Probe for fault actuation devices

Details Probe for fault actuation devices Probe for fault actuation devices

1998-08-07

2001-11-20

Brown, Glenn W. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of electrically operated apparatus

C324S527000, C324S531000, C324S754090

Reexamination Certificate

active

06320390

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to the so-called fault actuation or insertion techniques used to test the operation of electronic equipment, and concerns a probe or fault actuation devices, arranged to force a test point of an electronic equipment under test to a given signal level, the probe comprising: a transistor having a control electrode and two circuit terminals, which circuit terminals are connected respectively to the test point and to a given signal level, and control means acting on the control electrode of the transistor to selectively switch the transistor between a cut-off condition and a conducting condition.
BACKGROUND OF THE INVENTION
A probe with some similarity to the above probe is known from EP A 0 261 367. The probe is a mechanical probe which is brought into electrical contact with a test point of an electronic component and an alternating square wave test signal is applied to the test point through a transistor and extracted through a circuit connected to the probe. The transistor which is a field effect transistor applies to the test point the mentioned variable signal, so as to simulate regular operation conditions of the component. Parasitic capacitances within the transistor are likely to introduce some distortion into the amplified square-wave voltage.
In electronic equipment and systems (especially if very complex: by way of nonlimiting example, reference can be made to switching exchanges of telecommunications networks), the need often arises to check the behavior of the equipment and of the system in the presence of particular fault conditions. This check can be carried out not only in the testing phase, but it may be a part of the fault diagnosis and/or identification or of automatic reconfiguration functions which often are provided for in such equipment and systems to ensure that the equipment can still operate (at least in part) even in the presence of faults.
In digital equipment, the types of faults to be actuated or inserted (hereafter the terms “actuation” and “insertion” shall be used as synonyms) at the hardware level generally entail forcing certain points of the equipment to a pre-set signal level, corresponding for example to a logic “0” or to a logic “1”. A solution conventionally adopted in the art has thus been to establish, in correspondence with the point to be forced to the pre-set signal level, an electrical connection (usually by means of a jumper) towards the ground level or a given power supply level (+V
cc
or−V
cc
).
This solution is not particularly easy to be put in practice, also in view of its intrinsically “fixed” nature, once the jumper has been applied, the point involved is constantly maintained at the signal level to which the jumper is connected. Hence, it is not possible to monitor quickly the reaction of the equipment at the moment the fault is inserted and/or, which can be of no less interest, at the moment the fault is eliminated.
To overcome these drawbacks, a solution has been proposed, at least at the experimental level , which entails connecting electrical conductors, coming out of the equipment under test, to the fault insertion points. Such conductors lead to a set of electromechanical switches (such as, typically, relays) which allow the required connections to the reference voltages to be established.
This solution cannot be considered fully satisfactory, for several reasons.
Firstly, it is intrinsically cumbersome. Additionally, the conductors connected to the fault insertion points always disturb the equipment being tested. Thus, the fault conditions simulated for the test do not exactly correspond, from the electrical point of view, to the fault conditions likely to occur in the equipment (this is particularly true when current absorption at the fault point is also to be measured). Further, the conductors disturb the operation of the equipment even under regular service conditions, i.e. when there is no fault actuation.
OBJECTS OF THE INVENTION
It is, therefore, an object of the invention to provide a system capable of overcoming the problems set out above and, in particularly, which:
makes reproducing fault conditions very flexible, in order to allow a substantially instantaneous switching from the normal operating condition to the simulated fault condition of the equipment under test;
does not disturb the operation of the equipment both when a fault is being simulated and under normal operating conditions of equipment, with no faults applied;
is intrinsically not cumbersome, in order to allow simultaneous or nearly simultaneous fault insertion into a number of points of an equipment under test, for instance points belonging to a board inserted in a cabinet, according to a typical constructive embodiment of complex electronic equipment; and
allows automating testing operations.
Additionally, it should also be noted that the devices required, at least as concerns the components (probes) directly used for connection to the equipment under test, should have a negligible cost. Thus they can be left in place once the test has been completed, that is, they can be single-use products.
SUMMARY OF THE INVENTION
According to the present invention, this goal is reached with a device characterized in that in its conducting condition, the transistor in use is driven into saturation condition causing the test point to be forced to said given signal level. A capacitor is directly connected between the control electrode and the circuit terminal of the transistor opposite to that point, which capacitor has a substantially higher capacitance value than the value of the parasitic capacitance existing between control terminal and the circuit terminal of the transistor coupled to the test point.
From DE-B 23 63 360, it is known, per se, that in an amplifier, a series connection of a capacitor and a resistor is coupled between the base and the emitter of the amplifier transistor. The resistor is a part of a voltage divider. The transistor used as an amplifier operates in a linear zone of its characteristics in order to provide an output signal proportional to the input signal. The known circuit arrangement, thus does not give any hint to the person in the art to arrange the probe for fault actuation in the manner proposed by the invention.
Within the concept of the invention, the construction details may be changed widely with respect to what will be termed a transistor, working as an electronic switch. The “transistor” may be any electronic component with equivalent operating characteristics. The term “transistor” thus is to be taken to include such equivalent electronic devices as well; this also holds true for the terms “collector”, “emitter” and “base”, identifying the terminals of a bipolar transistor.


REFERENCES:
patent: 4309657 (1982-01-01), Lockhart, Jr. et al.
patent: 4489247 (1984-12-01), Ikeda et al.
patent: 4841240 (1989-06-01), Hsue et al.
patent: 23 63 360 (1975-06-01), None
patent: 0 262 367 (1988-04-01), None
patent: 62 183215 (1987-08-01), None

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