Apparatus and method for measuring relative compression
First Claim
1. In a measurement instrument adapted for measuring relative compression in an internal combustion engine, a method for obtaining improved measurement accuracy comprising:
- (a) sampling a battery voltage to obtain digital measurement values during a cranking phase of said internal combustion engine over a plurality of engine cycles;
(b) storing said digital measurement values as a time record to obtain a compression signal containing a set of compression peaks for each of said engine cycles;
(c) filtering said time record to remove noise;
(d) performing a zero-line operation on each of said compression peaks;
(e) averaging each of said compression peaks with corresponding compression peaks between said plurality of engine cycles to obtain a set of averaged compression peaks;
(f) calculating said relative compression from the amplitude of said averaged compression peaks; and
(g) visually displaying said averaged compression peaks as a trace graph.
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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.
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Citations
15 Claims
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1. In a measurement instrument adapted for measuring relative compression in an internal combustion engine, a method for obtaining improved measurement accuracy comprising:
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(a) sampling a battery voltage to obtain digital measurement values during a cranking phase of said internal combustion engine over a plurality of engine cycles; (b) storing said digital measurement values as a time record to obtain a compression signal containing a set of compression peaks for each of said engine cycles; (c) filtering said time record to remove noise; (d) performing a zero-line operation on each of said compression peaks; (e) averaging each of said compression peaks with corresponding compression peaks between said plurality of engine cycles to obtain a set of averaged compression peaks; (f) calculating said relative compression from the amplitude of said averaged compression peaks; and (g) visually displaying said averaged compression peaks as a trace graph. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A measurement instrument adapted for measuring relative compression in an internal combustion engine, comprising:
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(a) an analog to digital converter with an input coupled to receive a battery voltage during a cranking phase over a plurality of engine cycles of said internal combustion engine, said analog to digital converter producing digital measurement values from said battery voltage; (b) a memory for storing each of said digital measurement values; (c) a display for visually displaying said relative compression; and (d) a microprocessor coupled to said analog to digital converter to receive and store said digital measurement values in said memory as a time record comprising a compression signal which contains a set of compression peaks for each of said engine cycles wherein said microprocessor processes said compression signal to obtain a set of averaged compression peaks, calculates said relative compression, and provides said relative compression to said display for visually displaying said set of averaged compression peaks as a trace graph. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification