator 32 is insufiicient to support conduction
operatively connected to said driving means,
means responsive to positional disagreement of
between the main anodes of the valves 35 and 38
said pilot device and driven object for supplying
and the cathodes.
creased in accordance with the curve 43.
In
When the valves 35 and 35 cease conduction
a signal voltage to said circuit to cause said driv
both through the starting and main anodes, the 75 ing means to drive said object toward corre
2,407,866
10
device connected in said control circuit, means
driving means for said object, means for control
ling the energization of said driving means com
for reducing the synchronizing torque of said
prising electric valve apparatus provided with a
spondence with said pilot device, a voltage drop
control grid, means responsive to positional dis
driving means comprising an electric discharge
agreement of said pilot device and driven object
device connected to said circuit and responsive
for supplying a signal voltage to said control
to a predetermined value of said control voltage
grid to control said motor to drive said object to
for completing a current conducting path to pro
ward correspondence with said pilot device, an
duce a voltage drop across said voltage drop de
tihunting means comprising a capacitor connect
vice thereby to decrease said signal voltage and
means responsive to the speed of said driving 10 ed to said grid and means for supplying to said
capacitor a second voltage proportional to the
means for further modifying the torque of said
speed of said driving means thereby to modify
driving means.
the voltage applied to said grid in accordance
4. A follow-up control system for a pilot de
with the rate of change or speed of said driving
vice and driven object comprising in combination
driving means for said object, means for control 15 means, means responsive to said signal voltage
in excess of a predetermined value for substan
ling the energization of said driving means com
prising electric valve apparatus provided With a
control grid, means responsive to positional dis
agreement of said pilot device and driven object
tially decreasing said signal voltage, and means
responsive to said second voltage in excess of a
predetermined value for by-passing said capaci
for supplying to said grid a signal voltage vary 20 tor so that said grid voltage is modi?ed in ac
cordance with the speed of said driving means
ing with said positional disagreement to control
when the speed of said driving means is greater
said driving means to drive said object toward
than a predetermined value.
correspondence with said pilot device, means re
7. A follow-up control system for a pilot de
sponsive to a speed of said driving means in ex
cess of a predetermined value for modifying the 25 vice and driven object comprising in combina
tion driving means for said object, means for
voltage supplied to said grid in accordance with
controlling the energization of said driving
said speed, and means responsive to said signal
means comprising electric valve apparatus pro
voltage in excess of a predetermined value for
vided with a control grid, means responsive to
substantially decreasing the signal voltage there
by to reduce the synchronizing torque of said 30 positional disagreement of said pilot device ‘and
driven object for producing a signal voltage
driving means.
varying with said disagreement, electrical con
5. A follow-up control system for a pilot de
nections from said disagreement responsive
vice and driven object comprising in combination
means to said grid for applying said voltage to
driving means for said object, means for con
trolling the energization of said driving means 35 said grid to control said driving means to drive
said object toward correspondence with said pi
comprising electric valve means provided with a
lot device, antihunting means for said system
control grid, means responsive to positional dis
comprising a capacitor connected to said control
agreement of said pilot device and driven object
grid and means for supplying a second voltage to
for supplying a signal voltage to said grid to con
said capacitor proportional to the speed of said
trol said driving means to drive said object to
driving means, a variable voltage drop device in
ward correspondence with said pilot device, an
cluded in said connections, means for substan
tihunting means comprising an energy storage
tially reducing said signal voltage comprising an
device connected to said grid and means for sup
electric valve device having a cathode and an
plying a voltage to said energy storage device
proportional to the speed of said driving means 45 anode connected to said connections and respon
thereby to modify the voltage supplied to said
grid, means responsive to positional disagree
sive to a voltage in excess of a predetermined
ment of said pilot device and driven object in ex
cess of a predetermined amount for substantial
ly decreasing said signal voltage, and means re
sponsive to a speed of said driving means in ex
cess of a predetermined value for rendering said
energy storage device ineffective.
6. A follow-up control system for a pilot device
to produce an increased voltage drop across said
and driven object comprising in combination 55
value for completing a conducting path thereby
voltage drop device, said electric valve device
having a, second anode coacting with said cath
ode in response to a predetermined value of said
second voltage to complete a by-pass circuit
about said capacitor thereby to render said ca~
pacitor ineffective.
JOHN L. BOWER.
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