Abstract: A proximity detection system having two eddy current probes, one a measurement and the other a reference probe. In one embodiment, one probe is energized by a high frequency AC signal and the other by a DC signal. The energizing signals are periodically switched between the two probes and the difference between responses of the probes when AC energized is detected. The difference eliminates drift and variations in the probe outputs from environmental effects like temperature, one of the probes measures the proximity of a selected material, and the other probe is set-up with a target of the same material at a constant distance, as a reference. The DC constant current signal which alternately energizes each probe when not energized by the AC signal, prevents each probe from being dead when not energized by the AC signal. The probes are operated in a resonant mode to increase both the system linearity and sensitivity to target position.

Abstract: Apparatus for determining time of occurrence of the maximum excursion, or top dead center or bottom dead center, of an engine piston or similar structure. The piston excursion is continuously measured, and a signal, corresponding to the portion of the cycle having the closest proximity, is selected. The signal is compared to a threshold, and the duration wherein the signal exceeds the threshold is measured by a first digital counter. The measured duration is divided by two, the resulting number counted by a second counter during the subsequent piston cycle, beginning simultaneously with the first counter. The second counter completes the count of one-half of the duration at the midpoint of the measured duration. The apparatus produces an output signal at the midpoint of the measured duration, which corresponds to the maximum excursion, or top dead center or bottom dead center, of the piston motion.

Abstract: An extent of travel detection system particularly adapted for measuring piston bottom excursion in an internal combustion engine. Two eddy-current position transducer probes are provided for each piston, the first being positioned to sense piston bottom travel position and the second being operated as a reference probe, mounted in close proximity to the first probe. The first probe of each pair is only operated to measure piston travel within the cylinder during the brief moment that the piston is near its bottom. The actual point of the bottom travel is detected, using the reference probe to compensate for environment effects such as temperature. The measured bottom point for each piston is displayed either by a separate or shared display. Changes in the displays over time indicate engine wear or impending failure. The measured bottom points are typically averaged over a selected number of engine cycles.

Abstract: A system for monitoring misalignment between two in-line rotating shafts and for indicating the direction of shaft misalignment wherein alignment sensors are mounted directly to and rotate with the shafts. The sensors are mounted to detect position or stress variations between elements on coupled shafts as a function of the rotational position of the shaft and thus errors normally encountered where the sensor is positioned off the shaft are avoided. A coupling system such as a rotary transformer is employed to apply power to the sensors and associated circuitry on the shaft and to receive from the shaft signals indicative of sensed misalignment. A signal representative of relative phasing between the rotating shaft and surrounding equipment is provided and is used in electronically processing the misalignment signals to provide output signals indicative of the direction and orientation of misalignment between the rotating shafts on orthogonal axes.