DMM UNI-T UT139C

DSC_2480

Uni-T has a large selection of DMM in their program, this model exist in A, B and C version, main difference is 2000, 4000 and 6000 count display, there is also a small variation of included functions. In this review I will look at the C version.

DSC_2386 DSC_2387 DSC_2388 DSC_2389

The meter arrived in a red box with English and Chinese writing.

DSC_2504
DSC_2500

The probes are branded UNI-T and rated for 10A and 1000V

DSC_2499

The removable tip must be on for best safety.

DSC_2821

The plug is fully shrouded.

DSC_2496
DSC_2497

The thermocoupler has a single connector to the multimeter end, that is considerable better than the two loose bananaplugs.

DSC_2481


DSC_2483

DSC_2484 DSC_2482

The tilting bale is just about stable enough to change range and use switches with one hand.

DSC_2487

The 600mA fuse is accessible from the battery compartment.

DSC_2488
DSC_2489
DSC_2490





Display

DSC_2502


The above picture shows nearly all the segments on the display.

DSC_2503

Typical display during usage, it will show the number and what measurement is selected.
The circle with arrow shows that auto power off is enabled, hold down SELECT when turning on to disable this.

DSC_2495

The electric field detection (NCV) shows from 1 to 4 bar depending on field strength.



Functions

DSC_2486

Buttons: Rotary switch:
Input

DSC_2485



Measurements
1uF

A look at the capacitance measurement waveform.

DMMInputVoltageSweepHz

Frequency input impedance depends on voltage.

DMMschema

It is just outside tolerances on the high ohms measurements (2% out)



Tear down


DSC_2721

3 screws (One was for the battery cover) and the back could be removed.

DSC_2722

DSC_2723

The front required 4 screws for the terminals and 3 small screws for the circuit board.

DSC_2724


DSC_2725

There is something under the display

DSC_2726

Two screws more to remove the display, but not the backlight, it is soldered to the circuit board.

DSC_2728

But I can bend it up (at least a few times).

DSC_2727

Here is the DMM chip (U1: DTM0660L) and the memory (U3: T24C02A) for calibration and functions setup. At the front is the NCV antenna and the indicator led (FG2). One of the voltage dividers are here (R1A, R1B, R1C, R1D: 4x2.5Mohm)

DSC_2730

Here is the range switch and some resistors.
A input chain (R2A, R2B, R2C: 3x300kohm), the uA shunt (R4: 99ohm) and the mA shunt (R5: 1ohm)

DSC_2731

On this side is the fuses, I wonder why the 600mA (F1) is longer than the 10A (F2). There is four MOV's and two PTC for input protection. The transistors (Q2, Q3, Q8, Q9) do also look like protection. The 5 diodes (D1..D5) is protection for the uA and mA current range.

DSC_2729

DSC_2732

DSC_2733 DSC_2734

DSC_2735



Conclusion

This meter has all the usual functions and a few extra like NCV, VFC, external clamp (Any meter can use an external clamp, but this meter places the decimal point correct). As usual the burden voltage in the high mA is very bad.
The meter has a lot of protection and the fuses are rated for 600V, but I am lacking a current interrupt rating for the fuses.

This meter looks like it is fine for mains voltage and anything below.



Notes

UNI-T makes two versions of some meters, one living up to its CAT rating and one that do not.
UNI-T sell rebranded versions of their meters, i.e. you can get this meter with another name on it.

How do I review a DMM
More DMM reviews