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Патент USA US2412263

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DeqlO, 1946.
'
H. E. HARTIG
2,412,263
CONTROL APPARATUS
Filed Feb. 24, 1943
LD/ID
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Gttorneg
Patented Dec. 10, 1946
‘2,412,263
UNITED STATES- PATENT OFFICE
2,412,263
CONTROL APPARATUS
Henry E. Hal'?g, Robbinsdale, Minn., assignor
to Minneapolis-Honeywell Regulator Company,
Minneapolis,
Minn, a corporation of Delaware
Application February 24, 1943, Serial No. 476,907
8 Claims.
1
This invention relates to electrical networks,
and especially to networks of the normally bal
anced type, which are adapted for use in electri~
cal measuring or control systems.
Such normally balanced networks are so con
structed that two electrically separated points in
the network are at the same potential when the
network is balanced. When an impedance con
nected in the network, sometimes termed the con
(Cl. 172-239)
2
vide an improved electrical network for use in
control on measuring systems.
Another object of the present invention is to
provide an improved electrical network of the
normally balanced type, wherein the disturbing
e?’ect of the distributed capacitance between var
ious parts of the network and ground is main
tained at a minimum. A further object is to
provide such a network, which because of its low
trol impedance, is varied, the changed electrical 10, capacitance to ground, is especially adapted to
conditions in the network cause a difference of
have its output potential ampli?ed by an elec
potential to appear between the two points, which
tronic ampli?er.
may be termed the output terminals of the net
A further object of the invention is to provide
work. This difference of potential between the
an electrical network including a pair of sources
output terminals may be utilized to operate suit~ 15 of electrical energy and a pair of impedance
able measuring or controlling apparatus. An
means, and circuit means connecting the sources
other variable impedance, sometimes termed the
and the impedance means alternately in series in
rebalancing impedance, may be connected in the ‘
a single loop circuit.
network and varied simultaneously with the op—
Other objects and advantages of the present
eration of the measuring or controlling appara
invention will become apparent from a consider
tus. This rebalancing impedance is so connected
ation of the accompanying speci?cation, claims,
in the network that its variation by the operation
and drawing, in which the single ?gure repre
of the measuring or controlling apparatus re
sents an electrical control or measuring system
stores the network to its balanced condition,
embodying my invention.
thereby reducing the potential between the net 25 Referring to the drawing, there is shown a load
work output terminals to zero and stopping op
device I0, which is to be operated in accordance
eration of the measuring or controlling apparatus.
with the temperature adjacent a resistance ele
In electrical control systems employing such
ment H, which may be of nickel or some other
networks, it is common to use a source of alter
material having a high temperature coef?cient
nating electrical energy to supply the network. 30 of resistance. The load device I 0 may be any
The network then operates to produce at its out
suitable measuring, recording, or controlling ap
put terminals an alternating potential of a given
phase if the control impedance varies in one sense,
and of the opposite phase if the control imped
ance varies in the opposite sense. Where such
an alternating current network is used, the out
put potential of the network may be ampli?ed
by a suitable electronic ampli?er, and the out
put current of the ampli?er may be utilized to
operate suitable measuring or controlling appara
tus in a. sense depending upon the phase of the
signal supplied to the ampli?er input. A suit
able rebalancing impedance device may be con
nected in the network and operated concurrently
with the measuring or controlling apparatus to
rebalance the network. In such a network, un
paratus.
For example, it may be a valve con
trolling the ?ow of a temperature changing ?uid
to a heat exchanger located adjacent the tem
perature responsive resistance l l.
The load device I0 is operated by a motor 12
through a gear train schematically indicated at
IS. The motor I 2 also operates, through the gear
train l3,'a slider M which moves along a resist
ance IS. The slider M and resistance 15 together
form a rebalancing potentiometer I6.
The temperature responsive resistance H, and
‘the resistance l5 of rebalancing potentiometer 16,
are connected in a balanceable network H, which
is constructed in accordance with the principles
of the present invention. The network ll in~
balanced capacitances between the various ele
cludes, in addition to the resistances II and IS,
ments of the circuit and ground give rise to out
a pair of transformer secondary windings 20 and
of-phase potentials between the output termi
2|, a slide-wire resistance 22, a ?xed resistance
nals. Ordinarily these out-of-phase potentials 50 23,
and a variable resistance 24, the latter being
can only be reduced by inserting capacitance ele
connected in parallel with resistance l5.
ments in the network to produce a capacitive bal
The network ll comprises a single loop circuit
ance in addition to the resistive balance which
which may be traced from the upper terminal of
is used for control purposes.
,
It is an object of the present invention to pr0~ 55 transformer secondary winding 20, through the
winding 20, a conductor 25, resistances i l, 22, and
3
amazes
23, a conductor 26, winding 2|, a conductor 2?,
resistances l5 and 2t in parallel, and a conductor
28 back to the upper terminal of secondary wind
ing 20. '
61.
32 is determined by the characteristics of the
ampli?er 42 and the various circuit elements
controlling the transfer of electrical energy be
tween winding 32 and motor winding 5|. In the
The transformer secondary windings 20 and CH usual system, some ?xed shift in phase will take
2| are located on the same transformer 30, which
is provided with a primary winding 3| and two
additional secondary windings 32 and 33. It
should be noted that the secondary windings 2t
place during this transfer of energy.
The con—
denser 513 is so proportioned and chosen so that
the current ?owing through winding 52 is al
ways substantially 9O electrical degrees out of
and 2| are connected so that their potentials aid 10 phase with the current ?owing in winding 5|.
each other in the network ll, thereby causing a
Whether the current in winding 52 leads the cur
circulating current to continuously ?ow around
rent in winding 5|, or vice versa, depends upon
the loop in that network. The impedance ele
the phase of'the signal potential applied to the
ments of. the network and the potentials of the
input terminals of ampli?er 42. The phase of
transformer secondary winding may be so chosen 15 this signal potential depends in turn upon the
that this circulating current is not sumciently
sense of unbalance of the network |'|. Since
large to heat the resistance elements appreciably.
the motor I2 is operated in one direction or the
A slider 34 cooperates with resistance 22. The _ - other, depending upon whether the current in
slider St is movable along the resistance 22_by
winding 5| leads or legs the current in wind
means of a manually movable knob 35' which 20 ing 52, it may be seen that the direction of op?
carries a pointer 36 cooperating with a stationary
eration of motor i2 is determined by the sense
scale. Movement of slider 34 across resistance
of unbalance of network I7.
22 by means of knob 35 adjusts the control point
Operation
of the system. In other words, the position of
slider 36 on resistance 22 determines the par
Consider the potential distribution conditions
ticular value of resistance H at which the net
existing in the network i'i during a half cycle
work I‘! is balanced, for any given position of
when the lower terminals of transformer wind
the rebalancing slider It and load device it).
ings 2D and 2| are positive with respect to their
Slider 31% is connected through a conductor 37 to
upper terminals. At such a time, the current
ground at 38.
'
30 ?ow around the loop circuit is in a clockwise
The sliders M and 34 serve as the output ter~
direction, as viewed in the drawing. Starting
minals of the network ll. ‘Slider Ill is connected
from the upper terminal of transformer sec
through a conductor 40 to an input terminal
ondary winding 20, and following around the
All of an electronic ampli?er generally indicated
loop circuit in a clockwise direction, it may be
at 42. The ampli?er 62 may be of any suitable 35 seen that a potential rise takes place in the wind
type. For example, it may be an ampli?er of
ing 20, followed by a series of potential drops '
the type shown in the co-pending application
across resistances ||, 22, and 23, another poten
of Albert P. Upton, Serial No. 437,561, ?led April
tial rise across secondary winding 2|, and an
3, 1942. The ampli?er 132 is provided with a sec
other drop across the resistances l5 and 24 in
ond input terminal 433, which is connected to 40 parallel, back to the upper terminal of secondary
ground at £343, and through ground connection 38
‘Winding 2c. Taking ground potential, which is
and conductor 31 to slider 3%. The ampli?er 62
that of slider body 3%, as a reference, it may be
is provided with power supply terminals 45, t6,
seen from the foregoing that points on the re
and Ill, which are connected to the opposite ter
sistance 22 to the right of slider 3d are negative
minals and a center tap, respectively, of trans 45 with respect to ground, while parts to the left
former secondary winding 32. The ampli?er 62
of slider 36 are positive with respect to ground.
is also provided with a pair of output terminals
Furthermore, since by Kirchhoff’s1aw,_the sum of
48 and 49.‘
the potential rises and drops around the loop
The motor i2 is of the split phase type, and is
circuit must be zero, it may be seen that there
provided with a pair of ?eld windings 5i and 52
are four points on the loop circuit which are at '
which are displaced from each other 90 electrical
ground potential. One of these points is of
degrees in space. A condenser 53 is connected in
course the slider 36, another is located on resist
parallel with motor winding 5|. The winding
ance | 5, and the other two at some point in each
52 is connected in a series circuit which includes
of the transformer windings 20 and 2|. If the
the transformer secondary winding 33 and a con
network H is balanced, the point at ground po
denser 54.
tential on resistance I5 is that point engaged by
The motor winding 52 is supplied with alter
slider iii. If the sum of the resistances | I, 22,
nating current whose phase with respect to the
and 23 equals the equivalent resistance of the
alternating potential supplied by secondary
parallel resistances i5 and 24, the points of
60
winding 33 is ?xed by the condenser 56. The
ground potential on windings 2|] and 2| will be
motor winding 5| and its parallel condenser 53
the center points of those windings. If the sum
are connected across ampli?er output terminals
of the resistances | i, 22, and 23 is not equal to
88 and 49. As explained in detail in the co
the equivalent resistance of the parallel resist
pending Upton application, Serial No. 437,561,
ances I5 and 24, the points on the windings 20
previously referred to, the ampli?er 62 operates
and 2| which are at ground potential will be
in response to the application of an alternating
displaced from the center points of those wind
signal potential to its input terminals to supply
ings in one direction or the other, depending
the motor winding 5| with an alternating cur
upon which group of resistances is the largest.
rent of a given phase or the opposite phase, de
Furthermore, it may be pointed out that since
pending upon the phase of the alternating po
the average potential to ground of all points along
tential applied to the input terminals iii and
any one half of the loop circuit is zero, under
63. The phase of the alternating current sup
balanced conditions, the effect of distributed ca
plied to winding 5| with respect to the alternat
pacitance in the network H is minimized.
ing potential supplied by transformer winding 75
Consider now the conditions obtained in ‘the
2,412,263
network I7 if the resistance II increases, such
as would occur upon an increase in the tempera
ture adjacent it. Such an increase in resistance
-II increases the sum of the potential drops on
the left hand side of the loop between sliders
34 and I4, above the sum of the potential drop
along the right hand side of the loop between
the sliders.
The point of ground potential on
6
essary to cause movement of the valve from its
fully closed to its fully open position.
While I have shown and described a preferred
embodiment of my invention, other modi?cations
thereof will readily occur to those skilled in the
art, and I therefore wish my invention to be lim
ited only by the appended claims.
I claim as my invention:
resistance I5 is thereby shifted to the left along
1. Temperature control apparatus, comprising
resistance I5, making slider I4 positive with re 10
in combination, a pair of sources of electrical
spect to ground. In a similar manner, if the re
energy, a pair of impedance means, means con
sistance H decreases, the potential of slider I4
necting said sources and said impedance means
alternately in a series circuit, one of said imped
ance means comprising, in series, a temperature
potential of slider I4 were made under the as
sumption‘that only the conditions existing when 15 responsive resistance element and a ?xed resist
ance element, the other of said impedance means
the lower terminals of secondary windings 20 and
comprising a potentiometer resistance element,
2| were positive were being considered. Consid
said potentiometer resistance element having a
ering the conditions existing during an alternate
contact slidable with respect thereto to complete
half cycle, when the transfomer secondary wind
ings 20 and 2| have their upper terminals positive 20 an electrical connection with any of a plurality
of spaced points thereon, temperature control
with respect to their lower terminals, it is be
means, electrical motor means for driving said
lieved to be readily apparent that the opposite
temperature control means and said slidable con
conditions as to the potential of slider I4 exist.
tact, and potential responsive means for control
Therefore, when alternating current is supplied
ling said motor means connected between said
to the network I‘! from windings 20 and 2|, the
contact and a point on said other impedance
potential difference between sliders I4 and 34 is
means intermediate said temperature responsive
zero when the network I1 is balanced. When
resistance element and said ?xed resistance ele
the resistance II increases above its normal value,
ment.
>
a potential of the same phase as that existing
2. Control apparatus, comprising in combina
30
between the lower and upper terminals of sec
tion, a pair of sources of electrical energy, a pair
ondary winding 20, respectively, appears between
of impedance means, means connecting said
sliders I4 and 34, and is impressed upon the
sources and said impedance means alter
input terminals 4I and 43 of ampli?er 42. Sim
nately in said series circuit, an electronic
ilarly, when the resistance II decreases, an al
ternating signal of a phase opposite to that exist 35 ampli?er having input terminals and out
put terminals, a connection between an inter
ing at the terminals of secondary winding 20 is
mediate point on one of said impedance means
impressed on the input terminals of ampli?er 42.
and one of said ampli?er input terminals, con
Therefore, it may be seen that the motor I2 is
nections between ground and a normally equipo
rotated in one direction when the resistance of
tential point on the other of said impedance
element I I increases from a predetermined value,
means and between ground and the other of said
and is rotated in the opposite direction when the
input terminals, control means connected to said
resistance of element II decreases from that
ampli?er output terminals, and means for vary
value. If the load device I0 is controlling the
ing at least a portion of one of said impedance
supply of a heating ?uid to a space in which re
45 means to produce an unbalance potential between
sistance II is located, the direction of rotation
said points.
of motor I2 is so chosen that the supply of heat
3. A balanceable electrical network, comprising
ing ?uid is increased when resistance element
in
combination, a pair of sources of electrical
II decreases, and the supply of heating ?uid is
energy, a pair of impedance means, means con
decreased when the resistance of element II in
50 necting said sources and said impedance means
creases.
alternately in a series circuit, one of said im
It is believed that the functioning of the slider
pedance means comprising a potentiometer im
34 as a control point adjuster for the system will
pedance element having a contact slidable with
be readily understood from the foregoing with
respect thereto to complete an electrical con
out further explanation.
The resistance 24 determines the total resist 55 nection with any of a plurality of spaced points
thereon, potential responsive means connected
ance between the terminals of the parallel group
between said contact and a normally equipo
consisting of resistances I5 and 24. It therefore
tential point on the other of said impedance
determines the total potential drop across this
is made negative with respect to ground.
The foregoing statements with'respect to the
parallel group. Furthermore, its setting deter
means, means for varying at least a portion of one
mines the resistance drop per unit length of the 50 of said impedance means to produce an unbalance
potential across said potential responsive means,
slider wire resistance I5. Therefore, when a
and
means operated by said potential responsive
change in the resistance element II causes a
means for driving said contact along its associated
given change in the potential of slider I4, the set
impedance element so as to reduce said unbalance
ting of resistance 24 determines the distance 65 potential
substantially to zero.
along resistance I5 through which the slider I4
Ll.
A
balanceable
electrical network, comprising
must be driven by the motor I2 in order to re
in combination, a pair of sources of electrical
balance the network IT. The resistance 24 there
energy, a pair of impedance means, means con
fore determines the width of the range of tem
necting said sources and said impedance means
peratures adjacent resistance II which causes
slider I4 to be moved from one end of its travel 70 alternately in a series circuit, one of said imped
ance means comprising a potentiometer im
to the other. If the load device III is a valve
pedance element having a contact slidable with
controlling a supply of heating ?uid, the setting
respect thereto to complete an electrical con
of resistance 24 therefore determines the total
nection with any of a plurality of spaced points
change in temperature adjacent resistance I I nec 75 thereon, potential responsive means connected be
2,412,283
lb)
tween said contact and a normally equipotential
point on the other of said impedance means,
means for varying at least a portion of one of
said impedance means to produce an unbalance
potential across said potential‘ responsive means,
means operated by said. potential responsive
means for driving said contact along its associated
impedance element so as to reduce said unbalance
potential substantially to zero, and a variable
impedance device connected in parallel with said 10
ating said control device and means connecting
said potential responsive means between said
‘taps on said pair if impedance means, said con
necting means including means for varying the
ratio between the impedances of the portions of
one of said impedance members on either side of
said tap.
'7. A balanceable electric network, comprising
in combination, a pair of sources of electrical
energy, a pair of impedance means each includ
potentiometer impedance element to control the
potential di?erence per unit length of said ele
ing end terminals and an intermediate tap, means
connecting said sources and said impedance
ment and hence the distance moved by said con
means alternately in a single series circuit, poten
tact in response to a given operation of said
tial responsive means, means connecting said
impedance varying means.
15 potential responsive means between the taps on
5. A balanceable electrical network, comprising
said impedance means, said taps being normally
in combination, a pair of sources of electrical
at the same potential, means for varying the
energy, a pair of impedance means, means con
the ratio between the impedances of the portions
necting said sources and said impedance means
of one of said impedance means on either side
alternately in a series circuit, an electronic am 20 of said tap to produce an unbalance potential be
pli?er having a pair of input terminals and a
pair of output terminals, means connecting each
of said input terminals to a point on one of said
impedance means, said points being of the same
tween said taps, and means operated by said
potential responsive means for varying the ratio
between the impedances of the portions of the
other of said impedance means on opposite sides
potential when said bridge is balanced, means 25 of the intermediate tap to restore a potential
for varying at least a portion of one of said im
difference between said taps to zero, thereby re
pedance means to produce an unbalance potential
balancing said network.
between said points, and means connected to said
8. An electrical network for producing an alter
ampli?er output terminals for varying a different
nating potential variable in phase and magnitude _
portion of one of said impedance means to re ~30 in accordance with the departure of a variable
store the potential between said points to zero,
condition from a predetermined value compris
thereby rebalancing said network.
_
ing in combination a pair of transformer second
6. Control apparatus, comprising in combina
ary windings, a pair of impedance means each
tion, a pair of transformer secondary windings, a
including end terminals and an intermediate
pair of impedance means each including end
tap, means connecting said sources and said im
terminals and an intermediate tap, a single cir
pedance means alternately in a series circuit, out
cuit connecting said windings and said impedance
put terminals for said network connected to said
means in series, said windings being connected
intermediate taps, and means responsive to said
into said circuit to aid each other, each said
condition for varying the ratio between the por
secondary winding being connected to one ter 40 tions of one of said impedance means lying on
minal of each of said impedance means, a con
trol device, potential responsive means for oper
opposite sides of said intermediate tap.
HENRY E. HAR'I‘IG.
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