Method of measuring strain

A method of measuring strain of an object with a bridge having in an arm thereof a strain gage applied to the object for producing a resistance change depending on the strain developed in the object, and resistors in respective remaining three arms thereof, said resistors having respective resistances independent of the strain developed in the object, said bridge having a pair of power corners respectively at a pair of diagonally opposite joints thereof and a pair of signal corners respectively at a pair of other diagonally opposite joints thereof, said method comprising the steps of:

• detecting an output voltage between said signal corners as an initial unbalanced output voltage e.sub.0 of said bridge while no strain is being detected by said strain gage;
• applying a power supply voltage between said power corners of the bridge and detecting an output voltage e between said signal corners to detect strain of the object;
• and
• measuring strain developed in said object based on a value .epsilon..sub.a determined using the detected output voltage e and said initial unbalanced output voltage e.sub.0 according to the following equation (1):
• ##EQU30## where V represents the power supply voltage applied between said power corners of said bridge, K the gage factor of said strain gage, R.sub.3 the resistance of the resistor in the arm of said bridge which is opposite to said arm with said strain gage;
• and R.sub.4 the resistance of the resistor in the arm of said bridge which is positioned adjacent to said arm with said strain gage across one of said power corners.