Abstract:
A detection system for remote monitoring of a contact condition comprises first, second, and third impedance means, and four comparators. Each impedance means is selectively coupled between the contact and the comparators. With a known voltage applied at the third impedance means, the three impedances produce a unique signal voltage at the comparators depending on a condition of the contact closure. Each comparator may detect one of the four unique voltages and produce an electrical signal corresponding to the detected condition, which may be converted into an optical signal, and be transmitted in a fiber optic cable to a receiver where it is converted back into an electrical signal. Four detectors are each adapted to detect one of the electrical signals, and trigger a relay and status LEDs, indicating a contact condition consisting of: normally open/closed, and short/open circuited. A fifth detector monitors for broken fiber optic cable.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority on U.S. Provisional Application Ser. No. 61/574,595 filed on Aug. 5, 2011, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to improvements in detection of fault conditions in an electronic system to be supervised, and more particularly to apparatus which are capable of providing remote indication of an electronic system&#39;s performance. 
     BACKGROUND OF THE INVENTION 
     There are many electronic applications today that are critical for the maintenance of personal safety and security, and whose undetected failure may pose grave risks for those who depend upon them. Such systems may encompass many different types of electronic applications, and may include burglar alarms, fire alarms, motors, pumps, valve controls, etc. An operational system may have a contact switch that may be closed to activate the system, or be opened to deactivate the system. System failure can occur through the result of a short circuit or an open circuit, and the failure may continue unabated and pose a threat, without notification to the party at risk. 
     For example, a fire alarm at a business or college dorm in a major metropolitan location may fail and send a signal to the local fire department, which responds by rushing to the scene, only to determine that being summoned was the result of a false alarm due to a short. In many cities and regions, the fire department charges the firm or school a fee for the unnecessary response. Unfortunately, faults in many such alarms are typically only detected under these kinds of circumstances, or worse yet, in an actual emergency, where the failure of the device may conversely result in no notice to emergency responders, so that the response may not occur at all, or only after a Good Samaritan personally makes a call to summon help. 
     The invention disclosed herein provides notifications to a receiver that is mountable in a convenient location for personnel to routinely monitor the status of the system, where the notification may be for a switch contact being normally open, normally closed, short circuited, or failed due to an open circuit. In addition, the invention disclosed herein provides notification that the connection providing remote monitoring of the system status is broken, and that monitoring is therefore no longer even occurring. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide a means of detecting a fault in an electronic system application. 
     It is another object of the invention to provide a means of detecting a normally open and a normally closed condition of a contact switch. 
     It is a further object of the invention to provide a means of detecting a fault condition in the form of an open circuit or a shorted circuit condition. 
     It is another object of the invention to provide a means of remote monitoring of a trouble condition in a system application switch contact. 
     It is also an object of the invention to provide a means of determining a failure in the communication enabling remote monitoring of trouble conditions. 
     It is another object of the invention to provide a means of remote monitoring of a trouble condition in a system application using fiber optic communications. 
     Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     A fault detection system for remote alarm status monitoring may be comprised of a transmitter unit, a receiver unit, and a suitable length of fiber optic cable to connect the transmitter to the receiver. The transmitter portion of the invention may comprise comparators. The comparators may be generic op amps with additional circuitry to do the comparator function, or, alternatively, a comparator chip can be used, or the comparator may comprise discrete logic or transistors. 
     In a preferred embodiment, the transmitter portion may comprise four comparators and input circuitry. The input circuitry may be in the form of three separate impedance means (which may be resistive, capacitance, or inductive), where the first impedance means may be placed in parallel with the contact closure to be monitored, the second impedance may be placed between the contact and the transmitter, and the third impedance may be placed between a voltage source, Vcc, and the receiver to be in parallel with the second impedance. With such an arrangement, the impedance values may be coordinated to produce different predictable voltage values at the comparators, Vx, for various conditions of the circuit. 
     For example, where the impedances are selected such that Z 1 =Z 2  and that Z 3 =2·Z 1 , and: where the contacts are open in a normal condition, the voltage at the comparators will be Vx=Vcc/2; where the contacts are in a normal condition, the voltage at the comparators will be Vx=Vcc/3.33; where there is an open circuit, Vx=Vcc; and where there is a short circuit, Vx=0. The comparator recognizing the specific voltage corresponding to a particular circuit condition may deliver an electrical signal to an encoder that converts the electrical signal into a modulated optical signal and transmits it through the fiber optic cable to the receiver, where it is decoded and detected to provide a visual signal, in the form of a LED, to alert the user as to the circuit&#39;s status. The system herein may be used to monitor four separate contact closures over a single optical fiber conductor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of the receiver, and transmitter of the current invention, shown being connected schematically with fiber optic cable. 
         FIG. 1A  is a prior art terminal block connector usable for the transmitter portion of the current invention. 
         FIG. 1B  is a schematic of the input wiring for channel no. 1. 
         FIG. 2  is a block diagram of the contact closure system of the current invention. 
         FIG. 3  is a schematic of the input circuitry of the current invention. 
         FIG. 4  is a schematic of receiver circuitry of the current invention. 
         FIG. 5  represents a typically fiber optic contact closure application. 
         FIG. 6  lists the technical specifications for one embodiment of the current invention. 
         FIG. 7  lists the power terminal block connections. 
         FIG. 8  lists the signal terminal block connections. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In many electronic applications, it is advantageous, if not critical, for the system to be supervised so that an observer may quickly be alerted to its status—whether it is fully operational and functional, being in a normal condition, or whether there is an electronic fault. It is also desirable for this notification to be delivered to a location remote from the system itself. Electronic faults may comprise a short circuit, an open circuit, or other fault condition, and may be reportable to the observer as a trouble condition. Moreover, it may be invaluable to the person monitoring an electrical system to also know the status of the supervising system—that it is fully functional and is actively monitoring the underlying system, and has not itself experienced an undetected failure. The present invention is therefore capable of remotely sensing valid states for a switch: intended close (on); intended open (off); unintended close (short); or unintended open (cut wires). 
       FIG. 1  shows a first embodiment of the present invention, which includes a transmitter  20 , receiver  40 , and cable  60 , which may preferably be a fiber optic cable, but may also be wire-a twisted pair or coax. Receiver  40  may comprise a housing  41  to support the electronic circuitry therein. The housing  41  may comprise a plurality of orifices to expose at least a portion of a plurality of LED indicator lights, which may include a power LED  43 , an alarm LED  44 , a link LED  45 , status LED numbers  1 - 4  ( 46 - 49 ), and may also include trouble LED numbers  1 - 4  ( 51 - 54 ). (Note that generic indicators, such as bulbs, electro-luminescence, etc., may be used as an alternative or in addition to the use of LEDs). The “Link” LED  45  may provide notification of a broken fiber optic cable. The four “Status” LEDs  46 - 49  may provide notification of the proper functioning within each of the four different underlying electronic systems that are being monitored by the device. These LEDs  46 - 49  may be green colored. The four “Trouble” LEDs  51 - 54 , where utilized, may provide notification of a problem within any of the four different underlying electronic systems that are being monitored. These LEDs  46 - 49  may be red colored. Alternatively, rather than utilizing the separate trouble LEDs, indications may be only by the status LEDs, where a lighted green status LED indicates the system is ok, and an unlighted status LED indicates “trouble.” In addition to the trouble LEDs  46 - 49 , an alternative embodiment may incorporate individual trouble indicator LEDs into the device, where one of which may light up to indicate the particular type of trouble being detected (i.e., open circuit, short circuit . . . ). 
     The transmitter  20  and receiver  40  may comprise separate units to permit convenient location of the detection portion of the invention—found within the transmitter unit- to be proximate to the contact, while the receiver may be more suitably located in an office or other convenient place where it may be routinely observed by personnel to permit quick resolution of any detected system problems. The transmitter  20  may comprise, for the convenience of the users of the system, a removable sixteen block terminal connector  25 . The connector may be a standard European removable terminal block, having 16 positions with each being 3.50 millimeters. The block may accept 16 to 24 AWG wire gauge, and the connectors may have a 300V, 8A electrical rating, with wire strip length of 5.0 mm, and max torque of 3 in-lbs. Suitable manufacturers and part numbers include: the Molex 39500-0116, 39351-0016, and the On Shore ED1550-16-BK/12345 L-R. The stripped wire of the underlying system goes into the connectors, and a screw on top of each connector clamps down onto each wire making electrical contact with connector. The terminal block connector  25  may plug into the housing of transmitter  20 . The terminal block  25  may comprise multiple instances of the prior art terminal block reproduced in FIG. 1A from U.S. Pat. No. 5,203,716 to Martucci, or it may be the terminal block available from Molex in Lisle, Ill., which may be found at www.molex.com/pdm_docs/sd/395000016_sd.pdf, with the disclosures of each being incorporated herein by reference. Standard connections for the terminal block  25  are shown in Table 3. Also, the connections to the power block  26  of transmitter  20  are shown in Table 2. The transmitter  20  may also comprise an on/off alarm switch  27 . 
     The connection between transmitter  20  and receiver  40  may comprise a cable, preferably being a fiber optic cable, which may connect to optic port  24  on transmitter  20 . Fiber optic cable offers numerous advantages over a hard-wired connection. Fiber optic networks operate at very high speeds, and may transmit many terabits per second (Tera being one trillion) over a 160 kilometer distance (see NTT Corp. news release on Sep. 29, 2006, titled “14 Tbps over a Single Optical Fiber: Successful Demonstration of World&#39;s Largest Capacity,” available at http://www.ntt.co.jp/news/news06e/0609/060929a.html) The fiber optic signal can thus also be transmitted much farther without needing to be boosted or strengthened. Fiber optic transmissions also offer better resistance to electromagnetic noise, they are immune to lightening strikes, and it costs less to maintain. Lastly, wire melts at a lower temperature than the glass optical fiber, which is an important feature when the device is used in a fire alarm system, and there is concern for maintaining system integrity in a building fire situation. All of these advantages serve to increase the robustness of the device, for its use in conjunction with a safety-critical underlying system. 
     Therefore, while the invention herein may be practiced using conventional cable, it may preferably be practiced with the use of fiber optic cable. Use of fiber optic cable requires converting an electrical signal to an optical signal using a transmitter  20 , which then transmits the optical signal through the fiber, and a receiver for receiving the optical signal and converting it into an electrical signal. The fiber optic cable used with the invention herein may be either a single mode type of fiber optic cable, or a multi-mode type of fiber optic cable. The transmitter, receiver, and cable may therefore need to be adapted to be compatible with each other. In one embodiment, they may each be selected for transmission of an 850 nm multimode signal. In another embodiment they may be selected for transmission of a 1310 nm multimode signal. In other embodiments they may be selected for transmission of a 1310 nm or a 1550 nm single-mode transmission. Table 1 lists technical specifications for one embodiment of the current invention to be illustrative, and is not intended to be limiting as to the technical specifications for other possible embodiments of the invention herein. 
     As seen in the block diagram of  FIG. 2 , fiber optic transmitter  20  may be electrically coupled to a subject system that is to be monitored using the invention disclosed herein. The invention may be used to monitor fire alarm systems, burglar alarm systems, a motor, a pump, a valve control, etc. The transmitter  20  may also be connected, as previously described, to fiber optic receiver  40  using fiber optic cable  60 . 
       FIG. 3  illustrates operation of the Input Circuitry. In one embodiment of the present invention, three different impedances, Z 1 , Z 2 , and Z 3 , may be selectively arranged around the contact to be monitored, as shown. Generally speaking, impedance is the degree to which an electrical circuit resists current flow when a voltage is applied across its terminals. In alternating current circuits, impedance is a function of the resistance, the inductance, and the capacitance therein. Electrical components in the form of inductors and capacitors build up voltages, which serves to oppose the flow of current in the circuit in a phenomenon known as reactance. Where a mix of electrical components is used in a circuit, the total impedance therein is the sum of the total resistance and total reactance of the components in the circuit. 
     As seen in  FIG. 3 , impedance Z 2  may be wired to be in parallel with the contact switch  15  that is to be monitored, and may connect to wire  151  at point  102 , as well as to wire  152  at point  101 . Beyond point  101 , a wire  154  may connect to ground  16 . Impedance Z 1  may have one end that also connects to end wire  151  at point  102  and a second end that connects to wire  153  at point  103 . Impedance Z 3  may have one end connected to wire  153  at point  104 , and a second end may be connected to a known or measured voltage, Vcc. Wire  155  may connect between point  103  and point  105 , where it may connect to wire  156  and  157 . Wire  156  may further split at point  106  into wire  160  and  161 , with wire  160  providing a connection to a first comparator  81 , and wire  161  providing a connection to a second comparator  82 . Wire  157  may also split at point  107  into wires  162  and  163 , with wire  162  providing a connection to a third comparator  83 , and wire  163  providing a connection to a fourth comparator  84 . 
     Determination of a fault condition or normal operating condition through operation of the input circuitry is dependent upon recognition of a unique voltage Vx in wire  155  in the circuit ( FIG. 3 ), which may result from the particular condition of the circuit. In one embodiment, the value of impedance Z 1  is equal to the value of impedance Z 2  (so, Z 1 =Z 2 ), and the value of impedance Z 3  may be equal to twice the impedance value of Z 1  (so, Z 3 =2·Z 1 ). Each of the comparators  81 - 84  is selected to be able to recognize a certain voltage value for the variable Vx, which corresponds to the different circuit condition, which may be predictable with these known impedance differences and possible fault conditions. Recognition of the appropriate voltage by one of the comparators diagnoses the status of the circuit. 
     For example, in the above embodiment, where the contacts are open in a normal condition, Vx=Vcc/2. Where the contacts are closed in a normal condition, Vx=Vcc/3.33. The present invention is also capable of detecting an open circuit in wire  153  due to a break, because in that case, Vx=Vcc. Where there is a short in the wire  153 , Vx=0. Each comparator is therefore selected to recognize those voltage conditions. Upon recognition of the particular voltage condition, the comparator delivers an electrical signal to encoder  88 . The encoder  88  portion of the transmitter may encode the electrical signals defining the various states, into modulated optical signals, which is then launched into fiber optic cable  60 . 
     The modulated optical signals are transmitted through fiber optic cable  60  to receiver  40 , where, as seen in the receiver circuitry of  FIG. 4 , decoder  89  decodes the modulated optical signals back into an electrical signal. The resulting decoded signal is applied to the four detectors  91 - 94 , each of which is designed to operate with the specific signal. The output of two detectors is used to trigger the output contact relay (for normal signals) or and other detectors to trigger a disable relay for various fault indicators. 
     A fifth overall signal detector  95  is also connected to the detected decoded signal to signal a loss of all signals, which would be an indication of a fifth condition—a broken fiber. Since there is always a signal if the fiber optic cable is intact, the loss of any signal signifies a broken fiber. It should be noted that upon activation of the broken fiber detector, the contact relay is de-energized. 
     The relay driver  97  is application specific, because in certain circumstances, detection of a fault condition may warrant shutting down the system&#39;s applications, and conversely, for example with a system to alert a fire department, a short may not warrant shutting down the system, but must provide the necessary alert so that the system may be repaired. Also, in the case of a burglar alarm, where there is a short, it may be desirable to have the ability to determine if the premises being protected were breached before the short occurred. If it was not, a response may necessarily be different. 
     The system disclosed herein may be used to monitor four separate contact closures over a single optical fiber conductor, as illustrated schematically in  FIG. 5 . 
     The examples and descriptions provided merely illustrate a preferred embodiment of the present invention. Those skilled in the art and having the benefit of the present disclosure will appreciate that further embodiments may be implemented with various changes within the scope of the present invention. Other modifications, substitutions, omissions and changes may be made in the design, size, materials used or proportions, operating conditions, assembly sequence, or arrangement or positioning of elements and members of the preferred embodiment without departing from the spirit of this invention. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Technical Specifications 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Number of Channels 
                 Four Independent Channels 
               
               
                 Transmitter Input 
                 Supervised Contact Closure 
               
               
                 Receiver Output 
                 Relay Contact Closure 
               
               
                 Output Contact Switching 
                 0.5 A @ 125 VAC (62.5 VA) 
               
               
                   
                 1.0 A @ 24 VDC 
               
               
                 Output Contact Carry Current 
                 2.0 Amps maximum 
               
               
                 Output Contact Resistance 
                 100 milliohms maximum 
               
               
                 Speed of Response 
                 300 ms maximum 
               
               
                 Operating Wavelength 
                 850, 1310, or 1550 nm 
               
               
                 Optical Output Power 
                 −15 dBm (multimode) 
               
               
                   
                 −15 dBm (single mode) 
               
               
                 Optical Loss Budget 
                 0-10 dB (multimode) 
               
               
                 Optical Connector 
                 ST (multimode) 
               
               
                   
                 FCPC (single mode) 
               
               
                 Signal Connector 
                 Removable Terminal Block 
               
               
                 Operating Temperature 
                 −35° to +75° C. 
               
               
                 Power Requirements 
                 11-28 VAC/DC @110 mA 
               
               
                 Physical Size (mm) 
                 5.0″(127) H × 1.0″(25.4) W × 3.0″(76) L