ENME 351 – Electronics & Instrumentation II: Fall 2020 Department of Mechanical Engineering. Univers

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ENME 351 Assignment #9 Mitchell, Fall 2020

ENME 351 – Electronics & Instrumentation II: Fall 2020 Department of Mechanical Engineering Due Date

Thursday, November 19th, 2020

Submission Information

  

Submit via Gradescope by 11:59 pm Include your name, UID, date, assignment number, and signature on the top of the first page.

Clearly identify your final answers to each problem by drawing a box around each answer. No credit will be awarded for ambiguous answers.

Problem #1 (4 points) The pH meter shown at right uses a transducer made up of paired electrodes inside glass. This transducer can produce voltage potentials up to 1 V with an internal output impedance (R1) of up to 1 G. If you want to further filter/condition the transducer output signal: a) What is the minimum input impedance required to keep the loading error below 1 mV using the op-amp shown (i.e., not an ideal op-amp in this case)?

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ENME 351 Assignment #9 Mitchell, Fall 2020

b) Would a 741 op-amp provide the input impedance required for this application?

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ENME 351 Assignment #9 Mitchell, Fall 2020

Source: http://www.ti.com/lit/ds/symlink/ua741.pdf

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ENME 351 Assignment #9 Mitchell, Fall 2020

Problem #2 (6 points) A temperature sensor is put into the following circuit as Rsensor. An identical, matching reference sensor Rref is held at a constant 37oC.

a) What is the purpose of each amplifier in the circuit?

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ENME 351 Assignment #9 Mitchell, Fall 2020

b) Derive a relation for the output voltage Vout in terms of the problem parameters.

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ENME 351 Assignment #9 Mitchell, Fall 2020

c) Given Vin = 80 mV, Rsensor = Rref = 30 k at 37 oC, K = -5000 / oC for the sensor, and given R1 = 600 , R2 = 400 , and R3 = 60 k, what is Vout when the sensor is at 37.002 oC?

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ENME 351 Assignment #9 Mitchell, Fall 2020

Problem #3 (4 points) For each of the motor driver circuits below, answer the following questions. The nominal supply voltage Vmotor = 12 V, the motor resistance Rm = 115 , the motor torque constant KT = 6.61 mN-m/A, and the motor speed constant Ke = 0.692 V/krpm (Faulhaber Series 1516 012S motor). The transistors are each 2N7000 series. Use the typical values and the conditions that most closely approximate each case.

a) Is the transistor ON or OFF? If the transistor is ON, answer parts (b) through (d).

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ENME 351 Assignment #9 Mitchell, Fall 2020

b) What is the motor current?

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ENME 351 Assignment #9 Mitchell, Fall 2020

c) What is the voltage drop across the motor?

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ENME 351 Assignment #9 Mitchell, Fall 2020

d) If the motor is experiencing a load torque of 0.65 mN-m, what is the speed in rpm?

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ENME 351 Assignment #9 Mitchell, Fall 2020

Problem #4 (2 points) The rotor inductance for the Faulhaber Series 1516 012S motor is 900 μH. If the current through a transistor switch changes at a rate of 1 A/μsec when switched off, what is the voltage generated across the rotor inductance? As an engineer, does this voltage level cause you to be alarmed? If so, what can be done to prevent damage to the circuit?

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ENME 351 Assignment #9 Mitchell, Fall 2020

Problem #5 (4 points) Consider the motor circuit at right. Sketch the time-domain signals required at A and B to turn the motor forward at 50% full speed and reverse at 75% full speed. Label plot axes and all relevant axis values. Assume that the signals are provided by an Arduino Uno, that speed is proportional to voltage and that the threshold voltage for the transistors is 3.3V, and a VPWM period of 1 msec.

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ENME 351 Assignment #9 Mitchell, Fall 2020

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ENME 351 Assignment #9 Mitchell, Fall 2020

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