DMM UNI-T UT120C

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This is a small pocket DMM with voltage, current, frequency, ohms and capacity.

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The meter was in a clamshell pack. On the back is a comparison between the 3 models in this series, this one here is the only model with current and mVDC.

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In the pack was the meter and a manual in English.

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The probes are small, but they are rated for 600V.

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The probes are directly connected to the meter, no plugs and sockets. The meter can be used inside the box, this will give some splash protection.

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The range switch is easy to turn, but the detents are not very marked, it is easy to place it between ranges.

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Display

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The above picture shows all the segments on the display.

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Typical display during usage, it will show the selected range and value.



Functions

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Buttons: Selection of Rel and Hz/duty will disable auto ranging and it stays disabled

Rotary switch:

Input

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This meter only have a red and black probe coming out, no other connections.


Measurements
1uF

Capacity measurement waveform.

DMMInputVoltageSweepHz

Frequency input resistance in voltage frequency position.

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Frequency input resistance in voltage AC position.

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The meter cannot measure low AC volt when there is a large DC voltage.
Capacity has a 10nF offset, i.e. lowest range cannot be used, but meter is within specified tolerances. Lowest range is not specified and with REL the other are within tolerances.


Tear down

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I had to remove one screws, to open it, this is also required when replacing battery.

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Four clips to get the circuit board out, I did also remove the screw to the range switch, but that was not necessary.

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The bizzer is placed behind the lcd display and the connection is made with some springs on the circuit board. The display uses a zebra stribe as usual.

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This meter requires a lot of adjustment from the factory (VR1..VR4: Trimpots). On the input side we have a PTC for protection in ohm and frequency ranges, the ohm sense input (R19: 900kOhm), the 10Mohm input (R26 & R28: 2x5Mohm). There is also 3 protection transistor pairs (Q1 & Q2, Q3 & Q4, Q5 & Q6). R19 uses Q3 & Q4 as protection. PTC uses Q5 & Q6 in ohms and Q1 & Q2 in frequency.
Current shunts (R16: 1ohm, R17: 99Ohm) are protected by diodes (D5, D6, D8, D9) and the large PTC (PPTC2).

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This side is without parts, but some stuff on the other side needs holes in the circuit board.

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From this side the 3 springs to the buzzer can be seen.



Conclusion

The meter says CAT II 600V, if the range switch can handle 4000V without arching it may be correct.

The meter is well equipped with ranges for a pocket meter and can match many larger meters, precision is fairly good (Except low capacity range), safety looks decent for occasionally mains work at home.




Notes

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