# MULTIMETER by infojustwin

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```									ECE, ME – I SEM

BASIC
ELECTRONICS
Multimeter
a)   Types (Analog & Digital)
b)   Voltage Measurement
c)   Current Measurement
d)   Resistance Measurement
Multimeter
   Electrical Test Equipment - The Multimeter
   A multimeter is used to measure voltage, current or
   resistance, depending upon the function selected
   – A voltmeter is used to measure voltage across a
   component or circuit
   – An ammeter is used to measure current through a
   circuit
   – An ohmmeter is used to measure resistance
Measuring Voltages and Currents
when measuring voltage we connect across the component
when measuring current we connect in series with the
component
measurement
   our measuring instrument will have an effective resistance (RM)
   when measuring voltage we connect a resistance in parallel with
the component concerned which changes the resistance in the
circuit and therefore changes the voltage we are trying to
measure
measurement
 Our measuring instrument will have an effective
resistance (RM)
 when measuring current we connect a resistance
in series with the component concerned which
again changes the resistance in the circuit and
therefore changes the current we are trying to
measure.
Measuring a Resistor
   Remove power if necessary and isolate the
component from the circuit under test
Principle of Operation
  The analog multimeter make use of permanent
magnet moving coil (PMMC) mechanism. (Also
called D’Arsonal Movement)
 It is basically a dc current meter.

 Three essential components

a) Deflecting device

b) Controlling device

c) Damping device
Typical d’Arsonval Meter Movement
Meter Deflection is Proportional to
Current
Digital Multimeters
   Digital multimeters (DMMs) are often
(inaccurately) referred to as digital voltmeters
or DVMs
   At their heart is an analogue-to-digital converter

A simplified block diagram
Typical Digital Multimeters (DMM)
Digital Multimeter
   Measurement of voltage, current and resistance
is achieved using appropriate circuits to produce
a voltage proportional to the quantity to be
measured
   In simple DMMs alternating signals are rectified as
in analogue multimeters to give its average value
which is multiplied by 1.11 to directly display the
r.m.s. value of sine waves
   more sophisticated devices use a true r.m.s.
converter which accurately produced a voltage
proportional to the r.m.s. value of an input waveform
Digital Multimeter
Schematic Symbols for Meters

 The analog voltmeter and ammeter must be
connected to the circuit with proper
polarity to avoid damaging the meter
movement.
 The ohmmeter may only be used on
unenergized components
Key Points
   The magnitude of an alternating waveform can be
described by its peak, peak-to-peak, average or r.m.s.
value
   The root-mean-square value of a waveform is the
value that will produce the same power as an
equivalent direct quantity
   Simple analogue ammeter and voltmeters are based
on moving coil meters
   Digital multimeters are easy to use and offer high
accuracy
   Oscilloscopes display the waveform of a signal and
allow quantities such as phase to be measured.

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