Abstract: To permit physical separation and movement between an automotive vehicle and a test or diagnostic apparatus, the transducers transmitting signals representative of vehicle operating characteristics are coupled to a wireless transmitter, for example operating in long-wave, ultra-short-wave, infrared or ultrasonic mode; the signals are received in a wireless receiver constructed to receive the respectively transmitted signals, for application to a test or diagnostic apparatus. The system permits relative movement between the vehicle and the normally stationary diagnostic or test apparatus, for example to carry out diagnosis during movement of the vehicle.

Abstract: In order to generate a signal having a well-defined feature which exactly coincides with the zero-crossing point of an input signal, for example in order to define the top dead center position of the crankshaft of an engine for the purpose of valve and ignition timing, the invention provides a circuit which is prepared by the passage of the first half of an input signal across a predetermined threshold. When the first threshold is exceeded, the circuit opens a switch which connects a source of reference potential, equal to the zero crossing point of the input signal, to the threshold switch, to represent a second threshold. As the input signal crosses that second threshold level, which constitutes the zero crossing point, the threshold switch closes, thereby generating the trailing edge of the output signal which constitutes a signal feature coincident with the zero crossing point and hence with a fixed angular position of the rotating shaft.

Abstract: An instrument of the type employed to measure the conduction angle of the ignition coil of the battery-powered ignition system of an internal combustion engine comprises input connectors which are connected to terminals of such ignition system and an evaluating circuit which generates a signal corresponding to the conduction angle to be measured by ascertaining whether an input signal derived from the input connectors rises above or falls below a predetermined threshold voltage level. For differing types of conventional ignition systems, differing threshold voltage levels are required, but instead of resorting to manual switchover to such different levels, the instrument of the invention modifies the threshold voltage level employed in automatic dependence upon the value of the input signal derived by the input connectors. The threshold voltage level assumes a first value when coil conduction ceases and a second value when coil conduction recommences.

Abstract: To counteract the phase error in the signal from an rpm transducer of an engine test stand or analyzer at varying engine speeds, the signal processor of the invention receives the transducer signal whose amplitude varies with frequency and generates therefrom an output signal of constant amplitude. This signal is supplied to a threshold switch which includes circuitry for integrating periodic output signals and generating therefrom a control signal whose amplitude is proportional to the frequency of the input signal. This analog signal is used to alter the switching threshold of the threshold switch, thereby imparting to the output signal a frequency compensation which counteracts the inherent phase error and results in an output signal of constant phase with respect to the transducer signal. The apparatus of the invention is particularly useful for adjusting ignition timing, valve timing, etc. in internal combustion engines in which the input signal is derived from the crankshaft speed.