The Uni-T UT139C is a decent multimeter from Chinese brand Uni Trend. A True RMS device, it comes with extras like a voltage sensor and temperature input and is aimed at electronics enthusiast as well as electricians in the maintenance field. Uni-T today is more safety conscious than in the past, offering noticeably better input protection and category ratings.
- True RMS and variable frequency filter
- All current ranges, including micro-amps
- Can add on a current clamp
- Measures capacitance, frequency and duty cycle
- Non-contact voltage detector
- Auto/manual ranging
- Max/Min for changing signals
- Relative mode to compare and zero lead resistance
- CAT-III (to 600V) safety rating
- Weight: 13oz (370g)
- Size: 6.9″ (175mm) x 3.2″ (81mm) x 1.9″ (48.5mm)
- DMM and batteries (AA x2)
- Test leads
- Temperature probe
- English instruction booklet (uni-t ut139c manual)
Optional: current clamp, magnetic hanging strap
Complete Review of the Uni-T UT139C
Being a TRMS multimeter, the UT139C has the ability to measure variable frequency drives fairly accurately, which not all meters can do. It also comes with wide current-measuring ranges, to include milliamps and micro-amps (good for HVAC and electronics work).
Current clamp: You can also purchase an optional amp clamp that plugs into the meter jack inputs and can measure both AC and DC current up to 60A. Voltage is to 600V (CAT-III) and there is a separate millivolts range. Note that voltage and current default to DC, while AC bandwidth is 45Hz to 1kHz.
Both frequency and capacitance ranges are fairly generous, though as with most non-high-end meters, capacitance readings don’t come super-fast. The temperature range is also quite wide and is both Celsius and Fahrenheit.
NCV and modes: Many of the generic meters have non-contact voltage detection capability nowadays, which can be handy, with a range of a few inches (less with cables within walls). You also get a duty cycle monitor range with the UT139C, while the diode tester puts out an impressive 3V. Other pluses include MAX/MIN and REL (relative) modes. Input Impedance on DC voltage is 1GΩ.
|DC voltage||6V / 600V||±(0.7%+2)||10µV-0.1mV|
|DC millivolts||60mV / 600mV||±(0.5%+2)||1mV-1V|
|AC voltage||6V / 600V||±(0.8%+3)||10µV-0.1mV|
|AC millivolts||60mV / 600mV||±(0.5%+2)||1mV-1V|
|DC current (low)||600µA / 600mA||±(0.7%+2)||0.1µA-0.1mA|
|DC current (high)||6A / 10A||±(1.0%+3)||1-10mA|
|AC current (low)||600µA / 600mA||±(1.0%+3)||0.1µA-0.1mA|
|AC current (high)||6A / 10A||±(1.2%+3)||1-10mA|
|Resistance||600Ω / 60MΩ||±(0.8%+2) @ 6-600kΩ||0.1Ω-10kΩ|
|Capacitance||10nF / 100mF||±(4.0%+5) @100nF-1mF||1pF-10µF|
|Frequency||10Hz to 10MHz||±(0.1%+4)||0.001Hz-0.001MHz|
|Duty cycle||1% to 99.9%||-||0.1%|
|Temperature (°F)||40°F to 1832°F||±(1.5%+5) @ 32-212°F||1°F|
|Temperature (°C)||-40°C to 1000°C||±(2.0%+3) @ 100-1000°C||1°C|
|Optional Current Clamp|
It is well known that Uni-Trend is a Chinese company and that they have an inconsistent reputation, often erring toward cheap quality and lacking input protection. With the Uni-T UT139C review, however, they seem to have addressed this and have produced a tougher meter with better specs and yet still at budget.
It is a better build than some of the older ones, with a tough, soft rubber holster that features probe holders on the rear. This sits nicely around the combination kickstand/battery compartment lid, which is released with a single screw/nutsert. Along with the easy-to-access AA batteries is the main fuse.
Drop tested: 2m.
Display and Interface
The display on the UT139C is 3 5/6 digit (6,000-count), with a possible 5999. There’s no bar graph to observe voltage sweep, although it is nicely backlit and large and clear enough to be observed from an angle at distance.
With all of its functionality, the interface is a little cluttered. It is an auto-ranging meter, though, so simply requires a turn of the dial to the correct range and to measure away. Manual ranging is also possible and gives quicker response times.
Voltage detection has its own dial position, as does the amp clamp add-on. This is a nice touch on the Uni-T UT139C, allowing the potential for non-intrusive current measurements to 60A AC and DC. Although 60A is not a huge amount, it allows for the testing of large motors on the shop floor, or better ability to decipher parasitic draw on a vehicle battery, for instance. The clamp is optional and plugs across the voltage/COM jacks.
Other functions on the UT139C include auto power-off (about 15 minutes), a low battery level indicator, data hold, relative mode and MAX/MIN. The latter is one of the most useful aspects, allowing the user to evaluate high and low values of a changing signal. The variable frequency mode, meanwhile, is a low-pass AC filter to blank out the ‘noise’ that is typically induced in order to give clearer readings.
Safety and Protection
As mentioned, the UT139C is better protected. It does not support spurious category ratings like you might see on some of the other Uni-Ts, such as 1000V at CAT-III, or even CAT-IV (industrial) ratings. Its rating is CAT-III to 600V (with 6kV overload surge protection), meaning it is good for accommodating mains voltage of building installations post-switch gear, such as circuit breakers, socket outlets, motors and so on.
Input protection includes MOVs, a PTC and power resistor, along with the more expensive high rupture capacity fuses. These HRC fuses will (should) not explode when faced with a surge, or spike, thus better protecting both the meter and user. Fuses are rated to 600mA and 10A (1000V to ground). There are no trim potentiometers on the UT139C as with previous models, with serial memory providing more stable readings over time.
Uni-T UT139C vs UT61E Differences
These are quite different multimeters. The slightly more expensive and better rated UT61E is for more precise, with its 22,000-count display. It is also a data logging device. Other differences are the addition of backlight and voltage detection on the UT139C, as well as the current clamp add-on.
UT139 A and B models: These are the other two models of the 139 series. Most noticeably, there is a shift in the voltage/current ranges and they have fewer display counts. Model A also has battery capacity measurement, while the C can accommodate an amp clamp.
Uni-T UT139C Good and Bad
- Defaults to DC (convenient for electronics
- Decent input protection
- Realistic category rating
- Nice, large backlit screen
- Auto/manual ranging and Max/Min mode
- Soft holster
- Easy to replace batteries and main fuse
- Good overall build and sturdiness
- Capacitance quite slow
The Uni-T UT139C review has a solid meter for the electrician and electronics enthusiast. Functionality includes all current ranges, voltage detection and the ability to include an optional current clamp. It is quite accurate and nicely built, is more consistent over time and incorporates decent input protection. Price is also attractive.
Suits hobby electronics (defaults to DC) and electricians involved in everything from school and property maintenance to installations and general purpose work.