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Biomedical Engineering - Amplifier

  1. Dec 28, 2014 #1
    1. The problem statement, all variables and given/known data
    I- What is application of this circuit? What does it do?
    II- Simulate this circuit in a simulator software and by determine correct values for resistors, show heat losses (H) is nearly constant.
    III- Calculate H analytically (manually) (voltage division) and compare with part II in a software.
    Hint: 29dbo94.jpg (Comparator)
    IV- By proper ratio selection for resistors, show sensitivity of heat losses (H) with respect to thermal resistance (RT) is almost zero.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Dec 28, 2014 #2


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    Look at the schematic in part 1 of the problem statement and at least tell us this much.
  4. Dec 29, 2014 #3
    I only know this circuit is from Book "Medical Instrumentation Application and Design (by John G. Webster)"
  5. Dec 29, 2014 #4


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    Hint: the purpose of the circuit is written in the first figure.
  6. Jan 6, 2015 #5


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    @Paradoxs -- Per the PF rules, you must show some effort before we can offer tutorial help. Please post your thoughts on this problem.
  7. Jan 8, 2015 #6
    The circuit (part 1) is Thermal velocity meter circuit
    according to Book "Medical Instrumentation Application and Design (by John G. Webster) - 4th edition - Page 383" The main use of thermal-velocity sensors is to measure the velocity of blood and to compile velocity profiles in studies of animals, although such sensors have also been regularly used to measure velocity and acceleration of blood at the aortic root in human patients undergoing diagnostic catheterization.
    I simulate the circuit in Proteus:
  8. Jan 8, 2015 #7


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    Nice tool. Now for understanding of what's going on in the circuit. You familiar with Ohm's law ? Can you express VA/V0 in an expression with Rx and R1 ? Idem VB/V0 in an expression with RT and R2 ?

    [edit] initially assuming there is no current going into the operational amplifier, that is.
    Last edited: Jan 8, 2015
  9. Jan 8, 2015 #8


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    Your original circuit might be to used to measure the velocity of blood but the words "Temperature Sensor" suggest it's for measuring something more obvious.
  10. Jan 8, 2015 #9


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    Oh, and to Para: welcome to PF :) (must be a bit of a culture shock -- never mind)

    Now that CW has as good as given it away, we can proceed and try to bridge the gap between what is and what is advertised. Is it plausible there is a relation between the "obvious" and a blood velocity somewhere in the neighborhood of RT ?
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