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The Uni-T UT139, a True RMS multimeter with 4000 counts.

Uni-T UT139B Multimeter Review: First Impressions

Multimeter prices vary widely, and so does their quality. Depending on the model you choose, a multimeter could cost you $10 USD, $800, or more. Why? Everyone has their needs and applications. There are $10 models, which offer a few basic features suitable for checking automotive battery voltages, UPS battery voltages, and more.

The Uni-T UT139, a True RMS multimeter with 4000 counts.
The Uni-T UT139B DMM. Image credit: Kompulsa.

There are also better models that can measure temperature, frequency, irregular AC waveforms, among other things in the $50-$100 range. If that’s the type of multimeter you’re looking for, then you may find this review helpful. This is a review of the Uni-T UT139B digital multimeter. More specifically: A mention of the few things that stood out to me most.

The Uni-T UT139B is a true-RMS digital multimeter, meaning that it is able to properly measure both sinusoidal and non-sinusoidal waveforms, according to Fluke’s definition of the term. An example of a sinusoidal waveform (sine wave) is the power provided by your utility company. Examples of non-sinusoidal waveforms include, but are not limited to:

  • Square waves (they transition from on to off very abruptly, which is the opposite of sine waves). Square waves are often generated by pulsating DC power supplies, including DC motor controllers. There are also modified sine waves which hardly qualify as sine waves generated by low-cost inverter and uninterruptable power supply (UPS) systems.
  • Irregular and distorted waves. Irregular waves may include those generated by triac-controlled device such as some dimmer switches.
  • Sawtooth waves.

The UT139B typically sells for $40-$50 USD and sports features such as a backlight (common, but not available in many cheaper multimeters), frequency measurement, duty cycle measurement, non-contact voltage sensing, capacitance measurement, a hold feature, and more. Most of these features are common in $40-$100 meters.

As someone who previously used a multimeter without a backlight, I was delighted to see that the UT139B offered one. Where efficacy is concerned, it is a flawless backlight. The white (with a hint of blue) LED uniformly illuminates the entire screen (sadly, some products’ backlights fail to achieve this simple task), but I was sorely disappointed by my inability to keep it on, and equally disappointed by the fact that I had to hold down the ‘Hold’ button to turn it on.

This isn’t the biggest issue, unless you’re working in a poorly lit environment outdoors (you know how some work lamps may illuminate the item you’re working on adequately, but a pesky shadow might make it hard to see your multimeter?).

User Experience

The first thing I noticed about the UT139B is the solid feel it has to it, and overall comfortable design. It doesn’t look or feel cheap, and that makes me happy. What doesn’t make me happy is that it beeps every time I turn the dial, which is annoying if I need to turn it all the way around to the NCV to sense voltages. If you can’t stand the incessant beeping, there are many other meters on the market.

In addition to that, the screen was crystal clear, even when viewed from awkward angles (like from the side) at which I wouldn’t see some other multimeter’s digits correctly.


While the UT139B isn’t the quickest multimeter on the market, it is still reasonably quick to measure voltages and amperage. This isn’t very important, but if you’re impatient or don’t have enough time to breath, you may appreciate it’s speed. What burst my bubble is the fact that it took a long time to measure resistance.


I can’t say much about the accuracy of the UT139B. However, its voltage readings closely (and sometimes precisely) match the specs of a few power sources/devices tried it with, including a 3.3 volt microcontroller, a sensor operating in the 2 volt range, and 115 as well as 230 volt mains.

Ease Of Maintenance

The fuse (one of them, at least) and batteries can be easily replaced without dismantling the multimeter entirely, which makes the UT139B a little easier to maintain than most DMMs i’ve seen.

Customer Service

Concerning: I don’t know much about Uni-T customer service. However, I contacted them twice about this meter and they did not reply. If you’re purchasing an expensive multimeter, always take customer service into consideration.

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