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Digital Multimeter Introduction

Digital Multimeter Introduction. 2) DIGITAL MULTIMETER

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Digital Multimeter Introduction

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  1. Digital MultimeterIntroduction 2) DIGITAL MULTIMETER Digital multimetersoffer higher accuracy and input impedance, unambiguous readings at greater viewing distances, smaller size, and a digital electrical output (for interfacing with external equipment) in addition to visual readout. The main part of most of the digital multimeter (DMMs) is the analog to digital converter (A/D) which converts an analog input signal to a digital output. While specifications may vary, virtually such multimeters are developed around the same block .

  2. DMM

  3. Specifications • Voltage ranges are from + 200 mV to + 1000 V. • Accuracy is about + 0.03% • Resolution is about 10 µV. • The resistance range is from 200 Ω to 20 MΩ. • The current range is from 200 µA to 2000 mA.

  4. Advantages • High Accuracy • High Input Impedance. • Short measurement time • Programmability • Smaller size

  5. Operation • It consists of several A to D converters, decade counters and displays. • It is basically a dc voltmeter. In order to measure unknown current, current to voltage converter is used. • An unknown current to be measured is applied to one of the input terminals of Op-Amp and as the input current of Op-Amp is negligible therefore this current will pass through known Resistance Rf. The voltage developed across the known Rf is applied to A to D converter and digital display is obtained. • To measure an unknown resistance; a constant current source is used. • To measure ac voltage a rectifier and filter is used.

  6. Advantages • High Speed • Programmable • Automatic range selection • High Accuracy • Better Resolution • Output can be recorded.

  7. Specifications • Input range is from +1V to +1000V. • For a 3 digit DVM accuracy is about +0.1% • Resolution is 1 part in 1000000. • Input resistance is 10 MΩ.

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