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ECG Measurement System

ECG Measurement System. By Nick Rose Under guidance of Dr. Jack Ou Summer 2012. Built off of Chia -Hung Chen, Shi-Gun Pan, and Peter Kinget’s design for an ECG Measurement System from the Columbia Integrated Systems Lab. Full Circuit. Gain= 200. R=10 M. 9 V. Potentiometer.

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ECG Measurement System

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  1. ECG Measurement System By Nick Rose Under guidance of Dr. Jack Ou Summer 2012 Built off of Chia-Hung Chen, Shi-Gun Pan, and Peter Kinget’s design for an ECG Measurement System from the Columbia Integrated Systems Lab

  2. Full Circuit Gain= 200 R=10 M 9 V Potentiometer

  3. Bandpass Filter Transfer Function

  4. Op-Amp • Purpose: To bias voltage at output of AD624

  5. Opto-Coupler

  6. V(1) versus V(2) V(1) versus V(3)

  7. Instrumentation Amplifier Gain of 200

  8. Gain of 1000

  9. V(3) of op-amp versus: 2nd Harmonic Distortion 3rd Harmonic Distortion

  10. Gain of 200, V(3) of 741 op-amp = -4.4 V Adjusted V(3) to -4.4 V to minimize 2nd and 3rd harmonic distortion Magnitude of input sine wave versus gain (gain includes gain of opto coupler)

  11. Power Dissipation • The entire circuit (AD624, 741, optocoupler).. • Current draw: 114 mA • Voltage: dual power supply (+-9V)

  12. Shielded Versus Unshielded Cables • Untwisted cable, shielded by aluminum foil Aluminum shield is grounded

  13. Unshielded AD624 Output

  14. Shielded AD624 Output

  15. Unshielded ECG Output

  16. Shielded ECG Output

  17. Shield Input of ECG

  18. Unshield Input of ECG

  19. Shielded AD624 Output at DC

  20. Shielded AD624 Output (0 -12.5 Hz)

  21. Shielded AD624 Output at 60 Hz

  22. Unshielded AD624 Output at 60 Hz

  23. Unshielded ECG Output

  24. Shielded ECG Output

  25. Extra Components for stabilizing the Output Voltage of the AD624 • 10 Mohm resistors were used at pin 1 and 2 of AD624 in order to provide bias current transistors in the pre-amplifier stage • An input offset potentiometer with the middle pin attached to +9 V was used to reduce offset voltage. The voltage at pin 9 was used.

  26. Different Design Iterations • Breadboard • PCB • Equipment

  27. Future Work: Active Grounding Technique • Problems observed: • Common mode sensing resistors attached to node 16 and 3 of AD624 can affect of node 9 of AD624. • 25 Kohms, DC voltage at node 9 is disturbed. • 1 Mohm, DC voltage at node 9 is stabilized. • Large values of Rf makes it difficult to for negative feedback to pin node 2 of 741 op-amp to ground. • What is the right ratio of Rf/Ra?

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