DMM Sanwa PM3

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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 some explanation about using the meter.

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In the pack 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 easy to turn, there is not many selections, Sanwa has decided to use a buttons for many measurements

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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 Relative and Hz/duty will disable auto ranging and it stays disabled
The Select and Hz could have been 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 comming out, no other connections.


Measurements
1uF

Capacity measurement waveform.

DMMInputVoltageSweepHzVDC

Frequency input resistance in voltage DC position, mVDC is similar.

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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.



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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To get the circuit board out I had to remove 6 screws and a locking ring.

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The multimeter chip (FS9711_LP1 (See FS9721_LP1 datasheet)) is the most obvious feature on the circuit board. The circuit around D1 and R2 is rectifier for AC voltage. The range selection resistors are near the range switch (Most of R21..R30) and is selected by the chip. The input resistor is 5 resistors (R15, R17 & R31, R32, R33: 5x2Mohm) placed at two locations. The input is also going through a PTC (R14) and protection transistor (Q1), this is for ohm ranges, in ohm there is also a need for another input path (R12 1Mohm).
The buzzer has a transistor and inductor to get as much sound as possible (It is not very loud).

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On this side is only the buzzer and access to the battery, there is cut-outs for the crystal and the PTC.

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Conclusion

The meter says CAT II 500V, but this rating is either 300V or 600V, there is no 500V. The safety looks acceptable for 300V.
The meter does not have current ranges, this improves the safety, but limits the abilities of the meter. The meter has some limits in its range, but for a pocket meter is it fairly decent.



Notes

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