Patent ID: 6679100
Filing Date: 2004-01-20
Classification: G01L

Abstract:
A method of measuring a change in pressure inside an engine cylinder during combustion, said method comprising the steps of:affixing at least one thick film resistor to a metal shell of a spark plug that provides combustion ignition to the engine cylinder; including said at least one thick film resistor in a wheatstone bridge circuit; applying a voltage to said at least one thick film resistor; monitoring a change in resistance of said at least one thick film resistor in response to change in strain of the spark plug to sense change in pressure during combustion inside the engine cylinder; and amplifying the change in resistance of said at least one thick film resistor with an automatic drift compensating circuit; wherein said step of amplifying comprises: comparing the voltage from each side of said wheatstone bridge circuit to produce a first voltage output; inputting said first voltage output into a first amplifier, said first amplifier producing a second voltage output; balancing said first voltage output with said second voltage output; inputting said first voltage output and said second voltage output into a second amplifier; and adjusting the output of said second amplifier to a predetermined level when pressure in side the engine cylinder is equal to zero.