Electricity: measuring and testing – Plural – automatically sequential tests
Reexamination Certificate
1998-01-22
2001-03-13
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Plural, automatically sequential tests
C324S066000, C324S540000
Reexamination Certificate
active
06201383
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to electronic circuit testing, and more particularly to using a gang probe circuit tester to determine if short circuit conditions exist among a number of networks within a circuit under test.
BACKGROUND INFORMATION
The two basic types of electronic circuit testing employed today are gang probe circuit testing and flying probe circuit testing. With gang probe circuit testing a number of probes are held in simultaneous contact with a similar number of test points on the circuit under test as driving signals are applied to various probes, and as response signals are measured at various probes. With flying probe testing, a smaller number of probes, typically from one to four probes, are moved among, and into contact with, and the various test points for the application of test signals and the measurement of corresponding response signals.
A first conventional method for testing electronic circuits with gang probe testing involves the connection of two test points at a time, through a switching circuit connected to the various probes held in contact with the circuit under test, so that a test voltage is applied between these two test points. If these two test points are connected within the circuit under test, either by the deliberate design of the circuit under test or by an inadvertent connection, i.e. through a short circuit, current flows through the probes connected with these points.
This first conventional method for circuit testing is described, for example, in U.S. Pat. No. 4,471,298 to Frohlich, as being implemented within a circuit tester having a number of probes in a pair of contact bars simultaneously engaging test points. A circuit test is applied when two of these probes are electrically connected, by means of reed switches, to opposite sides of a power supply through a variable resistor. When current flows through the circuit under test between these test points, and hence through the variable resistor, a voltage developed across a portion of the variable resistor provides an indication that the test points are electrically connected, within the circuit under test, to a microprocessor controlling the test process. This method has a significant advantage of flexibility. Depending on the arrangement of test points, this method can be used both to determine both the presence of opens, or breaks in circuit patterns, and of shorts between adjacent circuit patterns. That is, a failure to conduct between two test points on an individual network indicates an open condition, while conduction between two networks indicates a short.
However, a particular problem with this first conventional method for circuit testing lies in the number of individual measurements which must be made to perform an exhaustive test of a reasonably complex circuit for short circuit conditions, and hence in the time required to perform circuit testing. For exhaustive testing, each pair of networks within the circuit under test must be separately evaluated, with a voltage being applied between the networks in the pair to determine if a current flow exists. For example, if the circuit under test includes 16 networks, a first side of the test circuit is connected through a first test point, while the second side of the test circuit is connected sequentially to the other 15 test points. Next, the first side of the circuit is connected through a second test point, while the second side of the test circuit is connected sequentially to 14 other test points. The number of test points to which the second side of the circuit is connected is reduced by one with each new connection of the first side of the circuit, since it is not necessary to retest pairs of points which have previously been tested. In general, the number of tests required, T, as a function of the number of networks to be tested, n, is given by:
T=(
n
−1)+(
n
−2)+ . . . +[
n
−(
n
−1)] 1)
In the example of a circuit under test having 16 networks to be examined, this method requires 120 tests.
A second conventional method for determining whether short circuit conditions exist between individual networks of a circuit greatly reduces the number of tests which must be made. With this method, a first side of the test circuit is connected to a first test point of the circuit under test, while the second side of the test circuit is connected to the remaining test points. The application of a test voltage in this way produces a current flow, indicating a short circuit condition, if the network connected to the first test point is electrically connected to a network connected to any other test point. Next, the first side of the test circuit is connected to the second test point, while the second side of the test circuit is connected to the remaining test points, with the test being repeated to determine if a short circuit condition exists between the network connected to the second test point and a network connected to another test point. When the first side of the test circuit has been connected in this way to every test point except one, the testing has been completed, since each relationship between the network connected to the last test point and a network connected to another test point has already been examined. Thus, the number of tests required, T, as a function of the number of networks to be tested, n, is given by:
T=
n
−1 2)
In the example of a circuit under test having 16 networks to be examined, this method requires 15 tests.
Despite the advantages of this second conventional method in the reduction of the number of tests required, for testing many modern types of circuits having hundreds or even thousands of networks which can be shorted, what is needed is a method further reducing the number of tests which must be made.
SUMMARY OF THE INVENTION
A first objective of the present invention is to provide a first method for rapidly determining whether a short circuit condition exists among two or more of the networks extending within a circuit under test.
A second objective of the present invention is to provide a second method to be used after it is determined, using the first method, that a short circuit condition exists, to determine which networks within a circuit under test are affected by the short circuit conditions.
A third objective of the present invention is to provide an alternative second method for determining which networks are short circuited to which other networks after it is determined, using the first method, that a short circuit condition exists.
A fourth objective of the present invention is to provide the first, second, and alternative second methods described above in a sequential fashion in the same test apparatus.
According to a first aspect of the invention, there is provided a method for determining the presence of short circuit conditions among a plurality of networks within a circuit under test, wherein the method comprises steps of:
a) bringing a first number of test probes into contact with the circuit under test, with the first number being greater than two, with each test probe within the first number thereof being in electrical contact with a network within the plurality thereof;
b) establishing electrical connections, in accordance with a predetermined connection pattern, between a drive line of a testing circuit and a first plurality of test probes, and between a sense line of the testing circuit and a second plurality of test probes, wherein the first and second pluralities of test probes are distinct from one another, wherein the first number of test probes is entirely comprised of the first and second pluralities thereof, with the testing circuit including a voltage source having a first side connected to the drive line and a second side connected to a current detector, with the current detector, additionally connected to the sense line, being responsive to current flowing therethrough;
c) determining whether current is flowing through the
Lo Jiann-Chang
Mahlbacher James Christopher
Davidge Ronald V.
International Business Machines - Corporation
Metjahic Safet
Tomlin Richard A.
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