Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B61—RAILWAYS
  • B61L—GUIDING RAILWAY TRAFFIC; ENSURING THE SAFETY OF RAILWAY TRAFFIC
  • B61L5/00—Local operating mechanisms for points or track-mounted scotch-blocks; Visible or audible signals; Local operating mechanisms for visible or audible signals
  • B61L5/12—Visible signals
  • B61L5/18—Light signals; Mechanisms associated therewith, e.g. blinders
  • B61L5/1809—Daylight signals
  • B61L5/1881—Wiring diagrams for power supply, control or testing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/327—Testing of circuit interrupters, switches or circuit-breakers
  • G01R31/3277—Testing of circuit interrupters, switches or circuit-breakers of low voltage devices, e.g. domestic or industrial devices, such as motor protections, relays, rotation switches
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
  • H01H47/002—Monitoring or fail-safe circuits

Definitions

• the invention relates to electronic circuit breakers or switches in general and in particular to electronic circuit breakers, switches or relays provided with an in-circuit current source for self-testing, which may be used in failsafe applications, which for example may be used in the railway, automobile, and chemical industries.
• Circuit breakers, switches or relays are widely used and in order to lower costs of production and to avoid the disadvantages of mechanical or electro-mechanical constructions, electronic circuit breakers or switches have been developed. For many purposes there is a need to have a failsafe circuit breaker, switch or relay, and by using electronic control circuits or computer systems, computer controlled test sequences can be imposed on the electronic circuit breaker, switch or relay to thereby test the functionality of the electronic circuit breaker, switch or relay. In the following the wording electronic circuit breaker is also meant to include electronic switches or relays.
• German patent application having publication No. DE 19606894 is disclosed an electronic circuit stage for safe control and monitoring of electrical loads in railway applications.
• the circuit stage has at least two series switches, which are in- dependently controllable and which are of non-safety standard.
• At least one switch is common for all loads circuit and each load circuit has at least one other switch, for opening and closing the load circuit.
• Independent computer channels of a safety computer system control the switches.
• At least one transducer detects a test voltage derived from a supply or test current flowing through the load, or a voltage meas- ured directly at the load and dependent on the load's operating state.
• Both computer system channels which can detect inappropriate open or closed state, evaluate the transducer signals from the occurrence of unanticipated transducer signals based on the expected transducer signal at the current time.
• a test of the circuit is performed by having a supply or test current flowing through the load.
• the disclosed circuit stage does not allow a circuit test to be performed without having a known load current, which makes it difficult to test the disclosed circuit stage when connected in series with another component or switch, which may switch off the connection to the load or when connected to a circuit with unknown load current.
• a circuit breaker com- prising a first switch circuit having first and second terminals, said first switch circuit comprising: a first controllable signal current switch for switching between a closed, current conducting state and an open, non-conducting state in response to a first control signal to thereby allow or prevent conduction of current through the first signal current switch between a first terminal and a second terminal of the first signal current switch , a first controllable test current switch for switching between a closed, current conducting state and an open, non-conducting state in response to a first test control signal to thereby allow or prevent conduction of current through the first test current switch between a first terminal and a second terminal of the first test current switch, a first test current source for providing a first test current flow through the first test current switch, and a first current sensor for measuring a current flow through the first signal current switch, said first terminals of the first signal current switch and the first test current switch being electrically conductively connected to each other and to the first terminal
• the circuit breaker further comprises a second switch circuit having first and second terminals with the second terminal of the first switch circuit being electrically conductively connected to the first terminal of the second switch circuit, said second switch circuit comprising: a second controllable signal current switch for switching between a closed, current conducting state and an open, non-conducting state in response to a second control signal to thereby allow or prevent conduction of current through the second signal current switch between a first terminal and a second terminal of the second signal current switch, a second controllable test current switch for switching between a closed, current conducting state and an open, non-conducting state in response to a second test control signal to thereby allow or prevent conduction of current through the second test current switch between a first terminal and a second terminal of the second test current switch, a second test current source for providing a second test current flow through the second test current switch, and a second current sensor for measuring a current flow through the second signal current switch, said first terminals of the second signal current switch and the second test current switch being electrically conductively connected
• the first switch circuit may then be designed so that when the first signal current switch and the first test current switch are closed, the first test current to be supplied by the first test current source can flow in the first test current loop and be measured by the first current sensor.
• the second switch circuit may then be designed so that when the second signal current switch and the second test current switch are closed, the second test current to be supplied by the second test current source can flow in the second test current loop and be measured by the second current sensor.
• the first switch circuit further comprises a first control circuit for providing the first control signal to the first signal current switch and the first test control signal to the first test current switch.
• the first current sensor may be adapted to output a first current output signal and the first control circuit may be adapted to receive and read the first current output signal.
• the second switch circuit further comprises a second control circuit for providing the second control signal to the second signal current switch and the second test control signal to the second test current switch.
• the second current sensor may be adapted to output a second current output signal and the second control circuit may be adapted to receive and read the second current output signal.
• the first and second control circuits may be adapted to perform a first self-test of the first current loop, with the first and second control circuits being adapted to control the current switches so that the first signal current switch and the first test current switch are closed at the same time during at least part of a period of the first self-test when both the second signal current switch and the second test current switch are open.
• the first control circuit may be adapted to control the first signal current switch and the first test current switch
• the second control circuit may be adapted to control the second signal current switch and the second test current switch.
• the first control circuit may be adapted to read a first current output signal value from the first current sensor during a period of the first self-test when the first signal current switch and the first test current switch are closed at the same time while both the second signal current switch and the second test current switch are open, and further may be adapted to compare the read first current value to a stored predetermined value representing the first test current flow and based on said comparison determining whether a first current failure signal should be gener- ated or not.
• a first failure signal may be generated when the read first current output signal value is smaller than the first test current value by a predetermined amount.
• the first and second control cir- cuits are adapted to perform a second self-test of the second current loop, with the first and second switch circuits being adapted to control the current switches so that the second signal current switch and the second test current switch are closed at the same time during at least part of a period of the second self-test when both the first signal current switch and the first test current switch are open.
• the first control circuit may be adapted to control the first signal current switch and the first test current switch
• the second control circuit may be adapted to control the second signal current switch and the second test current switch.
• the second control circuit may be adapted to read a second current output signal value from the second current sen- sor during a period of the second self-test when the second signal current switch and the second test current switch are closed at the same time while both the first signal current switch and the first test current switch are open, and further may be adapted to compare the read second current value to a stored predetermined value representing the second test current flow and based on said comparison determin- ing whether a second current failure signal should be generated or not.
• a second failure signal may be generated when the read second current output signal value is smaller than the second test current value by a predetermined amount.
• the first switch circuit further has a first voltage sensor for measuring a voltage including or representing the voltage across the first signal current switch.
• the first voltage sensor may be adapted to output a first voltage output signal and the first control circuit may be adapted to receive and read the first voltage output signal.
• the second switch circuit further has a sec- ond voltage sensor for measuring a voltage including or representing the voltage across the second signal current switch.
• the second voltage sensor may be adapted to output a second voltage output signal and the second control circuit may be adapted to receive and read the second voltage output signal.
• the first control circuit may be adapted to receive and read a first current output signal from the first current sensor and to receive and read a first voltage output signal from the first voltage sensor during a period of a first self-test when the first signal current switch and the first test current switch are closed at the same time while both the second signal current switch and the second test current switch are open, and further be adapted to compare the read first current value and the read first voltage output value to a stored predetermined value representing the on- resistance of the first signal current switch, and based on said comparison determining whether a first resistance failure signal should be generated or not.
• the first resistance failure signal may be generated when a value representing a resistance value obtained from the read first current output signal value and the read first voltage output value differs from a value representing the on-resistance value of the first signal current switch by a predetermined amount.
• the second control circuit may be adapted to receive and read a second current output signal from the second current sensor and to receive and read a second voltage output signal from the second voltage sensor during a period of a second self-test when the second signal current switch and the second test current switch are closed at the same time while both the first signal current switch and the first test current switch are open, and further be adapted to compare the read second current value and the read second voltage output value to a stored predetermined value repre- senting the on-resistance of the second signal current switch, and based on said comparison determining whether a second resistance failure signal should be generated or not.
• the second resistance failure signal may be generated when a value representing a resistance value obtained from the read second current output signal value and the read second voltage output value differs from a value representing the on-resistance value of the second signal current switch by a predetermined amount.
• the first and second control circuits are adapted to communicate with each other. It is within a preferred embodiment that the first and second control circuits are electrically galvanic separated, and here the first and second control circuits may be adapted to communicate with each other via optical communication.
• the circuit breaker according to the present invention discussed until now comprises one or two switch circuits, where a first and a second switch circuit may be arranged in series.
• a circuit breaker comprising more than two switch circuits.
• one, two or even more pairs of series connected switch circuits may be arranged in parallel with the series con- nected first and second switch circuits.
• a circuit breaker comprising the first and second switch circuit may further comprise: a third switch circuit having first and second terminals and a fourth switch circuit having first and second terminals with the second terminal of the third switch circuit being electrically conductively connected to the first terminal of the fourth switch circuit, said third switch circuit comprising: a third controllable current switch for switching between a closed, current con- ducting state and an open, non-conducting state in response to a third control signal to thereby all ow or prevent conduction of current through the third current switch between a first terminal and a second terminal of the third current switch , a third controllable test current switch for switching between a closed, current conducting state and an open, non-conducting state in response to a third test con-trol signal to thereby allow or prevent conduction of current through the third test current switch between a first terminal and a second terminal of the third test current switch, a third test current source for providing a third test current flow through the third test current switch, and
• the third switch circuit may then be designed so that when the third signal current switch and the third test current switch are closed, the third test current to be supplied by the third test current source can flow in the third test current loop and be measured by the third current sensor.
• the fourth switch circuit may then be designed so that when the fourth signal current switch and the fourth test current switch are closed, the fourth test current to be supplied by the fourth test current source can flow in the fourth test current loop and be measured by the fourth current sensor.
• the third switch circuit further comprises a third control circuit for providing the third control signal to the third current switch and the third test control signal to the third test current switch.
• the third current sensor may be adapted to output a third current output signal and the third control circuit may be adapted to receive and read the third current output signal.
• the fourth switch circuit further comprises a fourth control circuit for providing the fourth control signal to the fourth current switch and the fourth test control signal to the fourth test current switch.
• the fourth current sensor may be adapted to output a fourth current output signal and the fourth control circuit may be adapted to receive and read the fourth current output signal.
• the third switch circuit may further have a third voltage sensor for measuring a voltage including or representing the voltage across the third current switch.
• the third voltage sensor may be adapted to output a third voltage output signal and the third control circuit may be adapted to receive and read the third voltage output signal.
• the fourth switch circuit may further have a fourth voltage sensor for measuring a voltage including the voltage across the fourth current switch.
• the fourth voltage sensor may be adapted to output a fourth voltage output signal and the fourth control circuit may be adapted to receive and read the fourth voltage output signal.
• control circuits In order for the control circuits to control both the current switches of the third and fourth switch circuits during a test or a self-test, it is within an embodiment of the invention that the third and fourth control circuits are adapted to communicate with each other.
• the present invention furthermore covers an embodiment in which the first, second, third and fourth control circuits are adapted to communicate with each other.
• control circuits may be adapted to perform self-tests of the first and second test current loops
• the first and second control circuits may be adapted to control the current switches so that during a self-test of the first current loop, the first signal current switch and the first test current switch are closed at the same time during at least part of a period when the second signal current switch and the second test current switch are open
• the first and second control circuits may further be adapted to control the current switches so that during a self-test of the sec- ond current loop, the second signal current switch and the second test current switch are closed at the same time during at least part of a period when the first signal current switch and the first test current switch are open.
• control circuits may be adapted to perform self-tests of the third and fourth test current loops
• the third and fourth control circuits may be adapted to control the current switches so that during a self-test of the third current loop, the third signal current switch and the third test current switch are closed at the same time during at least part of a period when the fourth signal current switch and the fourth test current switch are open
• the third and fourth control circuits may further be adapted to control the current switches so that during a self-test of the fourth current loop, the fourth signal current switch and the fourth test current switch are closed at the same time during at least part of a period when the third signal current switch and the third test current switch are open.
• control circuits may be adapted to perform self-tests of the first, second, third and/or fourth test current loops when the circuit breaker is in an open state with the current switches being controlled so that during a self-test of a test current loop, the corresponding signal current switch and test current switch are closed at the same time during at least part of a period when the signal current switches and test cur- rent switches of the three remaining test current loops are all open.
• control circuits may be adapted to perform self-tests of the first, second, third and/or fourth test current loops when the circuit breaker is in a closed state with the current switches be- ing controlled so that during a self-test of the first current loop, the first signal and test current switches are closed at the same time during at least part of a period when the second signal and test current switches are open, the third and fourth test current switches are open, and the third and forth signal current switches are closed, and so that during a self-test of the second current loop, the second signal and test current switches are closed at the same time during at least part of a period when the first signal and test current switches are open, the third and fourth test current switches are open, and the third and forth signal current switches are closed.
• control circuits may be adapted to perform the self-tests of the first, second, third and/or fourth test current loops when the circuit breaker is in a closed state with the current switches being controlled so that during a self-test of the third current loop, the third signal and test current switches are closed at the same time during at least part of a period when the fourth signal and test current switches are open, the first and second test current switches are open, and the first and second signal current switches are closed, and so that during a self-test of the fourth current loop, the fourth signal and test current switches are closed at the same time during at least part of a period when the third signal and test current switches are open, the first and second test current switches are open, and the first and second signal current switches are closed.
• the first, second, third and fourth control circuits may be electrically galvanic separated.
• the first, second, third and fourth control circuits may be adapted to communicate with each other via optical communication.
• a method of performing a test of a switch circuit being part of a circuit breaker, which circuit breaker is selected from the circuit breakers according to the first aspect of the invention comprising: keeping both the signal current switch and the test current switch closed during a first period of time, and reading or detecting a current output signal value from the current sensor during said first period of time.
• This method may be referred to as a closed switch test.
• the method may further comprise comparing the current output signal value obtained during said first period of time to a stored predetermined value representing the test current flow and based on said comparison determining whether a closed current failure signal should be generated or not.
• a closed current failure signal may be generated when the current output signal value obtained during said first period of time is smaller than the test current value or smaller than the test current value by a predetermined amount.
• the method of the present invention may further comprise a so-called open switch test, thereby further comprising the steps of: keeping the signal current switch open and the test current switch closed during a second period of time, and reading or detecting a current output signal value from the current sensor during said second period of time.
• the method may further comprise comparing the current output signal value obtained during said second period of time to a stored predetermined value representing a maximum leakage current and based on said comparison determining whether an open current failure signal should be generated or not.
• an open current failure signal may be generated when the current output signal value obtained during said second period of time is larger than the maximum leakage current value or larger than the maximum leakage current value by a predetermined amount.
• the closed switch test may further comprise reading or detecting a voltage output signal value from the voltage sensor during said first period of time.
• the test method further comprises comparing the current output signal value and the voltage output signal value obtained during said first period of time to a stored predetermined value representing an on-resistance of the signal current switch, and based on said comparison determining whether a closed resistance failure signal should be generated or not.
• a closed resistance failure signal may be generated when a value representing a resistance value obtained from the current output signal value and the voltage output value obtained during said first period of time differs from a value representing the on-resistance value of the signal current switch by a predetermined amount.
• the open switch test may further comprise reading or detecting a voltage output signal value from the voltage sensor during said second period of time.
• the test method further comprises comparing the current output signal value and the voltage output signal value obtained during said second period of time to a stored predetermined value representing an off-resistance of the signal current switch, and based on said comparison determining whether an open resistance fail- ure signal should be generated or not.
• an open resistance failure signal may be generated when a value representing a resistance value obtained from the current output signal value and the voltage output value obtained during said second period of time differs from a value representing the off-resistance value of the signal current switch by a predetermined amount.
• the reading or detecting of a current output signal value during the first period of time comprises several readings of an output signal from the current sensor during said first period of time.
• the reading or detecting of a current output signal value during the second period of time com- prises several readings of an output signal from the current sensor during said second period of time.
• the reading or detecting of a voltage output signal value during the first period of time comprises several readings of an output signal from the voltage sensor during said first period of time, and in the same way it is preferred that the reading or detecting of a voltage output signal value dur- ing the second period of time comprises several readings of an output signal from the voltage sensor during said second period of time.
• the methods of testing a switch circuit according to the second aspect of the invention may also be used when the circuit breaker comprises two or more switch circuits.
• a third aspect of the invention there is provided a method of performing a self-test of two series connected switch circuits being part of a circuit breaker, which circuit breaker is selected from the circuit breakers according to the first aspect of the invention having two series connected switch circuits, said method comprising: for the switch circuit being tested, performing a test selected from the test methods according to the second aspect of the invention, while for the switch circuit not being tested, keeping both the signal current switch and the test current switch open during at least said first and/or second period(s) of time.
• a method of per- forming a self-test of two series connected switch circuits being part of a circuit breaker, which circuit breaker is selected from the circuit breakers according to the first aspect of the invention including four switch circuits said method comprising: for the switch circuit being tested, performing a test selected from the test methods according to the second aspect of the invention, while for the switch circuit not being tested but being connected in series with the switch circuit under test, keeping both the signal current switch and the test current switch open during at least said first and/or second period(s) of time, and for the remaining two switch circuits keeping the signal current switches and the test current switches open during at least said first and/or second period(s) of time.
• a method of performing a self-test of two series connected switch circuits being part of a circuit breaker, which circuit breaker is selected from the circuit breakers according to the first aspect of the invention including four switch circuits comprising: for the switch circuit being tested, performing a test selected from the test methods according to the second aspect of the invention, while for the switch circuit not being tested but being connected in series with the switch circuit under test, keeping both the signal current switch and the test current switch open during at least said first and/or second period(s) of time, and for the remaining two switch circuits keeping the signal current switches closed and the test current switches open during at least said first and/or second period(s) of time.
• each switch circuit comprises a corresponding control circuit for the control of the closing and opening of the signal current switch and the test current switch, and for the reading or detecting of the outputs of the current sensor and/or voltage sensor.
• a configuration of circuit breakers comprising: two or more two-switch element circuit breakers each having a first electronic switch circuit connected in series with a second electronic switch circuit, said first switch circuit having a first electronic control circuit and said second switch circuit having a second electronic control circuit, and a first main electronic control circuit and a second main electronic control circuit, wherein the first main control circuit and each first control circuit are part of a first communication ring, and wherein the second main control circuit and each second control circuit are part of a second communication ring.
• said two-switch element circuit breakers may be selected from the circuit breakers according to the first aspect of the invention having two series connected switch circuits both including a control circuit.
• the configuration may comprise several two-switch elements such as at least 3, 4, 5, 6, 7 or 8 elements.
• a configuration of circuit breakers comprising: two or more four-switch element circuit breakers each having a first electronic switch circuit connected in series with a second electronic switch circuit and a third elec- tronic switch circuit connected in series with a fourth electronic switch circuit, with said first and second switch circuits being connected in parallel with the third and fourth switch circuits, each said switch circuits including a corresponding electronic control circuit, and a first main electronic control circuit and a second main electronic control circuit, wherein the first main control circuit and each control circuit of the first and third switch circuits are part of a first communication ring, and wherein the second main control circuit and each control circuit of the second and fourth switch circuits are part of a second communication ring.
• said four-switch element circuit breakers may be selected from the circuit breakers according to the first aspect of the inven- tion having four switch circuits both including a control circuit.
• the configuration may comprise several four-switch elements such as at least 3, 4, 5, 6, 7 or 8 elements.
• each switch control circuit is linked via communication lines to two neighbouring switch control circuits or one neighbouring switch control circuit and the main control circuit.
• each of the main control circuits and each of the switch control circuits may be electrically galvanic separated from one another. It is also preferred that the main control circuits and the switch control circuits are adapted to communicate with each other via optical communication.
• the first main control circuit and the second main control circuit may be adapted to communicate to each other.
• the two main control circuits may be electrically galvanic separated from one another and they may communicate with each other via optical communication.
• the first main control circuit and the second main control circuit each may be adapted to receive or read a logic input signal. It is also within embodiments of sixth and seventh aspects the invention that the configuration further comprises one or more first input electronic detect circuits for detecting or receiving one or more corresponding logic input signals and for forwarding one or more corresponding output signals to the first main control circuit, and furthermore comprises one or more second electronic input detect circuits for detecting or receiving one or more corresponding logic input signals and for forwarding one or more corresponding output signals to the second main control circuit.
• each logic input signal may be input to both a first and a second input detects circuit.
• each of the main control circuits and each of the input detect circuits are electrically galvanic separated from one another. It is also preferred that the main control circuits and the input detect circuits are adapted to communicate via optical communication. It is preferred that the configuration of circuit breakers according to the sixth and seven aspects of the invention may communicate with computers or systems not being part of the configuration.
• the first main control circuit may have at least one communication line for forwarding and/or receiving information to and/or from a computer or system outside the first communication ring.
• the second main control circuit may have at least one communication line for forwarding and/or receiving information to and/or from a computer or system outside the second communication ring.
• main control circuits are electrically galvanic separated from any outside computer or system having a com- munication line to a main control circuit, and it is preferred that communication between the outside systems and the main control circuits is performed via optical communication.
• Figure 1 is a block diagram of an embodiment of a circuit breaker according to the present invention having a first switch circuit
• Figure 2 is a block diagram of an embodiment of a circuit breaker according to the present invention having first and second switch circuits in series,
• Figure 3 is a block diagram of an embodiment of a circuit breaker according to the present invention having first and second switch circuits in series and including first and second voltage sensors, each switch circuit having a corresponding first and second control circuit,
• Figure 4 is a block diagram of an embodiment of a circuit breaker according to the present invention having third and fourth switch circuits in series and including third and fourth voltage sensors, each switch circuit having a corresponding third and fourth control circuit
• Figure 5 is a block diagram of an embodiment of a circuit breaker according to the present invention having first, second, third and fourth switch circuits connected in a combination of parallel and series and including all four voltage sensors
• Figure 6 is a Wlarkov-chain diagram describing the mathematical probability theory of a duplicated failsafe system
• FIG. 7 is a block diagram of an embodiment of a controlled electronic circuit switch element named E-i,
• Figure 8 is a block diagram of an embodiment of a complete self-testing circuit breaker including four controlled electronic circuit switch elements
• Figures 9 a, b, c show an electrical circuit diagram of a current switch at the elec- tronic component level with the corresponding simple equivalent diagrams when the current switch is open and closed,
• Figure 10 is an example of an electrical circuit diagram corresponding to the block diagram of the Ei element illustrated in Figure 7 when implemented to work in an AC environment
• Figure 11 is a flow chart illustrating subroutines called from a self-test sequence according to the flow chart of Figure 15, when the circuit breaker is configured according to an embodiment as illustrated in Figure 2,
• Figure 12 is a flow chart illustrating the subroutines called from a self-test sequence according to the flow chart of Figure 15 when the circuit breaker is configured according to an embodiment as illustrated in Figure 3,
• Figure 13 is a flow chart illustrating a test sequence according to an embodiment of the circuit breaker as illustrated in Figure 2,
• Figure 14 is a flow chart illustrating a test sequence according to an embodiment of a circuit breaker as illustrated in Figure 8
• Figure 15 is a flow chart illustrating a self-test sequence according to the self-test routine called from the flowcharts at Figure 13 and Figure 14,
• Figure 16 shows a number of E x elements corresponding to the Ei element as illustrated in Figure 7 being configured to achieve the functionality of a failsafe mechanical relay
• Figure 17 shows different configurations of circuit breakers, which configurations are capable of communicating with other duplicated computer systems.
• FIG. 1 is shown an embodiment of a first electronic circuit breaker (091), named FSi, of the present invention.
• the first circuit breaker comprises a controllable first current switch (103), named F ⁇ , which is placed in series with a current sensor
• ⁇ can be adjustable.
• the connection points of the two parallel lines determine the first and second terminals of the circuit breaker (101, 102).
• current (105), named I flows from the input of first terminal (101) to the output of second terminal (102) of the circuit breaker.
• FSi can be in three states:
• Self-testing This state is named 'self-testing'.
• the state of F-i and Gi depends on the type of self-test. Typically a self-test involves a sequence of switching of Fi and Gi.
• Several different self-test sequences can be implemented.
• One self-test sequence can be dedicated to test if F ⁇ can switch between state open and closed and another self-test sequence can be dedicated to test if Ai is capable of measuring a low current etc.
• FS 12 of the present invention.
• the circuit breaker comprises of FSi shown at Figure 1 and a second circuit breaker (092), named FS 2 .
• FS 2 comprises a controllable second current switch (203), named F 2 , which is placed in series with a current sensor (207), named A 2 , and in parallel with F 2 and A 2 is placed a controllable test current switch (204), named G 2 , which is placed in series with a test current source (206), having a predetermined value ⁇ l 2 .
• the connection points of the two parallel lines determine the first and second terminals of the second circuit breaker (201, 202).
• the second terminal of the first circuit breaker (102) is connected to the first terminal (201) of the second electronic circuit breaker.
• FS 2 can be in the same states (open, closed and self-testing) as those described for FSi above.
• FS 12 in Figure 2 has several advantages to FS-i in Figure 1:
• FS ⁇ 2 can be used in fail-safe circuits, because it can open even if a first hazardous error occurs.
• Example: FS 12 is implemented as a switch in the electri- cal circuit of a green light lamp in a railway signalling system. If Fi fails in a way, so that it is permanent closed, then a self-test sequence of FSi can disclose this. F 2 is still working correctly and will therefore be able to open and thereby ensure that the green lamp will not be on due to one failure.
• FIG 3 is shown a preferred embodiment of an extended electronic circuit breaker (506) based on the circuit breaker shown in Figure 2.
• the first circuit breaker (091) has been added a first voltage sensor (108), named V ⁇ , across F ⁇
• This extended circuit (100) is named, SG
• the second circuit breaker (092) has been added a second voltage sensor (208), named V , across F 2 .
• This extended circuit (200) is named, SC 2 .
• the second terminal of SCi (102) is connected to the first terminal of SC 2 (201).
• the circuit comprising SC and CCi (109) is named Ei (115) and the circuit comprising SC 2 and CC 2 (209) is named E 2 (215).
• the circuit comprising E-i and E 2 in series (506) is named, SB 12 .
• SC is controlled by the first control circuit (109), named CCi which controls Fi, through the first control signal line ( 11) and Gi through the first test control signal line (110) and receives and reads the value of Ai through the first current output signal (112) and the value of Vi through the first voltage output signal (113).
• SC 2 is controlled by the second control circuit (209), named CC 2 which controls F 2 , through the a control signal line (211) and G 2 through the second test control signal line (210) and receives and reads the value of A 2 through the second current output signal (212) and the value of V 2 through the second voltage output signal (213).
• CC T and CC 2 communicate through the communication signal lines (114, 214).
• CCi receive input from input signal (116).
• CC 2 receives input from input signal (216).
• Input signals can be any information telling if SCi: • Should be open or closed.
• the communication lines (116 - 118 and 216-218) are described more detailed un- der Figure 7.
• CCi and CC 2 has several advantages: •
• the switch can be used for failsafe circuits.
• Example: CCi and CC 2 read from input (116,216) that the switch should be open, but then CCi fails in a way that keeps Fi closed.
• CCi starts a self-test sequence as described in Figure 11-15, CCi will disclose that it has lost control over ⁇ . This can be a hazardous failure as described above in connection with Figure 2. But CC 2 will still work correctly and keep F 2 open.
• Cd and CC 2 initiate the self-test.
• An example of an embodiment would be an initiation of internal timers in the control circuits, which ensures that the period between two self-tests never exceeds a maximum limit.
• the synchronization of the internal timers is done through communication signals.
• Figure 4 is shown a preferred embodiment of a third and fourth electronic circuit breaker.
• the embodiment is identical to Figure 3, except that 'third' has replaced 'first' and 'fourth' has replaced 'second'.
• FIG. 5 is shown a preferred embodiment of a connection of a first, second, third and fourth electronic circuit breaker (504), named CB ⁇ 4 .
• the first terminal of CB ⁇ (501) is connected to the first terminal of SB 12 (101) and the first terminal of CB 34 (301).
• the second terminal of CB ⁇ 4 (502) is connected to the second terminal of SB 12 (202) and the second terminal of SB 34 (402).
• current flows from the input of first terminal (501), splits between SB 2 and SB 34 and is assembled at the output of the second terminal (502) of CB 14 .
• a failsafe system has a safe state and then it can enter into one or more permissive states.
• Example 1 A failsafe switch is placed in series with a green lamp in a railway signal. When the switch is open the switch is blocking the green signal. This is the safe state. When the switch is closed the green lamp is lightning. This is the permitting state.
• Example 2 A failsafe switch is placed in series with a red lamp in a railway signal. When the switch is closed the red lamp is lightning. This is the safe state. When the switch is open the switch is blocking the red lamp. This is the permitting state.
• the two examples above show that the safe state of the switch depends on the surrounding circuit. The elements in S are well-working elements without any errors.
• the elements in F are elements with one error in system A or B. This error is not hazardous because the other system is working correctly. But as long as the failure is not disclosed the system is still active and there is a possibility that the next error occurs. If instead the error is disclosed, then the system can enter a safe state until it is repaired. After reparation the system can move back to S.
• the elements in D are elements with two failures. This can be a hazardous failure, if the two errors a placed in each system and they lead to a state change from safe to permitting.
• the elements in S have a failure rate (903) of ⁇ F [Failure/ ⁇ t].
• the elements in F have a failure rate (904) of ⁇ F [Failure/ ⁇ t].
• the elements in F have a repair rate (905) of ⁇ R [Repairs/ ⁇ t].
• Nso elements placed in S and zero elements in F and D.
• ti to + ⁇ t.
• t 2 t + ⁇ t and so on.
• N D2 N R * ⁇ F elements in D.
• the number of elements in F are increased from the supply of failing elements from S (903) and decreased from the supply of failing elements to D (904) and the supply of repaired elements back to S (905).
• a system is declared as failsafe if it can be proved that the number of elements in D never exceeds a certain limit after a certain simulating time. Therefore it is important to ensure, that the elements does not stay in F. This can be achieved in two ways: Either by keeping the failure rate, ⁇ F , very low or by keeping the repair rate, ⁇ R , high by ensuring that the disclosure time is low so the elements can enter safe state and be repaired. Furthermore it must be proved that A and B systems are independent.
• the Markov-chain shown at Figure 6 is the basis for the three Failsafe standards: The German M ⁇ 8004, the European Cenelec and the Scandinavian A/B-standard. A system that fulfils this Markov-chain is therefore able to fulfil all three standards al- though they seem very different from each other.
• E ⁇ from Figure 3 shown.
• Ei is identical to E 2 at Figure 3 and E 3 and E 4 later on at Figure 8.
• An example of an embodiment of CCi would be as a stan- dard micro controller or a programming logic unit (PLC).
• PLC programming logic unit
• a standard micro controller has the ability to communicate with another system in many different ways. Another system could be another micro controller or an electrical system. But another system could also be a LED-diode or a panel that is supervised by a human being. Therefore: • CCi may switch an output line between logic '0' or '1' and thereby send a signal to another system.
• This type of output is named 'Logic output'.
• the signal code can be designed for the purpose or any well-known one-line protocols can be used. Another logic output could be a steady '0' or '1' turning a LED on/off.
• • CCi may read an input line having the logic value O' or ' and thereby read a signal from another system or CCi can just read a steady '0' or '1' on the line from another system.
• This type of input is named 'Logic input'.
• • CCi can implement any well-known communication protocol: Example: Ethernet, ISDN, Blue tooth or RS232. The implementation involves software in the micro controller and physical implementation of the needed number of logic input and output lines.
• External logic input line (116) reads the state the switch should enter: 'open' or 'closed' from another system.
• External logic output line (117) could be used to turn on/off a LED telling which state the switch has entered.
• External protocol IO line (118) communicates with another system.
• Example of a protocol An RS232 communication protocol, which implements a standard access to Personal and Laptop. During production the input/output information could be test and configuration data.
• FIG 8 a controllable electronic circuit breaker (505), named SB 14 , consisting of: a first controlled electronic circuit switch element (115), named Ei, a second controlled electronic circuit switch element (215), named E 2 , a third controlled electronic circuit switch element (315), named E 3 , a fourth controlled electronic circuit switch element (415), named E 4 .
• the second terminal of E ⁇ (102) is connected to the first terminal of E 2 (201) and the second terminal of E 3 (302) is connected to the first terminal of E 4 (401).
• the first terminal of SB 14 (501) is connected to the first terminal of Ei (101) and the first terminal of E 3 (301).
• the second terminal of SB ⁇ 4 (502) is connected to the second terminal of E 2 (202) and the second terminal of E 4 (402).
• the control circuits (109, 209, 309, 409), named CCi - CC 4 , communicate with each other through the internal communication signal lines (114, 214, 314, 414).
• the internal communication is ar- ranged as a communication ring. This reduces the total internal communication line number to four and saves components.
• An implementation of the communication ring could be a slotted ring where each element, E x , has a slot with a fixed length.
• the technical aspects of implementing such a communication ring is described in the literature about this subject.
• a typically example of physical embodiment of the internal communication lines would be a galvanic communication line for the same reasons that there were for using galvanic communication lines between CCi and CC 2 (114, 214) at Figure 3.
• Each switch element, E x has the capability of receiving and sending signals through the external communication lines (116-118, 216-218, 316-318 and 416-418).
• Example 1: SB M is controlled by an external duplicated failsafe system with a logic A/B-output; named O A and O B .
• SB 14 has been split into a duplicated failsafe system where the A-system consists of E ⁇ and E 3 and the B-system consists of E 2 and E 4 .
• the A-system consists of E ⁇ and E 3
• the B-system consists of E 2 and E 4 .
• the same is the case for the B system and therefore a two-way communication between E 2 and E must also be added.
• Splitting into an A and B system does not affect the self-testing and the internal communication of a switch.
• Example: SB 14 is still self-testing according to the scheme shown at Figure 14 and the communication ring between all four E x elements keeps working.
• a LED is not considered as failsafe functionality and supervisory systems are not considered as having failsafe functionality as well.
• the internal self-tests can be initiated of one of the elements, for example Ei; Ei initiates the self-test sequence described in Figure 14. If an error occurs then an error signal can be send to the controlling failsafe-duplicated system, the supervisory system and the LED.
• the self-testing routine described in Figure 14 is running in a permanent cycle as long as SB ⁇ is active. How SB M should behave in error situations will depend of the circuit in which SB ⁇ 4 is placed. In a typically implementation SB ⁇ would send an error signal at the first error disclosed during self-test, but it would keep working normally in a certain time- period. In order to duplicate the time period it should be initiated in both the A and B system.
• the time period is started by both Ei and E 2 . If time-out occurs in any of the systems both systems must enter safe state. Having this time period will give the maintenance personal time to repair the switch without any system down time.
• FIG 9a is shown an embodiment of the current switch F 1t F 2 , F 3 or F , named F (103) at the electronic components level.
• F is connected to the surrounding circuit through the first terminal (125) and the second terminal (126).
• F consists of two semiconductor switches (120,121), named F + and F., which are placed in series with two resistors (123,124).
• the resistors improve the robustness of the switch to large pulses and can be used as current sensing resistors when implementing the current sensor, Ai, A 2 , A 3 or A 4 .
• the switches are controlled by the control signal (111).
• the ground level of the control signal (122) is placed between the two resistors.
• the switch becomes independent of the poles of the voltage across the terminals and thus the current switch can be used for AC or DC current.
• Figure 9b shows a simple equivalent model of F, when F is open.
• the model consists of a resistor, named R o n -
• Figure 9c shows a simple equivalent model of F, when F is closed.
• the model consists of a resistor, named R F o ⁇ .
• the con- trol circuits can calculate R FOn and R Foff using Ohm's law These calculated values of
• R FOn and R FOff can then be compared with the values determined from the data sheets of the electrical components inside F since the values will be well defined when the components are well working.
• Semiconductor switches can fail by showing non-linear behaviour, which can be difficult to disclose. This failure type can be disclosed by calculating R FOff and R FOn using different values of ⁇ l.
• Figure 10 is shown a typically embodiment of an electrical circuit diagram corresponding to the block diagram of the Ei element, when it is implemented to work in an AC or DC environment.
• Figure 10 shows the embodiment of the current sensor Ai, named A (107), the current sensor i, named V (108), the current switch Fi, named F (103) and the test current switch Gi, named G (104) at the electronic components level, when implemented in Ei.
• Ei is connected to the surrounding circuit through the two terminals (101, 102).
• the current switch F shown at Figure 9a has been implemented in Ei (111, 120, 121 , 122, 123 and 124).
• the Ammeter (107) is implemented using an operational amplifier and current sensing resistors (123, 124).
• the alternating output signal from the operational amplifier is rectified (130) before it is read by the control circuit (109), named CC, through the current sensor signal (112), named A.
• the control circuit CC is supplied with power from the power supply unit (106), named PSU.
• the PSU is supplied from another PSU through a galvanic transformer. The circuit at Figure 10 will not affect the surrounding circuit due to the superposition principle of electronic circuits.
• the test current switch (104), G is split into G + and G- (104, 133) to be able to lead current through both current switches F + and F. (120, 121) during self-testing.
• F and G are 'closed' in a test sequence described in Figure 15 then first F+ and G+ are closed and F- and G- are open, then F+ and G+ are open and F- and G- are closed.
• the PSU is placed in series with G + and G.. G is controlled by CC through the test current signal lines (110, 136).
• Standard semiconductor switches can be used for the G switch, but they must have a high enough V B REA KO VE R value to resist the voltage across the switch terminals supplied from the surrounding circuit when the switch is closed.
• test current controlling resistor In series with each switch G+ and G- is placed a test current controlling resistor (134, 135).
• the dimension of the test current controlling resistors together with the dimension of the PSU determines the value of the test current.
• the resistors could be replaced with variable resistors controlled by CC and thereby achieve a variable test current value.
• the Voltmeter (108) is implemented by placing an operational amplifier after the two test current switches G + and G..
• the alternating output signal from the operational amplifier is rectified (131) before it is read by CC, through voltage sensor signal (113), named V.
• the internal and external communication lines (114, 214, 116-118) use galvanic communication.
• the logic input/output lines are implemented by using a standard optocoupler:
• the logic output of another system (named O A or OB in the description in connection with Figure 8) is connected to the input side of the optocoupler.
• the output of the optocoupler is connected to the logic input signal (116).
• the logic input is transformed into a light signal, which again is transformed back to a logic signal on the outside of the optocoupler. Thereby a galvanic boarder is achieved.
• the same principle can be used for the protocol IO communication lines.
• the used micro controller (109), CC should have certain features:
• the semiconductor switch at Figure 8 was probably not the cheapest solution when compared with mechanical failsafe switches some years ago. But due to the fast development of cheaper and smaller standard semiconductor components and micro controllers and due to lowering of production cost of truly semiconductor products at the global market, then today the switch at Figure 8 can compete with mechanical solutions.
• an optional filter (137) to protect the switch components from large noise pulses.
• the filter must be dimensioned according to the surrounding system. Alternatively the filter can be a part of the surrounding circuit.
• the filter at Figure 10 (137) could include Gas Discharge Tubes, Varis- tors, inductors, capacitors and other components.
• FIG 11 is shown a typical embodiment of subroutine methods (170, 173, 175) of a single circuit breaker at Figure 1 or any extended embodiment that does not include a voltage sensor.
• Subroutine 'Read sensors and calculate' (170) is implemented in the corresponding control circuit.
• the subroutine is called every time the control circuit needs to achieve a value of the current, I, (172) through F.
• the control circuit performs a sequence of readings of the current sensor, A, thereby filtering and/or averaging the readings and eliminating noise.
• the control circuit knows the expected value of I since it controls the switches, F and G.
• F closed test case (175) F and G is closed and I must be approximately equal to the predetermined value of the current source, ⁇ l.
• the subroutine is called every time the control circuit needs to achieve a value of the current, I, through F and the voltage, V F , (182) across F.
• the control circuit performs a sequence of readings of the current sensor, A, and the voltage sensor, V, thereby filtering and/or averaging the readings and eliminating noise. Since the control circuit also controls the switches, F and G, the control switch knows which values of I, V and the current switch impedance, R F , to expect. R F is calculated using Ohm's law. At F closed test case (185) F and G is closed and R F must be approximately equal to the predetermined value of R FOn .
• F open test case (183) F is open and G is closed and R F must be approximately equal to the predetermined value of R F o ff .
• F Open (183) and then F Closed (185) (or vice versa) in a row it is possible to determine if the control circuit has control of F and is able to switch F between the two states 'open' and 'closed' and to disclose if F is showing non-linear behaviour.
• Figure 13 is shown a typical embodiment of a self-test sequence of the circuit breaker at Figure 2 or any extended embodiment, example: SB ⁇ 2 at Figure 3.
• the self-test sequence depends on whether the circuit breaker is open (140) or closed (141):
• SC ⁇ /(FS ⁇ at Figure 1) and SC 2 /(FS 2 at Figure 2) are open when self- test starts. Then SCi does self-test. When SCi has finished its self-test, then SCi opens and then SC 2 does self-test. When SC 2 has finished, SC 2 opens and then SB 12 has finished its self-test.
• the self-test sequence depends on whether the circuit breaker is open (150) or closed (151): If open, then SCi, SC 2j SG 3 and SC 4 are open when self-test starts. Then Ci does self-test. When SCi has finished its self-test, then Sd opens and then SC 2 does self-test. When SC 2 has finished, SC 2 opens and then SC 3 does self-test. When SC 3 has finished, SC 3 opens and SC 4 does self-test. When SC 4 has finished, SC 4 opens and then SB 14 has finished its self-test. If closed, then SCi, SC 2l SC 3 and SC are closed when self-test starts. Then SC 2 opens and SCi does self-test. When SCi has finished its self-test, then SC 2 closes.
• FIG 15 is shown an example of a self-test method (160) of a single circuit breaker at Figure 1 or any extended embodiment, example: Ei at Figure 7.
• a text is underlined in the flowchart, it is a call to a subroutine that can be found in Figure 11 or 12.
• Two subroutine numbers are mentioned (17x, 18x).
• the first numbers (17x) should be called by those embodiments of the circuit breaker that does not include a voltage sensor and those that do include a voltage sensor should call the second numbers (18x).
• step (161) it is determined if a current higher than the leakage current is running in the current switch F, and if so, the circuit breaker may be conducting a current and the self-test is completed before changing the state of any current switches F or G.
• a GR is a system of one or more switches in a row, that all responds synchronic to one or more logic inputs.
• a mechanical GR can be implemented by using an internal heavy metal 'anchor'. The gravity force on the anchor is used to ensure that each switch falls into the safe state of the switch at failures.
• Each switch is mechanically fixed to the anchor and thereby ensuring that the switches are synchronized.
• the GR enters the permissive state by lifting the anchor with electro magnetically forces and thereby activating the switches to change state. The switches can respond in opposite direction.
• the internal mechanical bindings ensure, that Si and S 2 always are in opposite directions. These bindings are used to achieve failsafe functionality in a relay logic system called an Interlocking system.
• a simple example of a relay interlocking system could be the Cenelec European railway signal, named "outer reduced signal”.
• This lamp consists of only a red and a green lamp. Si is placed in series with the green lamp and S 2 in series with the red lamp.
• a full failsafe railway interlocking system can be implemented by connecting many numbers of GR with a supervisory system and the elements at the railway: Signal, point, track detectors, Emergency buttons and so on.
• the system at Figure 16 is an electronically implementation of such a mechanical relay described in the above example.
• the relay consists of N+1 switches (601), named E2-0, E2-1,..., E2-N.
• E2- 0 corresponds to Si
• E2-1 corresponds to S 2 in the mechanical relay example above.
• an E2-x switch element is identical with SB ⁇ 2 (506) shown at Figure 3 or SB ⁇ 4 (505) shown at Figure 8.
• the version to be used depends on the relay cycle. Railway interlocking systems are constructed, so a GR always has an on/off cycle between each train passage. This means each switch will have an open period where it can self-test between each train passage. Therefore the simpler SB 12 version is sufficient.
• SB ⁇ 2 Another argument for using SB ⁇ 2 is that an E2-x element in this case consists of two E x switch elements: Ei and E 2 (115, 215) at Figure 3.
• E x elements (Ei and E 2 in Si and Ei and E 2 in S 2 ) must fail in a permissive state before the corresponding mechanical binding is broken.
• an E2-x switch in the GR is placed in series with an emergency button then the SB ⁇ version will be the appropriate, because obviously the emergency button is not activated/deactivated between each train passage.
• an E2-x element is identical with SB ⁇ 2 .
• a group relay can implement the functionality and the allowed lamp combinations in a railway signal with more than two lamps. Blinking functionality of a lamp can be implemented as an example.
• the inputs are read by input detects (607). If there is one input line (608) as shown at Figure 16, then the input line is split into an A input detect and a B input detect. If the input were arriving from another duplicated failsafe system, then the input lines would already have been split.
• a typical embodiment of the input detects would con- sists of a voltage and/or current detect system combined with a noise filter.
• the input detects are read by two main control circuits (602, 603). These main control circuits are identical to the controllers described in Figure 10 (109) concerning demands, communication lines and description of production and operational dataflow with other systems. They interpret the input detects and compare the result with each other through the internal communication lines (614, 715) of type logic input/output. Each main control circuit has the ability of reporting any internal state or other information's to a supervisory system or receiving any information through the external communication lines (609, 610) of type protocol IO. The main control circuits communicate with the E2-x in two separate communication rings.
• the imple- mented communication rings are one-way rings: A logic output from main A is connected to logic input (116) in Ei in E2-0, then logic output (114) in Ei in E2-0 is connected to logic input (116) in Ei in E2-1 and so on.
• the main A control circuit (602), named 'main A' communicates with all Ei switches in each E2-x element.
• the main B control circuit (603), named 'main B' communicates with all E 2 switches in each E2-x element.
• the A-system consists of: Input detects Ax elements (607), main A (602) and each Ei element inside each E2-x.
• the B-system consists of: Input detects B x elements (607), main B (603) and each E 2 element inside each E2-x. This is to achieve the independency needed to fulfil the Markov-chain in Figure 6. All communication lines are marked with a 'g' (606). This means that galvanic isolation is implemented between all internal and external communication lines. This has two reasons: It is necessary to achieve the independency needed to fulfil the Markov-chain in Figure 6 and it is necessary to avoid problems with voltage levels if the E2-x switches and the inputs are placed at differ- ent voltage levels in the same surrounding circuit.
• bit no. 0 arrives from E x in E2-n back to main A and main B.
• the number of bits is fixed and each Ex element knows which bit numbers are dedicated to data exchange with the main controllers.
• the data to be exchanged are the same data as described at Figure 7.
• Period 3, named P3, performs evaluation and comparison between the A and B data. The starting time of each period is synchronized between main A and main B.
• Main A and main B tells the E x elements to enter state 'open', closed' or 'self- testing'. This way main A and main B can control that Ei in E2-0 is Open' when E 2 in E2-0 is self-testing. E x answers back how the self-test performed. The main micro controllers can send other orders, if necessary. Example: 'What is the value of I, V and R O N' and so on. This way main A and B can compare the different data from the Ei and E 2 inside an E2-x element and thereby disclose errors. Main A and main B gives orders to each switch and receive their data. A special time order is send by main A and main B to inform the E x elements about the start- ing time of periods P1 , P2 and P3.
• the safe state is a configuration matter: It de- pends on the surrounding circuit.
• Example of a safe state E2-0 is permanent locked in state 'open' and E2-1 is permanent locked in state 'closed' independent of input signals.
• the main control circuits initiate PL Typically the time between two self-tests will be five minutes but it depends on system requirements. The timing will typically be controlled by the internal timers of main A and main B.
• circuit breakers described above, SB ⁇ 2 , SB 1 , and GR have the ability to be combined in any configuration with each other and with other duplicated failsafe systems (650, 651).
• the other duplicated failsafe system is symbolized with two personal computers at Figure 17, but it could be any duplicated system.
• the external communication lines of the circuit breakers can be used to create a network of circuit breakers. Since each circuit breaker can be viewed as a failsafe duplicated system and thereby be parted into an A system and a B system, then the network can be incorporated in any other duplicated failsafe system. It can also be connected to any supervisory system.
• Each switch can send a message to an Internet Web page telling its current status. An application at the Internet page can send an SMS to a mobile phone and thereby inform the maintenance personal if a failure has occurred.
• circuit breaker at Figure 8 is build up to fulfil the Markov-chain at Figure 6. This gives the circuit breaker the following characteristics:
• SB ⁇ 4 Since the circuit breaker at Figure 8, named SB ⁇ 4 , consists of four switches Ei, E 2 ,
• E 3 and E 4 it is robust enough to be well working even if one of the switches detects a failure during a self-test. If for example Ei fails in a permanent permitting state (closed) then E 2 can enter a safe state (open) and E 3 and E can keep working normally until a service man arrives and repairs the circuit breaker. This means the switch:
• the software in the control circuits can be adapted to any kind of functionality:
• the circuit breaker can behave intelligent and can be adapted to any special functionality due to the software in the control circuits. Due to capability of reading multiple inputs, to communicate with each other and other safety system the functionality can be extended:
• Switches that are used to implement the blinking functionality of lamps in a railway signal perform a large number of on/off switching during their lifetime. Failsafe mechanical contacts cannot implement this functionality because the in-rush current when the switch closes and the sparkling at the switch metal when it opens ruin the switch too fast. Instead are used expensive mercury contacts that swing like a pendulum. The in-rush current and the sparkling will not cause the same problems in a truly semiconductor switch which are proper dimensioned.

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