Download CHAPTER-2

MEASUREMENT DEVICES
OUTLINE
Multimeters
 Analog Multimeters
 Digital Multimeters
 Breadboard
 Oscilloscope
 Signal Generator
 Clamp Meter
 Voltage Transformer
 Current Transformer
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MULTIMETERS
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A multimeter also known as a VOM (Volt-Ohm meter), is an electronic measuring
instrument that combines several measurement functions in one unit. To measure voltage
(ac, dc), current (ac, dc) and resistance, two types of instruments, analog and digital meters,
are utilized.
 Analog Multimeters
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The main part of an analog multimeter is the D’Arsonval meter movement also known as the
permanent-magnet moving-coil (PMMC) movement. It have multiple scales on the dial, a
moving needle and many manual settings on the function switch.
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MULTIMETERS
 Analog Multimeters – Operating principle
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MULTIMETERS
 Analog Multimeter Scales and Zero Position Adjustment
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A typical analog multimeter has several scales. As illustrated in following, each scale consists
of a curved line that is marked off into sections or divisions. A range identifies the high and
low limits of a scale.
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The zero adjustment should not normally need to be touched, but it may vary slightly with
time and temperature. Adjustment should be made with the meter not in use and it should
be gently adjusted with a screwdriver to ensure the meter is properly zeroed.
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MULTIMETERS
 The Measurement of Current, Voltage and Resistance Using Analog Multimeters
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When using an analog multimeter, measurements for voltage, current and resistance need to
be made in different ways. To illustrate the way in which these different tests can be made
using an analog multimeter, the simple circuit shown below will be used:
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MULTIMETERS
 Digital Multimeters
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In laboratory, due to we will use digital multimeters, digital multimeters are very important
more than analog multimeter.
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For AC measurements, the digital multimeter is a true rms instrument that it measures true
rms value of any periodic signal
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 Measuring DC Voltage Using Digital Multimeter
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Connect the black test lead to the COM jack and the red test lead to the V jack.
Set the range switch at the desired V range position.
Connect test leads across the source or load under measurement.
You can get a reading from LCD display. The polarity of the red lead connection will be
indicated along with the voltage value.
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When only the figure ‘1’ is displayed, it
indicates overrange situation and the
higher range has to be selected.
When the value scale to be measured is
unknown beforehand, set the range
selector at the highest position.
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 Measuring AC Voltage Using Digital Multimeter
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Connect the black test lead to the COM jack and the red test lead to the V jack.
Set the range switch at the desired V range position.
Put down the "DC/AC" button, meter will be transformed to the AC measuring state.
Connect test leads across the source or load under measurement.
You can get a reading from LCD display.
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When only the figure ‘1’ is displayed, it
indicates overrange situation and the
higher range has to be selected.
When the value scale to be measured is
unknown beforehand, set the range
selector at the highest position.
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 Measuring DC Currents Using Digital Multimeter
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Connect the black test lead to the COM jack and the red test lead to the A jack for a
maximum of 400mA current. For a maximum of 10A, move the red lead to the 10A jack.
Set the range switch at the desired A range position.
Connect test leads in series with the load under measurement.
You can get reading from LCD. The polarity of red connection will be indicated along with
the voltage value.
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When only the figure ‘1’ is displayed, it
indicates overrange situation and the
higher range has to be selected.
When the value scale to be measured is
unknown beforehand, set the range
selector at the highest position.
A socket is 250mA, the maximum current
of 10A socket is 12.5A, over-current will
destroy the fuse.
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 Measuring AC Currents Using Digital Multimeter
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Connect the black test lead to the COM jack and the red test lead to the A jack for a
maximum of 400mA current. For a maximum of 10A, move the red lead to the 10A jack.
Set the range switch at the desired A range position.
Put down the "DC/AC" button, meter will be transformed to the AC measuring state.
Connect test leads in series with the load under measurement.
You can get reading from LCD.
•
•
•
When only the figure ‘1’ is displayed, it
indicates overrange situation and the
higher range has to be selected.
When the value scale to be measured is
unknown beforehand, set the range
selector at the highest position.
A socket is 250mA, the maximum current
of 10A socket is 12.5A, over-current will
destroy the fuse.
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 Measuring Resistance and Continuity Test
• Connect the black test lead to the COM jack and the red test lead to the
Ω jack.
• Set the range switch at the desired Ω range position.
• Connect test leads across the resistance under measurement.
• You can get reading from LCD.
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 Measuring Capacitance
• Connect the black test lead to the COM jack and the red test lead to the
jack.
• Set the range switch at the desired F range position and press “L/C”
button down.
• Before connect test leads across two sides of the capacitor under
measurement, be sure that the capacitor has been discharged fully.
• You can get reading from LCD.
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 Measuring Inductance
• Connect the black test lead to the COM jack and the red test lead
• to the H jack.
• Set the range switch at the desired H range position and press “L/C”
button down.
• Connect test leads across two sides of the inductor under
• measurement.
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Testing Diode
• Connect the black test lead to the COM jack and the red test lead to the V
jack. (The polarity of red lead is “+”)
• Set the range switch at the range position.
• Connect the red lead to the anode, the black lead to the cathode of the
diode under testing.
• You can get reading from LCD.
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The meter will show the approximate
forward voltage drop of the diode.
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Testing Transistor
• Set the rotary switch at the hFE range position.
• Put two plugs of multifunction testing equipment (spare parts) into COM
jack and V jack.
• Identify whether the transistor is NPN or PNP type and insert emitter,
base and collector leads into the proper holes of the transistor on the
multifunction testing equipment (spare parts) for testing.
• You can get reading from LCD.
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Changing the fuse and battery in Digital Multimeters
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The differences between Analog and Digital Multimeter
• Analog multimeters give the output as a reading on a scale against a pointer, while digital
multimeter output is in numerical form displayed on a LCD.
• Analog multimeters give a continuous output and carry a greater uncertainty in the
measurement (about 3%), while digital multimeter measurements have a far less
uncertainty (about 0.5% or less). Digital multimeters are more accurate than analog
multimeters.
• Digital multimeters have a better range of measurements than analog multimeters.
• Digital multimeters offer additional features such as capacitance, temperature,
frequency, sound level measurements and detection of semiconductor device pins
(transistor / diode).
• Analog multimeters have to be calibrated manually, while most digital multimeters are
calibrated automatically before every measurement.
• Analog multimeters have to be set for the specific range of measurement manually, while
some must digital multimeters have auto ranging feature.
• Analog multimeters require practice to take good measurements, while digital
multimeters can be operated even by an untrained person.
• Analog multimeters are less costly while digital multimeters are expensive.
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BREADBOARD
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A breadboard is a simple way to quickly create and change a developing circuit,
often called a prototype circuit. Parts are just inserted into the same column of
the breadboard to connect them. Metal clips underneath the breadboard connect
the wires or component leads.
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CADET
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OSCILLOSCOPE
• An oscilloscope is a voltage sensing electronic instrument that is used to visualize
certain voltage waveforms.
• An oscilloscope can display the variation of a voltage waveform in time on the
oscilloscope’s screen.
• Most oscilloscopes have at least two input channels and each channel can display a
waveform on the screen. Multiple channels are useful for comparing waveforms.
 Diffrent waveforms (sine, square, triangle, DC voltage)
 Amplitude measurement
 Phase diffrence measurement
 Frequency measurement
 The obtain characteristic curves of semi-conductor circuit elements such as diode,
transistor
 The obtain of charge and discharge curves of condansators
 Oscilloscope is NOT measure current
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 OSCILLOSCOPE
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 OSCILLOSCOPE
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 Signal Generator
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 Signal Generator
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 Signal Generator
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 Signal Generator
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 Voltage Transformer
• A transformer is an electrical device that transfers energy from one circuit to
another purely by magnetic coupling.
• Relative motion of the parts of the transformer is not required for transfer of
energy.
• If a loads is connected to the secondary, an electric current will flow in the
secondary winding and electrical energy will be transferred from the primary circuit
through the transformer to the load
• Transformers are often used to convert between high and low voltages, to change
impedance, and to provide electrical isolation between circuits.
MEASUREMENT DEVICES
 Clamp Meter
• It is simple to measure very high currents (hundreds of amperes) with the
appropriate current transformer.
• The electric current in the conductor to be measured, without having to make
physical contact with it, or to disconnect it for insertion through the probe. Accurate
measurement of low currents (a few milliamperes) with a current transformer clamp
is more difficult.
• Clamp meter is only measure RMS value of sine wave. Other waveforms readings
will be incorrect.
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 Current Transformer
•A current transformer (CT) is used for measurement of electric currents.
•The CT is isolate the circuit from high voltage side and is protect to the circuit.
•Current transformers are commonly used in metering and protective relays in the
electrical power industry.
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CADET