METHOD AND CIRCUIT FOR DETECTING A FAULT CONDITION

Abstract: In a test circuit and method for detecting a fault condition in a voltage bus (20), the bus (20) is connected to a resistor network (22) which is coupled to a data acquisition circuit (24) including a voltage sensing means (32). In the event a zero voltage condition is detected, a constant current source (58) is connected to the test circuit and a plurality of switches (38, 40, 42) in the data acquisition circuit are sequentially operated to connect corresponding circuit paths, one of which includes a resistor (28) in the resistor network (22), sequentially to the voltage sensing means (32). A processor (25) effects comparisons of the voltage drops sensed upon operation of the switches (38, 40, 42) to effect operation of an alarm (27) to indicate the fault condition in the voltage bus (20) or to indicate a short or open circuit in the test circuit or its connections.

Description: - METHOD AND CIRCUIT FOR DETECTING A FAULT CONDITION Technical Field This invention relates to a method for detecting a fault in a voltage distribution bus adapted to be supplied with a line voltage level by a voltage supply and which is connected to utilization means utilizing the line voltage. The invention also relates to a test circuit for detecting a fault condition in a voltage distribution bus adapted to be supplied with a line voltage by a voltage supply and which is connected to utilization means utilizing the line voltage. Background Art In a data processing system, one type of parameter which is especially important to the operation of the system is the bus voltage appearing on the input connection to various printed circuit boards on which are located the processing elements that form the data processing system. In monitoring such bus voltages, a zero voltage reading may indicate an actual zero bus voltage or may be due to various other causes such as open or short circuits in the monitoring device or its connections. Disclosure of the Invention It is an object of the present invention to provide a method and a test circuit of the kind specified having the capability of automatically determining the status of a fault indication. Therefore, according to one aspect of the present invention, there is provided a method of the kind specified, characterized by the steps of: connecting a test circuit including a resistor network and a data acquisition circuit to said voltage - 2 - distribution bus, supplying a current to said data acquisition circuit, sensing a first voltage drop in a first circuit path in said data acquisition network, forming a second circuit path including a first resistor in said test circuit, sensing a second voltage drop in said second circuit path, forming a third circuit path including a second resistor included in said resistor network, sensing a third voltage drop in said third circuit path, comparing the second voltage drop with the third voltage drop, and generating a first alarm actuating signal representing a failure of said voltage supply when the second voltage drop is greater than the third voltage drop. According to another aspect of the present invention, there is provided a test circuit of the kind specified, characterized in that said test circuit includes a resistor network adapted for connection to said voltage bus and a data acquisition circuit adapted for connection to said resistor ' network and including voltage sensing means connected to an output of said data acquisition circuit, and in that there are provided first switching means adapted to connect a first circuit path in said data acquisition circuit to said voltage sensing means, second switching means adapted to connect a second circuit path including a first resistor to said voltage sensing means, third switching means adapted to connect a second resistor included in said resistor network to said voltage sensing means, and fourth switching means adapted to connect a current source to said data acquisition network, and processor means responsive to the output of said voltage sensing means and adapted to operate said fourth switching means and to successively operate said first, second and third switching means thereby providing respective first, second and third voltage drops, whereby said processor means is adapted to operate alarm means to indicate a first fault condition when said second voltage drop is greater than said third voltage drop. It will be appreciated that a method and test circuit according to the invention have the advantage that the status of a fault condition can be determined without requiring the utilization of a plurality of additional sensing lines and associated measuring devices. Brief Description of the Drawings One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of the sensing system which includes the circuit of the present invention; Fig. 2 is ^ a circuit diagram of the present invention; and • ' . - Fig. 3 is a flow chart of the method for determining the status of various detected fault conditions. Best Mode for Carrying Out the Invention Referring now to Fig. 1, there is shown a block diagram of a portion of a data processing system which includes the circuit of the present invention. A voltage distribution bus 20 is connected to a voltage source 21 which supplies voltage to the bus 20 for operating elements in the data processing system such as printed circuit boards 19 connected to the bus 20. Also connected to the bus 20 over line 30 is a resistor network 22 which is connected over bus 23 to a data acquisition circuit 24. The circuit 24 will monitor the voltage level appearing on the bus 20 and when such level falls to zero, a processing unit 25 of the data processing system will determine the nature of the cause for such voltage reading. The cause of - 4 - such reading may include a failure of, the voltage source 21, the distribution bus 20 or the presence of an open or short circuit at point A or point B in the circuit. The resistor network 22 is designed to pre- scale the reading of the voltages appearing on the bus 20 to a range of plus or minus one volt when the bus voltages appearing on the bus 20 are at the required bus voltage level, e.g. plus twelve volts etc. Referring now to Fig. 2, there is shown a schematic diagram of the resistor network 22 and the data acquisition circuit 24 of the present invention. The resistor network 22 includes the resistors 26 and 28 which are wired in series over line 30 with the voltage bus 20. The resistor 28 is connected to a remote ground or ground bus. The acquisition circuit 24 includes a differential amplifier 32 whose positive or non-inverting input is connected over line 34 and through switch 38 to a node ' 39 which is.located inter¬ mediate the resistors 26 and 28. The negative or inverting input of the amplifier 32 is connected over line 46 and through the switch 50 to the other side of the resistor 28. The acquision circuit 24 further includes a parallel network including switches 40 and 42 and a IK test resistor 44 which are wired across the input lines 34 and 46 of the amplifier 32. The value of the resistor 44 must equal the total resistance of the parallel combination of the resistors 26 and 28. The amplifier 32 will normally measure the voltage drop across the resistor 28 when switches 38 and 50 are closed. The output line 33 of the amplifier 32 is connected to a A/D converter 35 whose output signal is connected over line 36 (Fig. 1) to the processing unit 25 which in turn is connected over line 37 to any type of alarm device 27 which may take the form of generating a flag or the display of an alarm condition on a CRT screen. The switch 50 is normally closed - 5 - during the operation of the data acquision circuit 24. The circuit 24 further includes a constant current source 58, and switches 52 and 60 for controlling the operation of the acquisition circuit in a manner to be described more fully hereafter. As previously described, if the output voltage signal V ou t of the amplifier 32 indicates the voltage on the bus 20 is zero, it is not known whether the reading is a result of a failure in the voltage source 21 or the presence of an open or short circuit. The present invention provides a method for detecting the cause of such a voltage reading and the setting of an alarm upon the detection of such a condition if the condition is required to be reported. The switches in the circuit of Fig. 2 may comprise transistors or other type of mechanical and electronic switches which can be electrically operated. Referring now to Fig. 3, there is shown a flow chart of the operation of the data acquisition circuit 24 which may, in the present embodiment, comprise a routine performed by the processing unit 25. In monitoring the voltage drop across the resistor 28 with switches 38 and 50 closed, the proc¬ essing unit will, upon detecting (block 70) a zero voltage level, close (block 72) switches 60, 42, and 52 and open switch 38 allowing one milliamp of current to flow from a constant current source 58 (Fig. 2) through the closed switches to ground enabling the amplifier 32 to sense (block 74) a voltage drop V]_ across the circuit which includes the inherent resistance of the circuit due to the length of lines 34 and 46 and the resistor network 22 together with the resistance of the switches in the circuit. The processing unit 25 will then open switch 42 and close switch 40 (block 76) allowing the amplifier 32 to sense (block 78) a voltage drop V2 across the circuit which includes the resistor 44. The processing unit - will then open switch 40 and close switch 38 (block 80) allowing the amplifier 32 to sense (block 82) a voltage drop V3 across the circuit which includes the resistor 28. The voltage drop V3 is then compared with a voltage drop V max (block 84) where V max is the maximum voltage that can be sensed by the amplifier 32. If the voltage drop V3 is greater than V max , then there is a break at point B (Fig. 1) which may be the result of an open circuit in one of the lines in bus 23. This condition results in the generation of a signal which activates a first alarm condition (block 86) notifying the operator of the existence of such a fault condition. If V3 is less than V max , the voltage drops Vτ_ and V3 are compared by the processing unit 25. If the voltage drop Vi is equal to V3 (block 88) indicating a short circuit in ' the bus 23, a signal is generated to activate a second alarm (block 90). If the voltage drop V3 is not equal to Vι_, the-processing unit 25 will then compare (block 9 ' 2) the voltage drop V3 with V2. If V3 is greater than V2 indicating an open circuit at point A (Fig. 1) in the circuit, a third alarm is activated (block 94) . If V2 is greater than V3 indicating the bus voltage level supplied by the voltage source 21 (Fig. 1) is zero, a fourth alarm 96 is activated. It will thus be seen that with this method and apparatus for detecting a fault in a voltage bus, various fault conditions can be automatically determined and an alarm activated which notifies the operator of the nature of the fault.

Claims: - 7 - CLAIMS : 1. A method for detecting a fault in a voltage distribution bus (20) adapted to be supplied with a line voltage level by a voltage supply (21) and which is connected to utilization means (19) utilizing the line voltage, characterized by the steps of: connecting a test circuit including a resistor network (22, 28) and a data acquisition circuit (24) to said voltage distribution bus (20), supplying a current to said data acquisition circuit (24), sensing a first voltage drop in a first circuit path in said data acquisition network, forming a second circuit path including a first resistor (44) in said test circuit, sensing a second voltage drop (V2) in said second circuit path, forming a third circuit path including a second resistor (28) included in said resistor network (22), sensing a third voltage drop (V3) in said third . circuit path, comparing the second voltage drop (V2) with the third voltage drop (V3), and generating a first alarm actuating signal (96) representing a failure of said voltage supply (21) when the second voltage drop (V2) is greater than the third voltage drop (V3). 2. A method according to claim 1, characterized by the step of generating a second alarm actuating signal (94) representing an open circuit in the connection of said resistor network (22) to said voltage bus (20) when the third voltage drop (V3) is greater than the second voltage drop (V2). 3. A method according to claim 2 , characterized by the steps of: comparing the first and third voltage drops (Vτ_, V3) and generating a third alarm actuating signal (90) indicating a short circuit in said data acquisition circuit (24) when the first voltage drop (V_) is equal to the third voltage drop (V3) . - 8 - 4. A method according to claim 3, characterized by the step of generating a fourth alarm actuating signal (86), representing an open circuit between said resistor network (22) and said data acquisition circuit (24) when said third voltage drop (V3) is greater than a predetermined value (Vj^ ) . 5. A test circuit for detecting a fault condition in a voltage distribution bus (20) adapted to be supplied with a line voltage by a voltage supply (21) and which is connected to utilization means (19) utilizing the line voltage, characterized in that said test circuit includes a resistor network (22) adapted for connection to said voltage bus (20) and a data acquisition circuit (24) adapted for connection to said resistor network (22) and including voltage sensing means (32) connected to an " output of said data acquisition circuit (24), and in that there are provided first switching means (42) adapted to connect a first circuit path in said data acquisition circuit (24) to said voltage sensing means (32), second switching means (40) adapted to connect a second circuit path including a first resistor (44) to said voltage sensing means (32), third switching means (38) adapted to connect a second resistor (28) included in said resistor network (22) to said voltage sensing means (32), and fourth switching means (52, 60) adapted to'connect a current source (58) to said data acquisition network (24), and processor means (25) responsive to the output of said voltage sensing means (32) and adapted to operate said fourth switching means (52, 60) and to successively operate said first, second and third switching means (42, 40, 38) thereby providing respective first, second and third voltage drops (V]_, * 2, V3), whereby said processor means (25) is adapted to operate alarm means (27) to indicate a - 9 - first fault condition when said second voltage drop (V2) is greater than said third voltage drop (V3). 6. A test circuit according to claim 5, characterized in that said processor means (25) is adapted to operate said alarm means (27) to indicate a second fault condition when said third voltage drop (V3) is greater than said second voltage drop (V2). 7. A test circuit according to claim 6, characterized in that said processor means (25) is adapted to operate said alarm means (27) to indicate a third fault condition when said first voltage drop (Vτ_) is equal to said third voltage drop (V3). 8. A test circuit according to claim 7, characterized in that said processor means (25) is adapted to operate said alarm means (27) to indicate a fourth fault condition when said third voltage drop is greater than a predetermined value (Vj^ ) .

Inventors: PIPKORN MARK GEORGE, PIPKORN, MARK, GEORGE
Applicants: NCR CO, NCR CORPORATION
Application year: 1986
Main classification: G01R19
IPC codes: G01R19, G01R31