Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-01-29
2001-04-24
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S503000, C324S556000, C324S762010, C340S651000
Reexamination Certificate
active
06222374
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates generally to fault detection systems, and, more specifically, to circuitry for detecting improperly connected or shorted wires in a wiring harness or the like.
2) Related Art
A typical vehicle has numerous solenoids, lamps and relays connected by a wiring harness to a vehicle controller. An incorrect voltage or incorrect load on a line can cause expensive damage to electrical and electronic components and may render the vehicle inoperable. During servicing of the vehicle or during manufacture of the harness, the connectors may by wired incorrectly so that battery voltage is applied directly to a semiconductor or the semiconductor is connected to a high current sink or ground resulting in damage to the controller or to other components in the circuit. For example, a high current pull-in coil for an engine enablement function such as the fuel pump drive sometimes is incorrectly wired to the output that is meant for a low-current hold-in coil. Fuses often are utilized in an attempt to protect the circuit, but each fuse must be durable enough for vehicle abuse and transients that occur during normal operation, and therefore the fuse may fail to open before a vital component in the circuit is damaged. Other protection methods include the use of individual series precision current sensing resistors, one at each output of the controller, with a series of operational amplifiers to provide a signal to the controller. Such circuits are relatively complex, costly and sensitive to variations in resistance. Other fault detection circuits utilize a test power supply having a voltage level well below the operating voltages to carry out a self-testing procedure and allow power up only if no low impedance paths are detected in the bus or harness. These circuits may require a special power supply and can also be costly and complex. Some circuits have a slow diagnostic time and cannot be used to provide checks during routine operation of the vehicle.
Diagnosing a system with numerous input and output lines is often tedious. Identifying a particular portion of a circuit on a circuit board or wiring harness connection can often require time-consuming references to a wiring diagram. As the number of input and output functions to and from a controller increases, the technician often finds that correlating the circuit diagram with a particular portion of the hardware is increasingly difficult.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved circuit for diagnosing wiring harnesses and similar components. It is a further object to provide such a circuit which overcomes most or all of the aforementioned problems.
It is a further object of the present invention to provide an improved circuit for diagnostic purposes which effectively detects wiring problems. It is another object to provide such a circuit which can detect faults quickly and which does not require special test voltages. It is still a further object to provide such a circuit which is sufficiently durable to operate reliably on a vehicle or other device wherein transients and over-voltage or under-voltage conditions occur relatively frequently.
It is another object of the present invention to provide an improved circuit for diagnosis of wiring harnesses or the like which is simple in construction and fast and reliable in operation. It is another object to provide such a circuit which does not require precision resistors or numerous operational amplifiers. It is a further object to provide such a circuit which can quickly and reliably check for over-voltages, wiring harness failures, and shorts to ground or to power line and protect electronic components before such faults cause permanent damage to the electronic system.
It is another object of the present invention to provide an improved circuit for on-the-go diagnosis of wiring harness connections or the like wherein the diagnosis takes place in a very short period of time without perceptible interruption of the normal operation of the vehicle or other device. It is yet another object to provide such a circuit wherein the circuit board as well as the wiring harness connected to the circuit board can be diagnosed. It is still another object of the invention to provide such a circuit which is relatively inexpensive and does not require precision resistors or a large number of operational amplifiers.
It is still another object of the invention to provide an improved diagnostic circuit which is relatively simple and inexpensive in construction and which facilitates easy identification of circuit functions and circuit faults without need for continual reference to a wiring diagram.
A circuit constructed according to the teachings of the present invention includes a plurality of inexpensive resistors connected at one end to the open collector outputs of an output array of NPN output transistors which are connected to a wiring harness or the like for selectively powering a preselected load. The opposite ends of the resistors are connected to the base of an NPN sense transistor. The output NPN transistors, when in the on condition, are biased well into saturation for normal loads and therefore provide a very low Vce (sat) when properly connected through the harness to the intended load. In the off condition, the output NPN transistors look essentially like an open circuit. Vce (sat) is lower than the base turn-on voltage of the NPN sense transistor which has a grounded emitter. The collector of the NPN sense transistor is connected to a source of voltage through a pull-up resistor and to an input of the microprocessor which controls the signals to the output array transistors.
To test the connections of the harness to the NPN output transistors, the microprocessor turns on all the output transistors simultaneously for a very short period of time, preferably only a few microseconds. If all the outputs are connected to the intended loads, the Vce of each of the transistors will be less than the base turn-on voltage of the sense transistor. if any of the outputs is improperly connected to the source voltage or to a high current sink, that transistor will come out of saturation and Vce will rise above the turn-on voltage of the sense transistor. The sense transistor then turns on to provide a signal to the microprocessor that a fault has been detected. During operation of the vehicle, the system continuously monitors for ground fault problems by turning on all outputs except one for a few microseconds. If the output that is not turned on is not shorted to ground, the voltage on that line will rise toward source voltage and turn on the sense transistor. Each output is checked in sequence. The microprocessor provides a fault code if a grounded condition is detected on a line or lines.
To provide diagnostics for a system wherein a positive turn-on voltage is necessary for enablement of the device connected through the harness, a similar detection arrangement is provided which utilizes the low Vce of a PNP output transistor in saturation. To aid in the diagnostics, each output transistor in the output array includes a base connected in series with an input LED so the technician can tell at a glance which inputs to the array are on and which inputs to the array are off. The technician therefore can determine which connections on the output array corresponds to a particular input or output function on the vehicle and if the output transistor on the array for that function is operating properly by simply activating that function while looking at the LED outputs. For example, by bouncing on the seat, the LED for the operator presence circuit will flash to tell the technician which line corresponds to that function. If no LED flashes when a particular function input or output is activated, the technician knows to look for problems in that portion of the system. The one-to-one correspondence significantly simplifies system troubleshooting and reduces the amount of time the
Deb Anjan K
Deere & Company
Metjahic Safet
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