Abstract:
A relay fault detection and correction system includes a signal detector structured to measure primary and secondary signals, and generates a fault output signal if the signals appear to be unterminated due to a relay not connecting the signals to the loads. A cycle circuit is structured to cause a relay controller to cycle a potentially under-performing relay between its states a number of times after the signal detector generates the fault output.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional application 61/808,129, entitled RELAY FAILURE DETECTION VIA SIGNAL LEVEL SENSING, filed on Apr.  3 ,  2013 , the contents of which are all incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure is directed to a failure detection system, and more particularly, to a system that detects a relay failure and generates a response based on the detection. 
       BACKGROUND 
       [0003]    Relays are commonly used to provide switching for signals. If a relay fails with an open circuit, then the system using the signal from the relay will not operate properly because the connection normally closed by the relay remains open. In general this disclosure relates to mechanical relays that continue to pass signal even when power to the relay is removed. 
         [0004]    A particular application for such relays include a video device called an Electronic Change Over (ECO) for video signals, such as the ECO422D available from Tektronix, Inc. of Beaverton, Oreg. In an ECO, relays are used to provide backup protection. For instance, a relay or relay network may be connected to two sources of the same video signal, a primary and a backup. In operation, the relay network begins by initially coupling the primary video signal to an output by moving the armatures to the primary state. If the primary input signal should fail, the relays can quickly change to the backup video source with a minimum of delay or interruption by simply changing the states of the relays. Relays are preferred for this application over electronic switches since a relay will continue to pass a signal even if power to the ECO is removed. 
         [0005]    The combination of a primary source and a backup source connected to an output makes a channel. In practice ECOs may have ten, twenty or more channels. 
         [0006]    It is common that whichever of the primary and secondary signals is not active in the ECO be connected to a load termination, such as a resistor, so that the non-active source is driving a nominal load rather than being connected to an open circuit. 
         [0007]    A problem with ECOs exists in that relays have two common failure mechanisms. One failure is that relay contacts wear after a relatively large number of change cycles. This failure is usually not problematic in ECOs since the relays only occasionally or rarely switch to the backup video signal. For instance the ECOs occasionally switch to the backup video signal to test the backup or to allow maintenance on the primary signal delivery system. The second failure mechanism is that the electrical contacts of mechanical relays tend to degrade after a long period without use. This degradation is usually caused by oxidation of the contact material or deposition of organic material on the open contacts of the relay. This second failure mechanism is problematic for ECOs since they may be connected to the primary video input for a very long time, for instance measured in years, before changing to the secondary video input. This long time period may allow degradation of the relay contacts that connect the secondary video input to occur. Having a degraded relay contact may prevent the secondary signal from being able to be switched, or may generate noise or other interference in the secondary video signal. 
         [0008]    Embodiments of the invention address these and other issues in the prior art. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    Embodiments of the invention include a relay fault detection system structured to detect relay faults within a switching system. Some embodiments of the relay fault detection system include a first relay coupled to a first signal and a second relay coupled to a second signal. Both the first and second relays are coupled to a system output. A control system is structured to make exactly one of the first or second signals the active output of the switching system. A level detector is coupled to the first signal and coupled to the second signal and is structured to generate a signal level output from the first signal and from the second signal. A low threshold detector is structured to detect a low signal level output as a signal fault and a high threshold detector is structured to detect a high signal level output as a relay fault. 
         [0010]    A cycle circuit is structured to cycle any or all of the relays between a first operative state and a second operative state a plurality of times after the high threshold detector generates a relay fault. 
         [0011]    Further, a notification unit is structured to generate a notification based on a presence of a relay fault. The notification may be, for example, an entry in an error log, a sound, a light, a text message, or an email. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a block circuit diagram of a conventional switching relay circuit commonly used in ECOs. 
           [0013]      FIG. 2  is a block circuit diagram of an improved relay failure detection system according to embodiments of the invention. 
           [0014]      FIG. 3  is a block circuit diagram of another relay failure detection system according to embodiments of the invention. 
           [0015]      FIG. 4  is an example flow diagram illustrating operations used by embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    As described herein, embodiments of the invention are directed to a relay failure detection system. Some embodiments additionally include a procedure that may correct a detected relay fault. 
         [0017]      FIG. 1  is a block circuit diagram of a conventional switching relay circuit  100  commonly used in ECOs. The switching circuit  100  includes two inputs  110 ,  120 , which are labeled as primary and secondary, respectively. The input labels “Primary” and “Backup” are names of the signals or the sync generator from which they come. One of the primary and backup signals is connected to an output  160  as an active signal, as described below. In  FIG. 1 , the primary input  110  is connected to a relay  130 , while the secondary input is coupled to a relay  140 . Both of the relays  130 ,  140  are coupled to a relay  150 . Depending on the state of the relays  130 ,  140 ,  150 , either the primary signal or backup signal may be the active signal, which is passed through the output of the relay  150  as the output  160  of the switching circuit  100 . 
         [0018]    The relays  130 ,  140  each include a single input and two outputs, as seen in  FIG. 1 . One output of each of the relays  130 ,  140  is coupled to and becomes a respective input to the relay  150 . The other output of each of the relays  130 ,  140  is coupled to a terminating resistor, labeled  134  and  144 , respectively. 
         [0019]    A level detector  112  is coupled to the input  110 , while a level detector  122  is coupled to the input  120 . The level detectors  112 ,  122  convert the amplitude of the signals to which they are connected into an output, such as an output voltage. In general, a level detector generates a higher output voltage the higher its input signal amplitude. Level detectors are widely known and the details of level detection are not central to the invention. 
         [0020]    Outputs of the level detectors  112 ,  122  are threshold detected by comparators  114 ,  124 , respectively. Outputs of the comparators  114 ,  124  are connected to a decision system  170 , which is used to control the state of the relays  130 ,  140 ,  150 . In operation, if the primary signal degrades below an acceptable threshold, this is termed a signal fault, and the output of the comparator  114  changes states. If a signal fault occurs on the primary signal while the backup signal remains satisfactory, the decision system  170  then drives the relays  130 ,  140 , and  150  to change states. The same detection may be made by the comparator  124  if the secondary input is the currently active input. 
         [0021]    In circuit operation, if any of the relays  130 ,  140 ,  150  fails to make good electrical contact, the signal on the primary or backup input will not be connected to either the output relay  150  or the terminating resistors  134 ,  144 . This condition is called being un-terminated. The un-terminated signal will have a different amplitude than one that is properly terminated. The un-terminated signal will also have a different amplitude vs. frequency profile. Typically the un-terminated signal will become approximately two times larger at low frequencies, and will generate standing waves that vary as a function of frequency. The switching relay circuit  100  of  FIG. 1  cannot detect such problems. 
         [0022]      FIG. 2  is a block circuit diagram of an improved relay failure detection system  200  according to embodiments of the invention that can detect relay faults in addition to detecting signal faults. Error condition detectors in the failure detection system  200  are better able ascertain problems on the primary and secondary inputs  210 ,  220  and problems with the relays than in the relay circuit  100  of  FIG. 1 . For brevity, like functions between the detection systems  100  and  200  are not repeated. 
         [0023]    An output of a level detector  212  is coupled to a first comparator  214  having a low threshold input, and also coupled to a second comparator  216  having a high threshold input. Each of the threshold values may be user-definable or pre-set. In operation, the low threshold comparator  214  detects the low signal condition described above, i.e., a signal fault, on the primary input  210 . The high threshold comparator  216 , however, may be able to detect the condition when the primary input is un-terminated, based on the increased level of signals described above. Such a detection could be caused by a relay fault. If either of the outputs of the comparators  216 ,  226  switch states, a decision system  270  can detect such a change, determine that an error condition exists, and take subsequent action. The actions the decision system  270  takes are described in more detail below. 
         [0024]    In these or other embodiments, the decision system  270  may additionally determine whether a relay fault occurred, after switching the relays, based on detecting the signal fault or other reasons for switching, such as a manual switching of inputs by a user. 
         [0025]    In some embodiments, the decision system  270  is coupled to or includes a relay cycler  272 . When the output from the comparators  216 ,  226  indicate that a relay fault has occurred, the relay cycler  272  causes the armature in one or more of the relays  230 ,  240 ,  250  to quickly cycle between states in an effort to mechanically remove any oxidation or organic material that may have appeared on the electrical contacts of the relay. For instance the relay may be cycled 2-40 times, and more preferably between 10 and 20 times within a short time period, such as one or two seconds. The particular number and time period of cycles may be chosen or modified depending on an operating environment or other factors. Because the relays  230 ,  240 ,  250  are mechanical relays, this rapid switching may sound like buzzing. 
         [0026]    It is not strictly necessary that all of the relays  230 ,  240 ,  250  be cycled simultaneously. In other embodiments only one or two of the relays may be cycled at the same time. In other embodiments each of the relays could be cycled sequentially, although not preferred because of the additional time necessary to cycle through all of the relays. It is also not strictly necessary that three relays be present in the circuit  200 . Relay  250  could be removed and the outputs from relays  230 ,  240  could simply be coupled together and the circuit still functions appropriately. Alternatively, in a single-relay embodiment, relays  230  and  240 , along with resistors  234  and  244  can be removed from the failure detection system  200 , and the signal inputs can be coupled directly to output relay  250 . In this configuration the fault detection will still function, but without a termination on the unused input. Although embodiments of the invention work in many configurations, the preferred switching method of an ECO uses the three relays as illustrated in  FIG. 2 . 
         [0027]      FIG. 3  is a block circuit diagram of another improved relay failure detection system  300  according to embodiments of the invention. The failure detection system  300  is similar to the detection system  200  of  FIG. 2 , except that the high threshold comparators  216 ,  226  are not present. Instead, the failure detection system  300  includes an Analog to Digital Converter (ADC)  316  coupled to outputs of a level detector  312  and a level detector  322  through operation of a multiplexor (MUX)  318 . The MUX  318  may be controlled to automatically cycle across all inputs to which it is coupled, and the ADC then converts those signals to numeric values indicative of the input signals. 
         [0028]    In operation, for example, the level detected by the level detector  312  is compared to the low threshold by the low comparator  314 , but is also converted to digital number by the ADC  316  and stored in a decision system  370  or elsewhere in the system  300 . In operation, a determiner in the decision system  370  may compare the digitized level to a pre-defined threshold in software, or by using a computer process, and so determine that a relay fault error condition exists. 
         [0029]    In another embodiment, a fault detector system such as the system  300  could, rather than detecting an absolute signal level, instead detect a change in amplitude of the signal level. For instance, the fault detector system  300  may first detect a level while the backup signal is internally terminated and store the level in the decision system  370  or elsewhere in the system  300 . Then, the stored level may be later compared to a level after the ECO switches to make the backup signal be the active signal. If the two signal levels are significantly different, i.e., the level changed significantly after the ECO switched inputs, then it is likely that there is a problem with at least one of the relays in the system  300 , and the decision system  370  may act accordingly. 
         [0030]    In a particular embodiment, the ADC  316  is coupled to many sets of primary and secondary inputs, respectively, in an ECO by using a multi-input MUX instead of a two-input MUX such as the MUX  318 . 
         [0031]    In operation, the ADC  316  may generate signal level data, for example, in terms of voltage, for each input every second. Then the generated data are compared to individual thresholds for each generated voltage. 
         [0032]    The decision systems  270  and  370  of  FIGS. 2 and 3  may perform particular functions when they detect a relay error condition. As described above, the decision systems  270 ,  370  may include a relay cycling circuit  272 ,  372 , structured to cause one or more relays in the ECO to cycle several times in quick succession. The decision systems  270 ,  370  may also generate a notice to an operator that the ECO had a relay error. For instance the notice may be made by generating an entry in an error log. Notice may also be given by causing an error light to illuminate or a sound to be generated. In other embodiments the decision systems  270 ,  370  may send an email message to a pre-determined address, or may send a text message to a particular phone number. Of course, other notices are possible. The decision systems  270 ,  370  may send error messages through multiple channels simultaneously or sequentially. The error messages may be sent in conjunction with cycling relays. In other embodiments cycling the relays may be triggered only by pressing a button or receiving other user action. In such an embodiment the decision systems  270 ,  370  may first send an error message to an operator who investigates and determines to cycle the relays by pressing such a cycle button. 
         [0033]    One particular embodiment of the invention is described with reference to  FIG. 4 , which is an example flow diagram illustrating operations used by embodiments of the invention. 
         [0034]    In the described embodiment, the system checks for a relay fault only after a signal source switch occurred. In one implementation the relay fault is only checked for within a period of time after a signal source switch, such as ten seconds. As described above, a signal source switch may occur due to a signal fault or due to a manual switching performed by a user. 
         [0035]    A flow  400  begins at operation  410  when the system checks to see if a signal source switch occurred. In one embodiment the operation  410  may check to see if a signal source switch has occurred by checking a flag or other indicator that is set by the decision system  370  when a signal source switch occurs. 
         [0036]    If no signal source switch occurred in the operation  410 , the operation  420  stores a value of the inactive signal, i.e., whichever of the input signals is internally terminated, so that a constantly updated record of a normal operating level exists for later reference, if necessary. In particular, the operation  420  may store the digitized output from the ADC  316  of all of the inactive signals in the ECO. 
         [0037]    After the value is stored in operation  420 , the system waits for a time period, such as one to five seconds in an operation  430 , and then checks again for a signal source switch on the same or on another channel within the ECO. 
         [0038]    The operations  410 ,  420 , and  430  make up a continuous loop called an idle loop  402 . If no signal source switches occur, then the system operation stays in the idle loop  402 . 
         [0039]    If instead a signal source switch occurred, such an occurrence is detected in operation  410 , and the flow  400  exits in the YES direction to an operation  450 . Operation  450  copies and stores the particular stored value of the inactive signal from a time before the switch occurred. In other words, because the operation  420  is constantly storing signal values, the operation  450  is able to retrieve a value from before the switch occurred. 
         [0040]    Then, provided the relay cycling feature is enabled, which is checked by an operation  460 , an operation  470  compares a present signal value from the now-active signal to the previously in-active signal. If the current active signal is larger than the in-active primary signal, or in some embodiments larger than a threshold difference, then this indicates a fault with one or more relays may be present, i.e., a relay fault, as described above. 
         [0041]    If there is a relay fault, then the system may cycle one or more of the relays in the particular ECO channel in an operation  480 , as described above. This cycling may correct the relay problem. 
         [0042]    A reporting operation  490  reports the relay fault. As described above, this may include generating an entry in an error log, a warning sound, or a warning light. The relay fault may also be reported by an automatic text or email message. In some embodiments the reporting operation  490  may precede the actual cycling of the relays in operation  480 . 
         [0043]    In various embodiments, components of the invention may be implemented in hardware, software, or a combination of the two, and may comprise a general purpose microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or the like. For instance, the decision systems  270 ,  370  may be implemented in hardware or programmable hardware, such as an FPGA, while the threshold detection and other functions of the relay fault detection circuit may be implemented by software running on a specifically programmed microprocessor, such as an embedded microprocessor. In other embodiments the software may be running on a general purpose processor, either coupled to the detection system or operating on a separate computer coupled to an ECO. 
         [0044]    Although specific embodiments of the invention have been illustrated and described for purposes if illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.