Usage of Multimeter
Note: Multimeter being used to measure the varies quantities such as Voltage ,Resistance, Current.Apart from this it is also used in continuity test, diode check etc.
Multimeter
Description:
A multimeter is an electrical instrument capable of measuring
voltage, current, & resistance.Digital multimeter have numerical displays, like
digital clocks, for indicating the quantities. Analog Multimeter indicate these
quantities by means of a moving pointer over a printed scale.
Some digital multimeters are
autoranging. An autoranging meter has only a few selector switch (dial)
positions. Manual-ranging meters have several different selector positions for
each basic quantity: several for voltage, several for current, and several for
resistance. Autoranging is usually found on only the more expensive digital
meters.
Set multimeter's selector switch to
the highest-value "DC volt" position available. Autoranging
multimeters may only have a single position for DC voltage, in which case need to set the switch to that one position. Touch the red test probe to the
positive (+) side of a battery, and the black test probe to the negative (-)
side of the same battery. The meter should now provide with some sort of
indication. Reverse the test probe connections to the battery if the meter's
indication is negative (on an analog meter, a negative value is indicated by
the pointer deflecting left instead of right).
If meter is a manual-range type,
and the selector switch has been set to a high-range position, the indication
will be small. Move the selector switch to the next lower DC voltage range
setting and reconnect to the battery. The indication should be stronger now, as
indicated by a greater deflection of the analog meter pointer (needle), or more
active digits on the digital meter display. For the best results, move the
selector switch to the lowest-range setting that does not
"over-range" the meter. An over-ranged analog meter is said to be
"pegged," as the needle will be forced all the way to the right-hand
side of the scale, past the full-range scale value. An over-ranged digital
meter sometimes displays the letters "OL", or a series of dashed
lines. This indication is manufacturer-specific.
ILLUSTRATION
Voltage:
Voltage is the measurement of electrical “push” ready to
motivate electrons to move through a conductor.It is the specific energy per
unit charge,defined as joules per coulomb. It is analogous to
pressure in a fluid system: the force that moves fluid through a pipe, and is
measured in the unit of the Volt (V).
INSTRUCTION
To measure voltage, follow these steps:
- Plug black and red probes into the appropriate sockets (also referred to as "ports") on multimeter. For most multimeters, the black probe should be plugged into the socket labeled "COM," and the red probe into the socket labeled with a "V" (it might also have some other symbols).
- Choose the appropriate voltage setting on multimeter's dial. Remember that most battery-powered circuits will have direct current.. If working with a manual-ranging multimeter, estimate the range need based on the battery (or batteries) powering your circuit. For example, if circuit is powered by a single 9V battery, it probably doesn't make sense to select the setting for 200V, and 2V would be too low. If available, would want to select 20V.
- Touch the probe tips to your circuit in parallel with the element you want to measure voltage across. For example, Figure shows how to measure the voltage drop across a light bulb powered by the battery. Be sure to use the red probe on the side connected to the positive battery terminal, and the black probe on the side connected to the negative battery terminal (nothing will be harmed if one get this backwards, but voltage reading will be negative).
Figure. Measuring voltage across a lightbulb by attaching the multimeter probes in parallel. Current flow
is represented by the yellow arrows. In voltage-measurement mode, the multimeter's resistance is very high,
so almost all of the current flows through the lightbulb, and the multimeter does not have a big impact on
the circuit. Notice how the knob has been set to measure DC voltage (DCV) and the red probe is plugged
into the correct port for measuring voltage (labeled "VΩ" because it is also used to measure resistance).
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- If multimeter is not auto-ranging, one might need to adjust the range. If multimeter's screen just reads "0," then the range you have selected is probably too high. If the screen reads "OVER," "OL," or "1" (these are different ways of saying "overload"), then the range you have selected is too low. If this happens, adjust range up or down as necessary.
Resistance:
Resistance is the measure of
electrical "friction" as electrons move through a conductor. It is
measured in the unit of the "Ohm," that unit symbolized by the
capital Greek letter omega (Ω).
Set your multimeter to the highest
resistance range available. The resistance function is usually denoted by the
unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word "ohms." Touch the two test
probes of meter together. Then, the meter should register 0 ohms of
resistance. If one using an analog meter, will notice the needle
deflect full-scale when the probes are touched together, and return to its
resting position when the probes are pulled apart. The resistance scale on an
analog multimeter is reverse-printed from the other scales: zero resistance in
indicated at the far right-hand side of the scale, and infinite resistance is indicated
at the far left-hand side. There should also be a small adjustment knob or
"wheel" on the analog multimeter to calibrate it for "zero"
ohms of resistance. Touch the test probes together and move this adjustment
until the needle exactly points to zero at the right-hand end of the scale.
Although your multimeter is capable
of providing quantitative values of measured resistance, it is also useful for
qualitative tests of continuity: whether or not there is a continuous
electrical connection from one point to another. One can, for instance, test
the continuity of a piece of wire by connecting the meter probes to opposite
ends of the wire and checking to see the the needle moves full-scale. What
would we say about a piece of wire if the ohmmeter needle didn't move at all
when the probes were connected to opposite ends?
Digital multimeters set to the
"resistance" mode indicate non-continuity by displaying some
non-numerical indication on the display. Some models say "OL"
(Open-Loop), while others display dashed lines.Connect the meter's test probes
across the resistor as such, and note its indication on the resistance scale:
The needle points very close to
zero, you need to select a lower resistance range on the meter, just as you
needed to select an appropriate voltage range when reading the voltage of a
battery.
If one using a digital
multimeter, should see a numerical figure close to 10 shown on the display,
with a small "k" symbol on the right-hand side denoting the metric
prefix for "kilo" (thousand). Some digital meters are
manually-ranged, and require appropriate range selection just as the analog
meter. If yours is like this, experiment with different range switch positions
and see which one gives you the best indication.
Note ....When touch the meter probes to the resistor terminals,
try not to touch both probe tips to fingers. If one do, he will be
measuring the parallel combination of the resistor and your own body, which
will tend to make the meter indication lower than it should be! When measuring
a 10 kΩ resistor, this error will be minimal, but it may be more severe
when measuring other values of resistor.
You may safely measure the
resistance of your own body by holding one probe tip with the fingers of one
hand, and the other probe tip with the fingers of the other hand.
Current
Current is the measure of the rate
of electron "flow" in a circuit. It is measured in the unit of the
Ampere, simply called "Amp," (A).
OR.............................................................................
The most common way to measure
current in a circuit is to break the circuit open and insert an
"ammeter" in series (in-line) with the circuit so that all electrons
flowing through the circuit also have to go through the meter. Because
measuring current in this manner requires the meter be made part of the
circuit, it is a more difficult type of measurement to make than either voltage
or resistance.
Some digital meters, like the unit
shown in the illustration, have a separate jack to insert the red test lead
plug when measuring current. Other meters, like most inexpensive analog meters,
use the same jacks for measuring voltage, resistance, and current.
When an ammeter is placed in series
with a circuit, it ideally drops no voltage as current goes through it. In
other words, it acts very much like a piece of wire, with very little
resistance from one test probe to the other. Consequently, an ammeter will act
as a short circuit if placed in parallel (across the terminals of) a
substantial source of voltage. If this is done, a surge in current will result,
potentially damaging the meter:
Caution:
Ammeters are
generally protected from excessive current by means of a small fuse located inside the meter housing.
If the ammeter is accidently connected across a substantial voltage source, the
resultant surge in current will “blow” the fuse
& render the meter incapable of measuring current until the fuse is
replaced. Be very careful to avoid this scenario!
Conclusion (while measuring Voltage & Current Of a Circuit).....
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