US 20170178825A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2017/0178825 A1 GLOSSER et al. (43) Pub. Date: Jun. 22, 2017

(54) UNIVERSAL CONTACT INPUT Publication Classification SUPPORTNG PROGRAMMABLE WETTING (51) Int. Cl. CURRENT HIH IMO (2006.01) GOIR 31/327 (2006.01) (71) Applicant: GE Intelligent Platforms, Inc., H02. I3/00 (2006.01) Charlottesville, VA (US) HIH I/60 (2006.01) (52) U.S. Cl. (72) Inventors: Richard Joseph GLOSSER, Salem, CPC ...... H0IH I/0015 (2013.01); H0IH I/605 VA (US); Venkatesh J. Hyderabad (IN) (2013.01); G0IR 31/327 (2013.01); H02J 13/00 (2013.01) (21) Appl. No.: 15/327,189 (57) ABSTRACT A system and method according to various embodiments can (22) PCT Fed: Jul. 22, 2014 include a universal contact input status detection circuit. A Voltage source wets a contact with a wetting Voltage. A (86) PCT No.: PCT/US2O14/0476OO current mirror circuit is connected across an input of the contact to provide a constant wetting current over a wide S 371 (c)(1), input Voltage range. The input voltage can be varied over a (2) Date: Jan. 18, 2017 range wide enough to include both AC voltages and DC Voltages. The current mirror circuit maintains the constant wetting current during varying wetting Voltage inputs across Related U.S. Application Data the input of the contact. A wetting Voltage sensor senses the (63) Continuation-in-part of application No. PCT/ wetting voltage provided to the contact so that the status of US2014/047223, filed on Jul. 18, 2014. the contact can be determined.

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102 104 Wetting Wetting Voltage Voltage Sense 106 118 120

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500

Passing a Wetting Voltage through the Contacts 502

Rectifying AC to DC, when an AC wetting 504 Voltage is used

Maintaining the wetting current constant using 506 a Current mirror circuit

Scaling down the Wetting voltage 508

Comparing the Wetting Voltage to a reference 510 Wetting Voltage FIG. 5 US 2017/0178825 A1 Jun. 22, 2017

UNIVERSAL CONTACT INPUT minimum current needed to flow through a contact to break SUPPORTNG PROGRAMMABLE WETTING through any film (contact oxidation) that may have been CURRENT deposited on the switch. Typically, this has been performed by different group of boards connected in order to Support a I. FIELD OF THE INVENTION wide range of contact input voltages. 0001. The present invention relates generally to control III. SUMMARY OF THE INVENTION ling a process. More particularly, the present invention 0008 Given the aforementioned deficiencies, a need relates to monitoring electrical contacts, especially relays, exists for a single circuit, capable of monitoring Switches, in and detecting the status of electrical contacts used in an general, and relay contacts, in particular, to determine the industrial or commercial process that are wetted with alter status of the contacts. There also remains a need for a single nating current (AC) voltage or direct current (DC) voltage. contact status detection circuit, which is capable of Support ing contact input voltage ranges, including both AC and DC II. BACKGROUND OF THE INVENTION Voltages. 0002. Over the years, a full range of relay products from 0009. A further need exists for a single circuit capable of highly specialized relays for communication equipment to maintaining constant wetting current across a wide input general-purpose relays have been designed to control nearly range. In addition, a need remains to provide a constant every function in commercial and industrial processes used current across a contact input (digital input) over a wide in everything from household appliances to industrial Voltage range as a means to abate contact oxidation (corro machinery. A power generation plant is one example of an sion/increased impedance) and improve reliability of the industrial process in which a large number of relays are used. signal chain. The relays in a power generation plant can be used to control 0010. A system according to various exemplary embodi a wide variety of equipment Such as motors, pumps, Sole ments can include a universal contact input status detection noids and lights. However, even the best relays may fail at circuit, comprising a Voltage source that wets a contact with Some point. a wetting Voltage. A wetting Voltage sensor senses the 0003. In the example scenario above, a control system wetting Voltage provided to the contact. A current mirror needs to monitor the relays within the power plant to circuit is connected across an input of the contact to provide determine their status in order to ensure that certain func a constant wetting current over a wide input voltage range. tions associated with the process are being performed. In The input Voltage can be varied over a range wide enough particular, contact input status detection circuits are used to to include both AC voltages and DC voltages. The current detect the status of relay contacts when in use in the field. mirror circuit maintains the constant wetting current during The contact input status detection circuit monitors provide varying wetting Voltage inputs across the input of the an indication of potentially degraded electrical relay perfor contact. A divider Scales down the wetting Voltage. A comparator that compares the wetting Voltage to a reference mance due to contamination. wetting Voltage to provide a digital output Voltage. A pro 0004. In industrial environments, contamination rou cessor determines the status of the contact in accordance tinely interferes with the operation of the relay's contact. with the digital output voltage. The detection circuit is Contaminants, which can include oxidation films or foreign integrated on a single circuit board configuration. particles, tend to produce contact resistance readings that are 0011. A method of detecting a status of a contact accord either high or unstable. Contamination commonly happens ing to various exemplary embodiments can include wetting with low current applications, usage in high temperature and a contact with a wetting Voltage; sensing the wetting Voltage humidity environments, and during extended periods of provided to the contact; providing a constant wetting current Storage. across an input of the contact over a wide input voltage 0005 For example, in small currents and low voltage range; maintaining the constant wetting current during vary applications, oxidation of relay contact is simply a buildup ing wetting Voltage inputs utilizing a current mirror con of corrosion on relay contact surfaces over a period of time. nected across an input of the contact, Scaling down the The contacts develop oxidation, which is a thin layer of wetting Voltage; comparing the wetting Voltage to a refer oxide on the contact Surface. It causes problems by increas ence wetting Voltage to provide a digital output voltage; and ing the resistance across the contacts which, depending on determining the status of the contact in accordance with the the amplitude of the Voltage being Switched, can cause loss digital output voltage. The detection of the status of the of signal or overheating of the contacts. contact is implemented on a single circuit board. 0006. Oxidation on relay contacts is especially a problem 0012. Further features and advantages of the invention, as with Small currents and low Voltages, because they cannot well as the structure and operation of various embodiments punch through the oxide layer once it accumulates and of the invention, are described in detail below with reference becomes too thick. However, higher Voltages may punch to the accompanying drawings. It is noted that the invention through the oxidation layer during relay Switching. Thus, the is not limited to the specific embodiments described herein. issue with Switch contacts is Voltage. Current through the Such embodiments are presented herein for illustrative pur contact is strictly a function of the Voltage and the imped poses only. Additional embodiments will be apparent to ance of the circuit the contact completes. By varying the persons skilled in the relevant art(s) based on the teachings current, the Voltage varies. Once the Voltage is great enough, contained herein. the punch through Voltage is achieved. 0007. One conventional approach to resolve this issue for IV. BRIEF DESCRIPTION OF THE DRAWINGS Small currents and low current applications is by passing the 0013 FIG. 1 shows a schematic diagram of an exemplary required wetting current through the relay contacts so that it circuit used to detect the status of an electric contact in punches through the oxide layer. The wetting current is the accordance with the present teachings; US 2017/0178825 A1 Jun. 22, 2017

0014 FIG. 2 is a schematic circuit diagram of an exem Supporting universal contact input voltage range, including plary contact status detection circuit in accordance with the both AC and DC voltages, and maintaining a constant present teachings; wetting current across a wide input range. 0015 FIG. 3 is another exemplary embodiment of a 0025 Various embodiments provide a system and schematic circuit diagram of a contact status detection method that provides a constant wetting current across a circuit in accordance with the present teachings; wide input range. Various embodiments provide a configu 0016 FIG. 4 is yet another exemplary embodiment of a rable wetting current. schematic circuit diagram of a contact status detection 0026. In various embodiments, a system and method circuit in accordance with the present teachings; and provides a constant current across a contact input (digital 0017 FIG. 5 is a flowchart of an exemplary method of input) across a wide Voltage range as a means to abate practicing the present invention in accordance with the contact oxidation (corrosion/increased impedance) and present teachings. improve reliability of the signal chain. Various embodiments 0018. The present invention may take form in various disclose a method that creates a Software and firmware components and arrangements of components, and in vari programmable wetting current and a method for multi-stage ous process operations and arrangements of process opera wetting currents. Various embodiments disclose a system tions. The present invention is illustrated in the accompa and method for monitoring the status of wetting Voltage and nying drawings, throughout which, like reference numerals wetting current. may indicate corresponding or similar parts in the various 0027 FIG. 1 is a schematic diagram of a contact status figures. The drawings are only for purposes of illustrating detection circuit 100 used to detect the status of an electric preferred embodiments and are not to be construed as contact (hereinafter "contact’) as used, for example, in an limiting the invention. Given the following enabling industrial or commercial process according to one embodi description of the drawings, the novel aspects of the present ment of the present invention. As used herein, a contact is an invention should become evident to a person of ordinary electrical component for joining electric circuits together or skill in the art. breaking the circuits by interrupting or diverting the current from one conductor to another. Examples of contacts include V. DETAILED DESCRIPTION OF VARIOUS electrical components such as Switches, relays, terminals EMBODIMENTS and connectors. 0019. The following detailed description is merely exem 0028. One example of an industrial process in which plary in nature and is not intended to limit the applications embodiments of the present invention is suitable for use is and uses disclosed herein. Further, there is no intention to be with a power generation plant where a large number of bound by any theory presented in the preceding background contacts are used to control a wide variety of equipment Such or Summary or the following detailed description. as motors, pumps, Solenoids and lights. Those skilled in the 0020. Throughout the application, description of various art will recognize that embodiments of the present invention embodiments may use “comprising language, however, it are applicable to other industrial processes where contacts will be understood by one of skill in the art, that in some are used to control the operation of process equipment and specific instances, an embodiment can alternatively be where it is desirable to ascertain the status of Such contacts described using the language "consisting essentially of or for the purpose of sequence of events (SOE) analysis. “consisting of.” 0029. Some of the exemplary features provided by detec 0021 For purposes of better understanding the present tion circuit 100 include a constant wetting current across a teachings and in no way limit the scope of the teachings, it wide input Voltage range, a system configurable wetting will be clear to one of skill in the art that the use of the current, and a single circuit board configuration capable of singular includes the plural unless specifically stated other Supporting a wide input voltage range. wise. Therefore, the terms “a,” “an and “at least one' are 0030. As shown in FIG. 1, detection circuit 100 provides used interchangeably in this application. a single circuit configuration to Support a universal contact 0022. Unless otherwise indicated, all numbers expressing having an input voltage range which permits both AC and quantities, percentages or proportions, and other numerical DC and is capable of maintaining a constant wetting current values used in the specification and claims, are to be across the wide input range. The “universal designation understood as being modified in all instances by the term indicates that the circuit is configurable to detect the status "about.” Accordingly, unless indicated to the contrary, the of relays controlling various devices. Detection circuit 100 numerical parameters set forth in the following specification provides a constant current across a contact input (digital and attached claims are approximations that may vary input) across a wide Voltage range as a means to abate depending upon the desired properties sought to be obtained. contact oxidation (corrosion), which increases the imped In some instances, “about can be understood to mean a ance and improves reliability of the signal chain. given value +5%. Therefore, for example, about 100 nm, 0031 Traditionally, the wetting current was provided by could mean 95-105 nm. At the very least, each numerical static resistor combinations requiring multiple resistor popu parameter should at least be construed in light of the number lations to achieve the desired currents. In contrast, circuit of reported significant digits and by applying ordinary 100, in addition to the various embodiments described in rounding techniques. accordance with the present teachings, provides a constant 0023 Various embodiments provide a system and current across a wide range of Voltage with a single circuit method consisting of a single circuit, which is capable of realization (non-changing). This eliminates the need to pro monitoring Switches, in general, and relay contacts, in duce and maintain customized circuit variants on a per particular, to determine the status of the contacts. wetting Voltage basis. 0024. Various embodiments provide a system and 0032. Additionally, detection circuit 100 is capable of method consisting of a single circuit, which is capable of implementing various methods of operation. For example, in US 2017/0178825 A1 Jun. 22, 2017

various embodiments, circuit 100 performs a method of from a voltage spike. A bridge rectifier AC/DC 110 can be operation for both DC and AC wetting voltages. Various incorporated in circuit 100 in various embodiments to embodiments provide a method to create a programmable accommodate AC wetting Voltages, as well as DC voltages. software/firmware (SW/FW) wetting current. 0041. A constant current 112 is provided across the 0033. Furthermore, circuit 100 is capable of implement contact input 106 (digital input) across a wide Voltage range ing a method of monitoring the status of wetting Voltage and as a means to abate contact oxidation (corrosion), increase wetting current. The “wetting Voltage' (also known as impedance, and improve reliability of the signal chain. The “sense Voltage) is the Voltage provided to electrical contacts constant current 112 across the varying wetting Voltage for status detection. The wetting voltage is used to detect the inputs is accomplished by the use of a current mirror across operation of either a contact opening or closing. the input section of the contact input 106 (digital input). The 0034. To monitor the status of the electrical contacts, an use of the current mirror forces the input to draw a current electrical voltage (e.g. a direct current Voltage (DC) or an from the wetting voltage source 102 as a function of the alternating current (AC) Voltage) is sent to the contacts in the constant current 112 within the detection circuit and not a field to determine whether this voltage can be detected. function of the input impedance of the detection circuit. Detecting the Voltage is an indication that the electrical 0042. In contrast, known prior attempts have focused on current is on or off. the source current in the wetting Voltage system for provid 0035. As discussed above, if the contact is operated in a ing a constant current output. In these conventional tech low Voltage application, the contacts will tend to accumulate niques, since wetting Voltage is typically applied as a bulk excessive resistance and may fail prematurely. In order to Source, it has become a requirement to Support as many keep the switch in good health, the “wetting current is the constant current wetting Voltage sources as there are contact minimum current needed to flow through a contact to break input circuits. This leads to a reduction in system flexibility. through any film (contact oxidation) that may have been 0043 Referring back to FIG. 1 according to the present deposited on the switch. teachings, a programmable resistance can also be provided 0036. Thus, detection circuit 100 is capable of detecting within the constant current 112. The programmable resis status conditions that include whether the contact is closed, tance in the internal constant current 112 can be varied to the contact is open, or the contacts are contaminated due to provide a software/firmware (SW/FW) programmable corrosion (oxidation). means in order to change the constant input current. 0037 Detection circuit 100 also is capable of performing 0044) A voltage divider and a resistor-capacitor (RC) a method for multi-stage wetting currents, wherein initial filter 114 scales down the wetting voltage and the output is higher currents are applied for punch through with second fed to a comparator 116 for comparison to a reference ary lower currents. It is advantageous to have initial currents wetting Voltage. The output of the comparator is passed higher than nominal wetting currents to provide a means to through a digital isolator 118 (opto-isolator) to a field punch through existing oxidation (corrosion) on external programmable gate array (FPGA) and processor 120, which contact tips and then fall back to the desired constant current detects the contact status and informs (declares) the system. level. The option for multiple current set points is not 0045 FIG. 2 shows a circuit diagram that depicts the available for a static input impedance circuit realization used operation of the detection circuit 100 shown in FIG. 1. In in conventional circuits. various embodiments, a wetting Voltage is used to drive a 0038. In comparison, conventional circuits derive a wetting current to abate the occurrence of high impedance nominal input current utilizing static resistance to common across the contacts connected to the contact input (digital (ground, earth, etc.) which are produced and maintained as input) of the detection circuit 100. In FIG. 2, wetting voltage separate input types for discrete wetting Voltages (nominal 102 is passed through the customer contacts 106 to sense the 24 VDC, 48 4 DC, 125 VDC, etc.). With tolerance on the status of relay contacts 106. Bridge rectifier 110 rectifies AC nominal Voltages, the wetting current derived will also vary to DC when AC wetting voltage is used. A current mirror due to the static resistance. Additionally, a conventional circuit keeps the wetting current constant 112. Voltage circuit for 24 VDC input will have half (A) the current of a divider 114 scales down the voltage so that comparator 116 48 Volt realization (due to the static input impedance) and compares it with reference wetting Voltage to detect the will require either a separate 48 volt implementation. Such COntact Status. a conventional circuit will also require use of different 0046. In FIG. 2, the current mirror replicates the input currents for differing wetting Voltages and in all cases will current to make a copy as an output current. Accordingly, require the acceptance of varying current with Voltage resistor R1 on the left changes the current flow in the left tolerance. half, which is mirrored in the right half by the current mirror 0039. In reference to FIG. 1, detection circuit 100 incor circuit. Irrespective of the wetting Voltage, the wetting porates a Switch, such as a relay, having a pair of contacts current is maintained constant. The current mirror serves as 106. Wetting voltage sense 104 is used as a sensing circuit a simple current regulator, Supplying nearly constant current for contact sensing. The status of contacts is typically over a wide input Voltage range. monitored by sending an electrical Voltage such as DC 0047 Resistors R4 and R5 scales down the voltage. The voltage or AC voltage in the field to the contacts and then RC filter 114, which is composed resistors R4 and R5 and determining whether this voltage can be detected. The capacitor C1, is incorporated in the circuit for bypassing wetting Voltage is the Voltage applied to a contact in order unwanted signals and for providing debouncing to filter out to detect its status, as discussed above. the rapid changes in the Switch output. The scaled down 0040 Wetting voltage 102 is passed through the contacts voltage is compared by the comparator 116 with reference 106 to sense the status of relay contacts 106. Input terminals wetting Voltage 122. The comparator 116 output is passed to (not shown) of the contacts 106 receive the wetting voltage the FPGA 120 through digital isolator 118 for detecting the 102 (AC/DC). A surge protection 108 protects the circuit contact status and declaring it to system. US 2017/0178825 A1 Jun. 22, 2017

0048. The detection circuit 100 can be implemented by customized by software when the constant current level is alternative methods. FIG. 3 is a circuit diagram, which determined to produce better abatement results at a different illustrates a first embodiment for implementing detection Setting. circuit 100. In FIG. 3, a wetting voltage 102 is passed 0055 An additional technical advantage is that the con through the contacts 106 to sense the status of relay contacts tact input health can be determined by varying the constant 106. Bridge rectifier 110 rectifies AC to DC when AC current input and monitoring for a change in detection state wetting Voltage is used. and an indication of unacceptable contact resistance (detects 0049 Current mirror circuit keeps the wetting current field contacts that are marginal). The contact input health constant 112. Current sense amplifier 124 senses the current check can be performed on a running input without the need and outputs the Voltage, which will be compared by com to interrupt the signal chain. parator 116 against wetting Voltage reference to detect the 0056 Alternative embodiments, examples, and modifi contact status. The digital signal is passed to the system cations which would still be encompassed by the invention through FPGA and processor 120. R1 is a programmable may be made by those skilled in the art, particularly in light resistor which can be used to self-test the response of the of the foregoing teachings. Further, it should be understood digital isolator 118. that the terminology used to describe the invention is 0050 FIG. 4 depicts a circuit diagram, which illustrates intended to be in the nature of words of description rather a second method for implementing detection circuit 100. In than of limitation. FIG.4, a wetting voltage is passed through the contacts 106 0057 Those skilled in the art will also appreciate that to sense the status of relay contacts 106. Bridge rectifier 110 various adaptations and modifications of the preferred and rectifies AC to DC when AC wetting voltage is used. A alternative embodiments described above can be configured current mirror circuit keeps the wetting current constant 112. without departing from the scope and spirit of the invention. Current sense amplifier 124 senses the current and outputs Therefore, it is to be understood that, within the scope of the the voltage, which in turn will drive the digital isolator 118 appended claims, the invention may be practiced other than to inform the system about the status of contacts through as specifically described herein. FPGA and processor 120. We claim: 0051 FIG. 5 is a flowchart explaining a method 500 for 1. A method of detecting a status of a contact, the method detecting the status of contacts according to the present comprising: teachings. In Step 502, a wetting Voltage is passed through wetting a contact with a wetting Voltage; the contacts to sense the status of the relay contacts. In Step sensing the wetting voltage provided to the contact; 504, a bridge rectifier rectifies AC to DC when AC wetting providing a constant wetting current across an input of the voltage is used. In Step 506, a current mirror maintains the contact over a wide input voltage range; wetting current at a constant level. In Step 508, a voltage maintaining the constant wetting current during varying divider scales down the wetting voltage. In Step 510, a wetting Voltage inputs utilizing a current mirror con comparator compares the scaled down wetting Voltage to a nected across an input of the contact; reference wetting Voltage to detect the contact status. Scaling down the wetting Voltage; 0052 Contact status detection circuits designed in accor comparing the wetting Voltage to a reference wetting dance with embodiments of the present invention have Voltage to provide a digital output voltage; and numerous commercial and technical advantages. For example, a commercial advantage of the circuit and method determining the status of the contact in accordance with is the ability to design, deploy and maintain a single contact the digital output voltage. input detection circuit which is applicable across the entire 2. The method according to claim 1, wherein the wide wetting Voltage range Supported, versus the need to employ input Voltage range comprises AC voltages and DC voltages. customized circuits for each nominal wetting Voltage. 3. The method according to claim 2, implementing the Improved performance is achieved with a simplified system detection of the status of the contact on a single circuit design. board. 0053. The use of the detection circuit in product designs 4. The method according to claim 1, further comprising simplifies manufacturing activities such as product assem providing the constant wetting current across the contact bly, product maintenance, and design maintenance. This input over the wide Voltage range to abate contact oxidation. eliminates the possibility of installing the wrong custom 5. The method according to claim 1, further comprising module in the field by mistake. In conventional circuits, implementing wetting current updates via at least one of a when each wetting Voltage is Supported by a custom circuit programmable Software and a programmable firmware. realization, the field replacements can install the wrong 6. The method according to claim 1, further comprising Voltage input circuit, which can be attributed to a plurality monitoring a status of the wetting Voltage and the wetting of error Sources to which the prior-art circuits are suscep Current. tible. 7. The method according to claim 1, further comprising 0054. One of several technical advantages is the ability to providing an initially high current to enable punch through provide a constant current, which is settable to a level of contact oxidation and Subsequently providing a lower determined to be most advantageous in contact oxidation constant current for preventing heating of the contact and (corrosion) abatement. Another technical advantage is the improving contact longevity. ability to provide a means to facilitate a higher current 8. The method according to claim 1, further providing a initially for punch through and then fall back to a lower programmable constant current source that is adjustable to setting to prevent heating/welding or improve contact lon another constant current level by Software in response to a gevity. A further technical advantage is to provide a pro determination that another level of constant current produces grammable constant current source that can be changed or better abatement results. US 2017/0178825 A1 Jun. 22, 2017

9. The method according to claim 1, further comprising 13. The circuit according to claim 12, wherein the detec determining the status of the contact input by varying the tion circuit is integrated on a single circuit board comprising constant current input and monitoring for a change in a the processor configured to control operation of the detec detection state. tion circuit. 14. The circuit according to claim 13, wherein the current 10. The method according to claim 1, further comprising mirror circuit provides the constant wetting current across performing a check on the status of the contact input during the contact input over the wide Voltage range to abate a running input without interrupting a signal chain. contact oxidation. 11. The method according to claim 1, further comprising 15. The circuit according to claim 13, wherein the wetting rectifying an AC wetting Voltage to a DC wetting Voltage, current is capable of being updated via at least one of a when the AC wetting voltage is received. programmable Software and a programmable firmware. 12. A universal contact input status detection circuit, 16. The circuit according to claim 13, wherein a status of comprising: the wetting Voltage and the wetting current is monitored. 17. The circuit according to claim 13, wherein an initially a Voltage source that wets a contact with a wetting high current is provided to enable punch through of contact Voltage; oxidation and Subsequently a lower constant current is a wetting Voltage sensor that senses the wetting Voltage provided for preventing heating of the contact and improv provided to the contact; ing contact longevity. a current mirror circuit connected across an input of the 18. The circuit according to claim 13, wherein a program contact to provide a constant wetting current over a mable constant current source is adjustable to another con wide input Voltage range and to maintain the constant stant current level by Software in response to a determination wetting current during varying wetting Voltage inputs that another level of constant current produces better abate across the input of the contact, wherein the wide input ment results. Voltage range comprises AC Voltages and DC voltages; 19. The circuit according to claim 13, further comprising wherein the status of the contact input is determined by a divider that scales down the wetting Voltage; varying the constant current input and monitoring for a a comparator that compares the wetting voltage to a change in a detection state. reference wetting Voltage to provide a digital output 20. The circuit according to claim 13, wherein a bridge Voltage; and rectifier rectifies the AC wetting voltage to the DC wetting a processor that determines the status of the contact in Voltage, when the AC wetting Voltage is received. accordance with the digital output Voltage. k k k k k