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Jan. 14, 1947.
' _ ‘
w. an. CLARK .
Filed Jami. 22.‘ 1944
‘ i240
I ‘ WmsLow B.M'. CLARK.
‘ 3"
Patented Jan.v 151947
Winslow s. M. can, West 0range,'N. 1., alslznor
Orange, N._J., a corporation of New Jersey
Application January 22', 1944, Serial No. 519,373
_' to Thomas A. Edison, Incorporated, West
4 Claims. (01. 111-95)
e _ My invention relates
to improved means and‘
cooperating ‘circuit elements in accordance with Q
methods for e?ecting adjustments in circuit ar
rangements, especially in circuit arrangements
for electrical measuring instruments, and has for
a primary object to provide‘ novel and improved.
. my invention;
Figure 3 is another elevational view of this ra
tlometer assembly, taken at right angles to the
line of view in‘Figure 2;
means and methods for calibrating electrical
measuring instruments.
My invention has particular commercial util
ity, and is‘ herein illustrated and described, in
Figure 4 is a perspective view of the coil ar
rangement of the present ratiometer; and
Figure 5 is a diagrammatic view of the ra
tiometer' circuit in accordance with my inven
terms of a circuit arrangement for ratiometer 10
In the illustration of my invention, I show a
instruments. These instruments, as is well
type of ratiometer instrument, purely by way of
known, are arranged to measure the ratio of two
example, such as is described and claimed in the
currents and the circuits into which they are
pending application of Frederick G. Kelly, Se
connected, which are typically bridge circuits, are
adapted for producing ,changes in the ratio of 15 rial No. 450,222, ?led July 8, 1942 (now Patent
No. 2.362.562), and having a common assignee
with the present application. This ratiometer in
dition to be measured. It is an object or my in
strument comprises a permanent bar magnet I
vention to provide a simpli?ed and economical
carried pivotally by a shaft‘ 2 which pivots in top
means and method for adjusting such circuits
whereby such instruments may be readily cali 20 and bottom jewel serews‘2a and 2b. The mag:
net has a generally symmetrical shape relative to
brated in production.
the shaft 2 and has its magnetic axis- at right
My invention has useful application to temper
angles to the shaft. Surrounding the magnet are
ature-compensated electrical ‘measuring systems,
two sets of ?eld coils 3 and 4 of which each set
particularly to remote indicating systems such
as telemeters and ratiometer systems or. the char 25 consists of two serially connected coils positioned
at diametrically opposite sides of the shaft 2
acter above explained. By way of illustration,
with their medial planes parallel to the shaft;
ratiometer systems are. commonly used for re
These sets of coils are positioned at angles to
mote temperature-indicating purposes,‘ in which
case an element- variable with temperature is 30 each-other about the shaft 2, one set oft coils
passing through the other. Surrounding the coils
immersed in the medium whose temperature is
1 and magnet is a cylindrical shield cup 5 held in
to be measured and is connected into a ratiometer
concentric relation to the-shaft 2. The shield
circuit the other elements of which are placed at
cup is preferably made of a- highly permeable and
a remote indicating point. Frequently, it is re
non-permanent magnetic material such as that I
quired that the ratiometer circuit be compen
known commercially. as “Mumetal” or “Perm
sated for changes in the ambient temperature at
alloyi? andthe magnet is preferably made of a
the remote indicating point. It is‘ another ob
permanentand highly efficient material such as a
ject of my invention to provide a novel and im
one of the. socalled "Alnicos'.” In response to
two currents in. response to variations in a con
proved means‘ and method for adjusting and
calibrating such temperature-compensated cir-v
changes in the relative current energization of
40 the coil sets, the magnet will de?ect to different ‘
positions according to the ratio of the currents in
the coil sets, and the positions of the magnet will
be indicated by readingsoi' a pointer 6 carried
A further object of my invention is to provide
can electrical measuring system incorporating an
improved form of rheostat .for adjusting and/or
calibrating the system.
‘_ ‘
Yet i'urther'and allied objects and features of
my invention are more fully pointed out in the
‘following description and the "appended claims.
In the description of my invention reference
is had to the accompanying drawing, of which:
Figure l‘is an axial view of a ratiometer, largely ‘
Figure 2 is an elevational view‘ of an assembled
unit comprising the ratiometer oiv Figure 1 and
by tlae'shaft 2relative to a scale I provided on a
Moreparticularly, the operation or the ratiom
eter is as follows: Upon considering the mag
netic ‘axis of the magnet to correspond to its
diagrammatically shown, with which‘ my inven
tion is herein illustrated; “
central‘ ‘longitudinal ' axis,- it ‘ will ‘be understood
that upon passing a current through only the coil
,set 3 (the two ‘coilsvot the set being of course
polarized in the same direction) the magnet will
assume ‘a position wherein its magnetic axis is
aligned withthe axis of that coil set, and upon
proper relative polarization of the coils and mag
tions will be unaiiected by material changes in
the voltage of the battery 9, for variations in bat
tery voltage produce like variations in the cur
rents of both coils without changing the ratio of
. net the pointer
‘ will register with the low end of
the scale ‘I. Similarly, upon passing a current
through only the coil set’ 4, and in the proper
direction, the magnet will assume a position
wherein the pointer 6 will register with the high
'end of the scale. When current is passedthrough
both coil sets, in proper relative directions as
above explained, the coil sets will exert torques
on the magnet in opposite directions and the
While the ratiometer system here shown is
basically a resistance-measuring system, it will be
understood that the resistance in may be varied
according to variations in any condition to be
magnet will assume intermediate positions where 10 measured‘ and that the meter may be calibrated ,
in these torques are in balance, the pointer then
directly in terms of that condition._ One such
reading at intermediate positions of the scale.
common application'oi the present ratiometer is
These intermediate positions are determined by
the ratio of the currents in the coil sets.
as a temperature-measuring device on aircraft,
In this application the resistance [0 comprises
For effecting changes in the ratio of the cure .
rents in the coil sets in response to changes in a _
I the active element of a resistor bulb l6 that is
immersed in the medium whose temperature is to
condition to be measured, I preferably employ a
be measured and whose resistance varies accord
bridge circuit such as is shown in Figure 5. this
ing to that temperature, a preferred example of
being a type of bridge circuit generally described
such bulb being that disclosed in the pending ap
and claimed in the Kelly application abovemen 20 plication of Frederick G. Kelly, Serial No. 493,9i7,
tioned. This bridge circuit has two branches con
?led July 8,1943, and assigned to the assignee of
nected in parallel across a source of direct cur
the ‘present invention.
rent such as a battery 9,. One branch serially in
cludes a variable resistance Ill to be measured and
In such applications the resistor bulb is located
remote from the ratiometer instrument and its
a?xed resistance I I, and the other branch serially
includes three ?xed resistances l2, l3 and M. The
other associated elements, and the instrument
two coil sets of the ratiometer are connected from
a junction l5 between resistances l0 and I I of one
sembled unit such as is shown in Figures 2 and 3.
This unit comprises a case only the base ll of
which is shown. ‘Secured to this base is an up
and those other elements are provided as an as
branch to the respective extremities of the, middle
resistance IS in the other branch.
30 standing bracket "! comprising two spaced-apart
As the resistance I0 is varied, the absolute po- ‘
upright members I8a having top and bottom legs
tential oi the junction point I5 is varied relative
l8b and lac, the members |8a being joined by a
to the absolute potentials present at the extremi
cross member "id. The bottom legs I80 seat on
ties of the resistance l3, and so long as the po
tential of junction I5 is between that of the ex
tremities of resistance I3, the voltage drop across
one coil set will increasehwhile that across the .
other coil set will decrease. Accordingly, for a
the base I‘! and are secured thereto by screws IS;
.the top legs support a cross arm 20, held thereto
. by screws 2|, which carries the top jewel screws
‘in and the dial 8; and the cross member 18d car
ries the ratiometer per se by way ‘of an L-bracket
prescribed lower value for the resistance Ill, the
22 onto which the shield cup 5 is seated and held
potential of junction 15 will correspond with that 40 by a screw v23. The side members |8a of the
of the junction between resistances i2 and I3.
bracket [8 serve to support the resistances of the
leaving zero voltage drop across one. coil set and
bridge circuit of Figure 5, these resistances being
maximum voltage drop across the other. Simi
respectively wound on spools 24 and held in place
larly, for a prescribed higher value of resistance
‘by screws 25. The ‘necessaryleads from the as
III, the potential of junction l5 will correspond 45 sembled unit to the resistor bulb l6 and battery
with that of the junction between resistances l3
9 are led through‘ the base II by way of a de
and 14, leaving only the other coil energized; and
pending tubular portion Ila. thereof and may
for intermediate values of the resistance l0,'cur
therein be connected to respective pins of a con
rents will pass through both coils in ratios ac
nector plug not shown.
cording to the values of that resistance. Thus, 50 - It will be understood that the currents which
the pointer 5 will register with one end of the
?ow through the respective coil sets 3 and 4 are
scale for one prescribed valueoiI resistance l0 -
determined, among other things, by the ‘re
and with the other end of the scale for another
‘sistances of the respective coils. Since these coils I
prescribed value of resistance Ill, and for inter
are preferably wound with copper wire, and copper
mediate values, oi that resistance the pointer will 55 has asubstantial temperature coe?icient, changes
assume intermediate positions, each position of '
in the ambient temperature of the meter unit
the pointer being one wherein the torques exerted
above described tend to produce errors in the
by the respective coil sets‘on the magnet are in
indications of the meter. Particularly in aircraft
balance. In order, however, that the pointer will
applications the meter unit is subjected to large
register with the low end of the scale-the left end
changes in the ambient temperature, and it is
of the scale as it appears in Figure 1—for low
important that the unit he therefore compen
values of the resistance Ill, and at the high end
sated so as to be substantially free of in?uence
of the scale for high values of the resistance It, . by those changes. This compensation has been
‘the coil sets 3 and 4 are directed axially ‘toward ‘ provided satisfactorily, in accordance with ‘the
the low and high end portions of the scale, and
teachings of the abovementioned Kelly applicae
the coil sets are connected respectively to the
tion Serial No. 450,222, by'making the resistances
right and left extremities of resistance It in the
II and I2 wholly of a material having a negligible
bridge circuit of Figure 5, Also, for a scale length ' temperature coe?icient,‘ a predominant portion
of 120° the axes of the coils are typically sepa
No of resistance l4 of such material and the
rated by this angle, or, in other words, the medial. 70 remaining portion Nb of copper and comparable
planes of the coils are separated by an angle of 60‘?
portions I31; and 13b of resistance I: of such
as shown.
material and copper respectively. Satisfactory
materials havingnegligible temperature coeiii»
It will be understood that with proper calibra
tion or the scale, the pointer will read directly
cients for this purpose are those known commer
vthe values of the resistance l0, and the indica 75 cially as "Manganin” and "Advance.”
For the case where the voltage of battery 9
ranges from 11 to 14 volts, the maximum per
missible current through the bulb I8 is approxi—_
mately 1'! ma., the resistance of the bulb is‘ ap
proximately 68 ohms at minus 70° (2., 108 ohms
at 50° C. and 152 ohms at 150°~C., and the re
sistances of the outer and inner coil sets 3 ‘and 4
are 290 and 230 ohms respectively (the inner coils
having less resistance for the same number of
been accomplished by a simple means without
materially compromising the compensation of the
meter unit‘ for changes in ambient tempera
ture. This simpli?cation has been made possible
by the observation that the variable portion of the
resistance [3 may wholly comprise a material of
negligible temperaturev coe?icient-i. e., totally
comprise the resistance IMP-and that, upon pro
viding this variable portion directly adjacent the
turns because of their smaller mean ‘length of 10 Junction of resistance II with resistance l2, it
turn), it has been found satisfactory to employ
and the variable portion of resistance l2, herein
resistances in thevbridgehaving average values
termed resistance He, may comprise a single and
as follows: resistance II, '700 ohms Manganin;
integral resistance element 26. By providing such
resistance I2, 91 ohms Manganin; resistance Ila,
resistance element with two movable contacts in
615, ohms Manganin; resistance 14b, 85 ohms 15 the form of _a simple rheostat, and electrically
copper; resistance Ba, 11 ohms Manganin; and
interconnecting the contacts to provide .a single
resistance I313, 24 ohms copper.
Typically, resistor'bulbs do not have a truly
linear characteristic for their resistance change,
junction for connection with the coil set 4, then
the resistances I2 and I3 may be varied inde
pendently of each other to permit a direct and
in response to‘ a given incremental temperature 20 easy calibration of the instrument. Also, by mak
change, is greater at high temperatures than it is
ing the total value of the resistance element 26
at low temperatures. The tendency of this non
. at least as great as the sum of the maximum
linearity of the bulb is thus to expand the high
values of the variable ranges required for the re
end portion of the scale. It however occurs that
sistances i2 and 13 in calibrating any one of a
the bridge circuit arrangement illustrated and. 25 group of instruments, the rheostat can be’stand
described has itself a non-linear response char
ardized since one such form of rheostat can be ,
acteristic which counteracts the non-linearity of __ used for calibrating each of the instruments.
1 the bulb and tends itself to contract the high
In Figures 2 and 3 I show a rheostat 21 for the
end portion of the scale. The non-linearity of
abovementioned purpose, comprising an in
the bridge. increaseswith increase in the range 30 sulating frame 28 made for example of Bakelite
of temperature to be measured, and for tempera
and having a base portion 28a seating on the
ture ranges greater than 100° it will generally
base I‘! and held thereto by a screw 29 to form a
over-counteract the non-linearity of the bulb to
permanent part of the meter unit. The frame
give a resultant contraction of the upper end por
has a cylindrical head 28b provided with an
tion of, the scale. Additionally, there are the 35 arcuate groove 30. The resistance element 26 is
factors that the inner coils I have closer magnetic
wound in the form of a helix of wire having a
coupling to the magnet I and have less resistance
negligible temperature coefficient, preferably of
than do the coils 3, the eifect of which is further
“Advance,” and this helix is ?tted into the groove
to accentuate the non-linearity of the bridge. To
30 and held therein by cement. Leads 3! from
correct for these effects which tend to over 40 the ends of the helix make connection to a pair
counteract the non-linearity of the bulb; and so
of terminals 32 mounted on the frame 28, and to
that there may be obtained a scale symmetrical
these respective terminals are connected the fixed
relative to its central point, there is placed a
component of resistance l2, indicated in Figure 5
resistance 25, typically about 115 ohms, in series
as Rb, and the ?xed component 13b of resistance
with the 0011s 4. This resistance is preferably 4.5 l3. Slidably engaging the‘ helix- are two in
made of copper so that the two cross arms of the
dependently adjustable spring contact arms 33
bridge will each have the same temperature
and 34. These contact arms have separate aper
tured hub portions which overlie one another and
Individual calibration of each ratiometer is
are pivoted to the central portion of the head 280.
required because in production variations occur 50 by a screw 35. Clamped against these hub-por
in the respective elements which make up the
tions also by the ‘screw 35 is a soldering lug 36
ratiometer system. It is found, however, that‘
which is held against turning about the screw 35 ‘
when resistances H and Il are held within suit
by a rivet 31. This lug constitutes a common
able tolerances, and the resistance 25 is properly
Junction for connection in the bridge to the coil
selectedas above explained, the calibration of 55 set E.
each ratiometer requires only a proper adjust
- It will be understood that the central portion
ment of the values of resistances l2 and i 3. This
of the resistance element 26 is shunted by the
is because the resistance 13 controls the angular
two contact arms and that it is only the end por
length of scale obtained in response to a given '
tions of the resistance element, beyond the re
range in temperature of the resistance l0—i. e., 60 spective contact arms, which are the active re
the distance of separation of the scale divisions
sistance portions comprised within the respective
and the resistance l2 controls the positioning of
resistances l2 and I3. Merely by way of ex
the temperature indications or of the scale rela
ample, it may be noted-that the 'total resistance
tive to the dial 8. These calibrating adjustment-s
of the element 26 may be 34 ohms, that in prac
have been heretofore carried out by determining 65 tice the range of variation for resistance 12a is
with decade boxes the proper values of the re
from 9 to 15 ohms and that of resistance 13a
sistances I2‘and I3, and then taking resistance
from 10 to 12 ohms, and that therefore, on the
spools having an excess number of turns and re
average,_the contact arms 33 and 34 will shunt
moving, by trial and error, enough turns until
out approximately 11 ohms of the resistance ele
the correct values of the resistances are obtained. 70 ment '26., it may, moreover, be noted that while
Obviously, this calibrating procedure was very
the resistances i2a and 'llc have to be critically‘
laborious and time-consuming, and materially in
creased the cost of the instruments.
By the present invention, the calibration pro
cedure has been vastly simplified and this has
determined, the adjustment of the arms 33 and 34
is however not critical in view of the resistance
element 28 being spread over a large diameter .
through nearly a complete circle. Moreover,
_ ‘2,414,100
, ‘7
while in the present invention all-oi the vari
ation of resistance 13 is con?ned to its portion of
negligible temperature coei?cient, this does not
have any material adverse e?‘ect on the tempera
ture compensation oi the bridge since the range
of variation of that portion is only approximately
dial for a given range of said variable element and Y
the other oisaid resistances controlling the posi
tioning of said de?ection range in relation to the
,scale on said dial; and a rheostat comprising a
single resistance element including portions of
said two resistances, and having two independent
_ l
ly movable contacts associated with said re
I have herein shown and particularly described
sistance element for varying the values of said
my invention in terms of apreferred embodi
resistances respectively.
ment, but it will be understood that this embodi~ 10 3. In an electrical measuring system including
ment is subject to changes ‘and modi?cations
an electrical bridge having two branches con
without departure from the scope of my inven
nected in parallel, one of said branches including
tion, which I endeavor to express according to
two serially-connected resistances, and an elec
the following claims.
trical indicating instrument adapted to be ‘elec
I claim:
trically connected across said branches to meas
1; In an electrical circuit system including a
ure the unbalance or said bridge, said instrument
' ratiometer, a bridge having a ?rst branch serially
including a coil adapted to be connected to the
including ‘a variable resistance to be measured
Junction 0! said two resistances: a device con
and a ?xed resistance and a second branch serial
necting said coil to said Junction, and adapted
ly including three ?xed resistances, the middle 20 for adjusting said resistances independently of
resistance or said second branch comprising one
> component having a‘s'ubstantially neglible tem
perature co?lcient and another component hav
ing a positive temperature coe?lcient and one of
the ?xed resistances of said second branch having
one another, comprising a unitary resistance
element including at: least portions of said two
resistances, and a pair of electrically intercon
, nected contacts associated with said resistance
element, said contacts being connected to said
coil and ‘independently adjustable along said re
sistance element.
and adapted‘ to be connected from a common
4. In an electricalmeasuring system compris
point in said ?rst branch to the respective ex
ing an electrical bridge having two branches in
tremities of the middle resistance of said second 30 parallel, said bridge including a variable resist
branch: means for connecting one or said coils to
ance to be measured and one of the branches of
one of said extremities and for varying said
said bridge including two serially-connected con
middle resistance and said one ?iled resistance,
trol resistances, an electrical indicating instru
comprising a resistance element having-a sub.
ment ‘for measuring the unbalance of said bridge,
stanti'ally negligible temperature coeillcient and
said instrument comprising a pointer and co
including a portion at said one component of said
operating scale, and an impedance element
middle resistance and a portion of said one ?xed
adapted to be connected across said bridge from
resistance; a pair of movable contacts associated
the junction of said two control resistances, one
with said resistance element; and electrical con
of said control resistances controlling the de?ec
a substantially neglible temperature coemcient,
and a pair of coils comprised in said ratiometer
nections from said one coil to both said contacts. 40 tion range or said pointer in response to a given
2. In an electrical meter system comprising an
range of variation of said variable resistance and
electrical indicating instrument having a pivoted
the other controlling the. position of said de
pointer and a dial, said dial bearing a scale with
?ection range relative to said scale: a rheostat
which said pointer cooperates: the combination
of an electrical bridge including a variable ele
ment to be measured and having a branch serially
including two resistances, a coil included in said
instrument and connected between the branches
of said bridge and having a connection to the
junction between said resistances, one of said
resistances controlling the range of de?ection of
said pointer in relation to the scale on said
connecting said impedance element to said junc
tion and adapted for adjusting said control re
sistances independently of one another, compris
ing two contacts associated with said control
resistances respectively, each of said contacts
being connected‘to said impedance element, and
said contacts being independently adjustable
relative to said respectively associated resistances.
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