Post on 26-Mar-2015
Basic Electrical Measurements 1
Basic electrical measurements 2
Basic Electrical Measurements
Skill 2 Unit 2:
Digital Multimeters
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Goals of this presentation:
• Understand how to safely operate a digital multimeter (DMM).
• Learn how to set a DMM to the correct function, for a given measurement.
• Understand how to use a DMM to perform basic measurements.
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A first look at the Digital Multimeter
• Display
• Function Dial
• Probe Input Jacks
• Function Buttons
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• Battery access
• Fuse ratings: 11 amp
On the back...
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Display
It’s important to understand the many different symbols.
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Display
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Function Dial
• OFF
• AC Volts & Hertz V • DC Volts V• Continuity (tone)
• Ohms
• Diodes
• Capacitance• AC Amps A• DC Amps A
))))Ω
Display backlight On/Off
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Probe Jacks
• Common (black)
• Volts, Ohms, etc.
( V Ω )
• Amps
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• Physical Condition
• Leads & Probes
• User Protection
Safety
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Safety Inspection
Physical damage:
• Case
• Display
• Function Buttons
• Selector Dial
• Probe Jacks
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Safety Inspection
Test leads and probes
Safe to 1000 volts (max).
Check test lead resistance: Step 1: Insert leads in V/ and COM
inputs
Step 2: Select , touch probe tipsGood leads are 0.1 - 0.5
How do you check a single test lead?
Visually check for:• Shrouded connectors not damaged: no
insulation pulled away from end connectors.
• Insulation not melted, cut, cracked, etc.
• Probes: Finger guards intact, tips: not loose, broken off or burned.
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Safety Inspection
Checking meter fuses on most meters: Step 1: Plug test lead in V / input.
Step 2: Select
Step 3: Insert probe tip into A input and read value.
(should be less than 0.5 )
Is the fuse okay?
What would an open fuse read?
Note: This test will only confirm that a fuse is good. It will not test for a wrong sized fuse being installed.
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Safety Features
• Auto Ranging
• Reversed Polarity Protection
• 1000 volts protection on leads(higher than maximum range of AC or DC volts)
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DMM Measurements
• Volts (AC & DC)
• Resistance (Ohms Ω)
• Diodes
• Continuity
• Amps (AC & DC)
• Frequency (Hertz)
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DMM Measurements
AC Volts
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DMM Measurements
DC Volts V
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DMM Measurements
Continuity• Tone can be heard when
resistance is typically less than 50 Ω (250 Ω max).
))))
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DMM Measurements
Resistance Ω• Maximum 40 M Ω• Six ranges (auto or manual)
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DMM Measurements
AC Amps A• 10 Amps maximum
• Protected by internal fuse
• Change positive lead to “A” input
• “LEAd” is displayed whenever switching to or from amps mode, as a reminder to change the positive lead.
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DMM Measurements
DC Amps A• 10 Amps maximum
• Protected by internal fuse
• Change positive lead to “A” input
• “LEAd” is displayed whenever switching to or from amps mode, as a reminder to change the positive lead.
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Common DMM / User Hazards
• Voltage contact while in continuity or resistanceProtection: Overload protection in ohms up to the meter’s volt rating.
• Measuring voltage with test leads in current jacksProtection: High energy fuses rated to the meter’s voltage rating.
• Shock from accidental contact with live componentsProtection: Test Leads double insulated, recessed / shrouded,
finger guards. Replace when damaged.
• Using meter or tester above rated voltageProtection: Good karma !
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Summary
What we learned:
• Functions of the DMM
• Safety inspection
• How to check for good test leads
• How to test for open fuses
• Function of overload protection
• Why amperage inputs need fuses
• How to take measurements
• Common user hazards
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Ohm’s Law
OHM’S LAW
POWER
I
II
I
I
I
I
R
RR R
R
R
RE
E
E
E
EE
E
PP
PP
P
P
P
VOLTS OHMS
AMPS
2
2
2
2
OHM’S LAW
REP
IE I
Primary Use: DC CircuitsPrimary Use: AC Circuits
- KEEPING IT SIMPLE -
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Review
• Safety check the meter and leads prior to use
• Place the Test Leads in correct input
• Amps input is low impedance 10 A max • Safety- fused use correct fuse only
• Select the correct function for the reading you want
• Min / Max and Hold functions can be useful
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END
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