CA2027931A1 - Instrinsically safe barrier device - Google Patents
Instrinsically safe barrier deviceInfo
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- CA2027931A1 CA2027931A1 CA 2027931 CA2027931A CA2027931A1 CA 2027931 A1 CA2027931 A1 CA 2027931A1 CA 2027931 CA2027931 CA 2027931 CA 2027931 A CA2027931 A CA 2027931A CA 2027931 A1 CA2027931 A1 CA 2027931A1
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Abstract
INTRINSICALLY SAFE BARRIER DEVICE
Abstract of the Disclosure An protection barrier provides voltage and current necessarily conveyed to hazardous, such as explosive, areas. The system includes a current sensing circuit which triggers a silicon control rectifier based crowbar circuit in the event over current is detected. This triggering, in turn, trips a relay severing the current path entirely. A
reverse polarity circuit provides for immediate clamping of improperly bias connections in a similar crowbar arrangement, and also provides for tripping of the circuit breaker. Thermistors are also provided in current series in the event the circuit breaker fails to trip, or is forcibly bypassed. The circuit breaker additional provides a visual indicator when it is in the tripped position. The intrinsic barrier system is suitable to serving as a first stage protection to zener barrier modules as utilized in the prior art.
Abstract of the Disclosure An protection barrier provides voltage and current necessarily conveyed to hazardous, such as explosive, areas. The system includes a current sensing circuit which triggers a silicon control rectifier based crowbar circuit in the event over current is detected. This triggering, in turn, trips a relay severing the current path entirely. A
reverse polarity circuit provides for immediate clamping of improperly bias connections in a similar crowbar arrangement, and also provides for tripping of the circuit breaker. Thermistors are also provided in current series in the event the circuit breaker fails to trip, or is forcibly bypassed. The circuit breaker additional provides a visual indicator when it is in the tripped position. The intrinsic barrier system is suitable to serving as a first stage protection to zener barrier modules as utilized in the prior art.
Description
f'l ~ h/ ~f J 3 ~
INTRIN~ICALLY ~AFE BARRIER DEVICE
13ackaround of th~ Invention This application pertains to the art of intrinsically saEe or protection barrier devices, and more particular to provision of such barrier devices which function in a non-destructive manner.
The application is particularly applicable to provision of electric power to devices disposed within hazardous areas, and will be descrlbed wi-th particular reference thereto. It will be appreciated, however, that the invention has broader applicatioll, such as in any application in which a device ls to be isolated against over voltages, over current, reverse polarity connectiolls, and the like.
Intrinsic safety is generally considered the safest method of supplying electricity to equipment disposed in hazardous areas. Such hazardous areas include highly combustible areas, and include such applications as monitoring devices disposed in fuel storage areas. Such intrinslc barrler devices provide a reliable, less expensive, and more desirable approach to providing power to systems in such areas then are found in the alternatives. Alternatives include such means as encasing an entire system within an explosion proof barrier. Such barriers are obviously bulky, high in weight, and extremely expensive to construct, and maintain.
Presently, several intrinsically safe barrier devices are available. These include "zener barrier modules" which typically incl-lde zener diodes, a resistor, and a fuse. The zener d:iode functions to clamp over voltages. In the event of excessive current or over voltage conditions, the fuse will blow. The blowing oE a use in such a barrier module typically requires replacement of the entire subsystem, given that a substantial possibility exists that the zener diode, or diodes, were damaged by -the clamping action. Such replacement is generally expensive. In addition, there is generally no means to readily discern whether, in fact, a fuse in such a zener barrier module has been blown.
Other attempts have been made to fabricate alternative secure intrinsically barrier devices, typically with systems utilizing a plurali-ty of electronic components. Rs electronic components themselves require power for operation, other disadvantages arise. In particular, a separate power supply must be provided to the device, or the devlce is sub~ect to voltage drops between its input and output. Such voltage drops are generally unacceptable, especially in areas where the voltage supplied -to the hazardous area must be maintained in close tolerance to generated voltage levels.
The present invention contemplates a new and improved intrinsically safe barrier device which overcomes all of the above-referred problems, and others, and provides a reusable barrier device which is reliable and economical.
In accordance with the present invention, there is provided an protection barrier device which includes first and second input terminals adapted for connection of the device with an associated direct current voltage source.
first series path is providad between the first input terminal and first output terminal. Similarly, a second series path is provided between the second input terminal and second output terminal. A current sensing means is provided to sensing current levels in at least one of the first and second series paths. Means is provided for generating a signal representative of an event in whlch ' 'SJ ~ ~ i excessive currents, defined to selected standardsl causing a triggering of a crowbar circuit disposed between the first and second series paths. This crowbar circui-t, in turn, provides a low resistance current path between the series paths. Current flowing through this crowbar circuit path, in turn, triggers a switching means which functions to impede current flow tnrough at least one of the first and second series paths.
In accordance with a more limited aspect oE the present invention, means is also provided for protecting the hazardous area from receiving signiEicant voltage when the first and second input terminals are misswired to reversed potentials.
In conjunction with a yet more limited aspect of the subject invention, a thermis~or is disposed in at least one of the first and second series paths, which thermistor functions to minimize current in the event the switchiny means is bypassed, or fails.
In accordance with another aspect of the present tnvention, a method of intr~nsic protection for operation of the afore-mentioned means is disclosed.
An advantage of the present invention is the provision of a system which reacts quickly to over current conditions, over voltage conditions, reverse polarity conditions, and short circuit conditions.
Another advantage of the present invention is the provision of a system having a readily discernable visual indicator of when a ault has been detected, and compensated for.
Yet another advantage of the present invention is the provision of a system for intrinsically safe voltage protection which maintains a minimum vol-tage drop between input and outputs thereof.
- 4 - ~ 31 Further advantages will be obvious to one of ordinary skill in the art upon a reading and understanding of the subject invention.
Br~ef Dss~ription of the Dr~winqs The invention may take physical form in certain partsl and arrangements of parts, preferred and alternate embodiments of which will be described in detail in this specification, and illustrated in the accompanying drawings which form a part hereof, and wherein:
FIGURE 1 illustrates, in schematic form, an intrinsically sae barrier circuitry of the subject invention; and FIGURE 2 illustrates, in block diagram form, a protection barrier module including the circuitry of FIGURE 1.
Detalled Descrlption of tha Pre~erred ~na Altern~to Embod~ents Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred and alternate embodiments of the invention only, and not for the purposes of limiting the same, FIGURE 1 illustrates an protection barrier circuit A which includes a current detection system B, a quick protection system C, and a long-term protection D~ Also illustrated is a zener barrier module E, such as is typ~cally utilized in the prior art.
The circuitry of FIGVRE 1 includes first and second input terminals or means 10 and 12 respectively. These terminals form first and second current series paths 14 and 16, with first and second output terminals 18 and 20, respectively. In the pref~rred embodiment, the circuitry of FIGURE 1, in addition to all circuitry disposed prior to input terminals 10 and 12 is found in a "safe area,"
defined as an area substantially devoid of combustible fuels, or the like. Outpu-t terminals 18 and 20 form and electrical connection to systems disposed in a hazardous area.
The zener barrier module E forms the sole protection in a typical protection barrier device. Included therein is a zener diode which functions to shunt first and second series current paths 14 and 16 in the event of over voltage or over current. Illustrated is first and second parallely mounted zener diodes 26 and 28 so arranged to divide current flow therebetween. It will be appreciated by one o~ ordinary skill in the art that the zener diode facilitates low resistance conduction once a threshold voltage, determined by diode characteristics, has been achieved. Over current conditions, such as would be introduced after triggeriny of the zener diodes, causing blowing of a fuse 30. A small voltage drop is introduced into the first series current path 14 by resistor 32.
As note above, though functional, upon action of zenar barrier module Pmploying circuitry such as that illustrated, no readily available visual indicator of a tripped condition is available. In addition, it is desirable to replace the entire unit after a fuse has been blown in the ev~nt that undetectable damage occurred to the zener diodes. The protection barrier circuit A may serve dual capacit~es. It may serve as a primary protection circuit for zener barrier modules such as that illustrated by E.
The current detection system B is sensitlve to current flow through first series current path 14. A base of transistor 34 i5 energized in accordance with a voltage difference dictated by relative values of resistors 36 and 38, and capacitor 40, as will be appreciated by one of ordinary skill in the art. Upon achieving current in current path 14 of a selected level as dictated by this combination, the transistor 34 is caused to conduct through its emitter-collector junction, providing current flow through biasing resistor 42 into the quick protection system C. Zener diode 44 serves to prevent the emitter-collector ~unctlon from damage due to transient voltages.
The quick protection system C includes a silicon controlled rectifier ("SCR"), the gate oE which is interconnected with an output of current detection system emanating from resistor ~2. The gate is also connected to a parallel resistor-capacitor t"R/C") network form from resistor 52 and capacitor 54. The anode oE SCR 50 is electrically connected to first series current path 14 to allow in flow of conventional current thereinto in a fashion which will be described further below. The cathode of SCR 50 is electrically connected to second series current path 16. It will be appreciated that upon triggering of the SCR 50 by application of voltage to its gate lead, a low resistance current path is therefore provided between first series current path 14 and second series current path 16, provided that conventional current flow is in that same direction. This shunting effect is commonly referred to as a "crowbar," thereby providing a common designation of the quick protection system C as a crowbar circuit.
As will be inferred from the above-description, the over current or over voltage problems compensated for by the combination of the current detection system E and quick protection system c are unaccounted for in a reverse polar~ty situation. That is, ln the event conventional current flow was to occur from second input terminal to first input terminal lo, the triggering would not QccUr .
This situation is independently accounted for by diodes 58 and 60, which are mounted, in series, to form a low resistance path for conventional current flow from the second series current path 16 to the first series current path 14. This combination provides quick reverse polarity protection for the intrinsically safe barrier circuit A.
Particular interconnections between a cathode of diode 58 and series connected anode of diode 60 will become apparent with the description of long-term protection system D, which follows.
The long-term protection system D includes a current sensitive switching circuit or means 6~ which, in the illustrat~d embodiment, employs a coil portion 64a and a normally closed contact portion 64b. It will be appreciated that current flow of a sufficient magnitude through coil portion 64a results in a tripping, or opening of coil portion 64b thereby causing an effective break in the first series current path 14. Such current may be introduced through coil 64a through diode 66 and SCR 50 upon triggering of the quick protection system C, as described above. Additionally, current flow through coil portion coil portion 64a is induced by reverse polarity connection of input contracts 10 and 12 given that the coils 64a is disposed in current series between an anode of diode 58 and cathode of diode 60. It will therefore be noted that tripping of the switching circuit 64 is accomplished in either condltion. In the illustrated embodiment, diodes 68 and 70 are also provided to protect the coll portion 64a from transient~ and back EMF, as will be appreciated from one of ordinary skill in the art.
It is often desirable that a remote signal be provided evidencing a tripping of a barrier d~vice. Such a signal is suitably provided by an additional pair of contacts 64c on the switching circuit 64. Such contacts add no additional voltage drop across the device, and may be installed as normally open or normally closed as a particular installation may warrant.
In the illustrated embodiment, the switching circuit 64 is comprised of a current operated circuit breaker or relay. As will be noted with FIGURE 2, reset switch is also utilized which additionally functions to provide a visual indicator o a tripping thereof. Utilization of a contact device is advantageous given that essentially 110 voltage drop Is experienced across the contacts. lt will also be appreciated that other suitable switchin~ means, such as transistors and especially field effects transistors may be suitable utilized in place of the illustrated breaker. With present technology, some voltage drop will be experience with most semi-conductor elements used for such switching purposes. It is envisioned that certain application may not be voltage sensitive allowing for the use of such elements or further advances in fabrication wlll minimize losses to within acceptable levels. When such semi-conductor elements are utilized as the switching means, an additional signaling device, such as a light-em~tting diode, or the like, are advantageously used to replace the visual indicator provided by the circuit breaker in the illustrated embodiment.
A thermistor network 74 is also advantageously applied in the circuit, and is illustrated in first series current path 14. It will be appreciated that such thermistors maintain a resistance proportional to temperature. A suitable thermistor is defined as having a normal resistance in around 3 n, and a high temperature resistance of over 20 n in overheated conditions induced by ~ ~ s~ ~J ~
excessive current flow therethrough. The thermistor network 74 is provided as a ~ail-safe mechanism in the event that the switching circuit 64 is forcibly shorted, notwithstanding an otherwise open condition, or in the event the element fails, in its entirety. In the illustrated embodiment, three parallely mounted thermistors 74a, 74b, 74c are utilized to minimize current handling requirements of any o~ the thermistors, individually.
Finally, a small input resistor 78 is provided to provide nominal isolation of the protection barrier circuit ~ from the actual power generating system. A suitable resistance ~alue of lOn provides nom~nal voltage losses in t~ptcal ranges (50m~) passed by the barrier device, but clissipates considerable power in excess current situations.
It will be seen from the figure that the illustrated components provide ~or quick protection for over voltage or over current condition by interaction of the current detection system B and the quick protection system C.
Reverse bias protection is afforded by interaction of the diodes 58 and 60. Reverse polarity connections, or tripping of the quick protection ~ircuit C result in opening first series current path 14 via long-term protection system D. A visual indicator is provided in the event the long-term protection system D has been utilized.
The system is resettable after tripping to eliminate the necessity of component replacement. Finally, thermistor network 74 provides a fail-safe mechanism in the event of bi-passing the protection system, or failure of selected components thereof. The system is envisioned to be usable in and of itself, or as a protection system to prevent destru~tion o~ zener barrier modu~es, such as zener barrier module E.
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Turning briefly to FIGURE 2, illustrated is the protection barrier circuit A and the zener barrier module E
of FIGURE 1 secured within a housing 82, to facilitate removal or replacement in mounting brackets such as are commonly used in the field. It will be apparent from the figure that no additional power supply is necessary to accomplish the functions of the subject system. Also illustrated is a reset button or means ~4 which interacts with the contacts ~4a ~FIGURE 1) for resetting of the switching circuit, and also provides a visual indlcator of when the system lies in the a tripplng condition. In the event that non-mechanical switching means is implemellted, the indicator 8~ is suitably replaced with a visual indicator such as a light emitting dlode, or like.
The invention has been described with reference to a preferred embodiment. ~bviously, modifications and alterations will occur to others UpOIl a reading and understanding of this specif~cation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
INTRIN~ICALLY ~AFE BARRIER DEVICE
13ackaround of th~ Invention This application pertains to the art of intrinsically saEe or protection barrier devices, and more particular to provision of such barrier devices which function in a non-destructive manner.
The application is particularly applicable to provision of electric power to devices disposed within hazardous areas, and will be descrlbed wi-th particular reference thereto. It will be appreciated, however, that the invention has broader applicatioll, such as in any application in which a device ls to be isolated against over voltages, over current, reverse polarity connectiolls, and the like.
Intrinsic safety is generally considered the safest method of supplying electricity to equipment disposed in hazardous areas. Such hazardous areas include highly combustible areas, and include such applications as monitoring devices disposed in fuel storage areas. Such intrinslc barrler devices provide a reliable, less expensive, and more desirable approach to providing power to systems in such areas then are found in the alternatives. Alternatives include such means as encasing an entire system within an explosion proof barrier. Such barriers are obviously bulky, high in weight, and extremely expensive to construct, and maintain.
Presently, several intrinsically safe barrier devices are available. These include "zener barrier modules" which typically incl-lde zener diodes, a resistor, and a fuse. The zener d:iode functions to clamp over voltages. In the event of excessive current or over voltage conditions, the fuse will blow. The blowing oE a use in such a barrier module typically requires replacement of the entire subsystem, given that a substantial possibility exists that the zener diode, or diodes, were damaged by -the clamping action. Such replacement is generally expensive. In addition, there is generally no means to readily discern whether, in fact, a fuse in such a zener barrier module has been blown.
Other attempts have been made to fabricate alternative secure intrinsically barrier devices, typically with systems utilizing a plurali-ty of electronic components. Rs electronic components themselves require power for operation, other disadvantages arise. In particular, a separate power supply must be provided to the device, or the devlce is sub~ect to voltage drops between its input and output. Such voltage drops are generally unacceptable, especially in areas where the voltage supplied -to the hazardous area must be maintained in close tolerance to generated voltage levels.
The present invention contemplates a new and improved intrinsically safe barrier device which overcomes all of the above-referred problems, and others, and provides a reusable barrier device which is reliable and economical.
In accordance with the present invention, there is provided an protection barrier device which includes first and second input terminals adapted for connection of the device with an associated direct current voltage source.
first series path is providad between the first input terminal and first output terminal. Similarly, a second series path is provided between the second input terminal and second output terminal. A current sensing means is provided to sensing current levels in at least one of the first and second series paths. Means is provided for generating a signal representative of an event in whlch ' 'SJ ~ ~ i excessive currents, defined to selected standardsl causing a triggering of a crowbar circuit disposed between the first and second series paths. This crowbar circui-t, in turn, provides a low resistance current path between the series paths. Current flowing through this crowbar circuit path, in turn, triggers a switching means which functions to impede current flow tnrough at least one of the first and second series paths.
In accordance with a more limited aspect oE the present invention, means is also provided for protecting the hazardous area from receiving signiEicant voltage when the first and second input terminals are misswired to reversed potentials.
In conjunction with a yet more limited aspect of the subject invention, a thermis~or is disposed in at least one of the first and second series paths, which thermistor functions to minimize current in the event the switchiny means is bypassed, or fails.
In accordance with another aspect of the present tnvention, a method of intr~nsic protection for operation of the afore-mentioned means is disclosed.
An advantage of the present invention is the provision of a system which reacts quickly to over current conditions, over voltage conditions, reverse polarity conditions, and short circuit conditions.
Another advantage of the present invention is the provision of a system having a readily discernable visual indicator of when a ault has been detected, and compensated for.
Yet another advantage of the present invention is the provision of a system for intrinsically safe voltage protection which maintains a minimum vol-tage drop between input and outputs thereof.
- 4 - ~ 31 Further advantages will be obvious to one of ordinary skill in the art upon a reading and understanding of the subject invention.
Br~ef Dss~ription of the Dr~winqs The invention may take physical form in certain partsl and arrangements of parts, preferred and alternate embodiments of which will be described in detail in this specification, and illustrated in the accompanying drawings which form a part hereof, and wherein:
FIGURE 1 illustrates, in schematic form, an intrinsically sae barrier circuitry of the subject invention; and FIGURE 2 illustrates, in block diagram form, a protection barrier module including the circuitry of FIGURE 1.
Detalled Descrlption of tha Pre~erred ~na Altern~to Embod~ents Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred and alternate embodiments of the invention only, and not for the purposes of limiting the same, FIGURE 1 illustrates an protection barrier circuit A which includes a current detection system B, a quick protection system C, and a long-term protection D~ Also illustrated is a zener barrier module E, such as is typ~cally utilized in the prior art.
The circuitry of FIGVRE 1 includes first and second input terminals or means 10 and 12 respectively. These terminals form first and second current series paths 14 and 16, with first and second output terminals 18 and 20, respectively. In the pref~rred embodiment, the circuitry of FIGURE 1, in addition to all circuitry disposed prior to input terminals 10 and 12 is found in a "safe area,"
defined as an area substantially devoid of combustible fuels, or the like. Outpu-t terminals 18 and 20 form and electrical connection to systems disposed in a hazardous area.
The zener barrier module E forms the sole protection in a typical protection barrier device. Included therein is a zener diode which functions to shunt first and second series current paths 14 and 16 in the event of over voltage or over current. Illustrated is first and second parallely mounted zener diodes 26 and 28 so arranged to divide current flow therebetween. It will be appreciated by one o~ ordinary skill in the art that the zener diode facilitates low resistance conduction once a threshold voltage, determined by diode characteristics, has been achieved. Over current conditions, such as would be introduced after triggeriny of the zener diodes, causing blowing of a fuse 30. A small voltage drop is introduced into the first series current path 14 by resistor 32.
As note above, though functional, upon action of zenar barrier module Pmploying circuitry such as that illustrated, no readily available visual indicator of a tripped condition is available. In addition, it is desirable to replace the entire unit after a fuse has been blown in the ev~nt that undetectable damage occurred to the zener diodes. The protection barrier circuit A may serve dual capacit~es. It may serve as a primary protection circuit for zener barrier modules such as that illustrated by E.
The current detection system B is sensitlve to current flow through first series current path 14. A base of transistor 34 i5 energized in accordance with a voltage difference dictated by relative values of resistors 36 and 38, and capacitor 40, as will be appreciated by one of ordinary skill in the art. Upon achieving current in current path 14 of a selected level as dictated by this combination, the transistor 34 is caused to conduct through its emitter-collector junction, providing current flow through biasing resistor 42 into the quick protection system C. Zener diode 44 serves to prevent the emitter-collector ~unctlon from damage due to transient voltages.
The quick protection system C includes a silicon controlled rectifier ("SCR"), the gate oE which is interconnected with an output of current detection system emanating from resistor ~2. The gate is also connected to a parallel resistor-capacitor t"R/C") network form from resistor 52 and capacitor 54. The anode oE SCR 50 is electrically connected to first series current path 14 to allow in flow of conventional current thereinto in a fashion which will be described further below. The cathode of SCR 50 is electrically connected to second series current path 16. It will be appreciated that upon triggering of the SCR 50 by application of voltage to its gate lead, a low resistance current path is therefore provided between first series current path 14 and second series current path 16, provided that conventional current flow is in that same direction. This shunting effect is commonly referred to as a "crowbar," thereby providing a common designation of the quick protection system C as a crowbar circuit.
As will be inferred from the above-description, the over current or over voltage problems compensated for by the combination of the current detection system E and quick protection system c are unaccounted for in a reverse polar~ty situation. That is, ln the event conventional current flow was to occur from second input terminal to first input terminal lo, the triggering would not QccUr .
This situation is independently accounted for by diodes 58 and 60, which are mounted, in series, to form a low resistance path for conventional current flow from the second series current path 16 to the first series current path 14. This combination provides quick reverse polarity protection for the intrinsically safe barrier circuit A.
Particular interconnections between a cathode of diode 58 and series connected anode of diode 60 will become apparent with the description of long-term protection system D, which follows.
The long-term protection system D includes a current sensitive switching circuit or means 6~ which, in the illustrat~d embodiment, employs a coil portion 64a and a normally closed contact portion 64b. It will be appreciated that current flow of a sufficient magnitude through coil portion 64a results in a tripping, or opening of coil portion 64b thereby causing an effective break in the first series current path 14. Such current may be introduced through coil 64a through diode 66 and SCR 50 upon triggering of the quick protection system C, as described above. Additionally, current flow through coil portion coil portion 64a is induced by reverse polarity connection of input contracts 10 and 12 given that the coils 64a is disposed in current series between an anode of diode 58 and cathode of diode 60. It will therefore be noted that tripping of the switching circuit 64 is accomplished in either condltion. In the illustrated embodiment, diodes 68 and 70 are also provided to protect the coll portion 64a from transient~ and back EMF, as will be appreciated from one of ordinary skill in the art.
It is often desirable that a remote signal be provided evidencing a tripping of a barrier d~vice. Such a signal is suitably provided by an additional pair of contacts 64c on the switching circuit 64. Such contacts add no additional voltage drop across the device, and may be installed as normally open or normally closed as a particular installation may warrant.
In the illustrated embodiment, the switching circuit 64 is comprised of a current operated circuit breaker or relay. As will be noted with FIGURE 2, reset switch is also utilized which additionally functions to provide a visual indicator o a tripping thereof. Utilization of a contact device is advantageous given that essentially 110 voltage drop Is experienced across the contacts. lt will also be appreciated that other suitable switchin~ means, such as transistors and especially field effects transistors may be suitable utilized in place of the illustrated breaker. With present technology, some voltage drop will be experience with most semi-conductor elements used for such switching purposes. It is envisioned that certain application may not be voltage sensitive allowing for the use of such elements or further advances in fabrication wlll minimize losses to within acceptable levels. When such semi-conductor elements are utilized as the switching means, an additional signaling device, such as a light-em~tting diode, or the like, are advantageously used to replace the visual indicator provided by the circuit breaker in the illustrated embodiment.
A thermistor network 74 is also advantageously applied in the circuit, and is illustrated in first series current path 14. It will be appreciated that such thermistors maintain a resistance proportional to temperature. A suitable thermistor is defined as having a normal resistance in around 3 n, and a high temperature resistance of over 20 n in overheated conditions induced by ~ ~ s~ ~J ~
excessive current flow therethrough. The thermistor network 74 is provided as a ~ail-safe mechanism in the event that the switching circuit 64 is forcibly shorted, notwithstanding an otherwise open condition, or in the event the element fails, in its entirety. In the illustrated embodiment, three parallely mounted thermistors 74a, 74b, 74c are utilized to minimize current handling requirements of any o~ the thermistors, individually.
Finally, a small input resistor 78 is provided to provide nominal isolation of the protection barrier circuit ~ from the actual power generating system. A suitable resistance ~alue of lOn provides nom~nal voltage losses in t~ptcal ranges (50m~) passed by the barrier device, but clissipates considerable power in excess current situations.
It will be seen from the figure that the illustrated components provide ~or quick protection for over voltage or over current condition by interaction of the current detection system B and the quick protection system C.
Reverse bias protection is afforded by interaction of the diodes 58 and 60. Reverse polarity connections, or tripping of the quick protection ~ircuit C result in opening first series current path 14 via long-term protection system D. A visual indicator is provided in the event the long-term protection system D has been utilized.
The system is resettable after tripping to eliminate the necessity of component replacement. Finally, thermistor network 74 provides a fail-safe mechanism in the event of bi-passing the protection system, or failure of selected components thereof. The system is envisioned to be usable in and of itself, or as a protection system to prevent destru~tion o~ zener barrier modu~es, such as zener barrier module E.
~J~ ~J.~ ~
Turning briefly to FIGURE 2, illustrated is the protection barrier circuit A and the zener barrier module E
of FIGURE 1 secured within a housing 82, to facilitate removal or replacement in mounting brackets such as are commonly used in the field. It will be apparent from the figure that no additional power supply is necessary to accomplish the functions of the subject system. Also illustrated is a reset button or means ~4 which interacts with the contacts ~4a ~FIGURE 1) for resetting of the switching circuit, and also provides a visual indlcator of when the system lies in the a tripplng condition. In the event that non-mechanical switching means is implemellted, the indicator 8~ is suitably replaced with a visual indicator such as a light emitting dlode, or like.
The invention has been described with reference to a preferred embodiment. ~bviously, modifications and alterations will occur to others UpOIl a reading and understanding of this specif~cation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (22)
1. An protection barrier device comprising:
first and second input terminals adapted for connection of the device with an associated direct current voltage source;
first and second output terminals adapted for connection of the device with an associated device disposed in a hazardous area, the first output terminal being in a first series path with the first input terminal and the second output terminal being in second series path with the second input terminal;
current sensing means for sensing current in at least one of the first and second series paths;
means for generating an excess current level signal in accordance with a sensed current level in excess of a selected current level sensed by the current sensing means;
crowbar circuit means for providing a low resistance crowbar circuit current path between the first and second series paths in accordance with the excess current level signal; and switching means for impeding current flow through at least one of the first and second series paths in accordance with current passing through the crowbar circuit current path.
first and second input terminals adapted for connection of the device with an associated direct current voltage source;
first and second output terminals adapted for connection of the device with an associated device disposed in a hazardous area, the first output terminal being in a first series path with the first input terminal and the second output terminal being in second series path with the second input terminal;
current sensing means for sensing current in at least one of the first and second series paths;
means for generating an excess current level signal in accordance with a sensed current level in excess of a selected current level sensed by the current sensing means;
crowbar circuit means for providing a low resistance crowbar circuit current path between the first and second series paths in accordance with the excess current level signal; and switching means for impeding current flow through at least one of the first and second series paths in accordance with current passing through the crowbar circuit current path.
2. The protection barrier device of claim 1 further comprising reverse polarity protection means for providing a low resistance reverse polarity current path between the first and second series paths in an event wherein a voltage potentials thereacross is inverted.
3. The protection barrier device of claim 2 wherein the switching circuit means includes means for impeding current flow through at least one of the first and second series paths in accordance with current passing through the reverse polarity current path.
4. The protection barrier device of claim 3 further comprising means for enabling a remote indicator representative of a state of the switching means.
5. The protection barrier device of claim 3 further comprising thermistor disposed in at least one of the first and second series paths.
6. The protection barrier device of claim 5 wherein the switching means includes a relay, a trigger mechanism of which is disposed in the crowbar circuit current path and the contacts of which are disposed in at least one of the first and second series paths.
7. The protection barrier device of claim 6 wherein the relay is formed as a circuit breaker having a visual indicator representative of a tripped condition.
8. The protection barrier device of claim 7 wherein the crowbar circuit means includes a silicon controlled rectifier triggered by the excess current level signal.
9. The protection barrier device of claim 8 wherein the current sensing means includes a transistor, the emitter-collector junction of which forms a path between one of the first and second series paths and a gate lead of the silicon controlled rectifier.
10. The protection barrier device of claim 9 further comprising a zener barrier module disposed across the output terminals, the zener barrier including a fuse element in one of the first and second series paths, and a zener diode disposed between the first and second output terminals.
11. An protection barrier device comprising:
first and second input terminals adapted for connection of the device with an associated direct current voltage source;
first and second output terminals adapted for connection of the device with an associated device disposed in a hazardous area, the first output terminal being in a first series path with the first input terminal and the second output terminal being in second series path with the second input terminal;
current sensing means for sensing current in at least one of the first and second series paths;
means for generating an excess current level signal in accordance with a sensed current level in excess of a selected current level sensed by the current sensing means;
crowbar circuit means for providing a low resistance crowbar circuit current path between the first and second series paths in accordance with the excess current level signal;
reverse polarity protection means for providing a low resistance reverse polarity current path between the first and second series paths in an event wherein a voltage potentials thereacross is inverted; and switching means for impeding current flow through at least one of the first and second series paths in accordance with current passing through at least one of the crowbar circuit current path and the reverse polarity current path.
first and second input terminals adapted for connection of the device with an associated direct current voltage source;
first and second output terminals adapted for connection of the device with an associated device disposed in a hazardous area, the first output terminal being in a first series path with the first input terminal and the second output terminal being in second series path with the second input terminal;
current sensing means for sensing current in at least one of the first and second series paths;
means for generating an excess current level signal in accordance with a sensed current level in excess of a selected current level sensed by the current sensing means;
crowbar circuit means for providing a low resistance crowbar circuit current path between the first and second series paths in accordance with the excess current level signal;
reverse polarity protection means for providing a low resistance reverse polarity current path between the first and second series paths in an event wherein a voltage potentials thereacross is inverted; and switching means for impeding current flow through at least one of the first and second series paths in accordance with current passing through at least one of the crowbar circuit current path and the reverse polarity current path.
12. The protection barrier device of claim 11 further comprising indicator means for providing a visual indication of when current flow through at least one of the first and second series paths has been impeded by action of the switching means.
13. The protection barrier device of claim 12 wherein the switching means includes a circuit breaker, a trigger of which is disposed in the crowbar circuit current path and the reverse polarity current path, and wherein a contact portion of the circuit breaker is disposed in at least one of the first and second series paths.
14. The protection barrier device of claim 13 further comprising a thermistor mounted in at least one of the first and second series paths.
15. The protection barrier device of claim 1 wherein the crowbar circuit means includes a silicon controlled rectifier disposed such that its anode extends to one of the first and second series paths and its cathode extends to the other of the first and second series paths, and wherein its gate is adapted for receiving the excess current level signal.
16. The protection barrier device of claim 15 further comprising a zener barrier module disposed across the output terminals, the zener barrier including a fuse element in one of the first and second series paths, and a zener diode disposed between the first and second output terminals.
17. A method for controlling electricity levels communicated to a hazardous area comprising the steps of:
sensing current in at least one of first and second series paths, the first series path extending between a first input terminal and a first output terminal of an protection barrier device, and the second series path extending between a second input terminal and a second output terminal of the protection barrier device;
generating an excess current level signal in accordance with a sensed current level in excess of a selected current level;
selectively providing a low resistance crowbar current path between the first and second series paths in accordance with the excess current level signal;
selectively providing a low resistance reverse polarity current path between the first and second series paths in an event wherein a voltage potentials thereacross is inverted; and impeding current flow through at least one of the first and second series paths in accordance with current passing through at least one of the crowbar circuit current path and the reverse polarity current path.
sensing current in at least one of first and second series paths, the first series path extending between a first input terminal and a first output terminal of an protection barrier device, and the second series path extending between a second input terminal and a second output terminal of the protection barrier device;
generating an excess current level signal in accordance with a sensed current level in excess of a selected current level;
selectively providing a low resistance crowbar current path between the first and second series paths in accordance with the excess current level signal;
selectively providing a low resistance reverse polarity current path between the first and second series paths in an event wherein a voltage potentials thereacross is inverted; and impeding current flow through at least one of the first and second series paths in accordance with current passing through at least one of the crowbar circuit current path and the reverse polarity current path.
18. The method of claim 17 further comprising the step of enabling a remote indicator representative of an impeded current flow through at least one of the first and second series paths.
19. The method of claim 17 further comprising the step of providing a visual indication of when current flow through at least one of the first and second series paths has been impeded by action of the switching means.
20. The method of claim 19 wherein the step of selectively providing a low resistance crowbar circuit includes the step of triggering a silicon control rectifier, the anode and cathode of which form a portion of the crowbar current path.
21. The method of claim 20 wherein the step of selectively providing a low resistance crowbar current path is completed prior to completion of the step of impeding current flow through at least one of the first and second series paths.
22. The method of claim 21 further comprising the step of clamping the anode and cathode to a generally equivalent potential upon completion of the step of impeding current flow through at least one of the first and second series paths.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42468089A | 1989-10-20 | 1989-10-20 | |
| US07/424,680 | 1989-10-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2027931A1 true CA2027931A1 (en) | 1991-04-21 |
Family
ID=23683490
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2027931 Abandoned CA2027931A1 (en) | 1989-10-20 | 1990-10-18 | Instrinsically safe barrier device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2027931A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4250504A3 (en) * | 2019-02-14 | 2023-12-13 | Eaton Intelligent Power Limited | Hazardous environment electrical feedback barrier device, assembly, system and method |
-
1990
- 1990-10-18 CA CA 2027931 patent/CA2027931A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4250504A3 (en) * | 2019-02-14 | 2023-12-13 | Eaton Intelligent Power Limited | Hazardous environment electrical feedback barrier device, assembly, system and method |
| US11978980B2 (en) | 2019-02-14 | 2024-05-07 | Eaton Intelligent Power Limited | Hazardous environment electrical feedback barrier device, assembly, system and method |
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