Abstract: An optical fiber propagation time measurement circuit. A light pulse is iteratively transmitted into a near end of a fiber under test (FUT) at a predetermined frequency and detected at a far end of the FUT after a propagation time. A repetitive propagation signal having a predetermined amplitude and a width corresponding the propagation time is developed by detection circuitry. The d.c. voltage average of the propagation signal is determined and used to compute the propagation time since the ratio of the d.c. voltage average to the predetermined amplitude is equal to the ratio of the propagation time to the period of the light pulses.

Abstract: A method and apparatus are provided for determining which path of a network transmission link having a receive path and a transmit path is carrying receive signals, and then automatically configuring a network tester such that an internal transmitter and an internal receiver match the transmit and receive paths of the network. Initially, both paths are monitored by the tester's receiver to determine whether there is traffic on the network. Then the tester automatically configures its interface to designate a first one of the paths as the receive path, and tests this configuration to determine whether the internal receiver receives a signal. If a signal is received, the configuration is verified. If no signal is received, the tester reconfigures the interface to designate the other path as the receive path. Once the network receive path is identified, the tester automatically configures its interface such that the transmit path is set opposite the receive path.

Abstract: A novel method of and apparatus for accurately measuring surge currents such as motor-starting inrush currents is provided. An input signal from a current sensor is monitored, and when the input signal changes and exceeds a predetermined threshold, a surge current is detected. The input signal is acquired over a predetermined time period by a fast sampling ADC, which converts the input signal into a series of digitized samples representative of instantaneous current values. These values are processed to compute average current or RMS current, which is then displayed.

Abstract: An apparatus and method of measuring capacitances are provided in which charge packets of known value are delivered to a capacitor of unknown value until a final voltage is determined, and the capacitance is calculated based on the known total charge and measured voltage.

Abstract: A pattern recognition system to qualify valid triggering for digital storage oscilloscopes. Valid trigger qualification may be established from recognition of triggering level and interval time information, as well as other pattern-related information, to start or stop waveform acquisition. Trigger qualification may be established from either a pattern match or a mismatch. The trigger recognition system may be further extended to the occurrence of complex signals, such as those associated with television, rotating machinery, or other phenomena occuring in predetermined or known patterns.

Abstract: An improved formable coil for an AC sensor having a predetermined length and a predetermined number of turns. The coil is wound in multiple passes in opposite directions, with a predetermined number of passes in each direction to fill in any gaps and provide a stable helical-wound coil. A preferred embodiment is wound on a collapsible mandrel to facilitate free removal of the coil from the mandrel.

Abstract: A link cable assembly is provided as an interface between a network cable test instrument and a network to be tested. The link cable assembly includes a link cable that is constructed to minimize cross talk and have long-term high quality reliability. Interchangeable connector personality modules releasably attached to the link cable permit testing networks having different electrical characteristics. Calibration data may be stored within the cable assembly to allow intrinsic “patch cord” return loss to be factored out of network cable measurements.

Abstract: A precision RMS measurement system is provided by extending the effective resolution of a medium-resolution sampling RMS converter. An AC or other time-varying cyclic signal is simultaneously applied to an average-responding AC-to-DC converter and to a high-speed medium resolution sampling analog-to-digital converter. The average voltage produced by the AC-to-DC converter is measured by a precision analog-to-digital converter to produce a highly accurate DC voltage measurement. The output of the sampling analog-to-digital converter is provided to a digital signal processor, which calculates the RMS and average values. A microprocessor then multiplies the ratio of the calculated RMS and average values by the highly-accurate DC average to produce a highly accurate RMS voltage. The precision RMS voltage is then displayed.

Abstract: A calibrated isothermal assembly for a thermocouple thermometer is provided to obviate a calibration step after manufacture of the instrument. A compact isothermal block is fabricated on a specialized printed circuit board which includes a thick metal plate to establish sufficient thermal mass and good heat conductivity. A temperature sensor is mounted at the thermocouple reference junction on the printed circuit board to track the reference junction temperature. The calibrated isothermal assembly also includes a current source for the temperature sensor, and a memory device containing stored calibration data specific to the temperature sensor.

Abstract: An improved capacitance measurement system employs a selectable constant current source which is switched into a capacitor in a charge measurement system. The capacitor produces a linear ramp voltage in response to the constant current. An analog-to-digital converter (ADC) measures the change in voltage along the ramp over a corresponding change in time. These values, together with the value of constant current, are used to calculate the capacitance. In the preferred embodiment, a multi-slope ADC is utilized for the measurement. This system offers a wide range of measurable capacitance, and is fast responding and accurate. In addition, visual feedback to the user on measurement progress can be provided, which is particularly advantageous when measuring large capacitors.

Abstract: A method of measuring capacitance is provided in which measurement speed is increased by as much as two orders of magnitude by optimizing timing parameters to rapidly charge and discharge the capacitor in small increments about an equilibrium voltage. The capacitor is charged at a linear rate by applying a predetermined constant current thereto, and discharged at an exponential rate determined by the RC time constant in the discharge path. Incremental charge and discharge times are selected in such a manner that results in an equilibrium voltage at a point where the charge voltage ramp and discharge voltage curve would cross if they were superimposed on one another. By appropriate selection of the incremental charge and discharge times, the equilibrium voltage may be conveniently established at a point well within the range of a measuring analog-to-digital converter (ADC). The voltage difference over the incremental charge time may be measured on one cycle and utilized to compute the capacitance value.

Abstract: A lock device for electronic apparatus is provided as a non-intrusive and removable attachment, The lock device has an actuating member that translates linear movement along a longitudinal axis to linear movement of a pair of retractable lugs along a transverse axis. The lock device is designed for use with an electronic instrument having an accessory-receiving cavity or recess built into its plastic case. The recess includes a pair of pockets on either side into which corresponding lugs of the lock device may be received.