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The multimeter is an indispensable part of any modern-day toolkit. For electrical repairs, it is as essential as a screwdriver and as versatile as a Swiss knife. Most professionals are already familiar with multimeters, and yet many make common and easily avoidable mistakes while using one. If you are a DIY enthusiast, have a passion for electronics or simply want to repair minor problems around your house, it's important that you understand how to use multimeters correctly. Irrespective of your familiarity with this versatile instrument, this article is for you.

The Very Basics

If you aren't sure what voltage, current and resistance mean, this section is for you. Imagine electricity as flowing water, and an electrical circuit as the plumbing that it flows across. Current is the flow of electricity across the circuit. It's measured in Amperes, or Amps. Just as the flow of water is affected by the width of the pipe, the flow of electricity is affected by different electrical components. The opposition that an electrical component provides is called Resistance, and it is measured in Ohms. If a pipe is narrow, how can we increase the flow of water? By increasing pressure, of course! Voltage is like water pressure; 1 Volt is the potential difference required to have a current of 1 A flow across a resistance of 1 Ohms. The voltage of a home is typically 110 V (Alternating Current, or AC), and that of a battery usually ranges from 8 V to 12 V (Direct Current, or DC).

The properties of any electrical circuit are affected by its voltage, current and resistance. So if you were testing a circuit or diagnosing problems, wouldn't it be great to have a single instrument that could measure them all, instead of having three different ones? That's exactly what a multimeter does! Next, we'll look at how you can choose a multimeter that's right for you.

Types of Multimeters

Most multimeters today are digital, offering precise readings and ease of use. Digital multimeters come in two broad designs. Manual switch multimeters allow a knob to be turned across calibrated ranges to get more accurate readings on voltage, current and resistance. The fine degree of control they allow can also protect the device - for instance, you can initially set the multimeter to a higher voltage to protect it from damage during a diagnostic check. Auto-ranging multimeters are more convenient to use, and can switch between ranges automatically for a quick reading.

How To Use Digital Multimeter

The General Tools DMM40 CAT III 600V multimeter in manual-switch (left) and DMM45 auto-ranging (right) models.

Did you know that external variables such as temperature and moisture can affect electrical fields? When specialized sensors are incorporated into their IC circuits, digital multimeters can measure temperature, moisture levels, airflow and more.

The conventional use of multimeters is for diagnosing electrical circuits. Such multimeters come with two probes - one red, and the other black. Each probe has a metallic tip, which is connected to the circuit at the position where a reading needs to be taken, and a plug at the other end that is inserted into the multimeter. The plug of the black probe is always inserted into the common port, usually labeled as COM. The appropriate port for the red probe depends on the type of reading to be taken. Many models of multimeters have distinct ports for measuring current in Amperes and milliAmperes, or for measuring voltage for an Alternating Current (for homes) and for Direct Current (for batteries). Some multimeters also offer separate ports for measuring continuity. So your choice of a model should be influenced by what you intend to use the multimeter for.

Rugged Service Multimeter

The General Tools Rugged Service Multimeter offers a microAmpere range for measuring tiny currents.

Measuring Voltage

1. Insert the plug of the black probe into the COM port, and that of the red probe into the port for measuring voltage (V). If your multimeter has separate ports for measuring AC and DC, insert the plug of the red probe into the AC port for circuits connected to the mains (e.g. your home's switchboards) or into the DC port if power is supplied by a battery.

2. To measure the voltage across an electrical component, first connect the two tips to the circuit on either side of the component (so that the tip of each probe touches the circuit on either side of the target).

3. Ensure that the probes are held parallel to each other. Make sure that they are not touching any other component, or each other.

4. If you are using a manual switch multimeter, turn the knob to a significantly higher voltage than anticipated.

5. Slowly dial down as you measure voltage. This can avoid overloading and damage to the multimeter.

6. Note the reading on the multimeter's display. The unit corresponds to the labeling of the port for the red probe.

Measuring Resistance

1. Measuring resistance allows us to understand where the circuit might be failing, or to detect a faulty component.

2. For measuring resistance, it's important that you first turn off the power.

3. If you're testing resistance for a component on a circuit board, remove the component from the electrical circuit, if possible, to get an accurate reading.

4. Insert the plug of the black probe into the COM port, and that of the red probe into the port for measuring resistance, labeled in Ohms.

5. If you are using a manual switch multimeter, dial down to the lowest possible setting for resistance.

6. Touch the tips of the probes to either side of the component and measure for the least value of resistance. If the circuit is overloaded, the display should state OL (overload). Dial up for a higher resistance level and repeat. An auto-ranging multimeter will automatically take the correct reading.

Measuring Current

1. To measure current across a circuit, first turn off the power source.

2. Disconnect the circuit at one end, or remove a component from the circuit, thus breaking the circuit (making it open-ended).

3. Insert the plug of the black probe into the COM port, and that of the red probe into the port for measuring current. If your multimeter has two ports for measuring current - one in Amperes and the other in milliAmperes, insert the red probe into the port labeled Amperes.

4. Connect the probes of the multimeter to either end of the open circuit (or in place of the removed component). The idea is that the current flowing in the circuit should pass through the multimeter.

5. If you are using a manual switch multimeter, dial to the highest Ampere setting.

6. Making sure that the probes are not touching any unintended part of the circuit, turn on the power again.

7. If you do not receive a reading, dial down in steps, till you receive a reading on the multimeter.

8. It's important that you start checking for readings at the highest Ampere setting, and not in milliAmperes, to avoid damaging the multimeter. Once you get the reading, the unit (A or mA) will correspond to the port for the red probe.

Testing for Continuity

Many multimeters offer a dedicated port for checking continuity of the circuit. This convenient feature is handy for detecting faulty components in the circuit without needing to remove each component in turn and take resistance readings. Multimeters with this feature have a sound that goes off when there is continuity between two points. It's pretty normal for your hands to shake when you look away from the circuit, and this can make the probes lose contact. The sound feature lets you test for continuity by simply listening to the multimeter readings. Testing a faulty component will generate no sound.

Caring for Your Multimeter

Like any instrument, the multimeter needs some basic care. A well-maintained multimeter will give you years of service and accurate readings.

If you have a manual-switch multimeter, always set the dial to a high voltage setting when you turn it off. If you ever need to take a quick reading and the multimeter is set to read a low value, there is a risk of damaging the multimeter as well as the circuit from overloading. Setting the multimeter to a high voltage reading can help you avoid this mistake. It's always safer to dial down to take a lower voltage or current reading, and then return the switch to a higher setting when the multimeter is turned off.

Periodically replace the tips of the probes. Over the course of normal wear and tear, the metallic tips can crack or get bent out of shape. Testing a high voltage circuit with damaged probes carries the risk of sustaining a nasty shock or damaging the circuit.

Before using the multimeter, ensure that you have enough juice in your batteries. Using weak batteries can give you an incorrect reading, and leaving batteries inside the multimeter for months at a stretch can cause them to leak and damage the instrument.

Last but not least, remember that the multimeter can give incorrect readings if the temperature is too high or too low, if moisture is excessive or if there are strong magnetic fields nearby. Many multimeters exploit the effect of external variables such as temperature and moisture on an electric field by incorporating sensors that can measure these parameters. However, remember that a multimeter that gives these readings is convenient to use, but will never be as accurate as a dedicated thermometer, moisture scale or airflow indicator.

Conclusion

The digital multimeter is a convenient instrument that is indispensable for a wide range of repair and diagnostic tasks, ranging from testing electrical circuits to testing masonry and furniture for moisture content. Your choice of multimeter will depend on what you intend to use it for. But knowing how to use a multimeter is a useful skill for working with a wide range of models and derivatives of this versatile tool.

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