How to choose a Multimeter
Gerardo Osorio

How to choose a Multimeter

choosing the correct is very important!

    A multimeter is a portable electrical device used to directly measure various
electrical quantities, these can be active as currents, voltages or
potentials, and also passive quantities such as resistors and capacities.

    There are mainly two types of multimeters, analog and digital. Generally
both types should be able to measure the three most common quantities: volts,
amps, and ohms.

    Digital testers are considered
to be better, since they have evolved a lot, reaching a level of
precision, manageability and portability that surpasses analog multimeters, and
they also have the possibility of including a great variety of extra functions
that allow them to do more than measurements only. 
multimeters are cheaper than digital multimeters, generally do not need
batteries to operate. However, on many occasions they are imprecise, and
much more fragile.

    A digital multimeter is an indispensable tool for all work involving electricity,
so it is very important to make the right choice. For choosing a
digital multimeter it is important to take several considerations, such as:

- The working environment, this includes thinking about the voltage level with
which to work, and types of measurements to be made.

- The extra features
or functions with which we want to count (frequency, temperature,
non-contact voltage, min-max register , etc.), these additions are
very helpful on many occasions and reduce the amount of different
tools or equipment that we must buy.

- Accuracy and resolution. This is one of the most important aspects and one that
largely defines the quality of the multimeter.

- Safety, test equipment must be designed to protect people working in high voltage and
high current environments. Multimeters must meet certain safety standards,
depending on the work environment where they will be used.

    In a more technical way, the main parameters to which we must pay attention
are the following:

    - Resolution:

    Resolution can be understood as sensitivity in measurement. The resolution of a
digital multimeter is expressed by the number of digits it can display on the
screen. A 3 ½ digit multimeter means it has 3 integer digits from 0 to 9
and one that can change between 0 and 1, so the resolution would be ± 1,999. Most
multimeters on the market have 3 ½ or 4 ½ digits with a range of ± 1,999
or ± 19,999. Some manufacturers specify the resolution as " count "
or counts. This count is the largest number you can measure
before you need to change range. A 4 ½ digit multimeter can be specified
as 19,999 or 20,000 counts.

    - Accuracy:

    The precision of a multimeter is the maximum error allowed in the readings. This
is normally expressed as ± (% error in reading + least significant digit or
LSD). The LSD represents the error caused by the circuitry, such as noise
and tolerances of the ADC converter.

    On a 4 ½ digit multimeter with a DC voltage accuracy ± 0.05% + 3. While measuring
12V VDC, the multimeter will be able to display something between 11,994 and
12,006 V. But when you take the LSD into account the last digit can vary
between ± 3, then you can have readings between 11,991 V to 12,009 V.

    - RMS:

    This particular feature can differentiate a cheap multimeter from a professional
one. This is used for AC measurements. Multimeters that do not
have this feature are known as "average responding meter". 
multimeter without True RMS will only be able to measure real values if the
waveform is perfectly sinusoidal. If not (generally it is not), the
measurement can be totally out of range , it can even measure twice the
actual value.

    - Input impedance:

    Compared to the impedance of most circuits, multimeters have a high impedance
input, so as not to affect or influence the circuit while measuring. Poor
quality multimeters have around 1MΩ input, which may be sufficient for general
applications. But if some sensitivity is needed to work with electronic circuits, it is important that a multimeter with a minimum impedance of 10MΩ is chosen to
ensure good precision and safety when handling it.

    - Standard safety CAT:

    The CAT refers to the overvoltage category in which the products are classified
according to the level of safety they handle, both for the equipment and for
the user who manipulates it when making electrical measurements.


- Cat I - Electronics: This
Category is used for electronic equipment that connects to the network and
protected and regulated electrical installations.


- Cat II - Residential
Electricity: For domestic installations, loads connected to single phase
outlets . It refers to measures appliances, portable equipment, etc.


- Cat III
- Three-phase distribution, including single-phase commercial lighting : For
electrical installations inside a building or factory. It is
recommended for Industrial use.


- Cat IV
- Three phases in the electrical power service connection, any external
conductor: For electrical installations that are outdoors and
that can receive a direct electric shock, such as lightning.

    Apart from these general characteristics, the equipment oriented to more
specific work areas have others such as IP68 certification, magnetic holder,
removable screen, among others.


    A very good multimeter that you can buy with a excellente price quality ratio is the MESTEK DM100C, I bought this multimeter and I am very satisfied with it.

    Have a excellent quality of construction and a lot of functions like Non Contact Detection Voltage (NCV), Lantern, True RMS, Manual range and automatic range, V.F.C variable frequency voltage measurement function, measurement of temperature, among other.

MESTEK DM100C Digital Multimeter Manual Automatic



    For some people, the instant it takes to select the range automatically can be a bit annoying. There is also a version without the function of said automatic range for a lower cost.

MESTEK DM100 Digital Multimeter Maintenance Tool



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