U.S. patent number 3,745,508 [Application Number 05/256,661] was granted by the patent office on 1973-07-10 for selectable fixed impedance device.
This patent grant is currently assigned to Bourns, Inc.. Invention is credited to Frank J. Bruder, James F. Parham, Victor F. Steuer.
United States Patent |
3,745,508 |
Bruder , et al. |
July 10, 1973 |
SELECTABLE FIXED IMPEDANCE DEVICE
Abstract
An impedance device in which the impedance can be selected
within a range of predetermined fixed values. The device is
comprised of an electrically insulating substrate on which is
attached an impedance network, a plurality of electrically
conductive terminations including at least two end terminations and
a number of intermediate terminations which are electrically
connected to the network at preselected locations, electrically
conductive collector means spaced a short distance from each of the
intermediate terminations and electrically insulated from the
network, spacing means for spacing the collector means from the
intermediate terminations and means for selectively connecting
selected intermediate terminations to the collector means.
Inventors: |
Bruder; Frank J. (Newport
Beach, CA), Parham; James F. (Yorba Linda, CA), Steuer;
Victor F. (San Jacinto, CA) |
Assignee: |
Bourns, Inc. (Riverside,
CA)
|
Family
ID: |
22973084 |
Appl.
No.: |
05/256,661 |
Filed: |
May 25, 1972 |
Current U.S.
Class: |
338/320; 336/200;
361/271; 336/192; 338/309; 361/330 |
Current CPC
Class: |
H01C
1/16 (20130101) |
Current International
Class: |
H01C
1/00 (20060101); H01C 1/16 (20060101); H01c
001/16 () |
Field of
Search: |
;338/320,295,308,309
;317/249R,261 ;336/192,200 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldberg; E. A.
Claims
We claim:
1. A selectable fixed impedance device comprised of
a. an electrically insulative substrate;
b. an impedance network on said substrate;
c. a plurality of electrically conductive terminations located on
said substrate, said terminations comprised of at least two end
terminations electrically connected to respective ends of said
network and adapted for connections to an external electric circuit
and intermediate terminations electrically connected to said
network at predetermined spaced intervals for dividing said network
into a plurality of separate impedances;
d. electrically conductive collector means adjacent to and spaced a
short distance from each of said intermediate terminations for
selective electrical connection thereto to form a desired electric
circuit path through said impedance network including predetermined
ones of said separate impedances;
e. and means for maintaining said collector means and said
intermediate terminations in an electrically insulated
relationship, at least part of said last mentioned means providing
an externally accessible open space between said collector means
and said intermediate terminations for enabling a provisional or
permanent electrical connection to be made between said collector
means and at least one of said intermediate terminations.
2. A device as in claim 1 wherein said collector means is embedded
in said spacer means.
3. A device as in claim 1 further including means for sealing said
impedance network.
4. A device as in claim 1 wherein said impedance network is a
resistance network.
5. A device as in claim 4 wherein said resistance network is formed
of a cermet material.
6. A device as in claim 1 wherein said impedance network is an
inductance network.
7. A device as in claim 6 wherein said inductance network is
comprised of a plurality of inductance portions connected in
series.
8. A device as in claim 7 wherein said inductance network is formed
of a winding of electrically conductive material around a core.
9. A device as in claim 8 wherein said winding is formed of printed
termination material and said core is formed of a printed layer of
a ferrite material.
10. A device as in claim 1 wherein said impedance is a capacitance
network.
11. A device as in claim 10 wherein said capacitance network is
comprised of a plurality of capacitance portions connected in
parallel.
12. A device as in claim 11 wherein said capacitance network is
formed of a common electrode for all of said capacitance portions,
a dielectric, a plurality of second electrodes each being
electrically connected to an intermediate termination.
13. A device as in claim 12 wherein said common electrode is formed
of a layer of termination material and said second electrodes are
each formed of a thin portion of termination material.
14. A device as in claim 1 in which said impedance network is
comprised of two separate resistance parts which are used to
provide a voltage divider.
15. A device as in claim 14 wherein said collector means includes
three separate collector members.
16. A device as in claim 15 wherein the first of said resistance
parts has a total resistance value of approximately 110 percent of
a nominal resistance value, the second of said resistance parts has
a total value of approximately 20 percent of the nominal resistance
value, and said intermediate terminations are divided into three
sets, the first two sets being connected to said first resistance
part and dividing it into resistance portions each having a value
of approximately 10 percent of the nominal resistance value and the
third set being connected to said second resistance part and
dividing it into resistance portions each having a value of
approximately 2 percent of the nominal resistance.
17. A device as in claim 16 wherein pairs of intermediate
terminations are provided, one termination from each of said first
two sets, which include therebetween a section of said first
resistance part having a total value of approximately 20 percent of
the nominal value, said first, second and third collector members,
respectively, being electrically connected to one end of said
second resistance part, said second collector member being
electrically connected to the other end of said second resistance
part so that said second resistance part is in parallel with said
section of said first resistance part whenever one of said pairs of
terminations is connected to the respective collector members;
whereby when a voltage is applied between the ends of said first
resistance part, after a selected pair of intermediate terminations
are each connected to their respective collector members and a
selected one of said third set of intermediate terminations is
connected to said third collector member, the output voltage
through an end termination connected to said third collector member
is a predetermined percentage of the input voltage as determined by
the three selected intermediate terminations.
18. A device as in claim 1 wherein said intermediate terminations
divide said impedance network into impedance portions having a
predetermined mathematical relationship to each other.
19. A device as in claim 18 wherein said impedance network includes
two or more sets of impedance portions a first of said sets being
comprised of portions of substantially equal impedance
approximately 10 percent of the nominal impedance value of the
device and a second of said sets being comprised of at least nine
portions of substantially equal impedance approximately 1 percent
of the nominal impedance value of the device.
20. A device as in claim 19 wherein said impedance network also
includes a portion having an impedance of approximately 50 percent
of the nominal impedance value of the device, and there are five
impedance portions in said first set.
21. A device as in claim 20 wherein said portions of said impedance
network are connected in series.
22. A device as in claim 1 wherein said impedance network further
includes a separate impedance portion having its own end
terminations.
23. A device as in claim 1 further including barrier means
interposed between adjacent ones of said terminations for
facilitating individual electrical connecting of said intermediate
terminations to said collector means.
24. A device as in claim 3 in which said impedance network and said
terminations are deposited to form a first layer on said substrate,
said sealing means is deposited to form a second layer in overlying
relation to said first layer for protectively encapsulating said
network with said terminations extending laterally outward of said
sealing means and in which said collector means, supported by said
spacer means, forms a third layer in overlying, closely adjacent
spaced relation to said terminations.
25. A device as in claim 1 further including electrically
conductive means for bridging the space between said collector
means and at least two selected intermediate terminations so as to
fix the impedance of said device.
26. A device as in claim 25 wherein said electrically conductive
means is solder.
Description
BACKGROUND OF THE INVENTION
The subject invention relates to the field of impedance devices
and, in particular to impedance devices whose value can be varied.
The term "impedance" is used herein to include resistance,
capacitance, inductance, semiconductor or any combination thereof
for use in AC or DC circuits.
In many situations it is extremely desirable, if not necessary, to
have an impedance device in which the impedance value can be
adjusted to either a preselected value or to an unknown value which
provides desired performance characteristics in an electric
circuit. In many instances, the device is to be adjusted once and
hopefully this value will remain fixed. For example, trimming
potentiometers are frequently used in electric circuits wherein the
potentiometer is first connected into the circuit during assembly
and adjusted to provide the desired electrical output
characteristics. Once this is done, the potentiometer may be left
in the circuit and never again adjusted or, in some cases, the
value of the adjusted resistance is measured and a fixed resistor
of as close as possible to the same resistance value is permanently
inserted in its place. Because a conventional trimming
potentiometer has a movable contact which is held in place against
the resistance element by some form of spring force, the resistance
value may vary somewhat due to shock, vibration, temperature
variations, aging and/or undesired tampering. Also, the cost of
potentiometers, particularly those that are stable and those which
have a locking feature is much higher than that of a fixed
resistor. The cost of the additional labor necessary to remove the
potentiometer, measure its resistance and insert a fixed resistor
in its place as well as the additional cost for the fixed resistor
and a supply of assorted value resistors are quite significant.
A number of attempts have been made in the past to provide resitive
devices in which the resistance value can be adjusted without using
a relatively movable contact as exemplified by the devices shown in
U. S. Pat. Nos. 3,489,980; 3,441,804; 3,329,921 and 3,071,749. Both
patent Nos. 3,489,980 and 3,329,921 are undesirable in that they
require that at least one connection between the device and the
electric circuit in which it is employed be made to a terminal on
the device which is selected after the desired resistance value is
selected. Thus it is impossible to permanently connect the device
in an electric circuit before adjustment is made and there is a
possibility of an open circuit or short circuit existing which
could damage portions of the circuit. Also, it is difficult to
accurately fix the adjusted resistance value within a small
percentage of the total resistance of the device. Patent No.
3,441,804 discloses a thin film resistive device in which
resistances in a resistance network are shunted by a severable
electrical connection wherein each resistance has a predetermined
numerical relationship to the other resistances and one or more of
these resistances can be connected in the circuit by severing its
respective shunting member. However, it is impossible to
provisionally select any one resistance value for the device
without permanently severing the shunting members. In another
embodiment of this patent, the use of a shunting bar to shunt out
one of the resistor portions is shown. However, it would be
difficult and expensive to adjust the value of such a resistance
using one or more shunting bars as disclosed in this patent. Patent
No. 3,071,749 discloses an adjustable resistor using a layer of a
metal sheet on which is bonded first a layer of thin insulating
plastic and resistor foil grid, the surface of the resistor grid
being exposed. A resistance is selected by choosing a location on
the grid, scraping away the underlying insulation and making a
solder connection between the grid and the metal sheet. However,
this device has many disadvantages in that it requires use of a
resistance element that can be soldered, the accuracy of selection
of a resistance value is determined by the skill and dexterity of
the person making the solder connection and, by necessity, the
resistor grid must be exposed and therefore cannot be sealed from
the environment or protected from mishandling.
In many instances, extremely small miniaturized electrical
components are needed. In all the examples described above, if it
were possible to make the devices in a very small or miniature
size, it would be extremely difficult and time consuming for even a
skilled operator to effect adjustment of the resistance value of
the device with even marginally acceptable accuracy.
While the prior art does disclose resistance devices in which the
resistance value is selectable and can be fixed, each of these
devices has one or more significant disadvantages.
SUMMARY OF THE INVENTION
Thus it is an objective of the subject invention to provide an
impedance device which is inexpensive to manufacture and whose
impedance value is both selectable and fixed;
Another object of the subject invention is to provide an impedance
device which can be easily and inexpensively installed in an
electric circuit and adjusted permanently and stably to the optimum
value using conventional equipment and processes;
Yet another object of the subject invention is to provide an
impedance device which is small in size and compatible with many
existing electric circuit configurations;
Still another objective of the subject invention is to provide a
selectable fixed impedance device which can be manufactured in a
wide range of nominal values;
Another object of the subject invention is to provide a selectable
fixed impedance device whose value can be provisionally adjusted
without permanently changing or damaging the device; and
A still further object of the subject invention is to provide a
selectable fixed impedance device which cannot cause a short or
open circuit across the end terminals of the device before, during
or after adjustment.
The above-mentioned objects are fulfilled in the subject invention
by providing a selectable fixed impedance device comprised of an
insulative substrate, an impedance network on the substrate, a
plurality of electrically conductive terminations which are
electrically connected to the network at preselected locations and
which include intermediate terminations and at least two end
terminations, an electrically conductive collector means located a
short distance from each of the intermediate terminations and
insulated from the network, means for spacing the collector means
from the intermediate terminations and means for electrically
connecting selected intermediate terminations to the collector
means. In its preferred form the impedance network is sealed for
environmental protection. The impedance network may include
resistances, inductances, capacitances, or semiconductors, or any
combination thereof. Preferably, the terminations divide the
impedance network into sets of impedance portions with a first set
having portions each approximately ten percent of the nominal
impedance value of the device and a second set having portions of
approximately one percent of the nominal impedance value of the
device.
The subject matter which is regarded as the present invention is
particularly pointed out and distinctly claimed in the concluding
portion of this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention, however, together with further objects and
advantages thereof, may best be understood by reference to the
following description taken in connection with the accompanying
drawings in which:
FIG. 1 is an isometric view of a device constructed in accordance
with the subject invention in its preferred embodiment;
FIG. 2 is a side sectional view of the device shown in FIG. 1 taken
along the line denoted II -- II;
FIG. 3 is an isometric view of the resistance element assembly of
the device shown in FIG. 1;
FIG. 4 is a schematic electrical diagram of the device shown in
FIGS. 1 - 3;
FIG. 5 is a schematic electrical diagram of a modified utilization
of the device shown in FIGS. 1 - 3 showing printed circuit board
connections;
FIG. 6 is an isometric view of another embodiment of impedance
device in accordance with the subject invention;
FIG. 7 is a schematic electrical diagram of still another
embodiment of impedance device in accordance with the subject
invention;
FIG. 8 is an isometric view of a voltage divider embodiment of the
subject invention;
FIG. 9 is a top view of a resistance element assembly of the device
shown in FIG. 8;
FIG. 10 is a schematic electrical diagram of the device shown in
FIG. 8;
FIG. 11 is a top view of an element assembly for an inductance
device in accordance with the subject invention;
FIG. 12 is a side sectional view of a device incorporating the
element assembly shown in FIG. 11;
FIG. 13 is a schematic electrical diagram of the inductance device
shown in FIGS. 11 and 12;
FIG. 14 is a top view of an element assembly for a capacitance
device in accordance with the subject invention;
FIG. 15 is a side sectional view of a device incorporating the
element assembly shown in FIG. 14; and
FIG. 16 is a schematic electrical diagram of the capacitance device
shown in FIGS. 14 and 15.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1 - 3, a preferred embodiment of a selectable fixed
impedance device 10 is shown.
The device 10 is comprised of an electrically insulative substrate
12 of material such as glass, ceramic or plastic; an impedance
network 14 (as best shown in FIG. 3) on substrate 12; end
terminations 16E and intermediate terminations 16I of electrically
conductive material which are also on substrate 12 and are in
electrical contact with impedance network 14 at preselected
locations thereon; sealing means 18 overlying impedance network 14;
collector means 20 of electrically conductive material; spacing
means 22 for spacing collector means 20 from network 14 and
terminations 16; and termination leads 24 for connecting device 10
to an electric circuit.
Substrate 12 can be formed of substantially any electrically
insulative material on which an impedance network can be applied or
otherwise attached. While in the preferred embodiment substrate 12
is formed of a ceramic material such as alumina; glass, plastics or
other electrically insulative materials may be used. Of course, the
substrate may be formed of multiple layers in which case it is only
necessary that the top layer be electrically insulative. For
example, a glass, ceramic or plastic coated metal substrate may be
used.
While the structure shown in FIG. 1 may be used with substantially
any type of impedance element in accordance with the subject
invention, the impedance element assembly shown in FIG. 3 has a
resistance network. In its preferred form the resistance material
is of a thick film, cermet composition which is printed on
substrate 12. Cermet compositions generally include one or more
noble metals or oxides thereof in particulate form in a glass
matrix. Usually the cermet material is formed in an ink which is
applied to an insulative substrate which is then heated so as to
form the final resistive composition. Substantially any effective
composition and process for producing the cermet material and
forming a resistive element on a substrate may be utilized. U. S.
Pat. No. 3,539,392 discloses example of compositions and processes
that may be utilized. Of course, the size, composition and
processing of the cermet resistance material will depend on the
resistance and other electrical and physical requirements for the
device. Some of the advantages of using a cermet resistance
material are that for a substrate surface area of approximately
0.20 square inches a resistance device in accordance with the
subject invention can provide models covering a wide resistance
range of approximately 30 ohms to over 4 megohms. Also,
manufacturing costs using such a material are quite low and cermet
material has many desirable electrical and physical
characteristics. It should be noted that any prior art selectable
resistive device such as that disclosed in U. S. Pat. No.
3,071,749, which requires that the resistance material be
solderable could not use such cermet resistance material.
Of course, it is possible, though not as desirable, to use other
resistance materials such as thin metallic films, carbon, wound
resistance wire, etc. In such cases, these other resistance
materials could be bonded or otherwise attached to the substrate in
a configuration substantially similarly to that shown in FIG. 3.
The use of these materials instead of cermet materials would be
less desirable in most instances generally due to their inferior
electrical and physical characteristics and the limitation of
resistance ranges in which such devices, particularly in a
miniature size, could be made available.
Terminations 16 which are preferably applied to substrate 12 before
resistance network 14 is applied, are formed of a substantially
metallic meterial, herein called termination material, of very low
resistivity which is printed on the substrate and fired at a high
temperature. Alternatively, a mask may be applied to substrate 12
and metallic terminations formed by sputtering a conductive
material onto the surface. Of course, it is also possible to bond
sheet metal termination pads of material such as copper, silver,
gold, or an alloy or laminate thereof to substrate 12 by use of,
for example, conductive epoxy or utilize any materials or process
well known in the art. It is obvious that when terminations 16 are
applied to substrate 12, before network 14 is applied, preselected
portions of the network will bond directly to terminations 16 and
thereby make permanent electrical contact therewith. Another reason
for utilizing such a process step order is that in the preferred
construction, the termination material must be fired at a high
temperature which would affect the properties of a cermet material
if it had been already bonded to the substrate. However, by
suitable choice of materials, it would be possible to first apply
the resistance network and then apply the terminals. For example, a
conductive epoxy could be used to bond terminals formed of a sheet
metal to the network. If solder is to be used to connect
intermediate terminations to collector means, it is desirable to
solder coat these terminals and possibly the collector means to
promote ease of soldering.
Sealing means 18 is preferably provided by use of a protective
coating of an electrically nonconducting material such as plastic
or glass over network 14. This serves to protect the device against
contamination or degradation due to humidity, dust, soldering,
etc.
In its preferred form, collector means 20 is in a form of a sheet
of highly conductive metal such as steel, copper, silver, gold or
alloys or laminations thereof. This member is embedded in spacing
means 22 and positioned so that a portion thereof is located a
short distance from each of intermediate terminations 16I with an
open space therebetween. When the device 10 is formed, spacing
means 22 which is of an electrically insulative material such as
plastic, also serves to electrically insulate collecting means 20
from network 14 and terminations 16. This positioning of collector
means 20 relative to intermediate terminations 16I permits
electrical connection to be made between selected intermediate
terminations and collector means 20 by any one of a variety of
means, as is described in a succeeding portion of this
specification.
Spacing means 22, which in the preferred embodiment is of a unitary
piece, plastic construction and is bonded to substrate 12 by means
such as adhesive, also serves a number of functions in addition to
positioning and insulating collector means 20. Spacing means 22
helps protect the device from physical damage and provides
structural rigidity. Notches 26 in spacing means 22 provide walls
which serve as barriers between adjacent intermediate terminations
16I to facilitate reliable connections between the terminations and
collector means. Also, in accordance with standard practice in the
electronic components art, an identifying notch 28 is provided on
one end of spacing means 22 as an orientation aid for use in
installing the device in an electric circuit.
Termination leads 24 are connected to end terminations 16E by any
suitable means such as soldering or swaging. The leads themselves
may be of any form, as is commonly known in the trade including
pins, DIP terminations, flexible leads, etc. Such forms of
termination leads and processes of connecting them to end
terminations are applicable to all embodiments of the subject
invention.
FIGS. 4 and 5 are schematic electric circuit diagrams of the device
shown in FIGS. 1 - 3. Impedance network 14 is shown as being
comprised of a primary network 14P made up of resistances R1
through R15 and a supplemental network 14S. Intermediate
terminations 16I are shown connected to network 14P and are labeled
by vertically adjacent indicia of percentages. End terminations 16E
are numbered 1 - 4 with terminations 1 and 2 being located at the
ends of primary network 14P and terminations 3 and 4 being located
at the ends of supplemental network 14S. Collector means 20 is also
shown.
The values of the resistance portions R1 - R15 are approximately
preselected percentages of a nominal resistance value for the
device. Resistance portion R1 is approximately 50 percent of the
nominal value, resistances R2 - R6 are each approximately 10
percent of the nominal value and resistance portions R7 - R15 are
each approximately 1 percent of the nominal value.
In the schematic shown in FIG. 4, end terminations labeled 1 and 2
are connected to termination leads 24. In this configuration, the
resistance of the device can be selected in approximately one
percentage increments from 50 to 109 percent of the nominal
value.
In the normal operational sequence, device 10 would be installed in
a circuit by making connection to the end terminations labeled 1
and 2 through their respective termination leads 24. Then probes
are inserted in two separate notches so as to temporarily connect
the intermediate termination in each notch to collector means 20.
One probe will be used for the terminations labeled 50 - 100
percent and one probe used for the terminations labeled 0 - 9
percent. When the optimum resistance is chosen, the selected
notches are marked or otherwise noted and a stable, permanent
connection between the selected intermediate terminations and the
collector means can be made. In the embodiment shown in FIGS. 1 and
4, a value of approximately 62 percent of the nominal value has
been selected and connection made by means of soldering. While the
preferable means for electrically connecting intermediate
terminations to collector means 20 is soldering, any other
connecting means such as conductive epoxy or an electrically
conductive insert member, which can be inserted between collector
means and intermediate terminations, may be utilized. However,
soldering is preferable in that the materials and equipment are
commonly used in the electronics industry and soldering is widely
accepted as a permanent, satisfactory means for making an
electrically stable connection.
If a somewhat higher value is needed than 109 percent of the
nominal value, supplemental network 14S may be connected in series
with primary network 14P by electrically connecting the leads of
end terminations 1 and 4 together and using the leads of
terminations 2 and 3 to connect the device into the electric
circuit, as shown in FIG. 5. This allows the range of selection of
resistance values in a device connected this way to be between 80
and 139% of the nominal value. If the same two intermediate
terminations as in FIG. 4 were connected to the collector means, a
resistance value of approximately 92 percent would be effected.
Of course, it is obvious that by connecting two intermediate
terminations to collector means 20 the intervening resistances
between the intermediate terminations are effectively shorted out
so that in the example shown in FIG. 4 the net resistance of the
device would be the summation of the resistances of portions R1,
R2, R14 and R15.
With such an arrangement of impedance portions the maximum
selection error would be about 0.5 percent of the nominal value or
in other words, an error of half the impedance of the smallest
impedance increment (which in this case is 1 percent of the nominal
value). In most cases the error would be much less than this.
Of course, the impedance network can be divided into any number of
portions having substantially any desired value. For example, a
first set of nine portions each having a value of 10 percent of the
nominal value and a second set of nine portions each having a value
of 1 percent of nominal value could be used to give a selection
range of 1 - 99 percent of nominal value. Alternatively a set of
portions each having a value of 0.5 percent of nominal could be
used to provide an even smaller maximum selection error, if
desired. Any other mathematical relationship consistent with the
general configuration may be used. The specific arrangement shown
and described is particularly advantageous as it provides for a
small maximum selection error, can be so constructed in a package
compatible with DIP packaging circuit connections and the selection
can be simply and easily accomplished.
While the normal selection operation for the device of the subject
invention would be as described above, it would also be possible to
preselect the resistance value of the device before insertion into
the circuit. For example, the device could be connected to an
ohmmeter and by properly probing the intermediate terminations the
closest value to a predetermined resistance value could be
selected. Thus, devices of the subject invention could be used
instead of fixed resistors. One device as shown would replace a
stock of 90 fixed resistors having values ranging from 50 - 139
percent of the nominal value in 1 percent increments.
Once selection of the two intermediate termination connections is
made and the connection effected, the value of the device is for
most purposes fixed. However, depending on which intermediate
terminations are initially selected and the desired change in
resistance, additional connections might be made. Alternatively,
one or more of the connections may be removed, such as by
desoldering, and new connection made. However, this generally would
not be recommended.
In FIG. 6 an alternate embodiment of selectable fixed impedance
device is shown with a partial cutaway section. A somewhat larger
insulative substrate 12' is used in this embodiment with the
impedance network 14 and terminations 16 being substantially the
same as that shown in FIGS. 1 - 3. Collector means 20' is shown as
a conductor of very low resistance which has been printed on
substrate 12' outside intermediate terminations 16I. In this
embodiment, spacing means 22' is shown to be part of the substrate.
A plurality of small grooves 26 are provided in substrate 12' (on
the spacing means 22' portion thereof) between each intermediate
termination 16I and collector means 20'. When electrical connection
is desired between any particular intermediate termination 16I and
collector means 20', connecting means 27 such as solder or
conductive epoxy is applied to the space between them with the
groove 26 being used to channel the conductive means therebetween.
Of course, it is not absolutely necessary to have such grooves as
other means for guiding or restricting the connecting means between
the two members to be joined may be used or it may not be necessary
at all to have such guiding means. Alternatively, collector means
20' could be in the form of a metal strip which is embedded in the
substrate. Also, some other electrically insulative material which
is bonded to the substrate may be used as the spacing means and
could support collector means 20'. Sealing means in the form of a
thin layer of sealing material 18 is shown for this embodiment. Due
to the generally exposed nature of the top surface, it may be
desirable to add a rigid protective member over a substantial
portion of the exposed surface. This member would also serve to
seal the impedance network.
In this embodiment, the electrical configuration of the device is
exactly the same as that shown in FIG. 5. In FIG. 6, solder
connections between the intermediate terminations and the collector
means are shown to provide a value for the device of approximately
69 percent of nominal value.
In FIG. 7, a schematic electrical diagram of another embodiment of
the subject invention is shown. In this embodiment, the impedance
network is formed of at least two parts 28A and B as well as a
supplemental portion 28S with the first part 28A being divided into
portions having relatively large impedance values and the second
part 28B being divided into portions having relatively small
impedance values. For example, in the schematic shown in FIG. 7,
impedance part 28A includes one portion having approximately 50
percent of the nominal value of the device and five portions having
approximately 10 percent of that value; whereas impedance part 28B
has nine portions each of which is approximately 1 percent of the
nominal value of the device.
In this embodiment, collector means 30 is formed of two separate
conductive members 30A and 30B. Intermediate terminations 16I and
end terminations 16E are provided as described in regard to the
above-mentioned embodiment with the intermediate terminations
connected to impedance part 28A being spaced a short distance from
collector member 30A, and the intermediate terminations connected
to impedance part 28B being spaced a short distance from collector
member 30B. End termination labeled 1 is electrically connected to
one end of impedance part 28A, collector member 30B is electrically
connected to end termination labeled 2. The electrical connection
between collector member 30A and impedance part 28B as well as
between collector member 30B and end termination number 2 can be
effected by any desired means, however, it would be most convenient
to provide a means for connecting them similar to that use in
regard to the intermediate terminations. Such connections could be
made by soldering during manufacture of the device.
The physical structure of this embodiment is preferably similar to
that shown in FIGS. 1 and 2 with both collector members 30A, B
being embedded in spacing means 22. Also, the structure shown in
FIG. 6 could be utilized in a suitably modified form. This
embodiment would have the same desirable electrical characteristics
as the other embodiments discussed above and would permit probing
and permanent fixing of the impedance values with the same ease. As
in the other embodiment, the maximum selection error would be
within 0.5 percent of the nominal value of the device when using
the impedance configuration shown.
In FIGS. 8 and 9, a voltage divider embodiment of selectable fixed
impedance device is shown. A Kelvin-Varley voltage divider circuit,
as shown in the schematic of FIG. 10 is used.
The construction is generally similar to that shown in FIGS. 1 - 3.
An electrically insulative substrate 32 is provided on which three
sets of intermediate terminations 36I.sub.1, 36I.sub.2 and
36I.sub.3 as well as end terminations 36E are located. An impedance
network 34 comprised of two separate parts 34A and 34B is located
on substrate 32 with the intermediate terminations being
electrically connected thereto at preselected locations so as to
divide each network part into portions having predetermined values
as shown in FIGS. 9 and 10. Each impedance network part is
preferably covered by sealing means 38 formed of a material such as
glass or plastic. Collector means 40 is formed of three separate
members 40A, B and C which are electrically conductive and of very
low resistivity. The collector members are partially embedded in
spacer means 42 which serves to position each collector member with
respect to the intermediate terminations with which it can be
connected and insulate each member from the impedance network and
each other. Spacing means 42 is designed to expose portions of the
collector members so that there is a small open space between each
of the intermediate terminations and its associated collector
member. This is preferably done by notches or apertures 44 in the
spacing means. In its preferred form, these notches or aperatures
44 are at least partially defined by walls which tend to isolate
each intermediate termination from its adjacent termination thus
tending to prevent faulty connections due to solder or other
material contacting the wrong termination.
Due to the circuit design, each of the collector members must be
connected to either an impedance network part or to an end
termination. This can be accomplished by substantially any suitable
means. In the embodiment shown in FIGS. 8 and 9, this is
accomplished by providing four connector terminations 45 on
substrate 32 at the desired locations. Exposed portions of a
particular collector member to which the connector termination is
to be connected are spaced a short distance from each such
connector termination 45 in a configuration substantially similar
to that used with respect to intermediate terminations 36I. These
connections will be made during the manufacturing process for the
device by any suitable means such as soldering or applying
conductive epoxy.
The electrical circuit for this device is shown in FIG. 10. The
total impedance of impedance network portion 34A is approximately
110 percent of the nominal value and is divided into 11
substantially equal portions each having a value of approximately
10 percent of the nominal value by means of intermediate
terminations 36I.sub.1, 36I.sub.2. Impedance network part 34B has a
total impedance value of approximately 20 percent of the nominal
value and is divided by means of intermediate terminations 36I.sub.
3 into ten substantially equal portions each having a value
approximately 2 percent of the nominal value of the device.
Collector member 40A is electrically connected to one end of
impedance part 34B, collector member 40B is electrically connected
to the other end of impedance part 34B, and collector member 40C is
electrically connected to end terminations labeled 2 and 3. For
selection of the desired voltage divider value, one connection is
made between collector member 40A and one of the intermediate
terminations 36I.sub.1 and another connection is made between
collector member 40B and one of the intermediate terminations
36I.sub.2 such that a section having a value of 20 percent of the
nominal value (two impedance network portions) on impedance network
part 34A is included between the two selected intermediate
terminations. Due to the electrical connections between collector
members 40A and 40B and the ends of impedance network portion 34B,
this 20 percent value segment on impedance network part 34A is
placed in parallel with the entire 20 percent value of impedance
network part 34B. Thus, the effective impedance between terminals
labeled 1 and 4 is 100 percent of the nominal value. At this point,
it should be noted that intermediate terminations 36I.sub.2 are
preferably made with a somewhat "S" shaped pattern connecting the
pad portion thereof to the impedance network so that each 20
percent section can be selected by merely connecting a pair of
intermediate terminations 36I.sub.1 and 36I.sub.2 which are
directly opposed on a line substantially transverse to the device.
However, this configuration is merely preferred for ease in
utilization of the device.
The choice of any particular 20 percent increment along impedance
network part 34A determines the 10 percent range for voltage
dividing as marked in FIG. 10 directly below intermediate
terminations 36I.sub.1. As impedance network part 34B is divided
into ten portions by intermediate terminations 36I.sub.3, each
portion thereof has a net effective value of 1 percent in the
voltage divider circuit, in accordance with the theory of operation
of the Kelvin-Varley circuit. Thus, by selecting a specific pair of
intermediate terminations 36I.sub.1 and 36I.sub.2 and making these
connections, the operator selects the particular 10 percent range
in which he wishes to operate (coarse adjustment); and by selecting
one of the intermediate terminations 36I.sub.3 and making the
suitable connection, the value, in 1 percent increments, within
this 10 percent range can be selected (fine adjustment). The
output, of course, would be through either of the end terminations
labeled 2 or 3 since collector member 40C is connected to both. For
example, as shown in FIG. 10, if the pair of intermediate
terminations with regard to the range of 31 - 40 percent are
selected and suitable connections made and the intermediate
termination corresponding to 4 percent is selected and suitable
connection is also made, the output voltage would be approximately
34 percent of the input voltage applied between end terminations
labeled 1 and 3.
It should be noted that the Kelvin-Varley circuit is accurate if
there is a negligible current flow through the circuit. If there is
any significant current flow, a small error may result. However,
since the primary utilization of such a device would be where the
terminations would first be probed so as to discover which
selection of termination would give the desired result, the
accuracy of the device would be unaffected. Only the accuracy of
the labeling of the terminations would be affected in such a
case.
While the device shown is a voltage divider using resistance
elements, a capacitance or inductance divider device is also
possible by substitution of the resistance network parts with
inductance or capacitance network parts. Also, any other suitable
construction such as the type of construction shown as discussed
above in regard to FIG. 6 may alternatively be used.
A divider device, in accordance with the subject invention, has
many advantages in that it can be made in a small size, is both
selectable and fixed, has a small maximum error (0.5 percent for
the embodiment shown in FIGS. 8 - 10), can be manufactured
inexpensively and can be adjusted easily and speedily. One further
advantage is that such a device could alternatively be used for a
rheostat type function similar to that disclosed in the
aforementioned embodiment of the subject invention shown in FIG. 7
merely by using intermediate terminations 36I.sub.2 and 36I.sub.3
in the same fashion intermediate terminations 16I are used in the
embodiments shown in FIGS. 1 - 7. The electric circuit utilized in
such a device would be effectively similar to that shown in FIG.
7.
In FIGS. 11 - 13 a selectable fixed inductance embodiment of the
subject invention is shown. This device includes the substrate 12,
intermediate and end terminations 16I and 16E, collector means 20
and spacer means 22 substantially the same as that described above
regarding the embodiment of FIGS. 1 - 3. An impedance network 46 is
provided on substrate 12 and includes a plurality of windings 46W
about a core 46C. Windings 46W, which are preferably flat in form,
are formed from a conductor of a material having very low
resistivity which is wound about core 46C with the intermediate
terminations 16I tapping winding 46W at preselected intervals so as
to define inductance portions. Preferably, inductance network 46 is
formed by first printing termination material to form termination
16 and the lower layer of windings 46W. Then a core of a material
having suitable magnetic properties, such as ferrite applied as a
thick film, is formed over the lower layer of windings leaving the
ends thereof exposed. Termination material forming the top layer of
windings 46W is then printed over the top of core 46C in a desired
pattern and so as to overlap and make electrical contact with the
exposed portions of the lower layer of windings 46W, thereby
forming an inductive coil. Sealing means 48, for example a plastic
or glass coating, is then applied over inductance network 46.
Collector member 20 and spacing means 22, substantially as shown in
FIG. 1, may then be utilized for such a device. Also, suitable
termination leads 24 are connected to end terminations 16E in a
manner similar to that disclosed above.
The inductance portions may be of equal value, as shown, or may be
in any desired mathematical relationship. The inductance network
may also be in two or more parts, if desired. In the electrical
diagram shown in FIG. 13, the last intermediate termination (shown
in the upper right corner) is permanently connected to collector
means 20, so that merely by selecting one additional intermediate
termination any inductance value in increments of "x" impedance can
be selected between 1x and 15x where "x" would be the impedance
value of a single portion of impedance network 46. Of course, the
entire impedance value (16x) could be utilized if none of the other
intermediate terminations were selected. It is expected that each
inductance portion could be formed to have a value of from 1.mu.h
to 1 mh.
In FIGS. 14 - 16, a selectable fixed capacitance embodiment of the
subject invention is shown. In this embodiment, an electrically
insulative substrate 12 is used with a capacitance network 50 and
intermediate terminations 16I and end terminations 16E located
thereon. Collector means 20 and spacing means 22 are also used.
Capacitance network 50 is preferably comprised of a common lower
electrode 50L which is formed of a sheet of termination material
printed on substrate 12, a layer of dielectric material 50D which
is formed over lower electrode 50L and a plurality of top
electrodes 50E which are formed of flat portions of electrically
conductive material such as termination material each of which is
connected to one of the intermediate terminations 16I. The top and
bottom electrodes can be formed of any one of a variety of
electrically conductive materials having low resistivity such as
metal films, pieces of sheet metal, or the termination material
shown. While the dielectric is generally an electrically insulative
material such as plastic (for example, mylar film) or glass, it is
also possible to use a suitable semiconductor so as to effect a
voltage controlled capacitor. Preferably, sealing means 52 is
applied over capacitance network 50.
Capacitance network 50 is divided into capacitance portions (16 are
shown) in which the lower electrode 50L is common to all the
portions and each portion has its own top electrode 50E next to its
respective intermediate termination. The actual capacitance value
of each portion is determined by a number of parameters including
the size and composition of the dielectric material and the size
and shape of the top electrode. In the embodiment shown, each of
the portions is of approximately equal capacitance, although
networks having capacitance portions which differ in value may be
utilized. For example, the capacitance would be different if top
electrodes of different surface area were used. Also, multiple
layers of alternating electrodes and dielectric material suitably
connected, as is known in the art, might also be utilized.
As shown in FIG. 16, a schematic electrical diagram of this
embodiment, one electrode of each capacitance portion is connected
to a common conductor. Lower electrode 50L serves as both the lower
electrode for each capacitance portion and the common conductor.
When a capacitance portion is desired to be added into the device,
suitable electrical connection is made between a selected
intermediate termination and collector means 20. When two or more
intermediate terminations are so connected, the capacitance
portions are placed electrically in parallel with each other and
hence their capacitance values are additive. The device shown in
FIGS. 14 - 16 thus would have a range of values of one to 15 times
the capacitance value of each portion. Any one or more of the
capacitance portions can be connected so as to give the desired
capacitance value.
Thus, the subject invention includes a family of selectable fixed
impedance devices including selectable fixed resistors, capacitors
and inductors as well as selectable fixed voltage dividers,
capacitance dividers and inductance dividers or any combination
thereof all of which have a number of significant advantages. Any
of the devices can be manufactured easily and inexpensively in a
small or miniature configuration and can be easily used in most
state of the art electric circuits. The devices can be quickly,
easily and reliably adjusted after they have been permanently
inserted into the circuit or prior to such insertion, if desired.
In all cases, the impedance values can be temporarily selected by
probing before permanent connections are made. The devices can be
made in a wide range of values. In many cases each device
effectively replaces a large number of components having fixed
impedance values of comparable electrical characteristics and at a
cost much lower than the total cost for all the fixed impedance
devices. Each separate device has the advantages of selectability
while also having the advantages of fixed impedance components.
It is obvious that many modifications may be made within the true
scope and spirit of the subject invention. Thus it is intended that
the scope of the invention be limited only by the appended
claims.
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