After reading this article, you will be in a better position to be able to narrow down your choices when deciding upon which multimeter to acquire for electronic testing, either for use in the test lab or for portable and field use.
I was recently in the market for a new multimeter and found the options quite daunting, but after applying some logical decisions and making choices for the work you need to do, I can hopefully help you to better understand your priorities and even if this article doesn’t pick an exact model for you then at least it may allow you to get down to fewer options.
Fluke or not Fluke?
Looking through the advertising and reviews for multimeters, it seems that some people have great confidence in Fluke meters and wouldn’t consider any other manufacturer. It does seem that Fluke is the meter that has set the standards by which all other meters are compared.
Flukes may not always have as many features for the price as other manufacturers, but what you are getting is dependability and sturdiness for a meter that will last for years, if not decades.
So should I go for a Fluke and not consider any other possibilities? Well, it depends. Fluke meters are very reliable workhorses in the industry and will not let you down. I would say that if you are buying a multimeter for professional use (ie, it’s part of your business or job to use one) then a high-end Fluke is an excellent choice. You should then consider the meters in the higher price range.
For non-business use, such as for hobby or general electronics work, the lower range of Flukes may be a good choice, though it is definitely worth looking at some other manufacturers as well.
Analog or digital
Analog multimeters were around long before digital ones were and there are still some being made. Analog meters are more used in analog circuitry where you need to see variations in a particular measurement, such as reading a slowly rising or falling voltage or current and being able to see the trend more clearly than you could with a digital meter that samples and updates its digital display in less ‘fluid’ steps.
Analog meters are usually quite limited in their functions, with mainly capabilities for the measurement of AC and DC voltages and currents and for resistance measurements.
Also, the input impedance of an analog meter is relatively low compared with the input impedance of a digital meter, which is in the order of 10 Mohms or more and is constant. If the input impedance is low, then it adds an extra load (shunting effect) on to the device you are measuring and may give a less accurate reading.
Many digital meters have an ‘analog’ bar on the digital display consisting of many small segments in a line type arrangement that gives an approximation to a moving pointer of an analog readout. This is a good choice when buying a meter.
Important and not so important functions
It’s easy to get enticed by all the elaborate functions of a multimeter. Many have additions such as capacitance testing; frequency and duty cycle readings, etc.
You need to decide which of the functions you will actually use, rather than options that you think would be nice to have but you’ll rarely, or perhaps never use. Weigh this up with the other side of the argument, that if you don’t need the more complex functions now, then you might have a use for them later and regret not thinking ahead.
Consider the most vital things that you will need to measure on a meter. You need these options for certain:
- AC voltage. Many meters will go up to 1000 V AC but 600 V AC is also common and may still be higher than you will need to generally measure. You may only need to measure household voltage in the high measurement range (110 V AC or 220/240 V AC depending on where you are located). Also check that the meter will measure AC millivolts and that the resolution is 1 millivolt or better. Some have a 0.1 mV resolution, but you may not really need that level of precision.
- DC voltage. You will usually find that the DC V and DC mV ranges follow the values of the AC V ranges.
- AC current. 10 Amps is a common maximum. If you need to measure higher current, then look for 20 Amps. Check for an AC milliamp range where you could read down to a 1 mA resolution. Some meters will also measure microamps if you are likely to need that low current reading.
- DC current. Again, DC current ranges often follow AC current for the higher ranges as well as the lower ranges. Make sure that the meter does have DC milliamp (and micro amp if you really need it) ranges.
- Resistance measurement is standard on most meters and is often used in electronic testing of resistors and resistance of sensors and transducers. A common maximum resistance range is 40 Mohm with a resolution of 0.1 ohm. Coupled with this, on some meters there is a continuity test where if a link measures as a closed-circuit then it makes an audible beep. This can be useful for testing fuses, wiring, PCB tracks, cold solder joints, etc.
If you don’t have a continuity test option, it’s not a deal breaker as you can just use a low resistance range and check for a near-zero ohm value (but without the gratifying beep of course).
Other functions that are nice to have
There are a range of other measurement types that a modern multifunctional meter can offer, but consider if you really do need them and if the extra cost of having these options can be justified. Here are some examples:
- Frequency and duty cycle. How necessary are these to have on your multimeter? A well-equipped lab will already have a frequency counter and an oscilloscope. Will having the capability of reading a frequency in reality be used on a multimeter? If you are on the road, then you might only be armed with the one device. If the multimeter will be the only option for frequency measurements and you think it will be used, then try to determine what frequency range you might be measuring. Some meters have a less than useful frequency range and may only read up to 50 KHz, whereas some will read up to 60 MHz. Also consider the lowest measurable frequency. Some will go down to around 10 Hz, but others can read a fraction of a Hertz.
Similarly with duty cycle – those meters that have it may still have a quite limited range, which might limit the lowest and highest cycle widths that you can detect. If you want this option, then look for a 1% to 99% range if possible. - Temperature measurement is a useful function to have in a lab to detect component and heatsink temperatures, etc., if you don’t have a separate temperature detecting device. Many multimeters have this option and come supplied with a temperature sensor. Some even have two sensors so that you can do comparison testing.
- Diode test. Useful to test diodes; LEDs; semiconductor junctions. You can make basic tests of diodes with the ohmmeter side of the meter, but the diode test will make a far better function check by showing the forward voltage drop of the device.
Functions that may not be the most useful
Some functions on multimeters are OK to have if they’re already part of the package, but probably not deal breakers in their own right:
- Capacitance testing. Used really just for testing capacitors. Values are usually marked on these anyway, although capacitors do routinely break down or change value over time. If the meter has a Relative Mode, it allows for the residual capacitance value in the test leads.
- Inductance testing. This is rare on multimeters as the required additional circuitry is costly. Might be useful if you were winding your own coils, but otherwise not something you would use at all unless you are doing this specifically.
If you really need to be testing inductance, buy an LCR meter designed for the purpose. In addition to inductance, these meters are also more accurate in testing capacitance than a standard multimeter. - Battery tester. More common on low-end devices, but found on a few higher quality meters as well. Most technical people have a battery tester as a separate device, or you can just test the voltage of the battery under load with the meter’s DC voltage range.
- A well-equipped technician will likely have some kind of lighting source and a small light on a multimeter will be less useful by comparison. A few meters have this function, but most don’t.
The meter’s operations
In the functions categories above we have looked at the different measurement options that the meter can measure, but now we will look at some of the functions that give support to the making of those measurements.
- True RMS. This will show a more accurate value when measuring AC power, especially on non-linear loads or where the sine wave is not pure, such as from some UPS devices or through a dimmer switch, for example. For the casual measurer of residential AC power, the RMS accuracy may be less important.
- Auto and manual ranging. This may be an important function as there are cases where both options are useful. If you don’t know what measurement value to expect, then auto ranging is really useful. If you do know what value to expect and especially if that value might change within that range, manual ranging will update the reading faster as it doesn’t have to take the time to start auto-ranging from the beginning. Some high quality meters can autorange much faster than the less expensive ones.
- Display counts and digits. The display count is the precision displayed. Typical values are 4000 or 6000 counts. Not necessary to have a really high precision unless you know of a reason where it will be of use to you. The display digits is the number of digits displayed. Typical is 3 ½ digits.
- Sampling rate. How many measurements are taken per second? Between 2 and 5 is common, with 3 being typical. Higher is better.
- Auto power off. May save battery power if you forget to switch the device off.
- Because the contrast ratio of LCD displays is generally poor, a backlight display can make a big difference in low light and is highly recommended.
- Low Z. Most measurements on a multimeter are taken with the default high impedance input so as to limit the effect on a reading. The Low Z, sometimes called Auto-V, or the meter is described as dual impedance, is used to counter ‘ghost voltages’, where adjacent wiring may cause capacitive coupling and stray voltages in the circuit you are measuring.
- Low-pass filter. This limits the bandwidth of AC voltage measurements to reject any high frequency component (for example higher than 1 KHz) and therefore gives a more accurate reading. Commonly used when measuring pulse modulated waveforms.
- Data hold. Freezes a value on the display. Useful when you want to transfer that value later to paper, or if you are not in a position to be able to see the display during the measurement taking. Auto hold will automatically hold the reading for you without having to press the button.
Also consider if a Min/Max button is useful in combination with the above. - Lead warning. This can be a very useful safety feature. For example, for meters with different lead sockets, the dial setting for the measurement you want to set your meter to may not be compatible with the socket where the lead is plugged into and you will get a warning on the display.
- Non-contact voltage detector. This is an addition usually fitted to the top of the meter to test for AC voltages without making physical contact with the wiring.
Other considerations
- The LCD display. Some LCD displays simply don’t look good. The digit segments are disjointed or the digits are too big or too small or close to the edge of the display. The screen may look too crowded. To have a comfortable looking, well-designed display, is more important than you would think.
- More buttons and switches on the meter are preferable in my opinion. If there are a lot of functions that have to be chosen by going through several menu options because of too few controls, this will get annoying.
- Test leads. Multimeters are often supplied with lower quality PVC leads or with probes that have limited use. You will often end up buying an additional lead set from a third party source.
Cheap leads feel too stiff. Good quality flexible silicone insulation with a high strand count and gold-plated connections will be quite expensive. You may not need the highest quality and some good leads can be found at reasonable prices. - The casing. You may need a rugged case, which will add to the cost. Also a fold-out stand is very useful. It saves having to prop up the meter on some other equipment.
- With repeated use over time and even physical damage, the accuracy of a multimeter may alter. The user manual supplied with the meter may have a section on calibration. For most low to mid cost meters you probably won’t even consider calibration to be necessary, though you can periodically verify the measurement capability by using a stable reference method, for example, a voltage reference module or a high precision passive component.
Conclusion and what I finally chose and why
Independent online reviews are very useful for getting opinions on a range of different products, but it really comes down to what functions you really need and how much you are able to afford.
Much of my own work with electronics is for small circuit design and interfacing with computer modules, sometimes in a work environment and also for hobby work.
I required a good all-around functioning meter that gives me a good range of options to cover most possibilities for measurements that I encounter, with reasonable accuracy. Something that lasts for many decades of use is of less importance to me as I could still get a good deal and one day replace it if it malfunctions in some years.
I narrowed it down to three possibilities in the end:
Klein Tools MM700. A well-respected company and the price of their meters is quite reasonable. This particular model had most of the functions that I required.
Amprobe AM-530. Very similar to the MM700 in functions and price and some capabilities were slightly better, but no duty cycle measurement, which is something I do need occasionally.
Amprobe AM-570. This is the one that I finally chose and am so far quite happy with it. It did cost almost double the price of the other two models I had picked, but the capabilities and functions really stand out. Especially of note are the 61-segment analog bar and the dual display. Also the very wide range frequency measurement. The duty cycle range lets it down somewhat as it only covers 10% to 90%. Also of note – the dual temperature probes.
What I do especially like about the Amprobe meters is the display itself, with very comfortable to read digits and a nice backlight for the display.
I hope by reading through this article that it may help you to think about the specific functions of multimeters and will help you to decide between models.