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Consider the strain-gage bridge circuit shown in the diagram below. The bridge is energized by a current source, i = 180 mA. The bridge has two fixed resistance ballast resistors, R = 100 ohms, and one variable resistor that can be used to null the bridge. The single strain gage is a Monel type with a gage factor of 1.9, and a temperature coefficient of 2000 ppm/A????1C. When the variable resistor is initially set to 100 ohms and at standard temperature (20 A????1C), the initial deflection voltage is -7 mV. The variable resistor is then adjusted until the deflection voltage is zero. Later, the strain gage experiences a strain of 65 units of micro-strain (i.e. 65A????110^-6 ). Later still, and while under the same strain, the temperature changes such that the deflection voltage decreases by 15 mV. Based on the given information determine: a) the nominal resistance of the strain gage at standard temperature (ohms), b) the resistance of the variable resistor required to null the bridge at standard temperature (ohms)
Show transcribed image text Consider the strain-gage bridge circuit shown in the diagram below. The bridge is energized by a current source, i = 180 mA. The bridge has two fixed resistance ballast resistors, R = 100 ohms, and one variable resistor that can be used to null the bridge. The single strain gage is a Monel type with a gage factor of 1.9, and a temperature coefficient of 2000 ppm/A????1½C. When the variable resistor is initially set to 100 ohms and at standard temperature (20 A????1½C), the initial deflection voltage is -7 mV. The variable resistor is then adjusted until the deflection voltage is zero. Later, the strain gage experiences a strain of 65 units of micro-strain (i.e. 65A????1½10^-6 ). Later still, and while under the same strain, the temperature changes such that the deflection voltage decreases by 15 mV. Based on the given information determine: a) the nominal resistance of the strain gage at standard temperature (ohms), b) the resistance of the variable resistor required to null the bridge at standard temperature (ohms)
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