Abstract: A test fixture is provided for testing the resistance associated with contamination material on the surface of electrical contacts mounted to a printed circuit board. A probe used to engage the contacts consists of first and second conductive probe segments which form a sandwich about a layer of insulating material. A current source provides a constant alternating current which is applied across the first and second probe segments. Circuitry is provided for amplifying the alternating current voltage developed across the first and second probe segments in response to the constant current. Circuitry is provided for rectifying the amplified alternating current voltage to provide a direct current voltage which is proportional to the measured resistance of the contact engaged by the probe. Data corresponding to the bulk and contact resistance associated with the clean contact is stored in memory of a computer.

Abstract: A test circuit (15 or 65), comprised of a plurality of parallel-connected circuit modules (15.sub.o-n or 65.sub.o-n), in response to both control signals from an associated commercially available automated test set (12), and output data from a test set-accessed read/write memory (14) under test, continuously senses for the presence of valid "one" or "zero" outputs on the data bit lines of the memory throughout a test set-established time window test period. When the memory output from a given data bit line, as applied to only an associated one of the circuit modules, is determined, as normally expected, to be continuously valid during each successive time window test period, a "pass" RESULT signal is generated by that circuit module and continuously applied to the test circuit (12) for flagging at any time between termination of the time window and the end of a given test set-established memory read cycle. Conversely, should the output on any memory data bit line be determined to be invalid (i.e.

Abstract: A probe for sensing the strength of the magnetic field that surrounds a current-carrying conductor has a square-loop magnetic material wrapped about a conductor which is placed in the magnetic field to be sensed. An alternating signal is applied to the conductor, of sufficient intensity to cause successive reversals of the polarity of the magnetic material. A sense winding around the magnetic material issues a switch signal every time the magnetic material reverses polarity. The switch signal is used to sample the alternating drive signal current in order to store the amplitude of the drive signal at the instant at which the magnetic material reverses polarity. The sampled signal amplitude is averaged over a period of time, and the resultant amplitude is a linear function of the strength of the magnetic field. A second conductor, magnetic material and sense winding are arranged in a position remote from the magnetic field in order to sense the effect of the Earth's magnetic field.

Abstract: To test certain structural characteristics of a weld formed between two dissimilar metals in order to test the quality, or structural integrity, of the weld, the emf generated at the weld bond interface during welding, as a result of the Seebeck effect (thermocouple), is monitored. As the weld cools, the emf decreases at a first essentially rapid rate with respect to time until the weld begins to recrystallize, or fuse, at which point the emf decreases at a second and slower rate since the latent heat of fusion of the metals decreases the cooling rate of the weld. When recrystallization is complete, the emf decreases at an essentially exponential rate. It has been discovered the rate of change of the emf with respect to time during recrystallization is an indication of the quantity of the metal involved in the weld where the weld is exposed to a constant heat sink, such as the atmosphere, since the more metal that is involved in the weld the slower the weld will cool during fusion, and vice versa.

Abstract: To convert an unregulated input voltage applied across an input and a reference terminal to a regulated output voltage across a load between the reference and an output terminal, a switching transistor is connected in series with an induction coil between the input and the output terminals. A flyback diode is connected between the reference terminal and the juncture between the transistor and the first coil, and is poled to be reverse biased when the transistor is conductive.