A Buying Guide for Multimeters
An Introduction to Multimeters
Multimeters have become as indispensable to electronics technicians as wrenches and screwdrivers. They measure current, voltage and, often, resistance as well over a wide range, allowing the electronics tech to have a single all-purpose meter instead of several different ones. They provide a quick check of whether or not the circuit is shorted and give you other fast answers when you’re troubleshooting.
A few multimeters measure capacity, duty cycle, decibels or other measurements. Some models let you add sensors and take measurements like humidity, wind speech light levels or temperature. Multimeters may be digital or analog, and different meters cover differing ranges for each parameter and vary in their sensitivity. Here are a few of the best multimeters for electronics technicians.
What Factors Should You Consider When Shopping for a Multimeter?
One factor to consider when shopping for a multimeter is price. You can find multimeters for less than fifty dollars that combine volt meters, ammeters and ohm meters, letting you test voltage, current and resistance with one unit.
Price tends to go up with the number of features and resolution. Cheap multimeters are usually not calibrated, so you’ll have to offset that low purchase price with the cost of getting it calibrated before you start using it. The range of values the unit can measure also tends to go up with price. For example, not all multimeters can test the resistance of a car battery relative to the lower resistance in a damaged circuit board. If it rated to read automotive systems, it may not be sensitive enough to give an accurate reading for components in an integrated circuit.
Some multimeter manufacturers let you send them the unit for calibration, while others have chips built into the multimeter that can calibrate the unit.
Another factor is the features built into the multimeter. We’ve already discussed what multimeters typically measure, as well as what a few models can measure. What do you need the multimeter to measure? A range selector that audibly clicks when you make a change is a plus, since it makes it clear you’ve changed the setting. If you need to test transistors in the electronics assemblies you’re building, you need a multimeter that can test them.
How important is that greater degree of accuracy or resolution? Digital multimeters are usually more accurate than analog ones. Analog multimeters only have the advantage of being the cheapest on the market.
How do you measure the resolution of a multimeter? The resolution of a multimeter refers to how fine the measurements are that it can capture. The resolution of a multimeter can be described in digits or counts. For example, a multimeter may show values to the tenths place or the hundredths place. That difference is resolution is in digits.
The counts of the multimeter refer to how many digits it can show. A 50,000 count meter could show you a voltage of 49.999V. If it reads 50 volts, it will display 050.00 volts instead. If the multimeter has a broad range, it will typically drop a digit from its accuracy. If you’re reading 500 volts, it will be plus or minus 5 volts, not plus or minus 0.1 volts that it can register if the voltage is 5 volts.
Many multimeters advertise that they read true RMS. Whether or not the multimeter reads "true RMS" matters depends on the application. True RMS multimeters are able to measure AC current or voltage accurately. Yes, multimeters can measure both of these things. However, the true-RMS meter is able to accurately measure both the sinusoidal (sine) and nonsinusoidal waveforms. The true-RMS is thus able to read spikes, pluses and distortions that must be read to properly diagnose a problem. If the current is purely sinusoidal and doesn’t have these distortions, then true RMS doesn’t matter.
True RMS multimeters are useful for troubleshooting variable speed motor drives, customers, HVAC systems, electronic ballasts, power lines and solid state electronics.
Brand is one factor that some people give more weight than others. Sometimes brand names matter simply to ensure that all of your sensors, chargers and devices are compatible with each other. Conversely, some multimeters work with any probe with a banana plug. You want the multimeter to come with good probes, but a multimeter that sells good replacement probes at a reasonable price is more attractive than one that sells the meter cheap and requires you to buy a whole new one later if a key component fails.
Warranty terms or serviceability matter to others; if you’ve paid several hundred dollars for a multi-meter, the ability to take it to a local provider for repair may be a reason to buy one model over another. Or you may want a multimeter that lets you change out a burned out fuse yourself.
Ease of use should be a deciding factor. There is a joke that any manual that provides instructions on how to read the manual is a warning not to buy the equipment. The ideal multimeter is intuitive, letting you figure out how to make your selections for variables and understand immediately how to plug everything in. If you’re often working in dark areas, a multimeter with a built in light has a point in its favor. A variation on this theme is power. Do you want a multimeter that uses commonly available batteries, draws power from a power plug or some combination thereof? An auto-off feature that conserves the battery life is a nice to have, but learn more about a multimeter before you buy one with this feature, since a unit that turns off too soon is an inconvenience.
Safety is often overlooked as a factor when shopping for a multimeter. You need to select a multimeter for the anticipated load. The cost of the multimeter goes up along with the load in kilowatts it can handle. The lowest category of multimeters are Category I; these multimeters are suitable for small electronics projects. Category II multimeters can test household appliances and portable tools. Category III multimeters can test bus bars, cables, distribution bars and socket outlets. They are able to safely test motors with permanent power connections. Going from a Category I to Category 3 multimeter improves the worker’s safety if you’re working in an industrial or commercial environment, though it comes with a higher price tag. Category 4 multimeters, those designed for utility or origin of installation measurements, are even more expensive. They’re also relatively rare, since it is almost exclusively linesmen and industrial equipment installers who use them.
© 2018 Tamara Wilhite