A multimeter is the most essential piece of electronic test equipment you can put on your workbench. Today, we will learn how to use this important test instrument.

Introduction

If, for some unknown reason, you could only own one piece of electronic test gear, your choice of equipment would be simple—get a multimeter.  It is easily the most versatile piece of equipment you could own.

A multimeter is your window into what is going on in your circuit. What is the power supply voltage, how much current is the LED consuming, and what’s the value of that unmarked capacitor? All of these common technician questions can be answered using a multimeter.

Multimeters can cost 25 dollars or less or $2,50 or more. Obviously, with such a wide price range, there are features and performance considerations that you should take into account when choosing a multimeter.

Today, we will learn how to use this vital piece of test equipment.

Multimeters

Multimeters traditionally combine the function of voltage, current, and resistance meters into one easy-to-use package. These days, they also add capacitance, frequency, and temperature to the list of parameters they can test.

Multimeters are available in different sizes and with different capabilities.  The video accompanying this article looks at five different multimeters, each with its own unique set of features and capabilities.

Let’s learn more about this valuable tool.

Multimeter History

Using meters to measure electrical properties dates back to the early 19th century when simple galvanometers were used to measure electrical charges.  These evolved into meters that could be used to measure current.

By adding resistors and batteries, the simple current meter could also measure voltage and resistance. While these measurement tools were initially used independently, it didn’t take long to combine them all into an all-purpose electrical test instrument.

Analog Multimeters

Analog multimeters, characterized by their moving pointer displays, were widely used for electrical measurements and are still used today. 

Analog meters quickly respond to voltage and current changes, so they are useful for monitoring fluctuating signals.  However, they require manual ranging and are susceptible to parallax errors, limiting their accuracy compared to their digital counterparts.

These meters are sometimes called VOMs or Volt-Ohm-Milliammeters.

Digital Multimeters

Digital meters use digital displays to convey information and are thus much easier to read than analog meters. They can also be much more accurate than analog meters by using precision analog-to-digital converters in their front ends. Almost all multimeters sold today are digital multimeters, also called DMMs.

Digital meters can measure much more than just voltage, current, and resistance. The parameters measured by digital meters include:

• AC & DC Voltage
• AC & DC Current
• Resistance and Continuity
• Diode voltage drop
• Capacitance
• Frequency
• Temperature

Advanced meters also have features to store data and interface with a computer or network.

Auto-Ranging vs. Manual Ranging

Auto-ranging multimeters automatically select the best measurement range for the current task, while manual-ranging ones require you to set the range (e.g., 200 ohms, 2000 ohms, etc.). 

Auto-ranging is convenient, but manual-ranging can be useful in situations with fluctuating values. Most auto-ranging multimeters can also be set manually to avoid changing ranges with a changing value.

Manual ranging meters can also work faster than auto-ranging ones, as they don’t need to determine the range before producing a display.

Basic Multimeter Operation

The key to getting the most value from your multimeter is knowing how to use it properly. This isn’t too hard, as most meters have a pretty intuitive display.

The following instructions are generic; after all, every multimeter is different. Still, they should be sufficient in getting you started with your meter.

Resistance

A very common use for a multimeter is to measure resistance, and it’s pretty simple.

Insert the probes into the COM and V jacks. Turn the function selector dial to the resistance (Ω) setting.

If you have a manual ranging meter, you will need to select a range; if you are unsure which one to select, try the highest and work your way down.

Now, touch the two probes across the resistor. The resistance should be displayed on the meter.

Continuity

Continuity testing is a very useful function, as just about every multimeter has it. It works as follows:

• Select Continuity mode (often indicated by a diode symbol and sound waves).
• Touch probes together – the multimeter should beep if there’s continuity.

This is an excellent way of tracing broken wires and bad connections, as you don’t need to see the meter to get a reading.

Diode Test

A Diode Test is a very handy function. It can quickly check a diode and determine its forward voltage drop.

• Select diode mode.
• Connect the red probe to the diode’s anode and black to the cathode.
• The multimeter will display the forward voltage drop of the diode (typically around 0.6V for silicon diodes).

If you reverse the diode the meter should show it to be open. 

DC Voltage

Another common use for a multimeter is to measure DC voltage. Make sure to heed the maximum voltage rating, which is usually printed near the meter jacks.

• Select DC voltage mode (V with a straight line).
• Connect the red lead to the positive terminal and the black lead to the negative terminal.
• Read the voltage value displayed.

If you have a manual ranging meter, you’ll need to determine the correct range setting. Always start at the highest range and work down.

DC Current

In order to measure current, you will need to do two things that differ from the previous operations:

• You will need to move the red test lead to the A or mA jack.
• You will need to insert the meter into the circuit by breaking the circuit and completing it with the meter leads.

After that, the procedure is pretty easy.

• Select DC current mode (symbol: A with a straight line)
• Observe correct polarity (red probe towards a more positive point)
• Read the results on the meter

Remember to reconnect the circuit after you complete your measurements.

AC Voltage

The procedure for measuring AC voltage is similar to that of measuring DC voltage.

• Select AC voltage mode (symbol: V with a wavy line)
• Connect probes in parallel as with DC voltage

Most meters use RMS (root means squared) to calculate AC voltage. Many meters offer “True RMS,” which means they can calculate RMS values accurately even with non-sinusoidal waveforms.

AC Current

There are two methods of measuring AC current; not all multimeters can use both:

• Direct Contact – The conventional method, connected in the same fashion as DC current measurement.
• Inductive – Use an inductive loop for non-contact current sensing.

We will deal with the conventional method right now; we’ll cover inductive current sensing shortly.

To measure AC current directly, place your black test lead into the COM jack and the red lead into either the A or mA jack. Then, select AC current mode (symbol: A with a wavy line). The current will be displayed.

Note that higher currents should always use the A jack, not the mA one.

Frequency

Not every multimeter can measure frequency, and even those that can do so don’t usually have a very wide range; however, they can be used for AC line and audio frequencies.

You will keep the test leads in the COM and V positions to measure frequency:

• Choose the frequency measurement mode (Hz symbol).
• Connect the multimeter across the signal source or load.
• The display will show the signal frequency.

As most meters only have a few digits you won’t get as accurate a reading as you would with a dedicated frequency counter. But for most purposes, the accuracy will suffice.

Capacitance

Many multimeters can also measure capacitance. As with frequency, the capacitance measurement range is limited with many multimeters.

• Set the multimeter to capacitance mode (often marked as F or C).
• Disconnect the capacitor and discharge it safely.
• Connect the test leads to the capacitor terminals to measure its capacitance.

Very few multimeters can measure small (i.e., picofarad) capacitors; they are more suited to larger values. When measuring electrolytic or tantalum capacitors, be sure to observe lead polarity.

Temperature

To measure temperature on a multimeter, you will need a thermocouple probe. This is a standard device and was likely included with your meter. 

A thermocouple probe responds very quickly, and it is ideal for testing integrated circuits to see if they are overheating. You can also use it for practical purposes, like testing the temperature of your refrigerator or furnace!

To measure temperature, proceed as follows:

• Select the temperature mode (°C or °F). Some multimeters default to °C.
• Connect a temperature probe to the multimeter.
• Place the probe at the point of measurement to read the temperature.

The end of the thermocouple is a bit delicate, so handle it with care!

Non-Contact Sensing

As its name implies, non-contact sensing allows you to sense or measure alternating current without actually connecting to the wires. This has obvious safety advantages, especially with high voltages or currents. 

There are two types of non-contact sensing that are popular in multimeters. Not every multimeter is capable of noncontact sensing.

NCV/ Live

Non-Contact Voltage (NCV) detectors or Live functions allow for detecting electrical fields in wiring without direct contact. This can provide a handy indication of the status of an electrical wire or outlet.

Simply activate the NCV mode and move the multimeter close to the conductor or outlet. A visual or audible signal will indicate the presence of voltage.

The actual NCV sensor is usually at the top of the meter.

Non-Contact Current Sensing

You can easily spot a multimeter with Non-Contact Current Sensing. These devices have a telltale “loop” or “clamp,” which is wrapped around a wire to sense its current flow.

This feature enables the detection of current flow in a conductor without needing to make a physical connection. By placing the multimeter near the conductor, it senses the magnetic field around it, allowing for safe and quick current checks.

The most important thing to note about using non-contact current sensing is that you must be sensing ONE wire, not a bundle or pair of wires. Clamping the sensor around a power cord won’t produce a reading. You need to break out the wires and measure the hot lead independently.

Conclusion

Multimeters are vital tools for any electronic experimenter, and they are pretty easy to use. By taking the time to read your user’s manual (search for the part number online if one wasn’t included with your meter) and getting to know your meter’s features, you’ll soon find your meter to be indispensable.

 

Now, go out there and measure something!