IMPEDANCE INCREASE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial Number 63/169,791 filed April 1, 2021, the contents of which are hereby incorporated by reference herein for all purposes.

TECHNICAL FIELD

[0002] Embodiments relate generally to electronic circuits, and more particularly to a snubber circuit for elimination of switch contact impedance increase.

BACKGROUND

[0003] Reports of switch failure are a commonly reported issue. In certain applications, such as aerospace pressure and temperature indicator switches, proper switch operation is critical. Failed switches often possess common characteristics based on the environment that these failed switches operated in. Switches that reported failure were sometimes seen to have operated in applications with higher temperatures (e.g., 70 degrees Celsius or above), high mechanical vibration (e.g., >10 G), and a continuously supplied voltage.

SUMMARY

[0004] An embodiment of a system and device disclosed herein includes an electrical circuit switch having an electronic snubber that eliminates arcing during a transition from closed state to open state to limit voltage that prevents arcing that would otherwise be sufficient to trigger a chemical breakdown of a surrounding atmosphere which can lead to increased contact resistance.

[0005] A system embodiment may include: a switch with an electronic snubber with the capability of eliminating arcing during a transition from closed state to open state to limit voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere which can lead to increased contact resistance.

[0006] Another system embodiment may include: values for a snubber circuit idealized to keep voltage buildup below thresholds that may cause high energy discharge across an opening switch contacts that may cause a local atmosphere to form solid contaminants between electrical contacts.

[0007] Another system embodiment may include: a switch snubber with the capability of eliminating arcing during a transition from a closed state to an open state to limit voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere.

[0008] A system embodiment may include: a switch comprising two or more contacts, where the switch may be configured to transition between an open state and a closed state; and a circuit comprising a snubber circuit in communication with the switch, where the snubber circuit may be configured to eliminate arcing during the transition between the closed state and the open state by limiting voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere on at least one of the two or more contacts.

[0009] In additional system embodiments, the chemical breakdown of the surrounding atmosphere on the at least one of the two or more contacts leads to an increased contact resistance of the switch. In additional system embodiments, the snubber circuit maintains a voltage buildup below a threshold that causes a high energy discharge across an opening switch contact of the two or more contacts that causes the surrounding atmosphere to form solid contaminants on a surface of at least one of the two or more contacts. In additional system embodiments, the snubber circuit may be configured to reduce mechanical adhesion properties of a contact surface of the two or more contacts through a secondary effect of reducing micro-arc welding surface roughness.

[0010] An alternate system embodiment may include: a switch comprising two or more contacts; and a snubber circuit in electrical communication with the switch, where the snubber circuit may be configured to eliminate arcing during a transition of the switch between a closed state and an open state by limiting voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere on at least one contact of the two or more contacts.

[0011] Additional system embodiments may further include: a sense resistor in electrical communication with the snubber circuit; a parasitic simulator in electrical communication with the sense resistor; and a power supply in electrical communication with the parasitic simulator. In additional system embodiments, the parasitic simulator simulates a parasitic inductance and a parasitic capacitance seen in a wire. In additional system embodiments, the parasitic simulator presents a transient voltage spike in a simulation that represents an arc that would cause the chemical breakdown of the surrounding atmosphere on at least one of the two or more contacts. In additional system embodiments, the parasitic simulator comprises: a parasitic inductance, where the parasitic inductance may be connected in series with the power supply; and a parasitic capacitance, where the parasitic inductance may be connected in parallel across the parasitic capacitance.

[0012] In additional system embodiments, the sense resistor detects a voltage drop to sense the closed state or open state of the switch. In additional system embodiments, the snubber circuit reaches a steady state zero state when the switch may be in the closed state. In additional system embodiments, the snubber circuit may be configured to limit voltage to a voltage threshold that causes an arc across the at least one contact of the two or more contacts of the switch when the switch may be transitioned between the open state and the closed state.

[0013] In additional system embodiments, the snubber circuit comprises: a resistor; a capacitor, where the resistor and the capacitor may be connected in series; a first diode, where the first diode may be connected in parallel across the resistor; a second diode, where the second diode may be connected in parallel across the capacitor. In additional system embodiments, a polarity of the first diode and a polarity of the second diode snub a ringing signal. In additional system embodiments, the first diode may be a Schottky diode and where the second diode may be a Schottky diode. In additional system embodiments, the capacitor discharges through the resistor to zero volts when the switch may be in the closed state. In additional system embodiments, when snubber circuit limits a maximum voltage generated from an inductive transient as a flow of current may be interrupted when the switch transitions to the open state.

[0014] A method embodiment may include: limiting arc energy and occurrence in a circuit comprising a switch via a snubber circuit in communication with the switch, where the snubber circuit may be configured to prevent at least one of: a chemical breakdown and a burning that leads to contact impedance increases due to organic atmospheres.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Like reference numerals designate corresponding parts throughout the different views. Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

[0016] FIG. 1 A depicts a high-level block diagram of a snubber circuit, according to one embodiment; [0017] FIG. IB depicts a circuit diagram of a snubber circuit, according to one embodiment;

[0018] FIG. 2 depicts a voltage diagram of the snubber circuit of FIGS. 1 A-1B, according to one embodiment;

[0019] FIG. 3 depicts a response diagram of the snubber circuit of FIGS. 1A-1B, according to one embodiment;

[0020] FIGS. 4A-4B depict a flow chart of a method for determining contact resistance problems in a switch, according to one embodiment;

[0021] FIG. 5 depicts a partial cut-away view of contacts in a snubber circuit, according to one embodiment;

[0022] FIG. 6 depicts a partial cut-away view of alternate contacts in a snubber circuit, according to one embodiment; and

[0023] FIG. 7 depicts a partial cut-away view of alternate contacts in a snubber circuit, according to one embodiment.

DETAILED DESCRIPTION

[0024] The following description is made for the purpose of illustrating the general principles of the embodiments disclosed herein and is not meant to limit the concepts disclosed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the description as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

[0025] In one embodiment, an electronic circuit disclosed herein prevents degradation in the contact resistance of switches or microswitches used to indicate the state of a physical parameter, such as pressure or temperature, in applications such as aerospace measurement switches. Embodiments incorporate an electronic “snubber” or attenuation circuit with components, topology and electrical component characteristics (values) determined through a process (e.g., an algorithm). The disclosed snubber circuit essentially eliminates arcing which occurs when an electrical current jumps a gap in a circuit or between two electrodes. The snubber circuit disclosed herein suppresses the phenomenon of voltage transients in electrical systems. The process disclosed herein may offer further improvements to limit the maximum voltage of arcing as the switch opens or closes. Uncontrolled arcing may induce burning or chemical breakdown of contaminants in the atmosphere surrounding a microswitch. These contaminants deposit at the site of the arcing, which may be the switch contacts. As this arc- induced coating of the contact site increases with a repeated “make and break” action, the contaminant builds up an insulating layer. This insulating layer may cause the contact to increase in contact resistance. Values for contact resistance initially may start at about 100 milliohms and increase to hundreds or thousands of ohms.

[0026] A system (100, 101) may include: a switch (110) comprising two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706), where the switch is configured to transition between an open state and a closed state; and a circuit (100) comprising a snubber circuit (102) in communication with the switch (100), where the snubber circuit (102) is configured to eliminate arcing during the transition between the closed state and the open state by limiting voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere on at least one of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706). In additional system embodiments, the chemical breakdown of the surrounding atmosphere on the at least one of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706) leads to an increased contact resistance of the switch (110). In additional system embodiments, the snubber circuit (102) maintains a voltage buildup below a threshold that causes a high energy discharge across an opening switch contact of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706) that causes the surrounding atmosphere to form solid contaminants on a surface of at least one of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706). In additional system embodiments, the snubber circuit (102) is configured to reduce mechanical adhesion properties of a contact surface of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706) through a secondary effect of reducing micro-arc welding surface roughness.

[0027] In another system (100, 101) embodiment, the system may include: a switch (166) comprising two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706); and a snubber circuit (102) in electrical communication with the switch (166), wherein the snubber circuit (102) is configured to eliminate arcing during a transition of the switch (166) between a closed state and an open state by limiting voltage that prevents arcing sufficient to trigger a chemical breakdown of a surrounding atmosphere on at least one contact of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706). Additional system embodiments may also include: a sense resistor (164) in electrical communication with the snubber circuit (102); a parasitic simulator (162) in electrical communication with the sense resistor (164); and a power supply (160) in electrical communication with the parasitic simulator (162). In additional system embodiments, the parasitic simulator (162) simulates a parasitic inductance and a parasitic capacitance seen in a wire. In additional system embodiments, the parasitic simulator (162) presents a transient voltage spike in a simulation that represents an arc that would cause the chemical breakdown of the surrounding atmosphere on at least one of the two or more contacts (122, 123, 502,

504, 506, 602, 604, 606, 702, 704, 706). In additional system embodiments, the parasitic simulator (162) comprises: a parasitic inductance (112), wherein the parasitic inductance (112) is connected in series with the power supply (118); and a parasitic capacitance (114), wherein the parasitic inductance (112) is connected in parallel across the parasitic capacitance (114). In additional system embodiments, the sense resistor (164) detects a voltage drop to sense the closed state or open state of the switch (166). In additional system embodiments, the snubber circuit (102) reaches a steady state zero state when the switch (166) is in the closed state. In additional system embodiments, the snubber circuit (102) is configured to limit voltage to a voltage threshold that causes an arc across the at least one contact of the two or more contacts (122, 123, 502, 504, 506, 602, 604, 606, 702, 704, 706) of the switch (166) when the switch is transitioned between the open state and the closed state. In additional system embodiments, the snubber circuit (102) comprises: a resistor (104); a capacitor (108), where the resistor (104) and the capacitor (108) are connected in series; a first diode (106), where the first diode is connected in parallel across the resistor (104); and a second diode (107), where the second diode is connected in parallel across the capacitor (108). In additional system embodiments, a polarity of the first diode (106) and a polarity of the second diode (107) snub a ringing signal. In additional system embodiments, the first diode (106) is a Schottky diode and wherein the second diode (106) is a Schottky diode. In additional system embodiments, the capacitor (108) discharges through the resistor (104) to zero volts when the switch (166) is in the closed state. In additional system embodiments, when snubber circuit (102) limits a maximum voltage generated from an inductive transient as a flow of current is interrupted when the switch (166) transitions to the open state.

[0028] A method embodiment may include: limiting arc energy and occurrence in a circuit (100, 101) comprising a switch (110) via a snubber circuit (102) in communication with the switch (110), where the snubber circuit (102) is configured to prevent at least one of: a chemical breakdown and a burning that leads to contact impedance increases due to organic atmospheres.

[0029] The effect of the increased contact resistance is to degrade the ability to differentiate between a closed contact and an open contact in a microswitch. In one example, this open or closed state of the microswitch may be used to indicate a critical or key parameter in a typical application, such as when used in a pressure indicating switch or a temperature indicating switch. Loss of this capability of differentiating the open or closed state of the microswitch may prevent the determination of the state of the physical parameter being measured. These physical parameters being measured may include: a proper fuel level, an oil pressure, an overheating of an engine, and similar uses.

[0030] Generally speaking, switch failures are known to occur in certain situations and applications, and are especially critical in applications such as aerospace pressure and temperature indicator switches. The reported environment these failed switches operated in had common characteristics. Switches that showed the high contact resistance failure were seen to have operated in aerospace applications with higher temperature (e.g., 70 degrees Celsius or above), high mechanical vibration (e.g., >10 G) and a continuously supplied voltage. A mechanism induced by this vibration is making and breaking the electrical connection of the switch contacts. The built-up resistance is due to arc jumping. Arcs produce sufficient energy and heat to “burn” organic compounds found in the surrounding atmosphere. These contaminants then deposit on the contacts where the burning occurs.

Even in an inert atmosphere such as Argon or Nitrogen, outgassing organics mix in the atmosphere and are subject to this arc burning.

[0031] The insulation layer is found to be on the gold interface of the electron-to- electron contact. Elemental analysis shows this layer is carbon based. Common industry explanations are that contamination is caused by unclean manufacturing, or outgassing effects. By further examining the interface surrounding the contact area, elemental analysis reveals no contaminant, ruling out both of these causes. To eliminate physical contact pressure as a cause of trapping contaminant, the disclosed snubber was designed based on a theory of arc burning, that limits arc energy. Testing showed no contaminant buildup with the snubber over many cycles of opening and closing. Removing the snubber and repeating the test cycling, induced contaminant and high impedance.

[0032] An indicator switch may be replaced to preemptively prevent failure, or a failed switch with may be replaced with a new switch. Periodic replacement may be expensive, but may be scheduled. Waiting for a failure may ground a plane, cause the plane to be sent for maintenance, and/or cause other undesired results.

[0033] Remote mounting of a switch from the source of the pressure or temperature monitored fluid could be implemented to reduce the vibration and temperature. Anything that may cause the contact to open and close may be capable of inducing an arc. Vibration is one cause of inducing an arc. High temperatures may cause reactions to occur more quickly so may aggravate the effect and/or reduce the arc energy needed. By reducing the vibration, the switch life may be extended. However the cost of this mediation may result in a higher weight, an added cost of parts, and a reduced time constant due to the extended travel of the fluid. In some cases, the accuracy of the measurement compared to a direct measurement may be degraded and there may be an increased error.

[0034] Other methods to eliminate and/or reduce contact resistance may include: maintaining a constant current, reducing an outgassing of materials contained in a sealed enclosure, providing vented enclosures, eliminating any internal migrating contaminants either by elimination of use in the build or by additional cleaning, increasing gold thickness, and providing a wiping action to abrade contaminant buildup. These mediation processes and actions may yield only incremental improvement in life for the microswitch as they do not address the fundamental mechanism which causes the majority of the contact impedance increase.

[0035] Snubber circuits may be used to clamp voltages for the purpose of eliminating welding of gold between the switch gold contacts. The reasons for use of the snubber circuit and the determination of values for the snubber circuit do not address the elimination of contaminant build up due to arcing.

[0036] A wiping action of switch electrical contacts may be employed during closing to eliminate contaminants which may migrate to the contact area, deposit due to condensation, and/or deposit due to surface adsorption. In the case of the arc contamination, the wiping action may contribute to increased insulation distribution over a wider area. Increased insulation distribution occurs as the level of vibration alters the mechanical gap and/or rate of change causing the arc deposition to occur over a wider wiping area. In this case, wiping may not clean the switch electrical contacts but may instead cause increased contamination.

[0037] An electronic circuit may sense contact impedance and divide by the gain of the amplifier. In one example, this electronic circuit provides a means of maintaining a constant lower impedance even in the case of a microswitch increasing its contact resistance. Embodiments of the snubber circuit disclosed herein may reduce the amount of voltage required across the contacts and allow for a higher initial contact resistance.

[0038] An embodiment of a snubber circuit disclosed herein may be used to clamp voltages for the purpose of eliminating and/or reducing the welding of gold between the gold switch contacts. The embodiment of the snubber circuit discloses herein may also essentially eliminate contaminant build up on the switch contacts due to arcing.

[0039] The values shown in FIGS. 1 A-3 are for example only. Different values are possible and contemplated.

[0040] FIG. 1A depicts a high-level block diagram of a snubber circuit 101. The snubber circuit 101 may include a power supply 160, a parasitic simulator 162, a sense resistor 164, a snubber circuit 102, and a switch 166. The power supply 160 may be a standard power supply seen in many applications such as aircraft. In some embodiments, the power supply 160 may be a 28 Volt power supply. The parasitic simulator 162 and sense resistor 164 may simulate wiring connections and power sense circuits to provide a transient characteristic. The parasitic simulator 162 may simulate the parasitic inductance and parasitic capacitance seen in a wire or wire harness of a setup. The values for the parasitic simulator 162 may change based on a wire length and/or a physical construction of the installation.

The values for the parasitic simulator 162 may present a transient voltage spike in a simulation that would represent an arc that would cause burning or chemical breakdown of atmospheric organic compounds on contacts of the switch 166. The sense resistor 164 may be a sense resistor or load where a voltage drop across the sense resistor 164 for the switch 166 open condition or switch 166 closed condition may be sensed. The switch 166 may be operated to determine some system state. In some embodiments, the system state of the switch 166 may be a temperature or pressure detection system set point. In some embodiments, the switch 166 may be a Single Pole Double Throw (SPDT) switch. Other switch types are possible and contemplated.

[0041] When the switch 166 is in a closed position, the components in the snubber circuit 102 may reach a steady state zero state. When the switch 166 transitions to a normally open condition from the closed position, the energy stored in the parasitic simulator 162 may start to build up a voltage spike. The combination of energy in the parasitic simulator 162 may oscillate with a sine wave to a high voltage peak. Any negative going transient may be clamped by the snubber circuit 102. Current may be limited by the series sense resistor 164 and the energy may be dissipated in the resistor and the diode D2. The snubber circuit 102 may act as a short circuit to the transient and the predominant effect is for the voltage to be clamped by the snubber circuit 102. The snubber circuit 102 acts to limit voltage that could cause an arc across an open contact of the switch 166 when the switch is transitioned between an open condition and a closed condition, or between a closed condition and an open condition. This voltage threshold is chosen to limit burning and chemical breakdown to prevent deposition of the carbon residue on the contacts of the switch 166.

[0042] With respect to FIG. IB, a circuit 100 having a snubber circuit 102 is shown, according to an embodiment disclosed herein. In one implementation, the electronic snubber circuit 102 reduces the contact resistance of microswitches used to indicate the state of a physical parameter, such as pressure or temperature in applications such as aerospace measurement switches. In one embodiment, the snubber circuit 102 may essentially eliminate an incidence of increasing contact resistance and error in measurement in high temperature, high vibration environments. In one embodiment, the snubber circuit 102 may be low cost with a small footprint.

[0043] In circuit 101, the parasitic inductance L3 112 is connected in series with the power supply 118. The parasitic inductance C2 112 is connected in parallel across the parasitic capacitance 114. The sense resistor R3 116 is connected in series with the switch 110. The snubber circuit 102 is connected in series with the switch 110. In some embodiments, the parasitic inductor 112 may have a value of about 300 microhenry. In some embodiments, the parasitic capacitance 114 may have a value of about 0.1 picofarad. In some embodiments, the sense resistor 116 may have about three-thousand Ohms resistance

[0044] In the snubber circuit 102, the resistor R2 104 and capacitor Cl 108 are connected in series. The first diode D1 106 is connected in parallel across the resistor 104. The second diode D2 107 is connected in parallel across the capacitor 108. In some embodiments, the resistor 104 may have about two hundred-sixty Ohms resistance. In some embodiments, the capacitor 108 may have a value of about 0.01 microfarad.

[0045] A parasitic inductance 112, a parasitic capacitance 114, a sense resistor 116, and a power supply 118 are configured to simulate the wiring connections and power sense circuits to provide a typical transient characteristic. The parasitic inductance 112 and the parasitic capacitance 114 form a parasitic simulator 113.

[0046] The polarity of the diodes 106, 107 in the snubber circuit 102 are chosen to snub a ringing signal. The values of all components 104, 106, 107, 108 in the snubber circuit 102 in combination are determined based on arc energy causing chemical breakdown or ignition. Snubbing to eliminate welding may not be sufficient to prevent this breakdown. Determining how to analyze the circuit is disclosed further in FIGS. 4A-4B. This disclosed method and value determination results in an elimination of chemical breakdown and deposition of carbon insulation between the electrodes of the switch 110 that will also eliminate the arc welding. [0047] The parasitic inductance 112 and the parasitic capacitance 114 that form the parasitic simulator 113 simulate the parasitic inductance and parasitic capacitance seen in a wire or wire harness of a setup. The values of the parasitic inductance 112 and the parasitic capacitance 114 may change between wire length and physical construction of the installation. The values of the parasitic inductance 112 and the parasitic capacitance 114 may be chosen to present a transient voltage spike in a simulation that would represent an arc that would cause burning or chemical breakdown of atmospheric organic compounds on contacts 122, 123 of the switch 110. Power supply 118 may be a power supply seen in applications such as aircraft. The sense resistor 116 may be a sense resistor or load where a voltage drop across the sense resistor 116 for the switch 110 open condition or closed condition may be sensed.

[0048] The switch 110 is the switch to be operated in determining some system state, such as a temperature or pressure detection system set point. An SPDT switch may include a normally closed contact 123 and a normally open contact 122. When the switch 110 is normally closed, the components in the snubber circuit 102 may reach a steady state zero state. This means that the capacitor 108 will discharge through resistor 104 to zero volts.

[0049] When the switch 110 transitions to the normally open condition, normally closed contact 123 opens to high impedance. On opening, the energy stored in the system wiring parasitic inductance 112 will start to build up a voltage spike. The combination of energy in parasitic inductance 112 and system parasitic capacitance 114 will oscillate with a sine wave to a high voltage peak. Any negative going transient will be clamped by the second diode 107, which may be a Schottky diode. Current may be limited by the series sense resistor 116 and the energy may be dissipated in the sense resistor 116 and the second diode 107.

[0050] Positive going spikes may pass through the first diode 106 and resistor 104 into capacitor 108. Capacitor 108 may act as a short circuit to the transient with an exponentially increasing value determined by the time constant of the sense resistor 116 and the capacitor 108. These values may be chosen so that the predominant effect is for the voltage to be clamped by the first diode 106. The determination of the value of the capacitor 108 and the sense resistor 116 may be critical to the limiting of voltage that could cause an arc across the open contact 123 of the switch 110. This voltage threshold may be chosen to limit burning and chemical breakdown to prevent deposition of the carbon residue on the open contact 123 of the switch 110. [0051] Resistor 104 may be selected to achieve one of two goals. The first goal is to provide a current of sufficient magnitude if desired, to break through any residual carbon contaminant and burn this away when the switch 110 is closed again. When the switch 110 is open for greater than roughly 5 R3C1 time constants, the capacitor 108 voltage will be that of the 28 volt power supply 118. Selecting the resistor 104 to achieve this current burning effect may eliminate any residual carbon that is deposited on the contacts 122, 123 of the switch. The second goal is a better practical practice, to prevent any contact resistance heating. This may be selected if the system parameters are known sufficiently to be sure that the carbon arc does not bum or break down atmospheric organics. When that is achieved, the value of the resistor 104 may be selected to be a small current during closure of the switch 110 to prevent any current heating of the gold to gold electrode contact resistance. This disclosed system and method solves the fundamental issue with increasing contact resistance as described.

[0052] In one embodiment, the snubber circuit 102 may include a resistor 104; one or more diodes 106, 107, such as Schottky diodes; a capacitor 108; and a switch 110. In another embodiment, other configurations of the disclosed snubber circuit 102 may be used to limit the maximum voltage generated from an inductive transient as the flow of current is interrupted by opening the electrical switch 110. These configurations may include a low threshold transistor or voltage mirroring circuits, which may generate opposite polarity voltage to an arc.

[0053] In one embodiment, a current may flow in a measurement system such as from a 28 volt supply in an aircraft. A physical sensing device may respond to a measured parameter, such as a spring pushing against a diaphragm in contact with a pressure media. As the media (e.g., fluid) pressure increases or decreases, a moveable structure contacts a spring loaded switch. As the pressure passes a threshold, through a number of different methods, the switch 110 may be activated to change states.

[0054] In the case where an electrical switch, such as a switch 110 that increases in impedance was closed and current was flowing, when the switch 110 state changes to open, and the current may be interrupted. Interrupting the current in the circuit 100 that typically has inductance through the wiring may be an intentional or a parasitic element, may cause the current flow to go to about zero, and may cause the voltage to increase to a high value (possibly hundreds or thousands of volts). This high value of voltage is called “arcing”.

[0055] The arcing typically occurs during the movement of the switch 110 contacts 122, 123 away from the closed position. The contacts 122, 123 of the switch 110 are depicted as small circles. Several variations on contacts 122, 123 of the switch 110 are further shown in FIGS. 5, 6, and 7. Opening the switch 110 contacts 122, 123 while a current was flowing interrupts the flow of current through the wiring inductance and resistance. This instantaneous or fast turn off causes the voltage generated by the collapsing field of stored magnetic energy to create a fast-rising transient through the inductance. Depending on the rate of collapse of this field in the inductor, the voltage can rise quickly and to very high voltages. The rate of change of the voltage spike depends on the inductance of the wiring and the speed of the open contact interruption of the current. During the time the voltage builds up, the mechanical switch 110 contacts 122, 123 may move from the closed position before sufficient voltage is generated to break down the atmosphere surrounding the contacts 122, 123. At some point during the switch 110 opening and the contacts 122, 123 moving from the closed to fully open position, the voltage becomes high enough to arc across the open contact area.

[0056] At the point where the arc occurs, any organic compound held within the atmosphere may be broken down to carbon, oxygen, hydrogen or other elements and form a new insulating compound that deposits around the arc and contact point. The chemical process is burning by igniting an organic in oxygen or air, but may also be a heat induced chemical breakdown and/or electrical induced breakdown. The predominant insulating element remaining is carbon. Oxygen, Hydrogen, or other trace elements typically will not permanently adhere to the surface. Note that a secondary effect of eliminating the arc is to eliminate micro welded surface roughness. Surface roughness can allow increased mechanical adhesion for the carbon deposition.

[0057] In one embodiment, the topology (electrical connections) of the resistor 104, the capacitor 108, and the diodes 106, 107 of the snubber circuit 102 may be selected based on a typical rate of change of the voltage spike and the mechanical movement characteristics. These values may be in the microsecond range for arc generation. Generally, outgassed materials found in the manufacture of contact switches have shown that the contact switches consist primarily of organic compounds from potting, PCB materials, adhesives, plastics, resins, wire insulation, solder flux residue, machine cutting oil, and trapped water. These materials break down under arcing with voltages as low as 0.5 volts.

[0058] In addition, with some contact materials such as Rhodium, Platinum and Palladium, materials may form polymers under only the energy of contact rubbing, so-called “contact polymerization.” This contact polymerization is not significant with gold contacts, but may require an amount of energy generated by effects such as arcing at the 0.5 volt level. [0059] Given this understanding of the arc generating voltage activation, the mechanical movement speed, and the rate of change of typical arc waveforms, values for the components (e.g., the resistor 104, the capacitor 108, and the diodes 106, 107 of the snubber circuit 102) may be selected to prevent sufficient voltage build up over time to prevent breakdown of the atmosphere and arc generation. In one embodiment, the threshold required to cause outgassing breakdown and generation of an insulating layer over the gold contacts may be prevented with the low voltage diodes 106, 107 and the RC time constant values. RC time constant values may be in a 100 ohm to 1,000 ohm range for resistance and a 0.001 uf to 0.1 uf range for capacitance.

[0060] The snubber circuit 102 may further include a power supply having a parasitic inductance 112, a parasitic capacitance 114, and a sense resistor 116.

[0061] In normal operation, without the snubber circuit 102, a closed contact of switch 110 is created by the state of a measured quantity such as a measured pressure by hardware (not shown). The closed contact causes current to flow from a 28-volt supply 118, which is typical for Aerospace applications through the switch 110 contacts 122, 123.

Sensing the voltage between a power return 120 and the right side of sense resistor 116 will indicate a low voltage for the correct operating condition. This low voltage represents the voltage drop across the impedance of the switch 110, which is ideally on the order of 100 milliohms. This impedance causes the sense voltage to be approximately zero volts.

[0062] When the physical parameter being measured causes the switch 110 to change to an open state, the impedance becomes infinite. This infinite impedance will cause a sense point of sense resistor 116 to drop to about zero current and indicate the full 28 volts.

[0063] In one embodiment, during the transition between closed and open, the transient voltage created by the stored energy in the parasitic inductance 112 and parasitic capacitance 114 may increase and ring. The peak voltage in the circuit 100 may depend on the actual value of these elements but may reach several hundred volts. In one example, the voltage may reach about 450 volts. FIG. 3 shows a model of electrical ringing fairly typical in applications with wires or harnesses several feet in length. With the integration of the snubber circuit 102, the voltages remain near zero in the closed position and do not overshoot the power supply 118. This is the circuit response modeled in FIG. 4. Additionally, there is no discernable arc voltage produced that is capable of bridging the contact gap and causing deposition of outgas material.

[0064] In one embodiment, the diodes 106, 107, such as Schottky diodes, may be a semiconductor diode formed by the junction of a semiconductor with a metal. In one embodiment the second diode 107 is provided to clamp any negative voltage excursions in a ringing system. The first diode 106 is the clamping diode previously described to limit peak voltage to low values about 0.25 typical for a Schottky diode.

[0065] With respect to FIG. 2, a graph 130 shows the voltage measured across the circuit (100, FIG. IB). An x-axis 140 shows units of time in milliseconds (ms) and a y-axis 142 shows the voltage measured across the snubber circuit (102, FIG. IB) in volts (V). There is a slow ramp up of the voltage after approximately 2.5ms from a closed state (0V) to an open state (about 28V). The voltage does not increase far enough or fast enough to bridge the gap of the moving contacts.

[0066] With respect to FIG. 3, a graph 150 shows the response of the circuit (100,

FIG. IB) without the snubber circuit (102, FIG. IB) included. An x-axis 152 shows units of time in milliseconds (ms) and a y-axis 154 shows the voltage measured across the circuit 102 in volts (V). A ringing feature 156 is present and there is fast ramp-up of voltage exhibited, which is sufficient in voltage and rate to induce arcing as the switch (110, FIG. IB) contacts (122, 123, FIG. IB) separate. Therefore, it is clear that the snubber circuit (102, FIG. IB) provides for mitigating the voltage as to not allow the current to bridge the cap of the moving contacts.

[0067] With respect to FIGS. 4A-4B, a flow chart of a method 200, 201 for determination of contact resistance problems in a switch or microswitch is shown. The method 200, 201 of FIGS. 4A-4B shows an algorithm used to characterize the unknown cause that leads to determining how to eliminate the high impedance condition. By performing this analysis, the common causes of high impedance stated in the industry are found to be incorrect. The common understanding is that contact arcing causes micro welding to occur. While micro-welding does occur and can lead to failure due to erosion of the gold top layer which exposes nickel substrate which then oxidizes to be an insulator, this has not been the finding as the major cause of early high impedance. This is an insulation layer that builds up over the gold surface.

[0068] The disclosed method 200, 201 for determining the design parameters for the snubber circuit solves the high contact impedance root cause. At least one switch is located which exhibits a high impedance contact characteristic (step 202). The history of service of the least one switch may be recorded to document the environment (step 204). Environments where switches showed the high impedance may be compared to those where there were no failures in service (step 206). The impedance may be traced to a source (step 208). Tracing of the impedance may rule out connector or interconnect as the cause of contact resistance issues, internal wire connections and solder joints, as well as all elements other than the switch itself.

[0069] In one embodiment, commonality among switches that exhibit the high impedance occur at temperatures over 70 degrees Celsius in high vibration conditions. The switch may be torn down and inspected to locate the cause of high impedance (step 210). Many types of switches may exhibit the effects described. One type includes switches that have integral cantilevered springs that provided a two-state contact condition as in Single Pole Double Throw (SPDT) switches. These switches have one contact normally closed, a lower contact with a contact in a center piece, and one contact on each side of the conductive cantilever. The second contact (top of cantilever and a second top contact) is normally open. The result showed the increased impedance of the closed contact. The normally open contact did not show high impedance. The high impedance contact may be examined for wear, such as exposed base metal under gold (step 212). In one embodiment, the metal may be nickel over beryllium copper. A connection between the method 200, 201 in FIGS. 4A and 4B is shown with reference to character A.

[0070] In one embodiment, an elemental analysis may be performed of the contact area and surrounding areas (step 214). If the high impedance contact area shows a carbon- based layer of insulator, and the surrounding areas of the switch and the normally open contact show no discernable contaminant, then there may be no migration of contaminant, gold wear, oxidation of base metal. Therefore, these elements may be eliminated as potential causes of contact resistance.

[0071] A theory may be proposed to explain why there would be a carbon-based insulator only at the normally closed contact area that created a high impedance was made (step 216). The carbon-based insulator may be due to either mechanical motion induced by the vibration or electrically induced arcing caused by material in the atmosphere surrounding the switch to deposit at the normally closed contact.

[0072] A search may be performed to find reports of contact polymerization in switch contacts made of metals such as Palladium, Rhodium and Platinum where there exists an atmosphere of outgassed carbon-based materials (step 218). In one embodiment, gold has been found to not show this effect. In order to test the theory of arcing in an atmosphere, an electronic snubber circuit may be developed, such as electronic snubber circuit that limits maximum arc voltage to 0.25V, which is below a reported 0.5 activation voltage for causing chemical reactions (step 220). The snubber circuit may slow and attenuate the arc through the limitation of current through the resistor, slow the response by the R-C time constant, and clamp the voltage and set the direction through the Schottky diodes (See the resistor 104, the capacitor 108, and the diodes 106, 107 of FIG. IB).

[0073] Tests may be performed with switches of similar configurations as the switches that exhibit increasing contact resistance with time (step 222). In one embodiment, the tests may consist of switches powered as in the failed configuration with high vibration.

In one embodiment, the circuits may be run at elevated temperatures, such as 135 degrees C, and room temperature.

[0074] Circuits with the snubber circuit may be added and run under the same conditions (step 224). In one embodiment, no resistance increase is found in such circuits, even for a 5 times longer period. This threshold may vary for different types of organic atmospheres, concentrations, and/or temperatures. All that is needed is an arc of sufficient energy produced by routine opening and closing. Being close to a threshold may not matter as long as it goes from no arc-to-arc discharge. Only the arc discharge causes sufficient energy to activate the action. The arc only occurs on opening or in contact bounce.

[0075] FIGS. 5, 6, and 7 depict various contacts for a snubber circuit. Opening the switch contacts while a current was flowing interrupts the flow of current through the wiring inductance and resistance. This instantaneous or fast turn off causes the voltage generated by the collapsing field of stored magnetic energy to create a fast-rising transient through the inductance. Depending on the rate of collapse of this field in the inductor, the voltage can rise quickly and to very high voltages. The rate of change of the voltage spike depends on the inductance of the wiring and the speed of the open contact interruption of the current. During the time the voltage builds up, the mechanical switch contacts may move from the closed position before sufficient voltage is generated to break down the atmosphere surrounding the contacts. At some point during the switch opening and the contacts moving from the closed to fully open position, the voltage may become high enough to arc across the open contact area.

[0076] FIG. 5 depicts a cross-sectional view of contacts in a snubber circuit 500. The contacts include a normally closed (NC) contact 502, a normally open (NO) contact 504, and a moveable contact 506. A contact gap 508 is present between the moveable contact 506 and the NO contact 504. The moveable contact 506 may move between contacting the NC contact 502 and the NO contact 504. Contaminants may form at a point of contaminant 510 where the moveable contact 506 contacts the NC contact 502 and/or the NO contact 504 (not shown). The moveable contact 506 is depicted as having a circular cross section. Other cross section sizes and shapes for the moveable contact 506 are possible and contemplated. [0077] FIG. 6 depicts a cross-sectional view of alternate contacts in a snubber circuit 600. The contacts include a normally closed (NC) contact 602, a normally open (NO) contact 604, and a moveable contact 606. A contact gap 608 is present between the moveable contact 606 and the NO contact 604. The moveable contact 606 may move between contacting the NC contact 602 and the NO contact 604. Contaminants may form at a point of contaminant 610 where the moveable contact contacts the NC contact 602 and/or the NO contact 604 (not shown). The moveable contact 606 is depicted as having a rectangular cross section. Other cross section sizes and shapes for the moveable contact 606 are possible and contemplated.

[0078] FIG. 7 depicts a cross-sectional view of alternate contacts in a snubber circuit 700. The contacts include a normally closed (NC) contact 702, a normally open (NO) contact 704, and a moveable contact 706. A contact gap 708 is present between the moveable contact 706 and the NO contact 704. The moveable contact 706 may move between contacting the NC contact 702 and the NO contact 704. Contaminants may form at a point of contaminant 710 where the moveable contact contacts the NC contact 702 and/or the NO contact 704 (not shown). The moveable contact 706 is depicted as asymmetrical and having a triangular cross section. Other cross section sizes and shapes for the moveable contact 706 are possible and contemplated.

[0079] It is contemplated that various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further, it is intended that the scope of the present invention herein disclosed by way of examples should not be limited by the particular disclosed embodiments described above.