An electrical meter has light-emissive display elements and a meter circuit featuring electrically floating input terminals relative to device ground, and offers a potentially significant cost advantage compared to available alternatives in low-accuracy measuring applications. A series string of the light-emissive display elements are physically arranged along a line in order of increasing turn-on current threshold of each element so that they are successively turned on along the line with increasing current to be measured. A control circuit included in the series string has first and second semiconductively-complementary active semiconductor devices, such as an NPN and PNP transistor, each with base, emitter, and collector. The input-sensing conductor, such as a base, of each active semiconductor is a respective floating input of the meter. The semiconductors have at least two output control conductors, such as collector and emitter, two corresponding control conductors being wired together (as emitter to emitter) and the other two being wired into the series string. The light-emitting elements are suitably semiconductor diodes (LEDs), incandescent bulbs, neon bulbs, or other devices, with resistive shunting where necessary. Two such meter circuits are wired back-to-back with their light-emissive elements arranged physically back-to-back to form an uncomplicated galvanometer device for measuring electrical currents of either positive or negative polarity.

The Digital Waveform Analyzer is a solid state highly portable device that approximates the operation of a cathode ray oscilloscope in time sweep mode by selectively lighting elements of a rectangular matrix of light emitting diodes. The LED array has its rows driven by a vertical circuit and its columns driven by a horizontal circuit. The vertical circuit converts the analog input signal to a "one-of-N" digital code. The converter utilizes an array of comparators and exclusive OR gates and does not require clocking. The horizontal circuit which corresponds to the sweep section of a standard cathode ray oscilloscope has a variable frequency clock generator, a binary counter, a decoder and synchronizing circuits.

An amplifier circuit controls the output current through an inductive load. A signal is amplified by one or more op amps, and sourced into a back to back coupling of an NPN transistor and a PNP transistor. In a positive circuit segment, current is sourced to an inductive load, and in a negative segment, current is sunk from the inductive load. The current at the output of the inductive load flows through a resistor, and the resultant voltage drop is negatively fed back to the op amp.

An apparatus for generating a current source test stimulus signal having a constant current regardless of an internal impedance value of a device under test includes a voltage source generation unit and a voltage to current (V/I) converter. The voltage source generation unit converts source data stored in internal memory into analog signals, and combines the analog signals and a reference signal of D/C voltage level to generate voltage source test stimulus signals. The V/I converter converts the voltage source test stimulus signals into current source test stimulus signals and outputs the current source test stimulus signal to a device under test. The V/I converter maintains the current levels of the current source test stimulus signals at a predetermined value, regardless of the internal impedance of input pins of the device under test. In this manner, the operating efficiency of the device under test can be accurately determined.

A load sensor generates a signal representing the amount of force applied to a workpiece during each blow of a multi-blow forming process. In a two blow process, a first amplifier is connected to the load sensor for amplifying the load sensor signals representing both blows in the forming process. A first gain control circuit is connected to the first amplifier for adjusting the amount of amplification to a first predetermined level. A logic control circuit is connected to the first amplifier for generating a first enabling signal during the first blow in the forming process and a second enabling signal during the second blow in the forming process. A second amplifier is connected to the first amplifier for amplifying the load sensor signals representing only the first blows in the forming process. A second gain control circuit is connected to the second amplifier for adjusting the amount of amplification to a second predetermined level. Circuits responsive to the signals generated by the first and second amplifiers and to the first and second enable signals are provided to measure the forces applied to the workpiece during each blow of the forming process.