US3745508A

US3745508A - Selectable fixed impedance device

Info

Publication number: US3745508A
Application number: US00256661A
Authority: US
Inventors: V Steuer; F Bruder; J Parham
Original assignee: Bourns Inc
Current assignee: Bourns Inc
Priority date: 1972-05-25
Filing date: 1972-05-25
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10
Also published as: FR2185894B3; GB1429009A; IT987799B; FR2185894A1; NL7305674A; JPS4956154A; DE2326043A1

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.

Description

United States Patent 1191 1111 3,745,508 Bruder et al. July 10, 1973 [54] SELECTABLE FIXED IMPEDANCE DEVICE 3,486,149 12/1969 Klein 336/200 X Appl. No.: 256,661

US. Cl 338/320, 317/249 R, 317/261,

Int. Cl H0lc 1/16 Field of Search 338/320, 295, 308, 338/309; 317/249 R, 261; 336/192, 200

References Cited UNITED STATES PATENTS 4/1957 Eisler 317/249 R 10/1965 Constatakes 336/200 9/1967 Kinkel 338/308 X 11/1968 Schiller 338/308 X Primary Examiner-E. A. Goldberg Attorney-William G. Becker [5 7 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.

26 Claims, 16 Drawing Figures 1 SELECTABLE FIXED IMPEDANCE DEVICE 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 elec trical 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 con ventional 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 l6l 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 resistancematerial 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 tired 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 termi' nals 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 ofa 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 is formed, spacing means 22 which is of an electrically insulative material such as plastic, also serves to electrically insulate collecting means from network 14 and terminations 16. This positioning of collector means 20 relative to intermediate terminations 161 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 16l 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 148. Intermediate terminations l6l are shown connected to network 14? 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 14? and

terminations

3 and 4 being located at the ends of supplemental network 148. 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 I09 percent of the nominal value, supplemental network 148 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 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 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 l 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 288 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 283 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 161 and end terminations 16E are provided as described in regard to the abovementioned 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 308 is electrically connected to end termination labeled 2. The electrical connection between collector member 30A and impedance part 288 as well as between collector member 303 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. 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 36],, 36l and 361 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 361. 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 1 10 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,, 36I Impedance network part 34B has a total impedance value of approximately percent of the nominal value and is divided by means of intermediate terminations 36]; 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 348, collector member 403 is electrically connected to the other end of impedance part 348, 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 361, and another connection is made between collector member 403 and one of the intermediate terminations 361 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 percent of the nominal value. At this point, it should be noted that intermediate terminations 36I 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 361 and 36I whiclkare 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 361,. As impedance network part 348 is divided into ten portions by intermediate terminations 361 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 36l and 361 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 361 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 and 361 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

161 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 IX and x 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 luh 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 161 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 161. 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 se' lectability 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.

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;

. 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 meansis 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 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 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 conductive means is solder.

* II i

Claims

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.

10. A device as in claim 1 wherein said impedance is a capacitance network.

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.

21. A device as in claim 20 wherein said portions of said impedance network are connected in series.

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.