Apparatus and method for measuring relative compression

Abstract

In accordance with the present invention, a measurement instrument employing an improved method for measuring relative compression is provided. The compression signal is first acquired by digitizing the battery voltage over multiple engine cycles using an analog to digital converter (ADC) to obtain a series of digital samples. The compression signal is filtered using a low pass digital filtering technique such as a finite impulse response (FIR) filter along with spike removal that removes high frequency noise and impulse-type ignition noise from the compression signal. The filtered compression signal is then "zero-lined", meaning that each of the peaks corresponding to a compression curve of a cylinder, which are bounded on either side, are re-scaled such that the local minima reside along a zero base line. Next, the zero-lined compression signal is averaged over the multiple cycles of the engine. Finally, the averaged signal is scaled and displayed in a manner allowing the relative compression levels between the cylinders of the engine to be readily ascertained.

Dependencies are inferred from the claim text.