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Formal ECE Lab 10 Report

Formal ECE Lab 10 Report - ABSTRACT The purpose of the work...

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ABSTRACT The purpose of the work included in this report was to build an attenuator that would accurately reduce (attenuate) a given voltage signal to a specified level within the given constraints. A circuit was constructed using a function generator to supply voltage, a coaxial-cable for capacitance and an oscilloscope to measure the resulting voltage waveform. A pair of resistors was used in the circuit to reduce the voltage level given by the signal generator to a specified level read by the oscilloscope, through the process of voltage division. The general purpose of the work is to write a procedure suitable for a technician to build similar attenuators. INTRODUCTION The given problem required a device that would reduce a voltage waveform given by a signal generator to a specified amount that would later be read by an oscilloscope. This required the construction of a circuit where the two previously mentioned devices were connected in parallel with a pair of external resistors and in parallel with a coaxial-cable. When this circuit was used the user found the values of the capacitance in the circuit as well as the value of the time constant using the oscilloscope. This allowed the user to determine the values needed for the external pair of resistors and use the concept of voltage division to reduce the voltage signal.
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One method to get this solution was by constructing a circuit called an Attenuator Coaxial-Cable Oscilloscope Interface. THEORY AND CALCULATIONS The attenuator circuit used in this project is based on a few basic principles and techniques. First the user constructed a model for capacitance measurement (Figure 1) which is shown below. To find the capacitance of the real capacitor in the circuit (modeled as a coaxial-cable), the user implemented the step response technique. This involved connecting a real voltage source (a signal generator with an internal resistance) and an external resistor ( R ext ) in series with the real capacitor to be measured. A real oscilloscope (a scope with an internal resistance) is then connected in parallel with the capacitor in order to measure the time constant ( T ) of the step response. In order to find the capacitance, the user must also know the total resistance. The user
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