Download Circuits3 – multimeter

ELECTRICAL CIRCUITS
Multimeter
1
OUTLINE
• Purpose
• Measuring Voltage
• Measuring Current
• Measuring Resistance
2
Purpose
• The purpose of a
Multimeter is to measure
voltage, current and
resistance
• The proper selection for
what you are measuring
must be selected
o
o
o
o
o
V dc
V ac
R
A dc
A ac
• In this course we will only
be measuring DC
3
Measuring Voltage
•
Set the Multimeter to Vdc
•
Attach the two probes, black
to “COM” or “ground”, and the
red to the port labelled “V” or
“Volts”
•
The number
on the screen
is the voltage
reading for
that power
supply
4
Measuring Voltage
•
Reversing the probes will
display a negative value on the
screen
•
Notice that it is the same
voltage, just a change in
polarity
5
Measuring Voltage
•
Voltage can be measured whether the power supply is
being used in a circuit or not
•
It can also be used to measure the voltage drop across any
element of a circuit
6
Measuring Voltage
•
Question
If the Multimeter displays 10.8 from the setup on the left, and
12.3 from the setup on the right, what would the Multimeter
display if the probes were placed on the two legs of the LED?
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Measuring Voltage
•
Answer
Since the two elements are in series, and there is a total of
12.3 volts from the power supply, if the first element (a
resistor) used up 10.8 volts, then the second element (an LED)
would have to use up the remaining 1.5
8
Measuring Current
•
Depending on how much
current we are measuring, we
might use the “A dc” setting or
the “mA dc” (milliamps)
setting
•
If we are not sure how much
current we will be measuring,
always select the larger, “A”,
setting
•
Connect the red probe to the
appropriate current port,
either “A” or “mA”
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Measuring Current
•
When measuring current it is important to NEVER place
the probes directly on the two battery terminals
•
This will cause a short
circuit
•
Remember V = I * R
•
If our resistance goes
down to zero, then our
current, I, goes up to
infinity
10
Measuring Current
•
To measure current we
always make the
Multimeter “an element of
the circuit”
i.e. – break the circuit and use
the Multimeter to complete it
11
Measuring Current
•
Since we are measuring
such a small current, we can
get a more accurate reading
by switching the Multimeter
and probe to the “mA”
settings
12
Measuring Current
=
13
Measuring Resistance
•
To measure Resistance we
simply select the resistance
setting on the meter, and Ω
port for the probe
•
Resistance is measured
with no power supply in
the circuit
14