HOW TO USE A MULTIMETER

DUMMIES GUIDE ON HOW TO USE A MULTIMETER LIKE A PRO IN JUST 1 HOUR.

In the journey of my career I realist a multimeter is the most important but underrated equipment, a proper guide on how to use a multimeter, a technician can diagnose and solve almost any problem.

You might be asking yourself what is a multimeter?

A multimeter is an indispensable tool for testing, diagnosing, and troubleshooting electrical circuits, components and devices. A typical multimeter can measure voltage, current, and resistance. There are two types of multimeter i.e. Analog and digital multimeter.


An Analog multimeters use a microammeter with a moving pointer to display readings.
Digital multimeters (DMM, DVOM) have a numeric display, and may also show a graphical bar representing the measured value.
The digital multimeter has proven much more accurate, reliable and increase impedance.

Fluke introduced its first digital multimeter in 1977 since then digital multimeters have been more common due to their lower cost and greater precision so we will base our focus on it.

GETTING FAMILIAR WITH A MULTIMETER

A multimeter is made up three main part:

multimeter

1. Display: This the screen of a multimeter where measurements are displayed, Sophisticated modern models may feature larger screens that allow them to include an oscilloscope function, displaying waveforms graphically as well as numerical data.

A few have illuminated displays for better viewing in low light situations

2. Selection Knob: The selection knob allows you to select the quality to be measured such as milliamps (mA) of current, voltage (V) and resistance (Ω).

multimeter probes

3. Ports: this is where you plug in the probes.
Ports
• The “COM” or “–“ port is where the black probe should be connected. The COM probe is conventionally black
• 10A is used when measuring large currents, greater than 200mA
• µAmA is used to measure current
• VΩ allows you to measure voltage and resistance and test continuity
Probes: are insulated metal “needles” that can be touched to wires, components or tracks on a printed circuit board. They are typically color-coded: red for positive, black for negative. The two probes are plugged into two of the ports on the front of the unit the black probe is always connected to the COM port and the red probe is connected to one of the other ports depending on what you want to measure)
Note: There isn’t any difference between the red and the black probes, just the color.

Understanding Multimeter Readouts

Since DMMs may display very large or small numbers, symbols will be used to clue the user if a number displayed (5, for example) should be multiplied or divided by a certain factor.

Exponential prefix symbols used are:

M (Mega) = 1,000,000 (used for ohms readings)
K (Kilo) = 1,000 (used for ohms readings)
m (Milli) = .001 or 1/1,000th (used for amp and volt readings)
µ (Micro) = .000001 (1/1-millionth)
n (Nano) = .000000001
p (Pico) = .00000000001
Additionally, users should be familiar with the following:

V = Refers to voltage, or the amount of electromotive pressure
Ω = The Greek alphabet symbol for Omega is used for ohms, or electrical resistance
A = Refers to amperes, or current flow
DC = Direct current. Current flows only one way from a DC source, an example of which is a battery (the DC voltage symbol would have a straight line (or combination of straight and dashed lines) beside or above the “V” for voltage.)
AC = Alternating Current. Current flows one way from a source, reverses, and then flows the other way. This happens many times a second at a rate determined by the frequency which is typically 50 or 60 hertz. The mains supply in a home is AC (the symbol for alternating current amps could appear as ~A, A~ or Ã).

Setting the Dial on Your Multimeter

multimeter dail

Once you understand the abbreviations and settings on your multimeter, you can start to actually use it. First, decide whether you’re measuring volts (V), amps (A) or ohms (Ω), and whether your current is AC or DC, and then turn the dial to the appropriate setting.

If your multimeter is “auto-ranging,” which means it automatically detects the scale of your measurements, its dial will be relatively simple. But if your multimeter is “manual-ranging,” which means you have to give it a general idea of how big or small the measurements will be, each segment of your dial may be further subdivided into different scales or units of measure.

Because you want to be sure you’re getting an accurate measurement, set the scale a little higher than you expect to read, but not so high that your reading will be an indiscernible blip at the bottom of the scale.

For example, if you’re measuring a 15 V circuit and your multimeter has 2 V, 20 V and 200 V settings, you’d choose the 20 V setting.

What Does a Multimeter Measure?

A basic multimeter facilitates the measurement of the following quantities: DC voltage, DC current
AC voltage, AC current (not all basic meters have this function), Resistance, Continuity – indicated by a buzzer or tone
In addition multimeters may have the following functions:
Capacitance measurement
Transistor HFE or DC current gain
Temperature with an additional probe
Diode test
Frequency
With all that being said i will cover four of the more common automotive tests you might want to run: voltage ,resistance, current, continuity, and diode testing.

HOW TO USE A MULTIMETER

How to measure voltage with a digital multimeter

• You can measure DC voltage or AC voltage. The V with a straight line means DC voltage while The V with the wavy line means AC voltage. set your Selection Knob to the appropriate mode depending on the voltage you want to measure.


• Plug the black probe into the COM port on your multimeter


• Plug the red probe into the VΩmA port.


• to measure voltage you have to connect your multimeter in parallel with the component you want to measure the voltage. this means the two test probes should be connected in parallel with the voltage source, load or any other two points across which voltage needs to be measured


• Touch the black probe against the first point of the circuitry


• Touch the other red probe against the second point of test.


• Take the reading on the LCD display

NOTE: if you switch the probes the the readings of the multimeter will give a negative value.

How to measure resistance with a digital multimeter

• To begin, make sure no current is running through the circuit or component you want to test. Switch it off, unplug it from the wall, and remove any batteries i.e if you want to test the resistance of the whole circuit but If you want to test an individual component such as a resistor disconnect one end of the component if it’s in a circuit. This may involve pulling off spade leads or desoldering. This is important as there may be other resistors or other components having resistance, in parallel with the component being measured.


• Plug the black probe into the COM port on your multimeter.


• Plug the red probe into the VΩmA port.


• Most multimeters are not autoranging, meaning you will need to set the correct range for the resistance you expect to measure. If you’re not sure, start with the highest setting


• Place a probe tip at each ends of the component being measured. It doesn’t matter which probe goes where; resistance is non-directional.


• If your multimeter reads close to zero, the range is set too high for a good measurement. Turn the dial to a lower setting


• If the display indicates “I”, this means that resistance is greater than can be displayed on the range setting you have selected, so you must turn the dial to the next highest range. Repeat this until a value is displayed.


How to measure current with a digital multimeter


• Determine if the current to be measured is ac or dc


• Determine the circuit’s anticipated maximum current by checking the nameplate of a component or the breaker rating


• Plug the black probe into the COM port on your multimeter.


• Plug the red positive probe lead either into the mA socket or the high current socket which is usually marked 10A (some meters have a 20 A socket instead of 10A). The mA socket is often marked with the maximum current and if you estimate that the current will be greater than this value, you must use the 10 A socket, otherwise you will end up blowing a fuse in the meter.


• To measure current you need to bear in mind that components in series share a current. So, you need to connect your multimeter in series with your circuit.


• Turn the dial on the meter to the highest current range.


• If the range is too high, you can switch to a lower range to get a more accurate reading.

How to test continuity with a digital multimeter

Continuity is one of the most useful tests for electronics repair. A continuity test tells us whether two things are electrically connected: if something is continuous, an electric current can flow freely from one end to the other


• Turn the selecting dial on the meter to the continuity range. This is often indicated by a symbol which looks like a series of arcs of a circle


• make sure no current is running through the circuit or component you want to test. Switch it off, unplug it from the wall, and remove any batteries.


• Plug the black probe into the COM port on your multimeter.


• Plug the red probe into the VΩmA port.


• Place the tip of a probe at each end of the conductor or fuse which needs to be checked


• If the probes are connected—either by a continuous circuit, or by touching each other directly—the test current flows through. The screen displays a value of zero (or near zero), and the multimeter beeps. Continuity!


• If there is break in continuity in the device being tested, an overload indication, usually the digit “1”, will be displayed on the meter.

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How to measure diode with a digital multimeter

A multimeter can be used to check whether a diode is short circuited or open circuited. A diode is an electronic one way valve or check valve, which only conducts in one direction. A multimeter when connected to a working diode indicates the voltage across the component.

A digital multimeter can test diodes using one of two methods:
Diode Test mode: almost always the best approach.


Resistance mode: typically used only if a multimeter is not equipped with a Diode Test mode
To carry out diode test:


• Turn the dial of the meter to the diode test setting, which is indicated by a triangle with a bar at the end


• Plug the black probe into the COM port on your multimeter.


• Plug the red probe into the VΩmA port


• Touch the tip of the negative probe to one end of the diode, and the tip of the positive probe to the other end.


• When the black probe is in contact with the cathode of the diode (usually indicated by a bar marked on the component) and the red probe makes contact with the anode, the diode conducts, and the meter indicates the voltage. This should be about 0.6 volts for a silicon diode and about 0.2 volts for a Schottky diode. When the probes are reversed, the meter should indicate a “1” because the diode is open circuit and non-conducting.


• If the meter reads “1” when the probes are placed either way, the diode is likely to be faulty and open circuit. If the meter indicates a value close to zero, the diode is shorted circuited.


• If a component is in circuit, resistances in parallel will affect the reading and the meter may not indicate “1” but a value somewhat less.

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