Experiment 3: Study of Operational Amplifier Task 1: Operational Amplifier Task 1a: Non-inverting Op-amp Operation, calculation of gain In this task, you will need the following: • A breadboard, wires, a power supply, and a DMM. • 10 or 20 kΩ pot • Op-amp LM741 or LM324. • Five 1 kΩ resistors. Fig 1: Circuit diagram for Task 1a, pin diagram and internal schematics of general purpose opamp Procedure: 1. Set Vin = 2.5 V by adjusting the pot. The gain will change depending on the number of 1 kΩ resistors that are connected to the negative input. 2. Add 1 kΩ resistor one by one as shown in fig 1 and calculate gain form the measured value. 3. Compare with theoretically calculated values. Task 1b: Repeat Task 1a with AC input, 5Vp-p and observe change in output in accordance with gain change. Task 1c: Inverting Op-amp Operation, calculation of gain Apply Vin to the negative input and ground the positive input of the op-amp. This is an inverting setup. Repeat all of Task 1a and measure Vout for four different gains. Are you able to observe saturation? Task 1d: Repeat Task 1c with AC input, 5Vp-p and observe change in output in accordance with gain change. Report: Question 1: State the basis of any discrepancy found in Task 1a - step 2 and 3. (Hint: Voltage saturation) Question 2: Estimate Vout with Vin = 3.0 V for (a) non-inverting setup with one, two, three, or four 1 kΩ resistors in parallel to the positive input (i.e., Task 1a), and (b) inverting setup with one, two, three, or four 1 kΩ resistors in parallel to the negative input (i.e., Task 1b). For which case will you be able to observe saturation? Task 2: Signal Conditioning for Temperature Sensor In this task, you will need the following: • A breadboard, wires, wire cutter/stripper, a power supply, and a DMM. • Two pots (10 or 20 kΩ). • Diode temperature sensor LM335. • Op-amp LM324. • Resistors: 1Ω, three 1, 100 and 5.1 kΩ. Procedure: 1. Set your first pot 1 to generate the proper current, 0.5 to 5 mA, to your LM335 temperature sensor. This current can be measured by checking the voltage drop across the 1Ω resistor (Vab from0.5 to 5 mV). Now, make sure that the LM335 generates a proper voltage output; it should correspond to the ambient temperature, Vb= +2.98 V for 298 K (250C). The 1st stage is buffer stage, so Vc should be identical to Vb, +2.98 V. 2. If the indoor temperature changes from 10 to 300C, or 283 to 303 K, Vb and Vc also vary from 2.83 to 3.03 V. 3. Zero adjust stage: Set the room temperature at 250C or 298 K, as our new zero point by using an adder circuit. As Vc = +2.98 V, we will provide Vd = -2.98 V to the negative input of the opamp (powered by a pot that is connected to -12 V power as shown in fig 2). As the summing junction is connected to the negative input of an op-amp, the output signal will be inverted, and the gain will be 1 kΩ /1 kΩ = 1. Adjust the 2nd pot to make Vd = -2.98 V, causing the output of this stage to become zero (Ve = 0 V). Fig 2: LM335 diode temperature sensor and pin diagram. Signal conditioning circuit (Task 2) 4. Gain stage: In this inverting configuration, and the gain is 5.1 kΩ/100 Ω =51. As Ve =0 V, the final output should also be 0V. Measure and record Ve, Vf, 5. Hold the LM335 with your fingers, and measure the voltage at various points; Vb, Vc, Vd, Ve, Vf. Vb = Vc should read +3.00 V. As Vd is unchanged and reads -2.98 V, measure and record Vf. Report: Question 3: In task 2, step 4, did you find Ve =0 V or not? Explain with proper reasoning. Compare theoretical value with measure value in Task 2, step 4. Question 4: Vb = +2.98 V (case 1) and +3.00 V (case 2), when Vd = -2.98 V. Find the currents flowing towards the summing junction for the above two. Question 5: If you were to repeat Task 2 for resistive temperature sensor with a Wheatstone bridge, the outputs from the Wheatstone bridge should be connected to both positive and negative input terminals of an op-amp. A zero adjust stage is not necessary, explain why?
