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: 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 shielded banana plug attached to one end of a test lead is suitable for connection to a corresponding input receptacle in an instrument. The plug includes an inner conductor having an first nonconductive shroud which is concentric with and spaced apart from the inner conducter. The shroud extends beyond the tip of the inner conductor. A conductive shield is concentric with and outside the first nonconductive shroud and is recessed from the end of the shroud. A nonconductive outer shroud is spaced apart from and concentric with the shield and extends beyond the tip of the inner conductor. An input receptacle suitable for mating with the shielded banana plug includes an conductive inner sleeve for receiving the inner conductor, a nonconductive shroud that is concentric with and outside the inner sleeve and which extends beyond the inner sleeve, and a conductive outer sleeve for receiving the conductive shield. The input receptacle is also suitable for mating with a conventional, nonshielded banana plug.

Abstract: A high input impedance AC buffer for use in an instrument that does not require high frequency compensation or calibration. An op-amp receives an input signal that is to be measured via a high resistance input resistor and produces an output signal proportional to the input signal. A feedback resistor block and a feedback attenuator form the feedback path of the buffer and establish buffer gain. The low resistances of the feedback block and the feedback attenuator are substantially less than the resistance of the high resistance input resistor, precluding the need for compensation and calibration capacitors. A switching circuit operates to select resistors in the feedback resistance block and the feedback attenuator to provide predetermined gains for the buffer.

Abstract: An instrument having a continuity test feature wherein a change in continuity state from open-to-short or short-to-open is captured and displayed. A comparator provides continuity state information for a circuit under test. A storage device receives the state information and provides logic indicative of the continuity state which is read by a controller that executes a continuity capture program initiated by keypad or function selector input. A first transition between different continuity states is captured during a present capture cycle and is displayed in a form indicative of the type of transition captured. Subsequent transitions during the present capture cycle are ignored.

Abstract: A multi-function, multi-mode switch for an instrument that changes the instrument between primary and secondary functions and between first and second modes of operation within the primary and secondary functions. The instrument changes from the first mode of operation to the second mode of operation when the switch is actuated for a first period of time. The instrument changes from the second mode of operation to the first mode of operation when the switch is activated for a second period of time. The instrument changes between the primary and secondary functions when the switch is operated for a third period of time. The switch controls a program that instructs the instrument to perform the appropriate operations. The program also instructs the instrument to confirm that an operation has occurred via audible and visual feedback.

Abstract: A low impedance overvoltage protection circuit includes a first MOSFET having a drain connected to an input signal and a source connected to a drain of a second MOSFET, the source of the second MOSFET being coupled to the output. The gates of the first and second MOSFETs are connected to voltage supplies which float relative to the input signal values so as to maintain the gates of the respective MOSFETs biased to a conducting state. The maximum and minimum values to which the floating voltage supplies will float are defined by clamping diodes and clamp voltage sources. When the input signal value exceeds a desired positive maximum value, the first MOSFET is no longer biased to an on state whereby the MOSFET turns off, shunting the input signal through a high impedance for limiting input current and removing the input signal from the output. Negative going peak values are removed in a like manner by the second MOSFET.

Abstract: A keypad structure includes a stiff backing element and an elastomeric cover that have between them a first membrane on which is defined a shorting conductive layer, a second membrane on which is defined a main conductive layer, the second membrane on which the main conductive layer is defined as being adjacent the elastomeric cover rather than the stiff backing element as in the prior art. A third membrane provides spacing between the main and shorting conductive layers when the keypad is not compressed. An elastomeric interconnect can then be used to connect exposed contacts on the main conductive layer with other circuitry in an instrument utilizing the keypad.