Biomedical Engineering - Amplifier

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Discussion Overview

The discussion revolves around a circuit related to biomedical engineering, specifically a thermal velocity meter circuit used for measuring blood velocity. Participants explore its applications, simulation, and analytical calculations related to heat losses and thermal resistance.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Participants inquire about the application and function of the circuit, emphasizing the need to refer to the schematic provided.
  • Some participants identify the circuit as a thermal velocity meter, referencing the book "Medical Instrumentation Application and Design" by John G. Webster.
  • One participant mentions that thermal-velocity sensors are primarily used to measure blood velocity and compile velocity profiles in animal studies, as well as in human diagnostic procedures.
  • There is a suggestion to simulate the circuit using software like Proteus and to express voltage ratios in terms of resistances.
  • Another participant raises a question about the relationship between the circuit's purpose and the term "Temperature Sensor," suggesting a potential ambiguity in its application.
  • Participants emphasize the importance of showing effort in problem-solving before receiving tutorial help.

Areas of Agreement / Disagreement

Participants generally agree on the identification of the circuit as a thermal velocity meter and its application in measuring blood velocity. However, there are differing interpretations regarding the specific purpose of the circuit, particularly concerning the mention of a "Temperature Sensor." The discussion remains unresolved on certain aspects of the circuit's function and the implications of its design.

Contextual Notes

Some assumptions about the circuit's operation, such as the absence of current into the operational amplifier, are noted but not fully explored. There are also unresolved questions about the relationship between the circuit's outputs and the thermal resistance.

Paradoxs
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Homework Statement


2jg584x.jpg

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.

Homework Equations


2qdu360.jpg

icphlf.jpg


The Attempt at a Solution

 
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Paradoxs said:
I- What is application of this circuit? What does it do?
Look at the schematic in part 1 of the problem statement and at least tell us this much.
 
Bystander said:
Look at the schematic in part 1 of the problem statement and at least tell us this much.
I only know this circuit is from Book "Medical Instrumentation Application and Design (by John G. Webster)"
 
Paradoxs said:
I only know this circuit is from Book "Medical Instrumentation Application and Design (by John G. Webster)"
Hint: the purpose of the circuit is written in the first figure.
 
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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.
 
berkeman said:
@Paradoxs -- Per the PF rules, you must show some effort before we can offer tutorial help. Please post your thoughts on this problem.
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:
circuit_simulation.jpg
 
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:
Paradoxs said:
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...

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.
 
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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