CA2241927C - Resistor and protector for transmission line - Google Patents
Resistor and protector for transmission line Download PDFInfo
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- CA2241927C CA2241927C CA 2241927 CA2241927A CA2241927C CA 2241927 C CA2241927 C CA 2241927C CA 2241927 CA2241927 CA 2241927 CA 2241927 A CA2241927 A CA 2241927A CA 2241927 C CA2241927 C CA 2241927C
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Abstract
The subject resistor can be reduced in size and acts to protect a transmission line. The resistor has a serpentine resistive element having bent portions. Electric field concentration in these bent portions and generation of a spark at these bent portions are prevented. A transmission line protector using this resistor is also provided. The resistor comprises an alumina plate, the aforementioned serpentine resistive element formed on the alumina plate, and electrodes formed over (or under) the inner portions of the bent portions of the serpentine resistive element.
Description
RESISTOR AND PROTECTOR FOR TRANSMISSION LINE
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a resistor and protector for protecting a transmission line. More particularly, the present invention pertains to a protector for protecting transmission equipment, such as switching equipment, from abnormal currents flowing through a transmission cable due to contact between the transmission cable and a power line (or due to other sources of abnormal current), and to a resistor used for this protector.
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a resistor and protector for protecting a transmission line. More particularly, the present invention pertains to a protector for protecting transmission equipment, such as switching equipment, from abnormal currents flowing through a transmission cable due to contact between the transmission cable and a power line (or due to other sources of abnormal current), and to a resistor used for this protector.
2 Description of Related Art Fig. 5 shows an equivalent circuit of a protector for a transmission line.
This protector, generally indicated by reference numeral 40, comprises a series combination of resistors 41a and 41b for protecting the transmission line and thermistors 42a and 42b having positive temperature coefficients. First ends of these two series combinations are connected with input terminals 43a and 43b, respectively, of the transmission line. Second ends of these two series combinations are connected with output terminals 44a and 44b, respectively, of equipment to be protected (referred to henceforth as "protected equipment"). Thus, two protector circuits for protecting the transmission line are formed. These protector circuits are not electrically connected.
The structure of one known transmission line protecting resistor for use in the transmission line protector 40 shown in Fig. 5 is shown in Fig. 6. The transmission line protecting resistor, generally indicated by reference numeral 41a, comprises an alumina plate 45 that forms an insulating substrate and a serpentine resistive component 46 formed on the alumina plate 45 by thick-film printing technology.
The resistor 41b for protecting the transmission line is constructed similarly and so description of the structure of this resistor 41b is omitted.
Referring back to Fig. 5, the operation of the transmission line protector 40 is described. Generally, the thermistors 42a and 42b having positive temperature coefficients exhibit nonuniform impedances at room temperature. This adversely affects the characteristics of the transmission line. Accordingly, the line protecting resistors 41a and 41b set at appropriate values are connected in series with the positive temperature coefficient thermistors 42a and 42b, respectively, thus rendering the impedances of the two transmission line protector circuits substantially uniform.
If contact between a transmission cable and a power line induces an abnormal current flowing from the transmission cable into the transmission line protector 40 constructed as described above, the current causes the thermistors 42a and 42b having positive temperature coefficients to increase in temperature (e.g., to get hot). The resulting heat rapidly increases the resistances of the thermistors 42a and 42b. This, in turn, decreases the current flowing through the thermistors. In this manner, the transmission equipment is protected from abnormal currents; otherwise, the equipment may be destroyed.
Even with this transmission line protector 40, if a transient overcurrent takes place due to a surge caused by an electrical storm (e.g., a "lightning surge"), for example, the thermistors 42a and 42b having positive temperature coefficients simply act as resistors. Therefore, diodes, varistors, and other devices for absorbing lightning surges are also fitted to the transmission equipment to supplement the protection.
In the aforementioned transmission line protecting resistors 41a and 41b (each of which is referred to generically as resistor 41), if a high-voltage overcurrent flows due to a lightning surge, for example, and if the bent portions of the serpentine resistive component 46 have a small radius, an electric field is concentrated in the inner portions of the bent portions, which may produce a spark. This creates the possibility of destruction of the serpentine resistive component 46. To avoid this, the radius of the bent portions of the serpentine resistive component 46 is set large to make the currents flowing in the inner and outer radial portions of the bent portions as uniform as possible. However, this increases the spacing between the adjacent straight portions, thus increasing the whole area of the resistive component 46.
Hence, miniaturization of the transmission line protecting resistor 41 is hindered.
In recognition of these problems, a resistor structure as shown in Fig. 7 is proposed in Japanese Unexamined Utility Model No. 172901/ 1981. This resistor, generally indicated by numeral 50, comprises an alumina plate 51 that forms an insulating substrate, straight resistive strips 52 formed on the alumina plate 51 in parallel relation to each other, and rectangular connector electrodes 53 for connecting adjacent ones of the resistive strips 52 at their opposite ends. As a whole, a serpentine resistive component is formed.
By constructing the resistor SO as described above, the resistor is free of bent portions. The connector electrodes 53 existing at the bent portions of the serpentine resistive component have low resistance and so the electric field is less concentrated in these portions. However, the end portions of the resistive strips 52 are made square, and the connector electrodes 53 are shaped rectangularly. The electric field is concentrated in these corners. An electric discharge easily occurs from these corners.
For instance, the portion consisting of two resistive strips 52 and one connector electrode 53 is equivalently expressed in Fig. 8, where the resistance RO of each resistive strip 52 and the resistance R 1 of the connector electrode 53 are arranged alternately and connected in series. The resistive strip 52 and the connector electrode 53 differ widely in resistivity. A strong electric field is applied to the junction of these two kinds of conductors. Again, an electric discharge easily takes place from this junction.
SUMMARY OF THE INVENTION
The present invention is intended to solve at least the foregoing problems.
It is an exemplary object of the present invention to provide a resistor which acts to protect a transmission line and can be miniaturized, and in which neither electric field concentration nor an electric discharge easily takes place.
It is another object of the invention to provide a transmission line protector using the resistor described in the immediately preceding paragraph.
A resistor for protecting a transmission line in accordance with the present invention comprises an insulating substrate having bent portions, a serpentine resistive component formed on the substrate, and electrodes (which comprise any low-resistivity components) having a resistivity lower than that of the serpentine resistive component and formed at least over the inner portions of the bent portions of the serpentine resistive component.
A transmission line protector in accordance with the present invention comprises two transmission line protector circuits each consisting of the transmission line-protecting resistor described in the immediately preceding paragraph and a positive temperature coefficient thermistor connected in series with the transmission line protecting resistor.
In the transmission line protecting resistor constructed in this manner, electric field concentration is less likely to occur in the bent portions of the serpentine resistive component. Therefore, an electric discharge is less likely to occur.
Furthermore, destruction of the serpentine resistive component is less likely to occur.
Hence, miniaturization can be accomplished by decreasing the radius of the bent portions. Additionally, the transmission line protector in accordance with the present invention can be fabricated in smaller size.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the present invention will be more readily understood upon reading the following detailed description in conjunction with the drawings in which:
Fig. 1 is a view illustrating an exemplary transmission line protecting resistor in accordance with the invention;
Fig. 2 is an equivalent circuit diagram of a bent portion and the vicinity portions thereof of the resistor shown in Fig. 1;
Fig. 3 is a view similar to Fig. I , but showing another exemplary transmission line protecting resistor in accordance with the invention;
Fig. 4 is a view illustrating an exemplary transmission line protector in accordance with the invention;
Fig. 5 is an equivalent circuit diagram of a transmission line protector;
Fig. 6 is a view illustrating the structure of a known transmission line-protecting resistor;
Fig. 7 is a view illustrating the structure of another known transmission line-protecting resistor; and Fig. 8 is an equivalent circuit diagram of a connector electrode portion and the vicinity portions thereof of the resistor shown in Fig. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, there is shown a resistor for protecting a transmission line, the resistor being built in accordance with one exemplary embodiment of the present invention. This resistor, generally indicated by reference numeral l, comprises an alumina plate 2 that forms an insulating substrate, a serpentine resistive component 3 formed on the alumina plate 2 by thick-film printing technology or other suitable technology, and substantially semicircular electrodes 4 formed over the inner portions of the bent portions of the serpentine resistive component 3 by thick-film printing technology or other suitable technology. More specifically, the term "inner portions" refers to a portion of the bent portions which is radially inward from the outer circumference of the bent portions. The resistivity (e.g., 0.00001 S~ ~
cm) of the electrodes 4 is sufficiently lower than the resistivity (e.g., 0.001 S2 ~
cm) of the serpentine resistive component 3. Here, the resistivity of the resistive component 3 is 100 times greater than the resistivity of the electrodes 4, but those skilled in the art will recognize that the resistances can vary by different amounts. The term "electrode" as used here refers generally to any member having a resistivity which is less than the resistivity of the resistive component 3.
The equivalent circuit of a transmission line protector having the transmission line protecting resistor 1 is the same as the equivalent circuit of the known structure shown in Fig. 5. Therefore, description of this equivalent circuit is omitted here.
In the transmission line protecting resistor 1 constructed as described above, the electrodes 4 are formed on top of the inner portions of the bent portions of the serpentine resistive component 3. Therefore, the resistivity of the inner portions of the bent portions is made lower than that of the straight portions. Therefore, if an overcurrent flows due to a lightning surge or the like, electric field concentration in the inner portions of the bent portions is reduced or suppressed. As a consequence, the possibility of creation of a spark or destruction of the serpentine resistive component 3 is made lower than the above-described conventional resistive component. Since the bent portions of the serpentine resistive component 3 and the electrodes 4 are shaped substantially semicircularly, any corner at which electric field concentration would normally take place does not exist. Hence, the possibility of occurrence of an electric discharge is low. An equivalent circuit of a portion of the serpentine resistive component 3 is shown in Fig. 2, which includes resistances R0, R2, and RO connected in series. More specifically, the two resistances labeled RO
designate the resistances of two immediately parallel resistive "straight portions." The resistance R2 designates the resistance of the bent portion between the two immediately parallel resistive straight portions. The resistance R3 of the electrode 4 is added as distributed resistance connected in parallel with the resistance R2.
Therefore, any portion in which a strong electric field would normally be concentrated does not exist between the serpentine resistive component 3 and the electrode 4. The possibility of an electric discharge at this junction is low.
As a result, the radius of the bent portion can be reduced. As a consequence, the spacing between the adjacent straight portions of the serpentine resistive component 3 can be decreased. Hence, the whole area of the transmission line protecting resistor 1 can be redUCed.
Referring next to Fig. 3, there is shown another exemplary resistor for protecting a transmission line. This resistor, generally indicated by reference numeral 10, comprises an alumina plate 11, a serpentine resistive component 12 formed on the alumina plate 1 I by thick-film printing technology or other suitable technology, and arc-shaped electrodes 13 formed over the bent portions of the serpentine resistive component 12 again by thick-film printing technology or other suitable technology. The electrodes 13 are similar in shape to the shape of the bent portions. The resistivity of the electrodes 13 is set lower than that of the serpentine resistive component 12.
By fabricating the transmission line protecting resistor 10 in this manner, the resistance of the bent portions of the serpentine resistive component 12 is reduced. If an overcurrent is induced by a lightning surge or the like, electric field concentration in the inner portions of the bent portions is suppressed. The possibility of a spark or destruction of the serpentine resistive component 12 is lowered. Furthermore, since the bent portions including the electrodes 13 are shaped into arcs, any corner at which electric field concentration would otherwise take place does not exist or is at least reduced. Hence, the possibility of occurrence of an electric discharge is low.
As a result, the radius of the bent portions can be reduced. The whole area of the transmission line protecting resistor can be decreased by narrowing the spacing between the adjacent straight portions of the serpentine resistive component 12.
In the above embodiments, the semicircular electrodes 4 and the arc-shaped electrodes 13 are formed over the bent portions of the serpentine resistive component 3 or 12. Alternatively, the electrodes 4 and the electrodes 13 may be previously formed under the bent portions. Generally speaking, the bent portions and the electrodes overlap each other, wherein the term "overlap" is intended to encompass the case where the electrodes are disposed over the bent portions, and the case where the electrodes are disposed under the bent portions.
In the above embodiments described above, an alumina plate is used as an insulating substrate. Instead, other substrates, such as a ceramic substrate or resinous substrate, may be employed.
Further, although the resistive component is shown having a back-and-forth (zig-zag) shape, the term "serpentine path" is used herein to designate any elongate path having curved portions, including various types of meandering paths and spiral paths.
Referring to Fig. 4, there is shown a transmission line protector in accordance with exemplary embodiments of the invention. This protector, generally indicated by reference numeral 20, comprises an alumina plate 21 (or other suitable plate) that forms an insulating substrate, serpentine resistive components 22a and 22b formed on the alumina plate 21 by thick-film printing technology or other suitable technology, substantially semicircular electrodes 23a and 23b formed over the inner portions of the bent portions of the serpentine resistive components 22a and 22b, respectively, by thick-film printing technology or other suitable technology, positive temperature coefficient thermistors 24a and 24b, interconnect electrodes 25a, 25b, 26a, 26b, 27a, 27b, metal parts 28a and 28b for connecting a first terminal of the positive temperature coefficient thermistors 24a and 24b with the electrodes 26a and 26b, respectively, input terminals 29a and 29b of the transmission line, and output terminals 30a, 30b of the protected equipment. The resistivity of the electrodes 23a and 23b is sufficiently lower than that of the serpentine resistive components 22a and 22b. The input terminal 29a of the transmission line is connected with the output terminal 30a of the protected equipment via the interconnect electrode 27a, the serpentine resistive component 22a, the interconnect electrode 25a, the positive temperature coefficient thermistor 24a, the metal part 28a, and the interconnect electrode 26a, in this order. Thus, one transmission line protecting circuit is thereby formed. Similarly, the input terminal 29b of the transmission line is connected with the output terminal 30b of the protected equipment via the interconnect electrode 27b, the serpentine resistive component 22b, the interconnect electrode 25b, the positive temperature coefficient thermistor 24b, the metal part 28b, and the interconnect electrode 26b in this order. In this manner, another transmission line protecting circuit is formed.
An equivalent circuit of the transmission line protector 20 constructed in this manner is identical with the known structure shown in Fig. 5 and so description of the protector 20 is omitted. The resistors for the transmission line protecting circuits are the same as the resistor described already in conjunction with Fig. 1. The area of the transmission line protecting resistors can be reduced in the same way as in the embodiment illustrated in Fig. 1. Consequently, the transmission line protector 20 itself can be miniaturized.
As mentioned, the transmission line protector 20 uses the same construction as the transmission line protecting resistor 1 described in connection with Fig. 1. The transmission line protector 20 may also use the same construction as the transmission line protecting resistor 10 described previously in connection with Fig. 3.
A transmission line protecting resistor in accordance with the present invention comprises an insulating substrate, a serpentine resistive component formed on the substrate, and electrodes formed over at least the inner portions of the bent portions of the serpentine resistive component.
As a consequence, the resistivity of the inner portions of the bent portions of the serpentine resistive component is lowered. If an overcurrent is induced due to a lightning surge, for example, electric field concentration in the inner portions of the bent portions is suppressed. The possibility of production of a spark or destruction of the serpentine resistive component is made lower than in the above-described conventional device. The bent portions and the overlying (or underlying) electrodes are shaped semicircularly or arc-shaped. Therefore, any corner at which electric field concentration would normally take place does not exist. Consequently, the possibility of an electric discharge is low. The electrodes overlying (or underlying) the bent portions are added in parallel with the resistance of the bent portions of the serpentine resistive component and distributed as a low-resistivity resistor. Therefore, no strong electric field concentration occurs in the junction of the serpentine resistive component and the electrode. An electric discharge is unlikely to occur. As a result, the radius of the bent portions can be made small. The spacing between the adjacent straight portions of the serpentine resistive component can be decreased. As a consequence, the whole area of the transmission line protecting resistor can be reduced. Thus, the transmission line protector can be miniaturized.
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims.
This protector, generally indicated by reference numeral 40, comprises a series combination of resistors 41a and 41b for protecting the transmission line and thermistors 42a and 42b having positive temperature coefficients. First ends of these two series combinations are connected with input terminals 43a and 43b, respectively, of the transmission line. Second ends of these two series combinations are connected with output terminals 44a and 44b, respectively, of equipment to be protected (referred to henceforth as "protected equipment"). Thus, two protector circuits for protecting the transmission line are formed. These protector circuits are not electrically connected.
The structure of one known transmission line protecting resistor for use in the transmission line protector 40 shown in Fig. 5 is shown in Fig. 6. The transmission line protecting resistor, generally indicated by reference numeral 41a, comprises an alumina plate 45 that forms an insulating substrate and a serpentine resistive component 46 formed on the alumina plate 45 by thick-film printing technology.
The resistor 41b for protecting the transmission line is constructed similarly and so description of the structure of this resistor 41b is omitted.
Referring back to Fig. 5, the operation of the transmission line protector 40 is described. Generally, the thermistors 42a and 42b having positive temperature coefficients exhibit nonuniform impedances at room temperature. This adversely affects the characteristics of the transmission line. Accordingly, the line protecting resistors 41a and 41b set at appropriate values are connected in series with the positive temperature coefficient thermistors 42a and 42b, respectively, thus rendering the impedances of the two transmission line protector circuits substantially uniform.
If contact between a transmission cable and a power line induces an abnormal current flowing from the transmission cable into the transmission line protector 40 constructed as described above, the current causes the thermistors 42a and 42b having positive temperature coefficients to increase in temperature (e.g., to get hot). The resulting heat rapidly increases the resistances of the thermistors 42a and 42b. This, in turn, decreases the current flowing through the thermistors. In this manner, the transmission equipment is protected from abnormal currents; otherwise, the equipment may be destroyed.
Even with this transmission line protector 40, if a transient overcurrent takes place due to a surge caused by an electrical storm (e.g., a "lightning surge"), for example, the thermistors 42a and 42b having positive temperature coefficients simply act as resistors. Therefore, diodes, varistors, and other devices for absorbing lightning surges are also fitted to the transmission equipment to supplement the protection.
In the aforementioned transmission line protecting resistors 41a and 41b (each of which is referred to generically as resistor 41), if a high-voltage overcurrent flows due to a lightning surge, for example, and if the bent portions of the serpentine resistive component 46 have a small radius, an electric field is concentrated in the inner portions of the bent portions, which may produce a spark. This creates the possibility of destruction of the serpentine resistive component 46. To avoid this, the radius of the bent portions of the serpentine resistive component 46 is set large to make the currents flowing in the inner and outer radial portions of the bent portions as uniform as possible. However, this increases the spacing between the adjacent straight portions, thus increasing the whole area of the resistive component 46.
Hence, miniaturization of the transmission line protecting resistor 41 is hindered.
In recognition of these problems, a resistor structure as shown in Fig. 7 is proposed in Japanese Unexamined Utility Model No. 172901/ 1981. This resistor, generally indicated by numeral 50, comprises an alumina plate 51 that forms an insulating substrate, straight resistive strips 52 formed on the alumina plate 51 in parallel relation to each other, and rectangular connector electrodes 53 for connecting adjacent ones of the resistive strips 52 at their opposite ends. As a whole, a serpentine resistive component is formed.
By constructing the resistor SO as described above, the resistor is free of bent portions. The connector electrodes 53 existing at the bent portions of the serpentine resistive component have low resistance and so the electric field is less concentrated in these portions. However, the end portions of the resistive strips 52 are made square, and the connector electrodes 53 are shaped rectangularly. The electric field is concentrated in these corners. An electric discharge easily occurs from these corners.
For instance, the portion consisting of two resistive strips 52 and one connector electrode 53 is equivalently expressed in Fig. 8, where the resistance RO of each resistive strip 52 and the resistance R 1 of the connector electrode 53 are arranged alternately and connected in series. The resistive strip 52 and the connector electrode 53 differ widely in resistivity. A strong electric field is applied to the junction of these two kinds of conductors. Again, an electric discharge easily takes place from this junction.
SUMMARY OF THE INVENTION
The present invention is intended to solve at least the foregoing problems.
It is an exemplary object of the present invention to provide a resistor which acts to protect a transmission line and can be miniaturized, and in which neither electric field concentration nor an electric discharge easily takes place.
It is another object of the invention to provide a transmission line protector using the resistor described in the immediately preceding paragraph.
A resistor for protecting a transmission line in accordance with the present invention comprises an insulating substrate having bent portions, a serpentine resistive component formed on the substrate, and electrodes (which comprise any low-resistivity components) having a resistivity lower than that of the serpentine resistive component and formed at least over the inner portions of the bent portions of the serpentine resistive component.
A transmission line protector in accordance with the present invention comprises two transmission line protector circuits each consisting of the transmission line-protecting resistor described in the immediately preceding paragraph and a positive temperature coefficient thermistor connected in series with the transmission line protecting resistor.
In the transmission line protecting resistor constructed in this manner, electric field concentration is less likely to occur in the bent portions of the serpentine resistive component. Therefore, an electric discharge is less likely to occur.
Furthermore, destruction of the serpentine resistive component is less likely to occur.
Hence, miniaturization can be accomplished by decreasing the radius of the bent portions. Additionally, the transmission line protector in accordance with the present invention can be fabricated in smaller size.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the present invention will be more readily understood upon reading the following detailed description in conjunction with the drawings in which:
Fig. 1 is a view illustrating an exemplary transmission line protecting resistor in accordance with the invention;
Fig. 2 is an equivalent circuit diagram of a bent portion and the vicinity portions thereof of the resistor shown in Fig. 1;
Fig. 3 is a view similar to Fig. I , but showing another exemplary transmission line protecting resistor in accordance with the invention;
Fig. 4 is a view illustrating an exemplary transmission line protector in accordance with the invention;
Fig. 5 is an equivalent circuit diagram of a transmission line protector;
Fig. 6 is a view illustrating the structure of a known transmission line-protecting resistor;
Fig. 7 is a view illustrating the structure of another known transmission line-protecting resistor; and Fig. 8 is an equivalent circuit diagram of a connector electrode portion and the vicinity portions thereof of the resistor shown in Fig. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, there is shown a resistor for protecting a transmission line, the resistor being built in accordance with one exemplary embodiment of the present invention. This resistor, generally indicated by reference numeral l, comprises an alumina plate 2 that forms an insulating substrate, a serpentine resistive component 3 formed on the alumina plate 2 by thick-film printing technology or other suitable technology, and substantially semicircular electrodes 4 formed over the inner portions of the bent portions of the serpentine resistive component 3 by thick-film printing technology or other suitable technology. More specifically, the term "inner portions" refers to a portion of the bent portions which is radially inward from the outer circumference of the bent portions. The resistivity (e.g., 0.00001 S~ ~
cm) of the electrodes 4 is sufficiently lower than the resistivity (e.g., 0.001 S2 ~
cm) of the serpentine resistive component 3. Here, the resistivity of the resistive component 3 is 100 times greater than the resistivity of the electrodes 4, but those skilled in the art will recognize that the resistances can vary by different amounts. The term "electrode" as used here refers generally to any member having a resistivity which is less than the resistivity of the resistive component 3.
The equivalent circuit of a transmission line protector having the transmission line protecting resistor 1 is the same as the equivalent circuit of the known structure shown in Fig. 5. Therefore, description of this equivalent circuit is omitted here.
In the transmission line protecting resistor 1 constructed as described above, the electrodes 4 are formed on top of the inner portions of the bent portions of the serpentine resistive component 3. Therefore, the resistivity of the inner portions of the bent portions is made lower than that of the straight portions. Therefore, if an overcurrent flows due to a lightning surge or the like, electric field concentration in the inner portions of the bent portions is reduced or suppressed. As a consequence, the possibility of creation of a spark or destruction of the serpentine resistive component 3 is made lower than the above-described conventional resistive component. Since the bent portions of the serpentine resistive component 3 and the electrodes 4 are shaped substantially semicircularly, any corner at which electric field concentration would normally take place does not exist. Hence, the possibility of occurrence of an electric discharge is low. An equivalent circuit of a portion of the serpentine resistive component 3 is shown in Fig. 2, which includes resistances R0, R2, and RO connected in series. More specifically, the two resistances labeled RO
designate the resistances of two immediately parallel resistive "straight portions." The resistance R2 designates the resistance of the bent portion between the two immediately parallel resistive straight portions. The resistance R3 of the electrode 4 is added as distributed resistance connected in parallel with the resistance R2.
Therefore, any portion in which a strong electric field would normally be concentrated does not exist between the serpentine resistive component 3 and the electrode 4. The possibility of an electric discharge at this junction is low.
As a result, the radius of the bent portion can be reduced. As a consequence, the spacing between the adjacent straight portions of the serpentine resistive component 3 can be decreased. Hence, the whole area of the transmission line protecting resistor 1 can be redUCed.
Referring next to Fig. 3, there is shown another exemplary resistor for protecting a transmission line. This resistor, generally indicated by reference numeral 10, comprises an alumina plate 11, a serpentine resistive component 12 formed on the alumina plate 1 I by thick-film printing technology or other suitable technology, and arc-shaped electrodes 13 formed over the bent portions of the serpentine resistive component 12 again by thick-film printing technology or other suitable technology. The electrodes 13 are similar in shape to the shape of the bent portions. The resistivity of the electrodes 13 is set lower than that of the serpentine resistive component 12.
By fabricating the transmission line protecting resistor 10 in this manner, the resistance of the bent portions of the serpentine resistive component 12 is reduced. If an overcurrent is induced by a lightning surge or the like, electric field concentration in the inner portions of the bent portions is suppressed. The possibility of a spark or destruction of the serpentine resistive component 12 is lowered. Furthermore, since the bent portions including the electrodes 13 are shaped into arcs, any corner at which electric field concentration would otherwise take place does not exist or is at least reduced. Hence, the possibility of occurrence of an electric discharge is low.
As a result, the radius of the bent portions can be reduced. The whole area of the transmission line protecting resistor can be decreased by narrowing the spacing between the adjacent straight portions of the serpentine resistive component 12.
In the above embodiments, the semicircular electrodes 4 and the arc-shaped electrodes 13 are formed over the bent portions of the serpentine resistive component 3 or 12. Alternatively, the electrodes 4 and the electrodes 13 may be previously formed under the bent portions. Generally speaking, the bent portions and the electrodes overlap each other, wherein the term "overlap" is intended to encompass the case where the electrodes are disposed over the bent portions, and the case where the electrodes are disposed under the bent portions.
In the above embodiments described above, an alumina plate is used as an insulating substrate. Instead, other substrates, such as a ceramic substrate or resinous substrate, may be employed.
Further, although the resistive component is shown having a back-and-forth (zig-zag) shape, the term "serpentine path" is used herein to designate any elongate path having curved portions, including various types of meandering paths and spiral paths.
Referring to Fig. 4, there is shown a transmission line protector in accordance with exemplary embodiments of the invention. This protector, generally indicated by reference numeral 20, comprises an alumina plate 21 (or other suitable plate) that forms an insulating substrate, serpentine resistive components 22a and 22b formed on the alumina plate 21 by thick-film printing technology or other suitable technology, substantially semicircular electrodes 23a and 23b formed over the inner portions of the bent portions of the serpentine resistive components 22a and 22b, respectively, by thick-film printing technology or other suitable technology, positive temperature coefficient thermistors 24a and 24b, interconnect electrodes 25a, 25b, 26a, 26b, 27a, 27b, metal parts 28a and 28b for connecting a first terminal of the positive temperature coefficient thermistors 24a and 24b with the electrodes 26a and 26b, respectively, input terminals 29a and 29b of the transmission line, and output terminals 30a, 30b of the protected equipment. The resistivity of the electrodes 23a and 23b is sufficiently lower than that of the serpentine resistive components 22a and 22b. The input terminal 29a of the transmission line is connected with the output terminal 30a of the protected equipment via the interconnect electrode 27a, the serpentine resistive component 22a, the interconnect electrode 25a, the positive temperature coefficient thermistor 24a, the metal part 28a, and the interconnect electrode 26a, in this order. Thus, one transmission line protecting circuit is thereby formed. Similarly, the input terminal 29b of the transmission line is connected with the output terminal 30b of the protected equipment via the interconnect electrode 27b, the serpentine resistive component 22b, the interconnect electrode 25b, the positive temperature coefficient thermistor 24b, the metal part 28b, and the interconnect electrode 26b in this order. In this manner, another transmission line protecting circuit is formed.
An equivalent circuit of the transmission line protector 20 constructed in this manner is identical with the known structure shown in Fig. 5 and so description of the protector 20 is omitted. The resistors for the transmission line protecting circuits are the same as the resistor described already in conjunction with Fig. 1. The area of the transmission line protecting resistors can be reduced in the same way as in the embodiment illustrated in Fig. 1. Consequently, the transmission line protector 20 itself can be miniaturized.
As mentioned, the transmission line protector 20 uses the same construction as the transmission line protecting resistor 1 described in connection with Fig. 1. The transmission line protector 20 may also use the same construction as the transmission line protecting resistor 10 described previously in connection with Fig. 3.
A transmission line protecting resistor in accordance with the present invention comprises an insulating substrate, a serpentine resistive component formed on the substrate, and electrodes formed over at least the inner portions of the bent portions of the serpentine resistive component.
As a consequence, the resistivity of the inner portions of the bent portions of the serpentine resistive component is lowered. If an overcurrent is induced due to a lightning surge, for example, electric field concentration in the inner portions of the bent portions is suppressed. The possibility of production of a spark or destruction of the serpentine resistive component is made lower than in the above-described conventional device. The bent portions and the overlying (or underlying) electrodes are shaped semicircularly or arc-shaped. Therefore, any corner at which electric field concentration would normally take place does not exist. Consequently, the possibility of an electric discharge is low. The electrodes overlying (or underlying) the bent portions are added in parallel with the resistance of the bent portions of the serpentine resistive component and distributed as a low-resistivity resistor. Therefore, no strong electric field concentration occurs in the junction of the serpentine resistive component and the electrode. An electric discharge is unlikely to occur. As a result, the radius of the bent portions can be made small. The spacing between the adjacent straight portions of the serpentine resistive component can be decreased. As a consequence, the whole area of the transmission line protecting resistor can be reduced. Thus, the transmission line protector can be miniaturized.
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims.
Claims (20)
1. A resistor, comprising:
an insulating substrate;
a serpentine resistive component formed on said substrate and having at least one bent portion having a radially inner portion; and at least one electrode having a lower resistivity than that of said serpentine resistive component and formed so as to overlap at least said inner portion of said at least one bent portion of said serpentine resistive component.
an insulating substrate;
a serpentine resistive component formed on said substrate and having at least one bent portion having a radially inner portion; and at least one electrode having a lower resistivity than that of said serpentine resistive component and formed so as to overlap at least said inner portion of said at least one bent portion of said serpentine resistive component.
2. The resistor of claim 1, wherein said at least one electrode is disposed at least partially over said inner portion of said at least one bent portion.
3. The resistor of claim 1, wherein said at least one electrode is disposed at least partially under said inner portion of said at least one bent portion.
4. The resistor of claim 1, wherein said at least one electrode has a semicircular shape.
5. The resistor of claim 1, wherein said at least one electrode overlaps said inner portion of said at least one bent portion, but does not overlap a radially outer portion of said at least one bent portion.
6. The resistor of claim 1, wherein said at least one electrode has an arc-like shape.
7. The resistor of claim 1, wherein said at least one electrode matches a shape of said at least one bent portion which it overlaps.
8. The resistor of claim 1, wherein said resistive component has a resistivity which is at least about 100 times greater than that of said at least one electrode.
9. The resistor of claim 1, wherein said at least one bent portion comprises a plurality of bent portions, wherein each of said plurality of bent portions is at least partially overlapped by a respective electrode.
10. The resistor of claim 9, wherein said plurality of bent portions are connected to each other by a plurality of parallel straight portions of said resistive component.
11. A transmission line protector comprising:
an insulating substrate;
at least one transmission line protecting circuit formed on said insulating substrate, comprising a series combination of a resistor and a thermistor having a positive temperature coefficient;
said resistor comprising:
a serpentine resistive component formed on said substrate and having at least one bent portion having a radially inner portion; and at least one electrode having a lower resistivity than that of said serpentine resistive component and formed so as to overlap at least said inner portion of said at least one bent portion of said serpentine resistive component.
an insulating substrate;
at least one transmission line protecting circuit formed on said insulating substrate, comprising a series combination of a resistor and a thermistor having a positive temperature coefficient;
said resistor comprising:
a serpentine resistive component formed on said substrate and having at least one bent portion having a radially inner portion; and at least one electrode having a lower resistivity than that of said serpentine resistive component and formed so as to overlap at least said inner portion of said at least one bent portion of said serpentine resistive component.
12. The transmission line protector of claim 11, wherein said at least one transmission line protecting circuit comprises two transmission line protecting circuits formed on said substrate.
13. The transmission line protector of claim 11, wherein said at least one electrode is disposed at least partially over said inner portion of said at least one bent portion.
14. The transmission line protector of claim 11, wherein said at least one electrode is disposed at least partially under said inner portion of said at least one bent portion.
15. The transmission line protector of claim 11, wherein said at least one electrode has a semicircular shape.
16. The transmission line protector of claim 11, wherein said at least one electrode overlaps said inner portion of said at least one bent portion, but does not overlap a radially outer portion of said at least one bent portion.
17. The transmission line protector of claim 11, wherein said at least one electrode has an arc-like shape.
18. The transmission line protector of claim 11, wherein said at least one electrode matches a shape of said at least one bent portion which it overlaps.
19. The transmission line protector of claim 11 wherein said at least one bent portion comprises a plurality of bent portions, wherein each of said plurality of bent portions is at least partially overlapped by a respective electrode.
20. The transmission line protector of claim 19, wherein said plurality of bent portions are connected to each other by a plurality of parallel straight portions of said resistive component.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9174234A JPH1145802A (en) | 1997-06-30 | 1997-06-30 | Communication circuit protecting resistor and communication circuit protector |
| JP9-174234 | 1997-06-30 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2241927A1 CA2241927A1 (en) | 1998-12-30 |
| CA2241927C true CA2241927C (en) | 2001-03-27 |
Family
ID=15975074
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2241927 Expired - Fee Related CA2241927C (en) | 1997-06-30 | 1998-06-29 | Resistor and protector for transmission line |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH1145802A (en) |
| CA (1) | CA2241927C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1342251A2 (en) * | 2000-12-14 | 2003-09-10 | Tyco Electronics AMP GmbH | Strip conductor having an additional layer in a curved section |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7414414B2 (en) * | 2006-07-19 | 2008-08-19 | Keithley Instruments, Inc. | Spatially distributed guarded impedance |
| JP5206083B2 (en) * | 2008-04-09 | 2013-06-12 | 日産自動車株式会社 | Infrared detector |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56172901U (en) * | 1980-05-23 | 1981-12-21 | ||
| JP2508671Y2 (en) * | 1990-03-24 | 1996-08-28 | 株式会社村田製作所 | Positive characteristic thermistor for communication line protection |
| JPH0595003U (en) * | 1992-05-28 | 1993-12-24 | 京セラ株式会社 | Anti-surge resistance parts |
-
1997
- 1997-06-30 JP JP9174234A patent/JPH1145802A/en active Pending
-
1998
- 1998-06-29 CA CA 2241927 patent/CA2241927C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1342251A2 (en) * | 2000-12-14 | 2003-09-10 | Tyco Electronics AMP GmbH | Strip conductor having an additional layer in a curved section |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2241927A1 (en) | 1998-12-30 |
| JPH1145802A (en) | 1999-02-16 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |