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Sunday, 7 October 2018

ECG Machine Block diagram and working

ECG Machine Block diagram and working:
ECG Machine Block diagram
Normally we use the above set up for the measurement and plotting of ECG. The main blocks of an ECG machine and the function of each block is explained below.

1. Electrodes: We know the ECG electrodes mainly used for the pickup of ECG are five in number. By placing these electrodes at appropriate parts of body.

2. Lead selector:  As told earlier each pair of lead conveys certain information. So for the appropriate waveform or view we have to select an appropriate lead pair. The lead pair can be selected by a lead selector switch which can be switched to different lead pairs according to the type of waveform needed.

3. Pre-amplifier: The ECG signal is having very weak amplitude levels. So it is necessary that for proper analysis and plotting purpose , the waveform is to be amplified. The pre-amplifier used here will be an operational amplifier or instrumentation amplifier with high gain. They have High CMRR and extremely high input impedance.

4. Driver:  We use a driver motor of suitable specification to drive the paper roller. Normally the ECG waveform is to be plotted on a moving chart paper to find out the irregularities (if there is ) in the P,Q,R,S,T and U regions of the ECG waveform .So the paper movement and the moving speed can be controlled by the driver motor, which supplies the trigger the roller.

5. PMMC Galvanometer: PMMC (Permanent Magnet Moving Coil) galvanometer is a special type of device, where the deflection of the coil depends on the amplitude and the polarity of the signal applied to its input. The writing tip of the hot tip pen is connected to the chart paper. So the pen will be at rest in the center of its travel when no current flows in the coil. So the direction of deflection in the coil and the amount of deflections is determined by the amplitude and polarity of the ECG waveform.

6. Hot - tip stylus and stylus heater:  In most common ECG recording techniques, we use hot tip stylus for thermal writing. It is because, we normally use thermal recorders for the plotting of waveforms. The stylus is kept hot always by the stylus heater power supply. The writing tip is a stylus heated by a resistance wire.

7. Recorders : As discussed now, usually we use thermal recorders for the representation of ECG waveform. The paper used in thermal recorders is of special material which turns black when heated. The hot tip of the stylus will turn the white paper black whenever it touches. The tip of the stylus moves in accordance with the movement of the coil which in turn is proportional to the amplitude and polarity of the ECG waveform. Since the tip of the stylus is in contact with the thermal chart recorder, a clear representation of the ECG waveform is obtained.

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