DIGITAL MULTIMETER PPT

DIGITAL MULTIMETER PPT

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  BY : PRAPTIBORTHAKUR POWIET
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  DEFINATION DESIGN WORKING PRINCIPLE BLOCK DIAGRAM METHODOF MEASUREMENT
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  It is acommon and important laboratory instrument .It contains three different meters in one. • It is use to measure AC or DC voltages • It is used to measure AC/DC current and resistance with digital display. • It gives digital output , which is very accurate. As the name suggest , multimeter are those measuring instruments which can be used to calculate multiple circuit characteristics.
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  A multimeter hasthree parts:- DISPLAY SELECTION KNOB PORTS
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  Two probes areplugged into two of the ports on the front of the units. COM stands for common and is almost always connected to the ground of a circuit. 10A is the special port used when measuring greater currents ( greater than 200mA) mAVΩ is the port that the red probe is conventionally plugged into.This port allows te measurement of current (upto 200 mA), voltage and resistance.
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  • The PCBcontains an assortment of various components including various types of resistors, capacitors, diodes and IC’s. Also it host the battery, crystal oscillator, PTC , LCD and the buzzer which test the continuity of device under test.
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  • The PCBis bound to the top casing og the multimeter with the help of screws.A LCD and a rotary knob switch are sandwiched between the top casing and the other side of the PCB. Allso,the contacts for switching the multimeter ON and OFF can be seen. • Some multimeter employs the rotary switch to handle the switching ON & OFF options while some requires a slider switch. • The selection knob allows the user to set the multimeter to read different things such as milliamps(mA) of current,voltage and resistance
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  • A LCDis embedded on the PCB and is interfaced through pinouts on the PCB itself. • A transparent plastic casing is over the LCD protecting it from the scratches.Also shock absorption is provided by the rubber pads closely attached at the top and bottom of the LCD. • The display usually has four digits and the ability to display a negative sign.A few multimeter have illuminated displays for better viewing in low light situations.
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  • The V–(*) setting is for measuring DC voltages. Eg. battery voltage. • The V~ (*) setting is for measuring AC voltages. Eg. house voltage • The 20 (*) setting is to measure DC voltages in the volts (V) range.
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  MEASURING VOLTAGE • Setthe dial to the a value greater than the voltage being measured. • For our labs, we will be working with the 20 V range.
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  FUNCTION SWITCH MEASURINGRESISTANCE & CURRENT • The Ω setting (*)is used to Measure electrical resistance in Ohms. The A setting (*) is used to measure DC current in amps.
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  MEASURING RESISTANCE Set thedial to a value greater than the resistor value being measured. The 1 in the display means the resistance is higher than the current dial setting For a 5000 ohm resistor, set the dial to 20K. For a 300 ohm resistor, set the dial to 2000
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  ADVANTAGES OF DIGITALMULTIMETER • Very high accuracy • Has very high input impedance which ensures less loading effect on the input • The numeric display of digital meters provides zero parallax error.
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  DISADVANTAGES OF DIGITALMULTIMETER • It does not do well with measurement fluctuations • It is more expensive than the analog type • It can be difficult to find one for your specific needs