ECG Tester

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ECG Tester

• Team Members
• Adam Dahlen
• Ibrahim Khansa
• Darshan Patel
• Steven Skroch
• Clients
• John G. Webster PhD, BME dept.
• Engineering World Health

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Background

• In order to avoid electrocardiograph
  malfunction, universal quality standards have
  been set up. Developing countries however are
  unable to afford the equipment necessary to test
  for these standards.

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Problem Statement

• Our goal is to design a low-cost device that
  could be used to test the conformity of ECG
  machines with as many quality standards as
  possible.

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Client Motivation

• Engineering World Healths volunteers comprise
  engineers, scientists, physicians, and students.
• EWHs goal is to to answer the needs of
  disadvantaged areas through providing and
  maintaining appropriate medical technology.

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Electrocardiographs

• Heart activity causes electrical changes
  throughout the body, with every heartbeat.
• ECG can detect these voltage changes on the skin.
• Output is printed in paper
• or on a computer screen.

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Why Test an ECG?

• Diagnosis is made by observing the amplitude and
  shape of the waves.
• Therefore, high accuracy is needed in both
  electrical measurements and output.
• A tester needs to act as a virtual heart signal.

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Standards to be Tested

• Accuracy and stability of the gain, time
  selection and alignment

V
mm
mm
s
input voltage
output trace
Gain mm/V Time selection mm/second
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Standards to be Tested (cont.)

• Low hysteresis
• Low noise, common mode rejection if Vinput 0V,
  then output 0mm

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Standards to be Tested (cont.)

• Frequency response Amplitude response should not
  differ significantly for different frequencies.
• The ECG should be able to superpose the heart
  signal over pacemaker pulses.

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Standards to be Tested (cont.)

• Input impedance if input impedance high ? Low
  losses of signal
• Input impedance should be more than 2.5MO)

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Standards to be Tested (cont.)

• AC voltage overload protection ECG must be able
  to resume function after overload.

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Device abilities

• Generate square and sine waves of amplitude
  variable within 5mV and frequency variable
  between 0.05Hz and 150Hz.
• Introduce a DC offset of 300mV into the
  oscillating signal.
• Generate an exponentially decreasing signal from
  an RC circuit for hysteresis testing.
• Introduce pacemaker-like pulses.

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Device abilities (cont.)

• Accuracy of 1 in voltage measure.
• Accuracy of 1 in frequency measure.
• Cost of less than 4 for quantities of 500.
• Size of less than 4 x 4 x 1 in storage.

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Oscillator design 1RLC
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Chosen Oscillator Design 555 timer
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DC Offset Design 1
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DC offset chosen Design
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Simulated output of dc offset circuit
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Advantages

• Can generate both square and sine waves.
• Can vary amplitude and frequency continuously.
• Easy introduction of DC offset
• Very low cost

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Limitations

• Opamps require high voltage supply.
• Three design alternatives
• Use low-voltage opamps
• Use wall outlet supply
• Use opamp alternatives (would decrease
  performance)
• Hard to attain 1 accuracy with low budget

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Future Work

• Design testing procedures for all criteria
• Find a power source for the opamps.
• Test the circuit, and add improvements

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References

• J. G. Webster (ed.), Bioinstrumentation, Hoboken,
  NJ John Wiley Sons, 2004.
• http//www.ewh.org
• AAMI manual

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Questions