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MCG4150: Midterm 2006
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Course:
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MCG 4150 - Bioinstrumentation
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Instructor:
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Andy Adler
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Date:
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Mar. 8, 2006
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Directions:
You have 80 minutes to complete this exam.
The exam has four questions; you are required to answer any three of them.
Each question is worth equal marks.
This is a closed book exam; however,
you are permitted to bring a 8.5"×11"
sheet of notes into the exam.
You are permitted to use a calculator.
You may not communicate with anyone during the exam except the instructor.
You may make assumptions to simplify the problems as long a they
don't change the calculations by more than 10%.
You may assume the following conditions and constants:
- Atmospheric pressure, Patm: 101.3 kPa
- Density of air at Patm: 1.21 kg/m3
- 1 cmH2O = 98.5 Pa
- 760 mmHg = 101.3 kPa
- 1 Amp= 6.24×1018 e−/s
1.
Flow Transducer Designs
Consider the following types of air flow transducers:
−Pneumotachometer
(which measures pressure differences accross a flow resistance)
−Hot-wire anemometer
(which measures the current required to maintain a thermistor
at constant temperature)
−Rotating-vane flowmeter
(which measures rotation of a turbine in the air stream)
- 1A.
Sketch each transducer type and describe
how it works.
- 1B.
Compare each type in terms of:
1) accuracy,
2) frequency response,
3) linearity of the underlying sensor eleement,
4) directional response (response to flow in different directions)
2.
Flow Transducer Frequency Limits
In this question, we want to compare the frequency response of the
hot-wire anemometer and pneumotachometer.
- 2A.
The pneumotachometer can be modelled as a 15 cm
long tube of inner diameter 3 cm. Atmospheric
pressure is 101.3 kPa.
Calculate the compliance and inertance of the gas in
pneumotachometer.
answer:
Compliance = V/Patm = πr²L/Patm
= π*(0.015m)²*(0.15m)/101300Pa
= 1.0467e-009 m^5/N
Inertance = ρ*L/π/r²
= (1.21 kg/m³)*0.15m/(π*(0.015m)²)
= 256 kg/m^4
- 2B.
The hot-wire anemometer acts as a first order system with
time constant τ=0.5s. The pneumotachometer acts
as a second order system with natural frequency fn.
Compare the frequency response of the
hot-wire anemometer and pneumotachometer.
Which is the highest?
answer:
ωn= (LcCc)−½
=( 1.0467e-009m^5/N * 256 kg/m^4)^(-.5)
=( 2.6876e-007 m-kg/N)^(-.5) = (2.6876e-007 m-kg-s²/kg-m)^(-.5)
=1929 1/s
fn = ωn/2/π= 307 Hz.
pneumotachometer is much higher freq than anemometer
3.
Electrode Types
Consider the following two electrode types:
−Ag/AgCl electrode
−Stainless steel (SS) electrode.
- 3A.
What is a polarizable electrode? Compare these two electrodes
in terms of polarizablility.
- 3B.
An ECG amplifier is connected to an Ag/AgCl electrode
and has an input resistance of 1 MΩ.
The QRS peak of the ECG lasts 50 ms and has an
average signal level of +20 mV.
How many CL− ions enter or leave the
body from the electrode during the QRS peak?
answer:
V=IR
I=V/R= 20mV/1MΩ= 20nA
Electrons = (20e-9 A)*(6.24e18 e/s/A)*(50e-3 s)
= 6.24e9 electrons
Valence of CL− is one.
Thus 6.24e9 ions leave body
- 3C.
Consider a body which touches an exposed live wire
carrying 120V at 60Hz..
Rank the following in terms of danger.
−Touching an SS electrode lead to the wire.
−Touching an Ag/AgCl electrode lead to the wire.
−Touching dry skin to the wire.
−Touching wet skin to the wire.
4.
Nerve Conduction Velocity
Consider the classic "knee-jerk" reflex test.
- 4A.
Sketch a diagram and describe the nerve signal
conduction pathway during this test.
What accounts for the time delay between the hammer tap
and muscle contraction?
- 4B.
We wish to measure the time between hammer tap
and muscle contraction.
Design a system to measure this time delay.
Sketch your system and describe how it works?
Last Updated:
$Date: 2006-03-10 09:30:52 -0500 (Fri, 10 Mar 2006) $
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Engineering