DMM SNDWAY SW-890C

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If you insist on manual range, this meter has a fairly complete set of ranges with a manual range switch. They have cheated a bit capacity and frequency is auto range.

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The box is in Chinese and covers both the C and D model of this meter (C includes temperature, D do not). The supplied instruction sheet was in English.

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In the box was the meter, probe leads, thermocoupler and an instruction sheet. The instruction sheet is for both C and D models.

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The standard probes are normal sizes and rated for CAT III 1000V and CAT IV 600V, but this cannot be a correct rating, because they are missing tip covers.

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The plugs are fully shrouded and standard probe size.

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The range switch is easy to turn, this means it can be turned single handed both when meter is lying on the table or standing on the tilting bale.

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Display

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All the segments are shown during power on.

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



Functions

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Buttons:
Rotary switch:


Input

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The COM terminal is not in the usual place!
This is not the common placement of terminals.



Measurements

1uF

A look at the capacity measurement waveform for 1uF.

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Tear down

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I had to remove 3 screws top open it, one of them was the battery cover screw.

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The circuit board is shaped after the enclosure.

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3 more screws and I could remove the circuit board. These screws was very tight.

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The display is mounted with 3 screws and a clip.

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Some of the input circuit is very obvious to see here. The volt input has 3 "legs", one with 3 resistors (R1A, R1B, R1C: 3x300k), one with a PTC (PTC1 on the other side) followed by protection (Q5, Q6 and Q1, Q2 in some cases) and one with four resistors (R2A, R2B, R2C and R2D: 4x2.5Mohm).
The uA and mA current range has diodes (D1..D5) for protection.
U2 is probably a EEPROM to store calibration in.

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On this side of the circuit board is not much. There is the two fuses, one of the glass. The PTC for protection the ohm and capacity range and a single capacitor.

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Conclusion

The CAT rating do not match the fuses used, i.e. it is not correct, but at least it use fuses.
For a "simple" meter this is fairly well designed, AC/DC volts works properly and it has some input protection. It has good specifications and it looks like it stays within the specified tolerances.



Notes

This meter may exist with many different names on it and small variations in functions.

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