Abstract:
A monitoring or control system includes a plurality of senders or sensors which are coupled to a central control unit by separate cables. The control unit includes a microprocessor which executes an intermittent fault detection algorithm while an operator manually flexes each cable in turn. When a cable with a fault is manipulated the algorithm responds by energizing a horn.

Description:
BACKGROUND 
     This invention relates to an electrical monitoring system and more particularly to diagnosing intermittent electrical faults which can occur in such a system. 
     Electrical monitoring and/or control systems are well known in the prior art. Such systems typically include sensor or sending devices coupled to a central processing or control unit via electrical cables or conductors. Intermittent faults, such as short or open circuit conditions in such cables and or connectors have always been difficult to isolate. For example, the fault may not occur when a service person is present, or it may disappear as the service person takes diagnostic action. Accordingly, it would be desirable to have a monitoring or control system with a built-in capability for facilitating detection and isolation of such intermittent faults. 
     SUMMARY 
     An object of the present invention is to provide an electrical monitoring and/or control system with a system for detecting and isolating intermittent faults. 
     These objects are achieved by the present invention wherein a plurality of sensors or senders are coupled by electrical cables or conductors to a central electrical processing or control circuit which includes a microprocessor. Actuation of a switch places the microprocessor in a mode wherein a special intermittent fault detection algorithm is repetitively executed while the service person flexes each of the cables, one after the other. Whenever the intermittent fault becomes active it will cause a change in the voltage or current in that cable and the fault detection algorithm will automatically energize an audible horn. 
    
    
     BRIEF DESCRIPTION 
     FIG. 1 is a simplified schematic diagram of a monitoring system including the intermittent fault detection feature of the present invention. 
     FIG. 2 is a logic flow diagram of an algorithm or compute executed by the central control unit of FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     A monitoring and/or control system 10 includes a control or processing unit 12 which is coupled to a plurality of sensors or sending devices, such as a normally closed switch 14, a normally open switch 16, a potentiometer type analog sensor 18 and a variable resistance analog sensor 20. Each device is coupled to the central unit 12 via a corresponding conductor or cable 22, 24, 26, and 28. Each cable may include one or more connectors 30. 
     The central unit 12 is connected to a potential source or battery 32 via a fuse 34 and a switch 36, such as the ignition switch in the case of a vehicle. An alarm device 38, such as an audible horn is connected to an output terminal of the central unit 12 and to the switch 36. An operator controlled mode control switch 40 is connected between the switch 36 and a mode control input of the central unit 12. 
     The central unit 12 includes a conventional microprocessor which may be programmed to monitor the functions sensed by devices 14-20 and/or to control various functions (not shown) in response to sensed parameters. Such monitoring and/or control functions form no part of the present invention. 
     According to the present invention, the central unit 12 also executes a diagnostic algorithm which is enabled when switch 40 is manually closed and which will be described with reference to the logic flow diagram of FIG. 2. 
     The algorithm begins at step 100 which is entered periodically, such as 32 times per second, as long as the switch 40 remains closed. Then, at step 102, a set of status signals for the plurality of switches 14 and 16, as represented by electrical parameters communicated via cables 22 and 24, are read and stored in memory. Then in step 104, the current set of status signals is compared to an initial set or to a previously stored set of status signals and if these sets differ, then the algorithm is directed to step 106 which causes the horn 38 to sound for a certain desired period. If the compared sets are the same, then the algorithm proceeds to step 108 which stores the current set of status signals into a set of last pattern memory locations. 
     Then in step 110, a current status signal for a first one of the analog sensors 18, 20 is read and stored. In step 112, the absolute value of the difference between the current status value and an initial or previously stored status value for this sensor is compared to a reference value. If the absolute value of this difference is more than the reference amount, Vref, then step 114 causes the horn 38 to sound for a desired interval. Otherwise, the algorithm proceeds to step 116 which replaces the initial or previously stored status signal with the current status value. If status signals for all the analog sensors have not yet been analyzed, then step 120 changes an index value and returns the algorithm to step 110 so that steps 110-116 will be repeated for each analog sensor in sequence. After the status signals for all the analog sensors have been analyzed, step 118 directs the algorithm to step 122 which terminates operation of this cycle of the algorithm. 
     Thus, with the present invention, if an intermittent fault in one of the cables or connectors is suspected, the operator can close switch 40 and manually flex each cable, one after the other. If such a fault exists, then the corresponding status signal will change from one cycle of the algorithm to the next and the algorithm will respond by sounding the horn 38. In this manner, intermittent faults in cables and connectors can be detected and isolated. In the case of a sending unit such as normally open switch 16, the switch should be removed and replaced by a jumper so that current can flow through cable 24 and so that manipulation of cable 24 will cause a change in the voltage or current sensed by the central control unit 12. 
     For more detailed information concerning this algorithm, reference is hereby made to the following annotated assembly language computer program listing description. In view of the above-described flow chart, and in view of the assembly language program listing included herein, it will be evident to those skilled in the art to implement the invention described herein in a monitoring or control system which includes a data processor, such as a microprocessor. 
     While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims. ##SPC1##