DMM Mustool MT109

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This is a smaller meter that has a lot of ranges.

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I got the meter in a brown cardboard box, the drawing mostly matches the meter.

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It included the DMM, a pair of probes, a thermocoupler and a manual.

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The probes has is rated for CAT III, but do not include the partial tip covers required for CAT III or CAT IV.

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The shrouded plug is the slightly short variety.

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A standard cheap thermocoupler.

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The range switch is a bit difficult to use single handed when meter is on the tilting bale, it slides around.

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There is a flashlight led on the front of the meter.

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Display

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The above picture shows all the segments on the display, not all are used.

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Typical display during usage, it will show the number and what measurement is selected.

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The NCV is the usual bars and the buzzer.



Functions

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Buttons: MAX/MIN will change to manual range and return to auto range when disabled.

Rotary switch:
Input

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Measurements 1uF

A look at the capacitance measurement waveform.

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Frequency input resistance depends on input voltage.

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As usual mVDC has high input impedance at low voltages.

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Ohm specification goes to 60Mohm
AC voltage may show low voltage when large DC offset is present.



Tear down

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There where four screws holding the meter together.

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The circuit board is rectangular with most parts on the other side.

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Six more screws and the circuit board could be removed.

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This side has the fuses, the PTC, the buzzer, the flashlight led and the crystal for the multimeter chip, basically anything that needs some space in height. The mounted A fuse is a 20A fuse, but the circuit board is marked 10A. For the mA range a 600mA/630mA fuse is used, this is a bit low for a 1000mA range.
The two points marked RCAL2 is accessible from the battery compartment without opening the meter.

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At the bottom near the input connectors are the current shunts, 0.01ohm wire for 10A and 0.99ohm for mA, this resistor is a bit small for 1W. There is also two MELF resistors for voltage input (2x5Mohm). There a transistor pair (Q3 & Q4) for protection together with the PTC. As is usual the case with cheap meters safety is based on a single SMD resistor (R53: 900kOhm), that will be directly connected to the input terminal in some ranges.
The PTC and transistor clamp is used in all ohm and frequency selections.
THE NCV antenna is at the top of the circuit board.
The multimeter chip (Circuit board says HY12P65) has an external calibration memory (24C08N)

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Conclusion

As usual CAT rating is overstated with 250V fuses and a single PTC it will not handle CAT III 1000V or CAT IV 600V.
The meter is fairly nice with 9900 display, but there is some missing ranges and way to much noise from the buzzer when measuring ampere and the mA range cannot handle the rated current for long. The max/min is a nice function, but it is rather slow.

It is a nice meter for around the house or hobby usage, as long as it is only occasional usage, due to the fairly short battery lifetime.



Notes

The multimeter was supplied by Banggood for review.

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