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THE SUMMING AMPLIFIER / AVERAGER OBJECTIVES: The purpose of this experiment is to demonstrate of a 3-input amplifier and a variation which allows the determination of the algebraic average voltage value of 3-inputs. MATERIALS: 1 741 General purpose OP-AMP 2 Electrolytic Capacitor, 10 µF/50V Resistor, 3.3K 4 3 Potentiometer, 50K 2 1 Digital VOM Breadboard Dual Regulated DC Power Supply 1 DISCUSSION: Formulas: Three-input summing amplifier output voltage Vo - PV1- (2) V2 - V3 Vo - (+) (V1 + V2 + V3) (if R₁ = R₂= R3) PROCEDURES: 1. Construct the summing amplifier circuit shown of the figure shown below. RVI SON UP RV2 RV3 11

Circuit 1 2. Adjust the three potentiometer to provide a value for VR1 = -4V, VR2 = +2V and VR3 = +V. (note: all voltage value must be in RMS value) 3. Measure the corresponding output voltage in RMS and record this value table below. 4. 6. Compare the result with the expected value. (compute use the equation). Adjust all three potentiometers to obtain the remaining three DC voltage listed on the table below and compare it with the expected value. V₁ V2 V3 Measured V. Expected Vo -4V +2V +5V +1V +2V -2V +3V -3V -3V +1V +1V +1V 7. Turn off and disconnect the power of the circuit and wire the summing amplifier circuit so that all three input resistor (R₁, R2 and R3) are 3.3k0, while feedback resistor (RF) is now 1k02. Adjust all three potentiometers to obtain the DC voltages the values of V₁, V2 and V3 listed in the table below. Measure the corresponding DC output voltages in RMS of the summing amplifier and compare it with the expected value. Record all values in the table below. V₁ V2 V3 Measured Vo Expected Vo -4V +2V +5V +1V +2V -6V +3V -3V -6V +1V +2V +3V Note: in each case you should measure output voltages that are equal to the algebraic average of the three input voltages, except that the output polarity

is inverted, or is opposite of what you might expect the average to be. A summing amplifier having N equal input resistor can be changed to take the average of its inputs by setting the value of the feedback resistor to 1/N times the value any one of the input resistors. QUESTIONS: 1. How was the equation for the output voltage of summing amplifier derived? Show your solution. OBSERVATION: CONCLUSION: