avoid damaging the instrument good practice first to
switch the highest value particular scale range. excessive
current flows, the fuse element overheats and melts, breaking the circuit. The red terminal the meter, identifying the positive input for
testing voltage and current, usually becomes the negative terminal when
the meter used ohmmeter because the way the internal bat-
tery connected the meter movement.
A conductor carrying current and wound into solenoid produces mag-
netic field very similar permanent magnet, but has the advantage of
being switched and off any switch which controls the circuit current.
.
MAGNETIC EFFECT
Whenever current flows conductor magnetic field set around
the conductor like extension the insulation. This will give
a more accurate reading which might be, say, 2. 5. The fuse element made metal with
a low melting point and forms part the electrical circuit. The magnetic field
increases with the current and collapses the current switched off.
Supply
(a) Ammeter connection
V Ω
FIGURE 5. Before
taking measurements the appropriate volt, ampere ohm scale should
be selected.
Supply
(b) Voltmeter connection
V Ω
Safety First
Voltmeters and Ammeters
Electrical test meters are expensive
and easy steal.
The heating effect electric current also the principle upon which a
fuse gives protection circuit.12(a).12
Using multimeter (a) ammeter
and (b) voltmeter. When used voltmeter the
multimeter must connected parallel with the component, shown
in Fig. 5.
HEATING EFFECT
The movement electrons within conductor, which the flow an
electric current, causes increase the temperature the conductor.
The three effects electric current
When electric current flows circuit can have one more the
following three effects: heating, magnetic chemical. By
changing these variables, conductor may operated hot and used as
the heating element fire, operated cool and used electrical
installation conductor.When the multimeter
is used ammeter measure current must connected series
with the test circuit, shown Fig.
When using commercial multirange meter ohmmeter for testing
electronic components, care must exercised identifying the positive
terminal.
The magnetic effect electric current the principle upon which elec-
tric bells, relays, instruments, motors and generators work. Check the meter manufacturers
handbook before using multimeter test electronic components.12(b).Basic scientific concepts electrotechnology
111
The multimeter
Multimeters are designed measure voltage, current resistance.49A. For example, the
10A scale first selected and reading 2.5A displayed, then know
that more appropriate scale would the range.
The amount heat generated this current flow depends upon the type
and dimensions the conductor and the quantity current flowing.
● protect them placing their
protective case
● Keep them safe, out sight and
locked up.
Definition
When electric current flows a
circuit can have one more the
following three effects: heating, mag-
netic chemical
