What's better, Manual Ranging, Auto Ranging, or Smart?

Meters these days have come a long way. Originally they were analog, and you had to set just about everything yourself. You would need to know some rules of thumb, for instance to pick a scale where the measurement needle in the middle third of the scale for best accuracy.

As digital multimeters (DMM's) became more common for consumers/hobbyists, they were made more friendly and brought about new rules for how to measure. A big part of the advancement was that automatic ranging was introduced. Just choose what type of measurement you want to do, and the meter figured out what multiplier scale to choose to most precisely display the result. I did so by a iterative routine of sampling the circuit under test.

Fast forward to today, and now meters can determine what it is you are trying to measure, not just the scale of the measurement. That's right, it can many of the decisions for you!

Often time these are called "smart" meters, although that term is sometimes used quite loosely, so buyer beware. For the purpose of this discussion, a "smart" meter will refer to one that chooses by default the type of test you are attempting (voltage, resistance, continuity by default). Often times these meters have fewer clicks of the rotary dial, or they do away with the dial and just use pushbuttons or a touch screen. Turn the meter on, and it might display "Auto". Does this mean we can throw the user manual instructions away, and just trust we are getting the right result? Hmmm...

By the end of this article, we hope you will understand the pros and cons of letting your meter decide what's your trying to do, so you can make a better purchase decision. Then once you have one of these meters, what you can do to make sure you aren't missing out on anything.

Here's an overview of the benefits or "pros" of a "smart" meter:

Simplicity. You can move the test leads from one task to another, and never need to touch the meter.

Stability. The meter can stay on the shelf or in your hand and not need to interrupt your work to be manipulated.

Coolness. Definitely fun and modern to be rocking the latest advances in testing. Color touch screen? Does it talk? Yes please!

Unfortunately, the smart meters often don't know when it's dark and you need a backlight. They won't know you're in a noisy environment and need to be louder. And they don't know when the test lead pulled out by mistake or a fuse was blown. Some things you will need to continue to watch out for!

The things that a smart meter may "miss" (or the cons), include the following:

Lack of range. Sometimes in order to self-decide whether to measure resistance or voltage, the unit may need to ignore very low values of resistance or voltage, thus not meeting your needs. The device may make the wrong decision about what you want to measure. For some smart meters, their automatic measurement range may start at 1V or 10 ohms, secretly hiding that it cannot figure out what's going on for certain ranges of input.

Slowness. In order to make the choice for the user, usually a sample period is necessary and then a subsequent change of mode may be is necessary. This may take a second to several seconds, in some cases briefly displaying empty or incorrect information. For instance, if you were looking for immediate continuity response, you might be disappointed how long you must wait for the beep when in the "smart" mode.

Confusion. Often the measurement result is in big digits, but the type of parameter being measured is in very small icons or letters on the display. Without understanding the circuit or component being tested, it may produce strange results, such as measuring a voltage or resistance on a capacitor when you really wanted Farads! Sometimes buttons are hard to read or may be surrounded by so many icons that it become alphabet soup. Do I short press, long press, or wait?

Hidden Features: Some owners of pushbutton "smart" meters may not bother reading the owner's manual and miss out on some of the features of the meter and how to activate them. Some examples might be diode check, fast continuity, capacitance, frequency, and live or NCV, only activated by a sequence of button presses.

Whew! OK so far, I hope we haven't scared you off from "smart" meters, because they really are cool and in the right hands can do a lot of things adeptly. It does however mean that you can't toss the user manual out the window just yet. In some cases, it becomes more important to keep the instructions with the meter.

Does deciding not to buy a smart meter mean going with a huge dial with all the modes and ranges clearly spelled out? Probably not. It's likely your comfort level might be somewhere in between. This is where an "auto-ranging" meter may provide the best compromise.

Pros of "auto-range" meters:

Simplicity. Instead of needing to think about what scale best fits what you are measuring, you just connect the circuit using basic safety considerations, and within a few seconds see a valid number instead of "OL". You will need to tell the meter what parameter you are measuring. However, your selector dial is usually very simple and easy to read. The exception to this rule is probably amperes of AC or DC current, you will often need to determine the gross range of your current to be tested, such as choosing between mA and 10A and moving the red lead to another jack.

Precision. In most cases, the meter will automatically display the result with the most decimal places of precision possible. It does so by moving to the highest range that still produces a valid result. As a friendly feature, the meter might avoid range-changing. Once the initial value was show, it might hold a certain range for you before stepping up or down when the live value is only changing a little.

Safety. Many of these meters will sound an audible warning if the voltage or current is going out of safe range. Also, some meters will remind you when changing ranges that you need to think about your test leads being in the wrong position or part of the circuit. Sometimes, these meters really look out for common user errors.

Cons of "auto-range" meters:

Slowness. The amount of time it takes to automatically select the range slow down your work. For instance, if you have 50 each 100 ohm resistors to measure, and your meter needs 3 seconds each time to move into range, you could be spending a lot of your time waiting for an answer. Fortunately, many meters allow you to change from automatic ranging to manual ranging which saves lots of time for type of usage.

Recordkeeping & Accuracy. When the measurement range is constantly changing, you may have a greater chance of error if you misplace the decimal place. Also, if your measurement move from one range to another, you might find the accuracy shifted due to the change in range. Once again, in these cases "manual" mode is your friend.

What would we recommend? Buy them all!

But really, if you need to buy just one, the non-smart, auto-ranging multimeter will often meet your needs. They have been around a few decades and do their job really well. This type of meter can take you from learning electronics theory - to working in the field or laboratory. The "smart" multimeter buyer might be for someone who simply needs to check the status of a circuit or simple troubleshooting on their appliance or vehicle, however for such a casual user, safety is a big concern. They sure can be handy and portable, but the professional may see no need for this type of intelligence in their meter. As they become even smarter, maybe they will become more highly recommended.

Bottom line, get your hands on something inexpensive that you think works for you first. With the low cost of meters in the Cheap-O Realm, you won't likely have too much regret. Practice with your meter on low voltage, low current circuits, and become a expert. You will have plenty of chances to move on to something else to supplement your measurements.

Be safe, have fun, and Keep On Testing!