DMM Uyigao UA18

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This is a small pocket DMM with voltage, ohms and capacity, but without current.

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The meter was in a clamshell pack. On the back is a comparison between the two meters in the series

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

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The probes and wires need some pressure to close the cover.

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The probes are small and without any markings.

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The probes are directly connected to the meter, no plugs and sockets.

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The range switch is a bit tight, but the way it is made gives a good grip and it is easy to turn without the meter moving around.

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Display

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The above picture shows all the segments on the display. Not all are used by the meter.

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



Functions

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Buttons: Selection of Relative and Hz/duty will disable auto ranging and it stays disabled
The Select and Hz could have combined, they are not used in the same ranges.

Rotary switch:

Input

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


Measurements
1uF

DMMInputVoltageSweepHzVDC

Frequency input resistance in voltage DC position.

DMMInputVoltageSweepHzVAC

Frequency input resistance in voltage AC position.

DMMschema

The specifications list a 400.0mV DC range and a 4.000nF range, they were not present on the meter.
The lowest capacity range (51nF) has a offset up to 0.4nF, this give a large error on low nF capacitors
The meter cannot measure DC when there is a large AC voltage.


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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There are a few details to make the meter as flat as possible (Like parts placed outside the circuit board or in cut-outs in the board).

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The round features are probably designed to put some pressure on the circuit board to make the meter more stiff.

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6 screws and a locking ring must be removed to get the circuit board out.

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The battery is mounted in a cut-out. The battery holder is not a standard holder, but some metal parts soldered to the circuit board

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it looks like 3 connections to the plus wire: A voltage divider (R3-1, R3-2, R3-3, R4-1, R4-2: 5x2Mohm) for the voltage ranges. A sense input for the ohm/capacity range (R26, R27: 412kOhm+487kOhm) and a current output with a PTC. There is a single transistor clamp (T1) on the PTC.
There are 3 trimpots for calibration of the meter.
The buzzer has an inductor (L1) to boost the voltage, and there is some holes in the circuit board for the sound.

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Conclusion

The meter says CAT II, but there is no voltage, i.e. not a valid CAT rating.
The meter do not have current ranges and is missing some ranges compared to the specifications, but for a pocket meter there is a fair amount of ranges and functions. The meter is often very slow on reaching the final value.
It is a fairly decent meter for it size, but be aware of its limitations.



Notes

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