Using a Multimeter (or you, too, can have fun with electricity)

1
Using a Multimeter(or you, too, can have fun
with electricity)

• Volts
• Ohms
• milliamps

2
Understand the Quantity to be Measured

• Is it voltage, current or resistance?
• Is it direct current or alternating current?
• What is the maximum expected value?
• Select the appropriate measurement range
• USE CAUTION WITH HIGH VOLTAGE (more than 30 volts
  or milliamps may be hazardous)

3
Voltage is measured across the source (in
parallel)
4
Alternating Current has no polarity
5
Current (ac or dc) is measured through the load
(in series)
6
Resistance is measured across a passive circuit
element
7
Digital Meters
Quantity is displayed on a fixed number of digits
Indicate polarity by displaying a minus sign
Decimal point moves with range setting
8
Moving Vane Meters

• Can be damaged by the wrong polarity signal
• Or by exceeding the maximum range

9
An Interactive Quiz
Feel free to give the answer if you think you
know it!
10
Choose the Correct Setting
200milli 2 20 200 400m 4 40 400 600
9-volt transistor battery
DC AC VOLTS OHMS MILLIAMPS
11
Choose the Correct Setting

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

9-volt transistor battery

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

This alkaline battery is 9 volts new, and drops
with age.
12
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
12-volt marine battery
DC AC VOLTS OHMS MILLIAMPS
13
Choose the Correct Setting

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

12-volt marine battery

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

Rechargeable batteries can be higher than their
rated voltage!
14
Choose the Correct Setting
DC-to-AC Power Inverter Output
200m 2 20 200 400m 4 40 400 600
DC AC VOLTS OHMS MILLIAMPS
15
Choose the Correct Setting
DC-to-AC Power Inverter Output

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

For safety, start with the highest range
16
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
AC-to-DC Wall Adapter
DC AC VOLTS OHMS MILLIAMPS
17
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
AC-to-DC Wall Adapter

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

Pick the best range according to the label
18
Choose the Correct Setting
200 2k 20k 200k 400 4k 40k 400k
2.7k ohm resistor
DC AC VOLTS OHMS MILLIAMPS
19
Choose the Correct Setting

• 200
• 2k
• 20k
• 200k
• 400
• 4k
• 40k
• 400k

2.7k ohm resistor

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

Reading the color code will tell you the expected
value.
20
Choose the Correct Setting
200 2k 20k 200k 400 4k 40k 400k
5-amp fuse
DC AC VOLTS OHMS MILLIAMPS
21
Choose the Correct Setting

• 200
• 2k
• 20k
• 200k
• 400
• 4k
• 40k
• 400k

5-amp fuse

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

A fuse should either be 0 ohms, or infinity if
blown, so choose the lowest resistance scale.
22
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
240-volt range outlet
DC AC VOLTS OHMS MILLIAMPS
Dont touch the metal probe tips with this
measurement!
23
Choose the Correct Setting

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

240-volt range outlet

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

Start with the highest range for line voltage
circuits.
24
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
1.5-volt watch battery
DC AC VOLTS OHMS MILLIAMPS
25
Choose the Correct Setting

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

1.5-volt watch battery

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

The lowest usable range will give the highest
accuracy.
26
Choose the Correct Setting
200m 2 20 200 400m 4 40 400 600
Current a battery produces
DC AC VOLTS OHMS MILLIAMPS
27
Choose the Correct Setting
Current a battery produces

• 200m
• 2
• 20
• 200
• 400m
• 4
• 40
• 400
• 600

• DC
• AC
• VOLTS
• OHMS
• MILLIAMPS

Wrong!
This will blow the meter fuse and/or damage the
meter!
28
Safety First

• Use caution when measuring dangerous voltages
• Understand the measurement you are making before
  using the meter
• Test the meter itself on a known value
• Make sure the meter is functioning correctly, has
  been calibrated, and has a good battery

29
Thank You

• For your attention