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Патент USA US2132264

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Oct. 4, 1938.
w_ R KING
2,132,264
CONTROL SYSTEM
Filed Feb. 1, 1936
Fig.1.
0
JHA/fE/Q
MA GA/ET
'William hing,
bgg/
Hi
6‘. MM
Attorney.
Patented ‘0.1.4, ‘1938
‘
'
2,132,264
UNITED STATES PATENT OFFICE
2,132,264
ooN'raoL stem
William R.,King, Schenectady, N. Y., minor- to
\General Electric Company, a corporation oi.’
New York
Application February 1, 1938, Serial No. 61,937
5 Claims. (01. TIL-240)
This invention relates to control systems, more the following speci?cation and to the accom
par'ticularly to systems for controlling the actu- panying drawing in which Fig. 1 is a simple dia
ation of reciprocating loads, and it has for an grammatical illustration 01' an embodiment of the
object the provision of a simple, reliable, e?lcient invention and Fig. 2 is a chart of characteristic
5 and improved system of this character.
'
More speci?cally, the invention relates to control systems for vibrating screens and the like in
which the coil that actuates the load is supplied
with a periodically varying voltage from an elec10 tric valve which in turn is supplied from a source
curves explaining the operation of the invention. 5
Referring now to the drawing, one terminal of
a magnet coil‘ i0, such for example as the shaker
magnet 01’ a vibrating screen, is connected to one
side of a suitable source of alternating voltage
represented by the supply lines ii. 12- An electric 1°
of alternating voltage. In most industrial areas
the frequency of the voltage supply has some
fixed value, such for example as sixty cycles. In
the absence of any special control apparatus, a
15 valve energized from such a source would deliver
sixty current impulses per second to the coil
which in turn would deliver sixty impulses to
valve I3 is interposed in the connections between
the opposite terminal of the magnet coil i0 and
the side l2 of the supply source. As shown, the
anode lit, of the valve is connected to the side
H of the supply source and the cathode lac is 15
connected through conductors iii and E5 to the
opposite terminal of the magnet coil ill. The
the load. For certain applications, it is often de~
sirable to cause the coil to deliver a lesser num~
20 her of impulses to the load, such for example as
valve is also provided with a control electrode or
grid 13b which serves to Cfmtrol the passage of
current between the'eathode and the anode.
2G
thirty, twenty or ?fteen impulses per second.
commutator devices and, synchronous switches
have previously been utilized for producing low
frequency voltage, but such devices are expensive,
Although the valve i3 may be of any suitable
type, it is preferably of the three or four~elec~
trode type. into the Envelope Of which a Small
quantity of an inert gas such for example as
,
g5 require costly maintenance and in general leave
mercury vapor is introduced after exhaust. The 26
much to be desired. Accordingly, a further 0bject of this invention is the provision of a control system of this character for controlling an
electric valve to pass the desired low ire uency
3-!) current impulses to the actuating coil and in
which the control is carried out entirely by means
presence of this gas within the envelope serves to '
convert the usual pure electronic discharge into
an arc stream thereby constituting the valve an
electrostatically or grid controlled arc recti?er.
In valves of this type, current will flow between 39
the anode
the electrode during that half
of stationary elements and apparatus.
In carrying the invention into effect in one
cycle of the applied voltage in which the voltage
of the anode is positive with respect to the
form thereof, an electric valve having an anode,
355' cathode and control electrode is connected between a source of alternating voltage
the
voltage of t‘ cathode, provided the voltage of _
the grid 15 mole Positive than a l?l‘efictel‘mined 3"’
critical value necessary to initiate the current
actuating coil. An energy storage device, for ex~
ample, a capacitance, is connected across the
output circuit of the valve with a connection to
49 the control electrode. When the valve passes‘
current to the coil during a positive half cycle of
the anode voltage, the capacitance becomes
charged and applies a negative voltage to the
control electrode which maintains the valve non45 conducting. Means are provided for discharging
the energy storage device at a predetermined rate
so that the valve is again rendered conducting
after an interval of one or more positive halt
flow. Once current has started to how, between
the anode and cathode, the grid does not readily
control the magnitude of the current flowing in
the output circuit. Consequently, the current ‘10
?ow in the output circuit can only be stopped by
interrupting the anode circuit or reducing the
anode voltage to zero. For the purpose of sup
plying a voltage to the grid sufficiently positive _
to initiate the flow of current between the anode 4"
and‘ cathode, a transformer i6 is provided, the
primary winding l6; of which is connected across
the supply line ii, 12. This transformer has a
cycles, as desired.
50
In illustrating the invention in one form thereof, it is shown as embodied in a system for controlling the actuating coil for a vibrating screen
or the like.
For a better and more complete understanding
55 of the invention, reference should now be had to
plurality of secondary windings I61), I60 and its.
One terminal of a capacitance I1 is connected 50
through a protective resistance i8 to the grid I31;
and the opposite terminal of this capacitance is
connected through variable resistance i9 and re
sistance 20 to the cathode '30- The terminals of
the secondary winding its are connected across 55
2
2,182,264
the capacitance I1 and a resistance 2| connected
in series relationship therewith so- that an al
ternating voltage is introduced into the grid or
input circuit of the electric valve I3. Energy for
heating the cathode I30 to the required degree of
incandescence is supplied from the secondary
winding Hid to which the heating ?lament of the
cathode is connected as illustrated.
_
As thus far described, the electric valve is
10 would become conducting once during each cycle
of the alternating voltage of the source ii, I 2
and would pass an impulse of current to the mag
net coil Ill once during each cycle. Since it is
desired to pass a lesser number of current im
15 pulses through the magnet coil than the num
ber of cycles of the voltage of the source, means
are provided for rendering the valve non-conduct
ing during one or more subsequent positive half
cycles of the applied voltage. To this end, an
20 energy storage device, illustrated as a capacitance
22, is connected from the cathode I36‘ to the side
H of the supply source through a recti?er 23
and a resistor and is also connected to the com
mon connection between the resistance 2| and
25 the capacitance I‘! which is connected to the grid
i3b. Thus, the capacitance 22 is connected from
the cathode I3c to the grid I21). When the valve
I3 is conducting during a positive half cycle
3? anode voltage, the capacitance 22 becomes
30 charged and applies a negative voltage to the
grid l3s so that during the following positive half
cycle of anode voltage, the voltage of the grid
is maintained more negative than the critical
grid voltage. As a result, the valve l3 does not
35 conduct current during the following positive half
cycle of anode voltage. In order to render the
valve conducting after one or more positive half
cycles of anode voltage, as desired, means are
provided for discharging the capacitance 22 at a
40 predetermined rate. These means are illustrated
as resistances I9, 20 connected in parallel with
the capacitance 22.
-
-
In order to prevent the discharge of the ca
pacitance 22 by the reverse voltage across the
45 coil ID, the recti?er 23 is included in the con
nections between the capacitance 22 and the side
ll of the supply source. Although the recti?er
23 may be of any suitable type it is preferably
a vacuum tube having anodes 23a and a~hot cath
50 ode 23b which is heated to the required degree of
incandescence by means of energy supplied from
‘the secondary winding “is to which the cathode is
connected as illustrated.
With the foregoing understanding of the ele
55 ments and apparatus and their organization in
tive than this critical grid voltage throughout the
positive half cycle of anode voltage the valve l3
will not conduct. If at any instance this critical
grid voltage is exceeded the valve it will become
conducting and will continue to pass current dur~
ing the remainder of the positive half cycle of ap
plied voltage and as long thereafter as the anode
remains positive.
Thus, since the grid voltage of the valve 68
becomes more positive than the critical value at 10
the beginning of the first positive half cycle of
the anode voltage 24, the valve l3 becomes con
ducting and a pulse of current represented by
the heavy curve 27 flows through the magnet
coil Hi. When the anode voltage 24 passes 15
through vzero, the current 2'8 would ordinarily
tend to stop ?owing, but owing to the inductance
of the coil ill the current continues to ?ow until
a time '1‘; during the negative half cycle of voltage.
At this point the current ?ow through the coil 20
ceases.
As the current through the coil Ill builds up,
the capacitance 22 becomes charged with the
polarity indicated in the drawing so that a nega
tive voltage represented by the curve 28 is ap- 25
plied to the grid l3». Now the actual grid volt
age is the algebraic sum of the voltage represented
by the curve 25 and the voltage represented by the
curve 28 and is represented in Fig. 2 by the un
dulating curve 29. When the capacitor 22 at 30
tains its maximum potential, the charge begins to
leak oil as represented by the upward slope of the
curve 28 at a rate depending upon the ohmic‘value
of the resistances i9 and 20.
During the second Positive half cycle of the 35
anode voltage 24, the actual grid voltage 29 at no
time exceeds the critical grid voltage 26 and con
sequently the valve l3 remains non-conducting
during the entire second positive half cycle of
anode voltage. However, during the third posi 40
tive half cycle of anode voltage, the actual grid
voltage becomes more positive than the critical
grid voltage and consequently the valve I3 again
becomes conducting and passes a second impulse
of current through the magnet coil l0 and there
after the previously described operation is re
peated. Thus, it will be seen that the valve l3
only becomes conducting during every other posi
tive half cycle of anode voltage and therefore, if
the frequency of the voltage of source il, i2 is of
some commercial value such for example as sixty.
cycles, the frequency of the current impulses
through the coil ill will be thirty impulses per
second.
By varying the value of the resistance [9, the
rate of discharge of the capacitance 22 can be
the completed system, the operation of the sys- ' still further decreased, and the number of cur
tern itself will be readily understood from the fol—
lowing detailed description.
In Fig. 2, the alternating voltage of the source
ll, i2 is represented by the sinusoidal curve 24
in which ordinates above the axis 0-0 represent
positive values of voltage and ordinates below
the axis 0—O‘represent negative values of volt
age. The voltage supplied to the grid circuit
65 through the secondary winding l6b of the trans
former is represented by the light sinusoidal
curve 25. Preferably the voltage represented by
the curve 25 leads the voltage 24 by an angle de
termined by the constants of the capacitance
70 I1 and the resistance 2|. However, for the pur
pose of simplicity, this voltage is shown and de
scribed as in phase with the anode voltage. The
critical grid voltage of the electric valve I3 is rep
resented by the dotted curve 26. v If the voltage
76 of the grid remains less positive, 1. c. more nega
rent impulses per second still further reduced.
In practice, the number of current impulses has
been reduced to one impulse for every thirty posi
tive half cycles of anode voltage, although there
was no indication that this was the limit.
When the voltage passes through zero at the
end of a positive half cycle in which the valve I3
is conducting the voltage across the magnet coil
i0 reverses. This voltage reversal would dis
charge the capacitance 22 if it were not for the
recti?er 23 which prevents passage of current in
such a direction as to discharge the condenser.
It will sometimes be found advantageous to ad
vance the AC grid voltage represented by the 70
curve 25 a substantial phase angle ahead of the
anode voltage in order to insure that the valve l3
will fire as early in the cycle as possible during
those positive half cycles of anode voltage in -
which the ‘valve is to conduct. As previously 75
3
amazes
pointed out, this is etiected by means of the
pacitance IT in the grid circuit.
08,
}
It will also sometimes be found advantageous
to substitute for transformer secondary winding
l6b a secondary winding on a separate trans
former of the type commonly known as a peaking
transformer. The peaked voltage wave obtained
from the secondary of this transformer will fur
ther insure that the valve I3 will ?re as early in
10 the cycle as possible during those half cycles of
anode voltage in which the valve is to conduct. '
Although in accordance with the provisions of
the patent statutes, this invention is described as
embodied in concrete form, it will be understood
15 that the elements and apparatus are merely
illustrative and that the invention is not limited
to the exact arrangement shown in the drawing
since alterations and modifications will readly
suggest themselves to persons skilled in the art
20 without departing from the true scope of the in
vention or from the scope of the annexed claims.
What I claim as new and desire to secure by
Letters Patent of the United States is:
1. A control system for a reciprocating load
25 comprising a coil for operating said load, means
for supplying a periodically varying voltage com
prising an electric valve connected between a
source of periodically varying voltage and said
coil, and having an anode, cathode and control
30 grid, means for supplying a voltage more positive
than a predetermined critical value to said grid
during a positive, halt cycle of the voltage of
said source thereby to energize said valve to pass
current, and means for maintaining the voltage
of said grid more negative than said critical value
during a succeeding positive half cycle thereby to
render said valve nongconducting comprising a
source to said grid so that the voltage of said grid
is more positive than a predetermined critical
value during a half cycle when the anode voltage
is positive thereby to render said valve conduct
ing, means for controlling the frequency of the
voltage supplied to said coil comprising a capaci
tance connected from said cathode to said grid
and having a connection to the other terminal of
said coil to maintain the voltage of said grid
more negative than said critical value during a 10
succeeding positive half cycle of anode voltage
thereby to render said valve non-conducting, and
a resistance connected in parallel with said ca
pacitance to control the rate of discharge thereof,
and ‘a rectifier in said connection for preventing 15
the discharge of said capacitance by reversal of
the voltage of said coil.
4. A control system for a reciprocating load
comprising a coil for operating the load, means
for supplying a periodically varying voltage to 20
said coil comprising an electric valve having an
anode, a cathode and control grid, means for
controlling the frequency of said voltage compris
ing means for supplying an alternating voltage to
said grid, an energy storage device connected 25
across said cathode and control electrode and
having a connection to one terminal of said coil,
and means for advancing the phase relationship
of the alternating component of the grid voltage
relative to the anode voltage to insure energiza 80
tion of said valve substantially at the beginning
of a positive hall’ cycle of anode voltage.
5. A control system for a reciprocating load
comprising a coil for operating the load, a source
of alternating voltage of predetermined fre 85
quency, means for supplying a periodically vary
ing voltage of reduced frequency to said coil com
capacitance connected across said cathode and
prising an electric valve having an anode con
grid and having aoonnection to one terminal of
nected to said source, a cathode connected to one
terminal or said coil, and a control grid, conec 40
tions from said source for supplying an alternat
ing voltage to said grid so that the grid voltage
is more positive than a predetermined critical
value when the anode voltage is positive thereby
to energize said valve to conduct current, a ca 45
pacitance connected from said cathode to said
grid and having a connection to'the opposite ter
minal of said coil for maintaining the voltage oi’
said grid more negative than said predetermined
said coil and a recti?er in said connection for
preventing discharge of said capacitance by re
versal of voltage of said coil.
’
2. A control system for reciprocating load com
prising a coil for operating the load, means for
45 supplying a periodically varying voltage to said
coil comprising an electric valve connected be
tween said coil and a source of voltage of pre
determined irequency and having a cathode,
anodeand control grid and means for controlling
50 the frequency or the voltage applied to said coil
comprising a ‘capacitance connected across said
cathode and‘grid and having a connection to said
coil, airesistance connected in parallel with said
capacitance for controlling the rate 01' discharge
thereof, and, a rectifier included in said connec
value during the following positive halt cycle of 50
anode voltage thereby to render said valve non
conducting, a rectifier included in said connec
tion for preventing discharge of said capacitance
by reversal of the voltage of said coil. a resist—
ance connected in parallel with said capacitance
tion for preventing discharge of said capacitance for controlling the discharge of said capacitance
by reversal oi.’ the voltage of said coil.
' to render said valve conducting during a subse
3. A control system for a reciprocating load quent positive halt cycle at anode voltage, and ‘a
comprising a coil for operating said load, means capacitance included in circuit with said grid
80 for supplying a periodically varying voltage to for insuring energization of said valve at approx
\said coil comprising an-electric valve having an imately the beginning of a positive hali cycle 0!
anode connected to a source of alternating volt
age, a cathode connected to one terminal 0! said
coil and a control grid, connections from said
said anode voltage.
-
WILLIAM R. KING.
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