Dr.G.Ravindranath

What is ECG and how the interpretation can be done . Introduction The electrocardiogram (ECG) is one of the simplest and oldest cardiac assessment of Heart condition With modern machines, surface ECGs are quick and easy to obtain at the bedside and are based on relatively simple electrophysiological concepts. Basic principles What is an ECG? An ECG is simply a representation of the electrical activity of the heart muscle as it changes with time, usually printed on paper for easier analysis. Like other muscles, cardiac muscle contracts in response to electrical  depolarisation  of the muscle cells. It is the sum of this electrical activity, when amplified and recorded for just a few seconds that we know as an ECG. The normal ECG It will be clear from above that the first structure to be depolarised during normal sinus rhythm is the right atrium, closely followed by the left atrium. So the first electrical signal on a normal ECG originates from the atria and is k...

Pulse width modulated converter: The voltage source converters are used in electrical drives.These converters utilize capacitors in the DC-link to store temporarily electricalenergy. Switching the power electronic devices allows the DC voltage tobe modulated which can result in a variable voltage and frequency waveform.The purpose of the modulator is to generate the required switching signalsfor these switching devices on the basis of user defined inputs. For this purpose,the voltage–time integral was introduced which in turn is tied tothe average voltage per sample U ( t k) that may be written as U(t)=(1/T s ) ∫ u(t) dt ranging between t k to (t k + T s ) where T s is a given sample interval and u ( t ) represents the instantaneousvoltage across a single-phase of a load.The introduction of the variable T s assumes the use of a fixed sampling frequency which is normally judiciallychosen higher than the fundamental frequency range required to controlelectrical machines.The u...

What is the Effect of Source Inductance? Most of the converter analysis is generally simplified under the ideal conditions (no source impedance). But this statement will not be justified as source impedance is basically inductive with a small resistive element. Source inductance will have major impact on the converter performance as its existence will change the output voltage of the converter. Consequently, output voltage will be decreased when the load current decreases. Additionally, input current and output voltage waveforms will be changing considerably. Source inductance effect on a converter can be analyzed in below two ways. Assume that the converter is operating in conduction mode and the ripple from the load current is going to be negligible. Here, open circuit voltage will become equal to average DC output at a firing angle of α. Below diagram describes a fully controlled converter with the source in single phase. SCRs T3 and T4 will be assumed to be in conductio...