ME 340 Project - Final

ME 340 Project - Final - Usman Ansari ME 340 05/10/2011...

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Usman Ansari ME 340 – 05/10/2011 MED-EKG (Medical Electrocardiogram) I am a mechanical engineering pre-med student, so I am very interested in learning about and analyzing any kind of medical engineering device. The EKG (electrocardiogram) is an innovative device that combines electrical and mechanical engineering. The EKG has the ability to detect irregular heart rhythms and therefore weaknesses in different parts of the heart muscle. It is a device that will continue to grow in its use and importance in the medical industry, helping to save human lives, as doctors are now becoming more dependent on its use to diagnose patients. The patients put their fingers on electrodes, which are sensors that read small voltages through the body produced by the contraction of the heart. As the signal travels along the internal circuit, it is passed through several filters. The signal is also amplified by several op amplifiers. Finally, the signal is passed on to a computer or oscilloscope where it can be seen and analyzed to check for irregular heart rhythms. I have decided to input a thermistor at the beginning of my electrocardiogram circuit. The right and left electrodes will be connected directly to the thermistor. When a patient applies pressure with his/her finger to the thermistor, the thermistor will vary in its resistance to correspond directly to the patient’s body temperature. For my wheatstone bridge diagram, I have chosen fixed resistor values for R1, R2, and R3 such that R1 = 1kΩ, R2 = 10kΩ, and R3 = 732Ω. In multisim I have decided to display the thermistor as the resistor R4. I will vary the resistor value R4 to show how the output voltage Vab will change correspondingly. I have connected a function generator to the input of my circuit in place of the AC voltage source. I have used a sinusoidal signal with 20V amplitude and 100Hz frequency such that Vin(t) = 20sin(200π) I have connected my oscilloscope cables across Vab to measure the output voltage across the detector. I want to see the correlation between a change in my resistor value R4 and the output voltage Vab. After conducting several runs for different values of R4 in multisim, I found that as I increase R4 up to a value of 7320Ω, the voltage output Vab correspondingly decreases until it becomes Vab = 0V at R4 = 7320Ω. Also, the output voltage signal reaches a positive peak when the input voltage signal reaches a positive peak while R4 < 7320Ω, or more simply put,
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ME 340 Project - Final - Usman Ansari ME 340 05/10/2011...

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