DMM UNI-T UT139C

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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.

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

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

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The removable tip must be on for best safety.

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The plug is fully shrouded.

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

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

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The 600mA fuse is assible from the battery compartment.

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Display

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

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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.

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



Functions

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Buttons:
Rotary switch:

Input

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Measurements

1uF

A look at the capacity measurement waveform.

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



Tear down


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

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

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There is something under the display

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

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

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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)

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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)

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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.

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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.

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